CA1254563A

CA1254563A - Imidazo ¬5,1-d| tetrazin-1,2,3,5 one-derivatives and related products, processes for their preparation and composition containing said derivatives

Info

Publication number: CA1254563A
Application number: CA000434582A
Authority: CA
Inventors: Malcolm F.G. Stevens; Edward Lunt; Ghouse U. Baig; Colin G. Straw; Roger J.A. Walsh; Christopher G. Newton; Brian L. Pedgrift; Christopher Smith; Peter J. Warren
Original assignee: May and Baker Ltd
Current assignee: May and Baker Ltd
Priority date: 1982-08-17
Filing date: 1983-08-15
Publication date: 1989-05-23
Also published as: CH657855A5; AU575782B2; HU189321B; ES524995A0; FR2531958A1; DK374983D0; IT8322566A0; SE455198B; IL69500A; GR78688B; FR2531958B1; FI832927A0; FI832927A; FI80273C; NL8302863A; ES8502441A1; DK374983A; IT1194375B; DE3329505A1; AU1796883A

Abstract

ABSTRACT
NEW TETRAZINE DERIVATIVES

Tetrazine derivatives of the general formula:

[wherein R1 represents a (C3-C8)cycloalkyl group, or a (C1-C4)alkyl, (C2-C6)alkenyl or (C2-C6)alkynyl group, each such alkyl, alkenyl or alkynyl group being unsubstituted or substituted by from 1 to 3 substituents selected from halogen atoms, (C1-C4)alkoxy, -alkylthio, -alkylsulphinyl and -alkylsulphonyl groups, and optionally substituted phenyl groups, A1 represents a nitrogen atom or a group -CR3= wherein R3 represents hydrogen or a substituent R4 wherein R4 represents a halogen atom, or a (C1-C6)-alkyl or -alkenyl group, which may carry up to 3 substituents selected from halogen atoms, optionally substituted phenyl groups, and (C1-C3)-alkoxy, -alkylthio and -alkylsulphonyl groups or R4 represents a (C3-C8)cycloalkyl group, a cyano, hydroxy, nitro or optionally substituted phenoxy group, or a group , -COR5 (wherein R5 represents a (C1-C4)-alkyl or -alkoxy group, a hydroxy group, or an optionally substituted phenyl group) or a (C1-C6)alkanoylamino group, or R4 represents a group -S(O)nR6, -SO2NR7R8 or -CZ2NR7R8 (wherein n represents 0; 1 or 2, R6 represents a (C1-C4)alkyl or (C2-C4)alkenyl group, which may carry an optionally substituted phenyl substituent, a (C3-C8)cyclo-alkyl group or an optionally substituted phenyl group, R7 and R8 each represents hydrogen or a (C1-C4)alkyl or (C2-C4)alkenyl group, which may carry an optionally substituted phenyl substituent, or a (C3-C8)cycloalkyl group or an optionally substituted phenyl group, or the group -NR7R8 represents a heterocyclic group, and Z2 represents an oxygen or sulphur atom), A2 represents a nitrogen atom or, when A1 represents a nitrogen atom, A2 represents a nitrogen atom or a group -CR3= wherein R3 is as hereinbefore defined, Z1 represents an oxygen or sulphur atom, and R2 represents a group of the formula -S(O)nR6, -SO2NR7R8, -CSNR7R8, -CONR7R9 or -CZ2NHNO2, wherein n, R6, R7, R8 and Z2 are as hereinbefore defined, and the group -NR7R9 represents a heterocyclic group, or R7 is as hereinbefore defined and R9 represents a (C1-C4)alkyl or (C2-C4)alkenyl group which carries an optionally substituted phenyl substituent, or an optionally substituted phenyl group or, when A1 represents a nitrogen atom or a group -CR4= wherein R4 is as hereinbefore defined and Z1 and A2 are as hereinbefore defined or, when Al represents a group -CH= and Z1 represents a sulphur atom and A2 is as hereinbefore defined, R2 represents a group of the formula -S(O)nR6, -SO2NR7R8, -CZ2NR7R8 or CZ2NHNO2 wherein n, R6, R7, R8 and Z2 are as hereinbefore defined] are new therapeutically useful compounds possessing antineoplastic activity.
Processes for the preparation of the tetrazine derivatives are inter alia described.

Description

- DESC~IPTION
"NEW TET~AZINE ~ERIVATIVES"
This invention relates to ne~ tetrazine derivatives, to processes for their preparation and to pharmaceutical compositions containing them.
The compounas of the present invention are the tetrazine derivatives of the general formula shown in Figure I of the drawings assembled at the end of the present speci~ication Lwherein Rl represents a cycloalkyl group, or a straight- or branched-chain alkyl, alkenyl or alkynyl group containing up to 6 carbon atoms, each such alkyl, alkenyl or alkynyl group being unsubstituted or substituted by from one to three substituents seLected from halogen (i.e.
bromine, iodine or, pre~erably, chlorine or fluorine) atoms, straight- or branched-chain alkoxy, alkylthio, alkylsulphinyl and alkylsulphonyl groups containing up to 4 carbon atoms, and optionally substituted phenyl groups, Al represents a nitrogen atom or a group -CR3= wnerein R3 represents a hydrogen atom or a substituent R4 wherein R4 represents a halogen atom, or a straight- or branched-chain alkyl or alkenyl group, containing up to 6 carbon atoms, which may carry up to 3 substituents selected from halogen atoms, optionally substituted phenyl groups, straight- or branched-chain alkoxy, alkylthio and alkylsulphonyl groups containing up to 3 car~on atoms, or R~ represents a cycloal~yl, cyano, hyciroxy, nitro or optionally substituted phenoxy group or a ~roup of the formula -CoR5 (wherein R5 represents an aLkyl or alkoxy group of up to 4 carbon atoms, or a hydroxy group, or an optionally substituted phenyl group) or an alkanoylamino group containing up to 6 carbon atoms, or R4 represents a group of the formula (O)nR , -So2NR7R8 or -CZ2NR7R8 (wherein n represents 0, 1 or 2, R~ represents a straight- or branched-chain alkyl or alkenyl group, containing up to 4 car~on atoms, which may carry an optionally substituted phenyl substituent, a cycloalkyl group or an optionally substituted phenyl group, R7 and R8, which may be the same or different, each represents a hydrogen atom or a straigbt- or branched chain alkyl or alkenyl group, containing up to 4 carbon atoms, which may carry an optionally substituted phenyl substituent, or a cycloalkyl group or an optionally substitutea phenyl group or the group -NR7R8 represents a heterocyclic group, and Z~ represents an oxygen or sulphur atom), A2 represents a nitrogen atom or, when Al represents a nitrogen atom, A2 represents a nitrogen atom or a group -CR3= wherein R3 is as hereinbefore defined, zl represents an oxygen or 3 ~2~ 3 sulphur atom, and R2 represents a group o~ the formula -S(o)nR5~ -S02NR7R&, -CSNR7P~, -CoNR7R9 or -CZ2NHN~2 wherein n, K6, K7, R~ and z2 are as hereinbefore defined, and the group -NR7R9 represents a heterocyclic group or R7 is as hereinbefore defined and R~ represents a straight- or branched-chain alkyl or alkenyl group containing up to 4 carbon atoms which carries an optionally substituted phenyl substituent, or an optionally substituted phenyl group or, when Al represents a nitrogen atom or a group -CR4= wherein R4 is as hereinbefore defined and zl and A2 are as hereinbefore defined or, when Al represents a group -CH= and zl represents a sulphur atom and A2 is as herein~efore defined, R2 represents a group of the formula -S(O)nR6, -So2NR7R8, -CZ2NR7R8 or CZ2NHN02 wherein n, R6, R7, R8 ana z2 are as hereinbefore defined~ and when R2 and/or R3 represents a sulphamoyl or monosubstituted sulphamoyl group and/or R3 represents a carboxy group, salts thereof, more especially alkali metal, e.g. sodium, salts. Whenever the context so permits reference in this specification to the compounds o~ the ~eneral formula shown in Figure I is meant to incluae reference to the said salts. The salts are particularly useful as intermediates.

q~

Within the definition of the forrnula showrl in Figure I the optional substituents on the phenyl and pherloxy moieties may be selected frorn, for example, haloyen atorrls and alkyl and alkoxy groups containing up to 4 carbon atoms, and nitro groups. Cycloalkyl groups wit~lin the definition of the formula shown in Figure I contain 3 to 8, preferably 6, carbon atoms. A heterocyclic group within the definition of the formula shown in Figure I is a 5-, 6- or 7-membered heterocyclic ring which may optionally contain a further heteroatom, i.e. nitrogen, oxygen or sulphur, and which may carry one or two straight- or branched-chain alkyl substitu-ents each containing up to 4 carbon atoms, e.g. a piperidino group or a 2-methyl-, 3-methyl-, 4-methyl-, 2,4-dimethyl-, or 3,5-dimethylpiperidino group, or a morpholino, pyrrolidin-l-yl, perhydroazepin-1-yl, piperazin-l-yl, 4-methylpiperazin-l-yl or 1,4-thiazin-4-yl group.

~y - 4a -Therefore, the invention relates to a process for the preparation of tetrazine de~iva~ives of the ge~neral formula:

~ N~
\~1 N ~ ~
zl ~R

Cwherein R1 represents a cycloalkyl group containing 3 to 8 carbon atoms, or a straight- or branched-chain alkyl, alkenyl or alkylnyl group containing up to 6 carbon atoms, each such alkyl, alkenyl or alkylnyl group being unsubsti-tuted or substituted by from one to three substituents selected from the group consisting of halogen atoms, straight- or branched-chain alkoxy, alkylthio, alkylsulphi-nyl and alkylsulphonyl groups containing up to 4 carbon atoms, and phenyl groups(unsubstituted or substituted by one or more substituents selected from the group consisting of haloyen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group); Al represents a nitrogen atom or a group -CR
wherein R3 represents a hydrogen atom or a substituent R4 wherein R4 represents a halogen atom, or a straight- or branched-chain alkyl or alkenyl group, containing up to 6 carbon atoms, which may carry up to 3 substituents selected from the group consisting of halogen atom, phenyl group, phenyl group substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group - 4b -containing up to 4 carbon atoms and nitro group, straight-or branched-chain alkoxy, alkylthio and alkylsulphonyl groups containing up to 3 carbon atoms, or r~4 represents a cycloalkyl group containing 3 to 8 carbon atoms, a cyano, hydroxy, nitro, phenoxy group or phenoxy group substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, or a group of the formula -CoR5 (wherein R
represents an alkyl or alkoxy group of up to 4 carbon atoms, a hydroxy group, a phenyl group or a phenyl group substi-tuted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group~ or an alkanoylamino group containing up to 6 carbon atoms, or R4 represents a group of the formula -S(O)nR6, -So2NR7R8 or -CZ2~R7R8 (wherein n represents 0, 1 or 2, R represents a straight- or branched-chain alkyl or alkenyl group, containing up to 4 carbon atoms, which may carry a phenyl substituent(unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group),a cycloalkyl group containing 3 to 8 carbon atoms or a phenyl group(unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group~ R7 and R8, which may be the same or different, each represents a hydrogen atom or a straight- or branched-chain alkyl or alkenyl group, containing up to 4 carbon atoms, which may carry a phenyl substituent (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up - 4c -to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group) or a cycloalkyl group containing 3 to 8 carbon atoms or a phenyl group (unsubstituted or substi-tuted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group) or the group -NR7R3 represents a 5,6 or 7 membered heterocyclic ring which may contain a further heteroatom selected from the group consisting of nitrogen, oxygen and sulfur, said heterocyclic ring being unsubsti-tuted on substituted by one or two substituents selected from the group consisting of straight- or branched- chain alkyl substituents each containing up to 4 carbon atoms, and Z represents an oxygen or sulphur atom)t A represents a nitrogen atom or, when A1 represents a nitrogen atom, A
represents a nitrogen atom or a group -CR3= wherein R3 is as hereinbefore defined, zl represents an oxygen or sulphur atom; and R represents a group of the formula -S(o) R , -So2NR7R8, -CSNR7R8, -CoNR7R9 or -CZ NHN02, wherein n, R, 20 R7, R8 and z2 are as hereinbefore defined, and the group -NR7R9 represents a 5,6 or 7 membered heterocyclic ring which may contain a further heteroatom selected from the group consisting of nitrogen, oxygen and sulfur, said heterocyclic ring being unsubstituted or substituted by one or two substituents selected from the group consisting of straight- or branched-chain alkyl substituents each containing up to 4 carbon atoms, or R7 iS as hereinbefore defined and R9 represents a straight- or branched-chain alkyl or alkenyl group containing up to 4 carbon atoms which carries a phenyl substituent(unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group) or a phenyl group(unsubstituted or substi-- ~d -tuted by one or more substi.tuerlts selected frorn th~ group consisting of halogen atoms, alkyl group containirlg up to 4 carbon atoms, alkoxy group contai.nirlg up Lo ~ carboll atoms and nitro group) or, when Al represerlts a nitro(3en a~oM or ~
group -CR4= wherein R4 is as hereinbefore defined and zl and Z are as hereinbe~ore defined or, when A1 represents a group -CH= and zl represents a sulphur atom and z2 is as hereinbefore defined, R2 represents a group of the formula -S(O)nR6, -So2NR7R8, -CZ2NR7R8 or CZ2NHNO2 wherein n, R6, R ,R and Z are as hereinbefore defined~ and, when RZ
and/or R3 represents a sulphamoyl or monosubstituted sulphamoyl group and/or R3 represents a carboxy group;
pharmaceutically acceptable salts thereof; excluding the derivatives of formula (I) in which Al represents a group -CR3= wherein R3 represents a hydrogen atom, A2 represents a nitrogen atom and either Rl represents a straight- or branched-alkyl, alkenyl or alkynyl group containing up to 6 carbon atoms, each such alkyl, alkenyl or alkynyl group being unsubstituted or substituted by from 1 to 3 substi-tuents selected from the group consisting of halogen atoms, straight-or branched-alkoxy, alkylthio, alkylsulfinyl and alkylsulfonyl groups containing up to 4 carbon atoms and phenyl group(unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group),or Rl represents a cycloalkyl group containing 3 to 8 carbon atoms and R2 represents a carbamoyl group which is substituted on the nitrogen atom i) by two groups selected from the group consisting of phenyl group, phenyl group substituted b~ one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, phenylalkyl group and phenylalkyl group substituted ~, ~

~ ~r~

- 4e -by one or more substituents selected frorn the group consisting of halogen atoms, alkyl group contairliny up to 4 carbon atoms, alkoxy group containing up to ~ carbon atorns and nitro group; or ii) a phenyl group substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, or a phenylalkyl group substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon a~oms, alkoxy group containing up to 4 carbon atoms and nitro group, or iii) a phenyl group (unsubstitu-ted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group) or a phenylalkyl group substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, and a straight- or branched- alkyl group containing up to 4 carbon atoms; which comprises:
(A) in the case of a tetrazine derivative of general formu~a (I) wherein R2 is other than a sulphamoyl, monophenylcarba-moyl, monophenylcarbamoyl substituted on the phenyl moiety by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, monophenylthiocarbamoyl, monophenylthio-carbamoyl substituted on the phenyl moiety by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, nitrocarbamoyl or nitrothiocarbamoyl group, and Rl, A1, A2 and zl are as hereinbefore defined, reacting a compound of the general formula:

.i ~ .

~A~N~
~ (ILL) Rl/2 N2~3 (wherein Al and A2 are as hereinbefore defined and R
represents a group within the abovementioned definition of R in relation to general formula (I) other than a sulphamoyl, monophenylcarbamoyl, monophenylcarbamoyl substituted on the phenyl moiety by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, monophenylthiocarbamoyl, monophenylthiocarbamoyl substituted on the phenyl moiety by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, nitrocarbamoyl or nitrothiocarbamoyl group, with a compound of the general formula:

R NCZ (IV) wherein Rl and zl are as hereinbefore defined, or (B) in the case of a tetrazine derivative of general formula (I) wherein R2 represents a monophenylcarbamoyl, a monophenylcarbamoyl substituted on the phenyl moiety by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, a monophenylthiocarbamoyl, a monophenylthiocarbamoyl substituted on the phenyl moiety by one or more substituents selected from the group consisting of halogen atoms, alkyl ~5~

'I g group containing up to 4 carborl atoms, alkoxy group containing up to 4 carbon atoms and nitro g~oup, and R], ~ , A2 and zl are as hereinbefore defined in relatiorl to that formula, the debenzylation of a cornpound of the general formula: SO NR7R13 CZ NR R

~ N~ l Z

(wherein R7 is as hereinbefore defined, R13 represents benzyl group or a benzyl group sustituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, and z2 is as hereinbefore defined) by the application or adaptation of methods known ~ se for the replacement of a benzyl group or a benzyl group substituted on the phenyl-moiety by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, by a hydrogen atom, or (C) in the case of a tetrazine derivative of general formula (I) wherein Rl, Al, A2 and zl are as hereinbefore defined in relation to that formula and R2 represents a group of the formula -CZ2NHNO2, z2 being as hereinbefore defined, the nitration of a corresponding compound of the general formula:

J~I

- 4h --~) ~ 7 ~ R (VA) (wherein Z , R , A , A and zl are as hereinhefore defined in relation to general formula (I)), to convert the grouping -CZ NH2 to -CZ2NHNO2, or, (D) in the case of a tetrazine derivative of general formula (I) wherein R1, Al, A2 and R2 are as hereinbefore defined in relation to that formula and zl represents a sulphur atom, reacting a compound of the general formula:
RlS

A2 ~ ~ (VI) (wherein R1, A1 and R2 are as hereinbefore defined in relation to general formula (I), and R15 represents a group of the formula -S(O) R6, -So2NR7R8, -CZ2NR7R8 or -CZ2NHNO
R6, R , R , n and Z being as hereinbefore defined in relation to general formula (I)) with phosphorus penta-sulphide to convert the \C~ moiety to ~C/ , or O ls~
(E) in the case of a tetrazine derivative of general formula (I) wherein R1, A1, A2 and zl are as hereinbefore defined in relation to that formula and R2 represents a group of the formula -CSNR7R8 wherein R7 and R8 are as hereinbefore defined in relation to general formula (I), reacting a corresponding compound of the general formula:

~r CONR R~

N

2 ~ I ~V~IA) Rl (wherein R1, A1, A2, zl, R7 and R8 are as hereinbefore defined in relation to general formula (I)J with phosphorus pentasulphide to convert the grouping -CoNR7R8 to -CSNR R , and optionally, when the tetrazine product obtained is a compound of general formula I wherein R2 and/or R3 represent a sulphamoyl or mono-substituted sulphamoyl group and/or R3 represents a carboxy group, converting by a method known per _ the product into a pharmaceutically acceptable salt (preferably an alkali metal salt).

Advantageously, for the preparation of a tetrazine derivative of general formula (I) wherein R is other than a sulphamoyl, monophenylcarbamoyl, monophenylcarbamoyl substituted on the phenyl moiety by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, monophenylthiocarbamoyl, monophenylthiocarbamoyl substituted on the phenyl moiety by one or more substituents selected from the group consisting of halogen atoms, alkyl.
group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, nitrocarbamoyl or nitrothiocarbamoyl group, and Rl, A , A2 and zl are as defined hereinbefore,which comprises reac-ting a compound of the general Eorrnll:l.a:

~2 ~ (III) wherein Al and A2 are as defined hereinbefore and R
represents a group within the above-mentioned definition of R , with a compound of the general formula:

R NCZ1 (IV) wherein Rl and zl are as hereinbefore defined, to obtain the desired compound.

~ dvantageously, for the preparation of a tetrazine derivative of general formula (I) as defined hereinbefore, wherein R represents a monophenylcarbamoyl, a monophenyl-carbamoyl substituted on the phenyl moiety by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, a monophenylthiocarbamoyl or a monophenylthiocarbamoyl substituted on the phenyl moiety by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to ~ carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, and R1, A1, A2 and zl are as defined hereinbefore in relation to that formula, which comprises the debenzylation of a cornpound of the general formula:

~q~

4 k S02NR R ('~ NR R

~ ~ R ~ ~`~ 1 (wherein R7 is as de~ined hereinbefore, R13 represen-ts a benzyl group or a benzyl group substituted on the phenyl moiety by one or more substituents selected frorn the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, and z2 is as defined hereinbefore by the application or adaptation of methods known per se for the replacement of a benzyl group or a benzyl group substituted on the phenyl moiety by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, by a hydrogen atom, to obtain the desired compound.

Advantageously,~or the preparation of a tetrazine derivative of general formula (I) as defined hereinbefore, wherein R1, A1, A2 and zl are as hereinbefore defined hereinbefore in relation to that formula and RZ represents a group of the formula -CZ2NHNO2, ZZ being as defined hereinbefore which comprises the nitration of a corresponding compound of the general formula:

~Z N~2 (VA) ~f I
\\ l N~

.~
`~`~1< ,.

(wherein z2, Rl, Al, AZ ~nd zl aI~ as defir~ed hereinbefore in relatio~ to general forrnul.a (I)), ~o convert ~lle groupirl-J
-CZ N112 to CZ NHNO2.

Advantageously, for the preparation of a tetrazine derivative of general formula (I) as defined hereinbefore, wherein R , Al, A2 and R2 are as defined hereinbefore in relation to that formula and zl represents a sulphur atom, which comprises reacting a compound of the general formula:

~ ~ 1 (VI) wherein Rl, Al and RZ are as defined hereinbefore, and Rl5 represents a group of the formula -S(O) R6, -SO2NR7R8, -CZ NR R or -CZ2NHNO2, R6, R7, R8, n and Z being as defined hereinbefore, with phosphorus pentasulphide to convert \_/ . \/
the ~ molety to ~ .
O S

Advantageously, for the préparation of a tetrazine derivative of general formula (I) as defined hereinbefore wherein Rl, Al, A2 and zl are as defined hereinbefore in relation to that formula and R2 represents a group of the for~ula -CSNR7R3 wherein R7 and R8 are as defined hereinbefore in relation to general formula (I), which comprises reacting a corresponding compound of the general formula:

- ~rn -coN~c71~3 ~N
~2 1 1 (VIIA) ~\A~N~N\

wherein Rl, Al, A , zl, Rl an-l R8 are as defined hereinbéfore, with phosphorus pentasulphide to convert th~ grouping -CoNR7R~ to -CSNR7R .

PreferabLy the process according to the invention may further comprise converting the resuLting product of formula ~I) wherein R2 and/or R3 represent a sulphamoyl or mono-su~stituted sulphamoyl group and/or R3 represents a carboxyl group, by a method known per se into a pharmaceu-tically acceptable salt thereof.

Preferably, the cycloalkyl group referred to in formula I is cyclohexyl.

Advantageously, the invention relates to a process for the preparation of 3-(N-benzyl-carbamoyl)-3-(2-chloroethyl)-C3H~-i.midazo-cS,l-d3-l,2,3,5-tetrazin-4-one, which comprises reacting 8-rN-benzyl-N-(4-methoxybenzyl) carbamoyl~-3-(2-chLoroethyl)-L3H~--imidazo CS,l-d~-l,2,3,5-tetrazin-4-one with anisole to ~orm the desired compound ~' i b ~

- 4n -Advantageously, the invention relates to a process for the preparation of 8~carbarnoyl-3-(2-chloroethyl)-6-methyl-C311]-imi.(l.lzo- ~'j,],_dJ-].,2,.3,5-tetra-zin-4-one, which comprises rcacting 5-diazo-2-rrtethyl-S imidazole-4-carboxamide with 2-chloroethyl isocyanate to form the desired compound.
Advantageously, the invention relates to a process for the preparation of 3-(2-chloro-ethyl)-8-(N,N'-dimethylsulphamoyl)-r3~ -imidazo-[S,l-~ -1,2,3,5-tetrazin-4-one, which comprises reacting 5-diazo-imidazole-4-(N,N-dimethylsulphonamide) with 2-chloroethyl isocyanate to form the desired compound.
Advantageously, the invention relates to a process for the preparation of 3-(2-chloro-ethyl)-8-(N-methylsulphamoyl)-~3~ -imidazo- Ls,1-d]-1,2,3,5-tetrazin-4-one, which comprises reacting 5-diazoimidazole-4-tN-methylsulphonamide) with 2-chloroethyl isocyanate to form the desired compound.
Advantageously, the invention relates to a process for the preparation of 3-(2-chloro-ethyl)-8-methylsulphonyl-C3~ -imidazo-C5,1~d~-1,2,3,5-tetra-zin-4-one, which comprises reacting 5-diazo-4-methylsulpho-nylimidazole ~ith 2-chloroethyl isocyanate to form the desired compound.
2S Advantageously, the invention relates to a process for the preparation of 3-(2-chloro-ethyl)-8-methylsulphonyl-[3~ -imidazo-[5,1-d~-l,Z,3,5-tetra-zin-4-one, which comprises reacting 5-diazo-4-methylsulpho-nylimidazole with 2-chloroethyl isocyanate to form the desired compound.
Advantageously, the invention relates to a process for the preparation of 3-methyl-8-methylsulphonyl-C3H~-imidazo-LS,l-d~-l,Z,3,5-tetrazin-4-one, which comprises reacting 5-diazo-4-methylsulphonylimidazole with methyl isocyanate to form the desired compound.

.5~

Advantageously, the inv~ntion re:Lates to a process for the preparation of 3-(2-chloro-ethyl)-8-[N-(~-methoxybenzyl)-s~llpharnoyl~ t3l~ imidazo-[5,1-d~-1,2,3,5-tetrazin-4-one, whic~l comprises reacting 5-diazoimidazole-4-cN-(4-methoxybenzyl)sulphonamide~ 2-chloro-ethyl isocyanate to form the desired compound.
Advantageously, the invention relates to a process for the preparation of 3-(2-chloro-ethyl3-8-sulphamoyl-[3~ -imidazo-L5,1-d~-1,2,3,5-tetrazin-4-one, whieh eomprises reacting 3-(2-chloroethyl)-8-L~-(4-methoxybenzyl)sulphamoyl~-C3~ -imidazoC5,1-d~-1,2,3,5-tetra-zin-4-one with anisole to form the desired compound.
Advantageously, the invention relates to a proeess for the preparation of 8-carbamoyl-3-(2-ehloroethyl-~3~ -pyrazolo-C5,1-d~-1,2,3,5-tetrazin-4-one, whieh eomprises reaeting 3-diazopyrazole-4-earboxamide with 2-ehloroethyl isoeyanate to form the desired eompound.
Advantageously, the invention relates to a proeess for the preparation of 3-(2-ehloro-ethyl)-8-piperidinocarbonyl-r3~ -imidazo-[5,1-d¦-1,2,3,5-tetrazin-4-one, whieh eomprises reaeting 4-diazo-5-piperi-dinocarbonylimidazole with 2-chloroethyl isocyanate to form the desired compound.
Advantageously, the invention relates to a proeess for the preparation af 6-butyl-8- ' -earbamoyl-3-(2-ehloroethyl)-L3H~-imidazo-[5,1-d~-1,2,3,5-tetrazin-4-one, whieh eomprises reacting 2-butyl-5-diazoimidazole-4-earboxamide with 2-ehloroethyl isoeyanate to form the desired eompound.
Advantageously, the invention relates to a proeess for the preparation of 8-earbamoyl-3-(2-ehloroethyl)-6-propyl-~3~ -imidazo-C5,1-d~-1,2,3,5-tetra-zin-4-one, whieh eomprises reacting 5-diazo-2-propyl-imidazole-4-carboxamide with 2-chloroethyl isocyanate to form the desired compound.

t~

~ 4P -Advan-tageously, the invention relates to a process for the preparation o~ 8-carbamoyl-3-(2-chloroethyl)-6-ethy~ 3ll~-imida~o--l5,l-d~-],2,3,5-~et~a-zin-4-one, which comp~ises re.lc~ g 5-~1;azo--Z-ethylirrli-dazole-4-carboxamide with 2-chLoroetl~yl isocyanate to form the desired compound.
Advantageously, the invention relates to a process for the preparation of 3-(2-chloro-ethyl)-6-methyl-8-sulphamoyl-[3H~-imidazo-~5~l-d~ 2~3~s-tetrazin-4-one, which comprises reacting 3-(2-chloroethyl)-8-(4-methoxybenzyl)sulphamoyl-6-methyl-r3H3-imidazo~5,1-dJ-1,2,3,5-tetrazin-4-one with anisole to form the desired compound.
Advantageously, the invention relates to a process for the preparation of 3-(2-chloro-ethyl)-8-dimethylsulphamoyl-6-methyl-C3~ imidazo-C5,1-d~-1,2,3,5-tetrazin-4-one, which comprises reacting 5-diazo-4-dimethylsulphamoyl-2-methylimidazole with 2-chloroethyl isocyanate to form the desired compound.
Advantageously, the invention relates to a process for the preparation of 3-(2-chloro-ethyl)-6-methyl-8-methylsulphonyl- r3 - 3 -imidazo-~5,1-d~-1,2,3,5-tetrazin-4-one, which comprises reacting 5-diazo-2-methyl-4-methylsulphonylimidazole with 2-chloroethyl iso-cyanate to form the desired compound.
Advantageously, the invention relates to a process for the preparation of 3-(2-chloro-ethyl)-8-(dimethylcarbamoyl)-r3H~-pyrazolo-C5,1-d~-1,2,3,S-tetrazin-4-one, which comprises reacting 3-diazopyrazole-4-(N,N-dimethylcarboxamide) hydrochloride with 2-chloroethyl isocyanate and 1,8-diazobicyclol5,4,0~undec-7-ene to form the desired compound.
Advantageously, the inventiGrl relates to a process for the preparation of 3-(2-chloro-ethyl)-8-(N-nitrocarbamoyl)-[3H~-imidazo-cs~]-dJ -l,2,3,5-- 4q -tetrazin-4-one, which cornprises reactirlg a mixture of concentrated sulphuric acid an~ ~3-carbarrloyl-3-(2-chloroethyl)-~3~l~-irnidazor5,1--d~-1,2,3,5-tetrazirl-4-orle with eoncentrated nitric acid to form the desired compound.
More partieularly, the inventi.on also relates to tetrazine derivatives of the general formula:
~2 A ~ N~N (I~
\~1 N ~ ~

Cwherein Rl represents a cycloalkyl group containing 3 to 8 earbon atoms, or a straight- or branehed-chain alkyl, alkenyl or alkylnyl group containing up to 6 carbon atoms, eaeh such alkyl, alkenyl or alkylnyl group being unsubsti-tuted or substituted by from one to three substituents seleeted from the group eonsisting of halogen atoms, straight- or branehed-ehain alkoxy, alkylthio, alkylsulphi-nyl and alkylsulphonyl groups eontaining up to 4 earbon atoms, and phenyl groups(unsubstituted or substituted by one or more substituents selected from the group eonsisting of halogen atoms, alkyl group eontaining up to 4 earbon atoms, alkoxy group eontaining up to 4 carbon atoms and nitro group); A1 represents a nitrogen atom or a group -CR
wherein R3 represents a hydrogen atom or a substituent R4 wherein R represents a halogen atom, or a straight- or branched ehain alkyl or alkenyl group, eontaining up to 6 carbon atoms, which may carry up to 3 substituents selected from the group consisting of halogen atom, phenyl group, phenyl group substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group

3~2 - 4r -containing up to 4 carbon atorns and nitro group, straight-or branched-chain alkoxy, alkylthio ancl a].kylsulphonyl groups containing up to 3 carbon a~oms, or l~4 represents a cycloalkyl group containi.ng 3 to 8 carbon atorns, a cyano, hydroxy, nitro, phenoxy group or phenoxy group substituted by one or more substituents selected from the yroup consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, or a group of the formula -CoR5 (wherein R5 represents an alkyl or alkoxy group of up to 4 carbon atoms, a hydroxy group, a phenyl group or a phenyl group substi-tuted by one or more substituents selected from the group eonsisting of halogen atoms, alkyl group containing up to 4 earbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group~ or an alkanoylamino group eontaining up to 6 earbon atoms, or R4 represents a group of the formula -S(O)nR6, -So2NR7R8 or -CZ2NR7R8 (wherein n represents 0, l or 2, R6 represents a straight- or branehed-ehain alkyl or alkenyl group, containing up to 4 carbon atoms, whieh may earry a phenyl substituent(unsubstituted or substituted by one or more substituents seleeted from the group eonsisting of halogen atoms, alkyl group eontaining up to 4 carbon atoms, alkoxy group eontaining up to 4 earbon atoms and nitro group~, a cycloalkyl group eontaining 3 to 8 carbon atoms or a phenyl group(unsubstituted or substituted by one or more substituents seleeted from the group eonsisting of halogen atoms, alkyl group eontaining up to 4 carbon atoms, alkoxy group eontaining up to 4 carbon atoms and nitro group) R7 and R~, which may be the same or different, each represents a hydrogen atom or a straight- or branched-chain alkyl or alkenyl group, containing up to 4 carbon atoms, which may carry a phenyl substituent (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group contalning up - 4s -to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group) or a cyc:LoaLkyl grotlp contairling 3 to 8 carbon atoms or a phenyl group(unsubstituted or substi-tuted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atorns and nitro group) or the group -NR7R8 represents a S,6 or 7 membered heteroeyclic ring which may contain a further heteroatom selected from the group consisting of nitrogen, oxygen and sulfur, said heterocyclic ring being unsubsti-tuted on substituted by one or two substituents selected from the group eonsisting of straight- or branched- chain alkyl substituents each eontaining up to 4 carbon atoms, and z2 represents an oxygen or sulphur atom); A2 represents a nitrogen atom or, when Al represents a nitrogen atom, A
represents a nitrogen atom or a group -CR3= wherein R3 is as hereinbefore defined, zl represents an oxygen or sulphur atom; and R2 represents a group of the formula -S(O)nR6, -So2NR7R8~ -CSNR7R8, -CoNR7R9 or -CZ2NHNO2, wherein n, R6, R , R8 and Z are as hereinbefore defined, and the group -NR7R9 represents a 5,6 or 7 membered heterocyclic ring whieh may eontain a ~urther heteroatom seleeted from the group consisting of nitrogen, oxygen and sulfur, said heterocyelie ring being unsubstituted on substituted by one or two substituents selected from the group consisting of straight- or branched-chain alkyl substituents eaeh containing up to 4 carbon atoms, or R7 is as hereinbefore defined and R represents a straight- or branched-chain alkyl or alkenyl group containing up to 4 earbon atoms whieh earries and phenyl substituent(unsubstituted or sub~stituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group) or a phenyl group(unsubstituted or substi-~5~

- 4t -tuted by one or more substituer,ts selected from the group consisting of halogen atoms, alkyl group contai.nirlg up to 4 carbon atoms, alkoxy group contailliflg up to 4 carbon atorns and nitro group~ or, when A1 represents a nitrogen atom or a group -CR4= wherein R4 is as hereinbefore defined and zl and z2 are as hereinbefore defined or, when A1 represents a group -CH= and zl represents a sulphur atom and z2 is as hereinbe~ore defined, R2 represents a group of the formula -S(O)nR , -SO~NR R , -CZ2NR7R8 or CZ2NHNO2 wherein n, R6, R,.R . and Z are as hereinbefore defined~ and, when R
and/or R represents a sulphamoyl or monosubstituted sulphamoyl group and/or R3 represents a carboxy group;
pharmaceutically acceptable salts thereof; excluding the derivatives of formula (I) in which A1 represents a group -CR3= wherein R3 represents a hydrogen atom, A2 represents a nitrogen atom and either Rl represents a straight- or branched-alkyl, alkenyl or alkynyl group containing up to 6 carbon atoms, each such alkyl, alkenyl or alkynyl group being unsubstituted or substituted by from 1 to 3 substi-tuents selected ~rom the group consisting of halogen atoms,straight-or branched-alkoxy, alkylthio, alkylsulfinyl and alkylsulfonyl groups containing up to 4 carbon atoms and phenyl group(unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group),or Rl represents a cycloalkyl group containing 3 to 8 carbon atoms and R2 represents a carbamoyl group which is substituted on the nitrogen atom i) by two groups selected from the group consisting of phenyl group, phenyl group substituted by one or more substituents selected ~rom the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, phenylalkyl group and phenylalkyl group substituted . ~

~z~
- ~u -by one or more substituents selected from the yroup consisting of halogen atoms, alkyl group corltairlirl~ up to ~
carbon atoms, alkoxy group containirlg up to 4 carbon atomS
and nitrogroup~ or ii) a phenyl group substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, or a phenylalkyl group substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, or iii) a phenyl group(unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group) or a phenylalkyl group substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, and a straight- or branched- alkyl group containing up to 4 carbon atoms.
Advantageously, the invention relates to tetrazine derivatives of formula (I) wherein Rl is as defined hereinbefore~R2 represents a car-bamoyl group unsubstituted or substituted on the nitrogenatom by one or two groups selected from straight- and branched-chain alkyl and alkenyl groups, containing up to 4 carbon atoms, and cycloalkyl groups containing 3 to 8 carbon atoms, Al represents a group -CR4= whe-rein R4 represents a straight- or branched-chain alkyl or alkenyl group containing up to 6 carbon atoms, which may carry up to 3 substituents selected from halogen atoms, phenyl group and phenyl groups substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl - ~v -group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, or R
represents a cycloalkyl group contai.ning 3 to 8 carbon atoms, A2 represents a nitrogen atorn, and zl represents an oxygen atom.
Advantageously, ~he invention relates to tetrazine derivatives of formula (I) wherein Rl is as defined hereinbefore, R2 represents a group of the formula -S(O) R6 or -So2NR7R8, wherein n represents 0, 1 or 2, R6 represents a straight- or branched-chain alkyl or alkenyl group, containing up to 4 carbon atoms, which may carry a phenyl substituent(unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group~, a cycloalkyl group containing 3 to 8 carbon atoms, or a phenyl group (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group), R7 and R8, which may be the same or different, each represents a hydrogen atom or a straight- or branched-chain alk~l or alkenyl group, containing up to 4 carbon atoms, which may carry a phenyl substituent (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group), or a cycloalkyl group containing 3 to 8 carbon atoms, or a phenyl group (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to ~ carbon atoms and nitro group), Al represents the group =CH-, A
represents a nitrogen atom, and zl represents an oxygen - 4w -atom.
~ dvantageously, the inverlt:iorl reLates to tetrazine derivati.ves of forrnula (I) wherein Rl is as defined hereinbefore,R2 represents a group of the formula -S(O) ~6, -So2NR7R8 or -CZ2NR7R8 (wherein n represents 0, 1 or 2, R6 represents a straight- or branched-chain alkyl or alkenyl group, containing up to 4 carbon atoms, which may carry a phenyl substituent(unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group),a cycloalkyl group containing 3 to 8 carbon atoms, or a phenyl group (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group)), R7 and R8, which may be the same or different, each represents a hydrogen atom or a straight- or branched-chain alkyl or alkenyl group, containing up to 4 carbon atoms, which may carry a phenyl substituent (unsubstituted or substituted by one or more substituents selected ~rom the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group), or a cycloalkyl group containing 3 to 8 carbon atoms or a phenyl group (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group), represents a nitrogen atom, A2 represents a group -CR =, wherein R3 represents a hydrogen atom or a substituent R4 as defined hereinberofe,and zl represents an oxygen or sulphur atom.:

- ~x -Advantageously, the inventiorl re:Lates to aforesaid tetrazine derivative.s o~ forrnuLa (I) in whiGh the cyGloalkyl group referred to is cyclohexyl.
Advantageously, the invention relates to aforesaid 5 tetrazine derivatives of formula (I), which have one or more of the following features:
(i) R represents a methyl or 2-haloethyl group (preferably the 2-chloroethyl group);
(ii) R represents a group of the formula -SOR , -SO2R6, -So2NR7R3, -CoNR7R8 or -CONHNO2, wherein R , R7 and R8 are as defined hereinbefore (iii) one of A and A2 represents a nitrogen atom and the other represents a group -CR3= wherein R3 is as defined hereinbefore (iv) R3 represents a substituent R4 wherein R4 represents an alkyl group containing up to 6 carbon atoms-(v) A2 represents a nitrogen atom;
(vi) zl represents an oxygen atom; and/or (vii) Z represents an oxygen atom.
Preferably, R represents a group -SOR , -SO2R , -So2NR7R8, -CoNR7R8 or -CONHNO2 wherein R6 represents an alkyl group containing up to 4 carbon atoms, R7 represents a hydrogen atom or an alkyl group containing up to 4 carbon atoms, and R8 represents a hydrogen atom, an alkyl group containing up to 4 carbon atoms, a benzyl group or a benzyl group substitu~ed by an alkoxy group containing up to 4 carbon atom.
Preferably, R3 represents a butyl, propyl, ethyl or methyl group.
Advantageously, the invention relates to aforesaid tetrazine derivatives of formula (I) which have one or more of the following features:
(i) Rl represents a methyl or 2-haloethyl group;
(ii) R2 represents a group of the formula -SOR , 5~i~
- 4y -SO2R6, -SO NR7R~, -CoN~7RB or -corl~lNo~ wherein R , R and R~ are as defirle~ hereirlbefore;
(iii) one of A1 and A2 represents a ni.trogen atorn an~
the other represents a group -CR3= wherein R3 is as defined hereinbefore;
(iv) R represents a methyl group;
(v) A represents a nitrogen atom;
(vi) zl represents an oxygen atom; and/or (vii) Z represents an oxygen atom.
Advantageously, the invention relates to aforesaid tetrazine derivatives of formula (I) which have one or more of the following features:
~i) Rl represents the 2-chloroethyl group;
(ii) R2 represents a group of the formula SOR6, -SO2R
-So2NR7R8, -CoNR7R8 or -CONHNO2, wherein R6, R7 and R8 are as defined hereinbefore;
(iii) one of Al and A2 represents a nitrogen atom and the other represents a group -CR3= wherein R3 is as defined hereinbefore;
(iv) R3 represents a methyl group;
(v) A represents a nitrogen atom;
(vi) zl represents an oxygen atom; and/or (vii) z2 represents an oxygen atom.
The invention also relates to pharmaceutical composition, characterized in that it comprises in association with a pharmaceutically acceptable carrier, at least one of tetrazine derivatives described hereinbefore.
The specification of British Patent Application No. 2104522 describes compounds of the general formula shown in Figure II of the drawings wherein Rl represents a hydrogen atom, a cycloalkyl group or a straight- or branched-chain . _ .

alkyl, alkenyl or alkynyl group containing up to 6 carbon atoms, each such alkyl, alkenyl or alkynyl group being unsub.stituted or substituted by trom one to three substituents selected from halogen atoms, straight- or branched-chain alkoxy, alkylthio, alkyl-sulphinyl and alkylsulphonyl groups containing up to 4 carbon atoms, and optionally substituted phenyl groups, and Rll represents a carbamoyl group which may carry on the nitrogen atom one or two groups selected from straight- and branchea-chain alkyl and alkenyl groups, each containing up to 4 carbon atoms, and cycloalkyl groups.
The said tetrazine derivatives of tne formula shown in Figure II possess valuable antineoplastic activi~y, for example against carcinomas, melanomas, sarcomas, lymphomas and leukaemias, and tbey also possess valuable immunomodulatory activity and are of use in the treatment of organ grafts and skin grafts and in the treatment of immunological diseases.
The compounds of the formula shown in Figure I of the present invention possess similar properties with, in certain aspects, an improvement.
The said tetrazine derivatives of the formula shown in Figure II are useful as intermediates in the preparation of some of the compounds of the formula shown in Figure I of the present invention, Eor example as described later in this specification.
Particularly important clas6es of compounds of the formula shown in Figure I include those which exhibit one or more of the following features:-(i) Rl represents a methyl or, more especially, a 2-haloethyl group, in particular a 2-chloroetnyl group;
(ii) R2 represents a group of the formula --SO~6,-S02R6, -So2NR7R&, -CoNR7R8 or -CON~N~2, especially those wherein R6 represents an alkyl, e.g. methyl, group and those wherein R7 represents a hydrogen atom or an alkyl, e.g. methyl, group and R8 represents a hydrogen atom or an alkyl, e.g. methyl, group or a benzyl group optionally substituted by an alkoxy group, e.g. a 4-methoxybenzyl group;
(iii) one of Al and A2 represent a nitrogen atom and the other represents a group -CR3=;
(iv) R3 represents a group R4 wherein R4 represents an alkyl, e.g. butyl, propyl, ethyl or, more particularly, methyl, group;
(v) A2 represents a nitrogen atom;
(vi) zl represents an oxygen atom; and/or (vii) z2 represents an oxygen atom.
Important individual compounds of the general formula shown in Figure I include the following:-&-(N-benzyl N-phenylcarbamoyl)-3-methyl-~3H]-imi~azoL5~l-d~ 2~3~s-tetrazin-4-one~ A, 8-LN-benzyl-N-(4-methoxy~enzyl)carbamoylJ-3-(2-chloroethyl)~-L3H]-imidazoL5~l-dJ-L~2~3~5-tetrazin-4-one, B, &-(N-benzylcarbamoyl)-3-(2-chloroethyl)-L3HJ-imidazoL5,1-d]-1,2,3,5-tetrazin-4-one, C, 3-(2-chloroethyl)-8-LN-(4-metnoxybenzyl)-N-phenylcarbamoyl~-L3H]-imidazoL5,1-d]-1,2,3,5-10 tetrazin-4-one, D, 3-(2-chloroethyl)-8-(N phenylcarbamoyl)-L3H]-imidazol5,1-d]-1,2,3,5-tetrazin-4-one, ~, 8-(N-benzyl-N-phenylcarbamoyl)-3-(2-chloroethyl)-L3HI-imidazoL5,1-d~-1,2,3,5-tetrazin-4-one, F, 3-(2-chloroethyl)-8-(N-methyl-N-phenylcarbamoyl)-L3H]-imidazoL5,1-d]-1,2,3,5-tetrazin-4-one, G, &-car~amoyl-3-(2-chloroethyl)-6-methyl-L3H]-imidazoL5,1-d]-1,2,3,5-tetrazin-4-one, H, 3-(2-chloroethyl)-8-(N,N-dimethylsulphamoyl)-l3H~-imidazoL5,1-d]-1,2,3,5-tetrazin-4-one, I, 3-(2-chloroethyl)-8-(N-methylsulphamoyl)-L3H]-imidazoL5~l-d]-l~2~3~5-tetrazin-4-one~ J, 3-(2-chloroethyl)-8-methylsulphonyl-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one, K, 3-methyl-8-methyls~lphonyl-L3H]-imidazo[5,1-d]-1,2,3,5-tetrazin-4-one, L, 5~
, 3-(2-chloroethyl)-&- LN- (4-methoxybenzyl)-sulphamoyl~-L3HJ-imidazoL5,1-cl]-1,2,3,5-tetrazin-4-one, M, 3-(2-chloroethyl)-8-sulphamoyl-L3H~-imidazoL5,1-d~-1,2,3,5-tetrazin-4-one, N, 8-carbamoyl-3-t2-chloroethyl)-L3H~-pyrazoloL5,1-d~-1,2,3,5-tetrazin-4-one, 0, 8-carbamoyl-3-methyl-[3H¦-pyrazoloL5,1-d~-1,2,3,5-tetrazin-4-one, P, 3-(2-chloroethyl)-8-piperidinocarbonyl-L3H]-imidazoL5,1-d]-1,2,3,5-tetrazin-4-one, Q, 6-butyl-8-carbamoyl-3-(2-chloroethyl)-L3H~-imidazo[5,1-d]-1,2,3,5-tetrazin-4-one, R, 8-carbamoyl-3-(2-chloroethyl)-6-cyclohexyl-L3H~-imidazo[5,1-d]-1,2,3,5-tetrazin-4-one, S, 8-carbamoyl-3-(2-chloroethyl)-6-phenethyl-[3H]-imidazo[5,1-d]-1,2,3,5-tetrazin-4-one, T, 6-benzyl-8-carbamoyl-3-(2-chloroethyl)-L3H]-imidazo[5,1-d]-1,2,3,5-tetrazin-4-one, U, &-carbamoyl-3-(2-chloroethyl)-6-isopropyl-L3H~-imidazo[5,1-a]-1,2,3,5-tetrazin-4-one, V, 8-carbamoyl-3-(2-chloroethyl)-6-propyl-[3H~-imidazo[5,1-dJ-1,2,3,5-tetrazin-4-one, ~, 8-carbamoyl-3-(2-chloroethyl)-6-ethyl-[3H]-imidazo[5,1-d~-1,2,3,5-tetrazin-~-one, X, ~7 ~f~ 7 3-(2-chloroethyl)-&-(4-metnoxybenzyl)sulphamoyl-6-methyl-L3H]-imidazoL5Jl-d~-lt2~3l5-tetrazin-~-oneJ Y, 3-(2-chloroethyl)-6-methyl-8-sulphamoyl~L3~1]-imidazoL5,1-d]-1,2,3,5-tetrazin-4-one, Z, 3-(2-chloroethyl)-8-dimethylsulphamoyl-6~methyl-L3H]-imidazo[5,1-d]-1,2,3,5-tetrazin-4-one, AA, 3-(2-chloroethyl)-6-methyl-8-methylsulphonyl-L3HJ-imidazo~5Jl-d~ 2~3~5-tetrazin-4-one~ BB, 3-(2-chloroethyl)-8-(dimethylcarbamoyl~-[3H]-pyrazoloL5,1-d]-1,2,3,5-tetrazin-4-one, CC, an~ 3-(2-chloroethyl)-8-(N-nitrocarbamoyl)-~3H]-imidazoL5,1-d~-l,2,3,5-tetrazin-4-one, DD, 3-methyl-8-methylsulpbonyl-[3HJ-pyrazolo~5~l-d3-1,2,3,5-tetrazin-4-one, EE, 3-(2-chloroethyl)-8-methylsulphonyl-L3H]-pyrazolo-[5,1-d]-1,2,3,5-tetrazin-4-one, FF, 3-(2-chloroethyl)-6-methyl-~-methylsulphinyl-[3H]-imidazo[5,1-dJ-1,2,3,5-tetrazin-4-one, GG, 3-(2-chloroethyl)-&-ethylsulphonyl-6-methyl-[3H]-imidazo[5,1-d]-1,2,3,5-tetrazin-4-one, HH, and 3-(2-chloroethyl)-6-methyl-8-propylsulphonyl-3H]-imidazo[57l-d]-l~2~3~5-tetrazin-4-one. II.
The letters A to II are allocated to the compounds for easy reference later in the speci~ication.

'~ r~

-Compounds o~ particular irnportance include compounds C, K, L, ~, 0, Q, R, ~, X and DD, more especially compounds I, J, N and BB, and most especial-ly compounds H, Z, AA and CC.
The new tetrazine derivatives of the general formula shown in Figure I have proved particularly active in mice at daily doses between 0.2 and 320mg/kg animal body weigh~, administered intraperitoneally, against TLX5(S) lymphoma according to the procedure of &escher et al., Biochem. Pharmacol. (1~81), 30, &9 and ADJ/PC6A and M5076 (reticulum cell sarcoma).
Against leukaemia L1210, grafted intra-peritoneally, intracerebrally and intravenously, and P3&8, according to the proceaure described in "Methods of Development of New Anticancer Drugs" (NCI Monograph 45, March 1977, pages 147-14~, National Cancer Institute, Bethesda, United States), the compounds were active both intraperitoneally and orally at doses of between 1 and 320mg/kg animal body weight.
Inhibition of both primary tumour and metastasis was obtained against the Lewis lung carcinoma by similar dosage regimes. Against the B16 melanoma and C3&
tumour in mice (NCI Monograph 45, op. cit.) the compounds were active intraperitoneally at doses of between 6.25 and 40 mg/kg animal body weight. Against colon carcinoma C26 in mice, grafted subcutaneously, the compounds were active orally at doses o~ between 2 and 40mg/kg animal Dody weight.
The compounds of the general formula shown in - Figure I may be prepared by the application or adaptation of methods known per se.
According to a feature of the present invention, the compounds of the general formula shown in Figure I wherein R2 is other than a sulphamoyl, mono(optionally substituted phenyl)carbamoyl, mono(optionally substituted phenyl)thiocarbamoyl, nitrocarbamoyl or nitrothiocarbamoyl group are prepared by the reaction of a compound of the general formula shown in Figure III of the drawings ~wherein Al and A2 are as hereinbefore defined and R12 represents a group within the above definition of R2 other than a sulphamoyl, mono(optionally substituted phenyl)carbamoyl, mono(optionally substituted phenyl)-thiocarbamoyl, nitrocarbamoyl or nitrothiocarbamoyl group] ~ith a compound of the general formula:-R1NCZl IV
wherein Kl and zl are as hereinbefore defined.
The reaction may be effected in the absence or presence of an anhydrous organic solvent, for example a chlorinated alkane, e.g. dichloromethane, or ethyl acetate, acetonitrile, N-methylpyrrolidin-2-one or hexamethylphosphoramide, at a temperature between 0 and 120C. The reaction may be continued for up to 30 days.
Light should preferably be excluded from the reaction mixture.
According to a further feature of the present invention, compounds of the general forrnula shown in Figure I wherein R2 represents a sulfamoyl, monosubstituted sulfamoyl, carbamoyl, monosubstituted carbamoyl, thiocarba-moyl, monosubstituted thiocarbamoyl group, R , A , A and Z
being as hereinbefore defined, are prepared from corresponding compounds, within the general formula shown in Figure I, wherein R2 represents a group of the formula -S2NR R or-CZ NR R (wherein R13 re~resents an optionally substituted benzyl group and z2 and R7 are as hereinbefore de-fined) by the application or adaptation of methods known per se for the replacement of optionally substituted benzyl groupsbyhydrogen atoms. Suitable reaction conditions include, for example, catalytic hydrogenation (using a catalyst such as palladium on charcoal and in a solvent such as ethyl acetate or dimethylformamide); or when R13 represents a substituted benzyl group in which the substituent or at least one of the substituents carried by the benzyl group is an al~oxy (e.g.
methoxy) group in the o- or _-position, preferably by reaction with trif1uoroace i' ' ~ r presence of anisole, and usually at or near room temperature.
Accordin~ to a further feature of the present invention, compounds of the general formula shown in Figure I wherein R2 represents a group of the formula -CZ2NHNO2 (z2, Rl, Al, A2 and zl being as hereinbefore defined) are prepared by the nitration of compounds of the general formula shown in Figure V of the drawings wherein R14 represents a group of the formula -CZ2NH2 (z2, Rl, Al, A2 and zl being as hereinbefore defined). The reaction may be carried out near or below room temperature, preferably between 0 and 10C, in the presence of a nitrating mixture such as a mixture of concentrated sulphuric acid and concentrated nitric acid.
According to a further feature of the present invention, compounds of the formula shown in Figure I
wherein Rl, Al, A2, and R2 are as hereinbefore defined and zl represents a sulphur atom are prepared from compounds of the general formula shown in Figure VI of the drawin~s (wherein Rl, Al and R2 are as hereinbefore defined) and R15 represents a group of the formula -S(O)nR6, -So2NR7R&, -CZ2NR7R8 or -CZ2NHN02, R6, R7, R~, n and z2 being as hereinbefore defined) by the action of phosphorus pentasulphide. The reaction may be carried out in an organic solvent, for example an aromatic solvent such as benzene, toluene or xylene, or in pyridine or a derivative such as lutidine, and preferably at an elevated temperature, for example between 50 and 120C.
According to a further feature of the present invention, compounds of formula I wherein Rl, Al, A2 and zl are as hereinbefore de~ined and R2 represents a group of the formula -CSNR7R8 are prepared from compounds of the formula shown in Figure VII of the drawings wherein Rl, Al, A2 and Z1 are as hereinbefore defined and Rl6 represents a group of the formula -CoNR7R8 (R7 and K~ being as hereinbefore defined) by reaction with phosphorus pentasulphide under conditions similar to those described hereinbefore for the reaction of phosphorus pentasulphide with compounds of the formula shown in Figure VI.
The aforementioned salts of certain compounds of the formula showo in Figure I are prepared by the application or adaptation of methods known per .se, for example by reaction of the parent compound of the formula shown in Figure I with an alkali metal hydroxide, carbonate or, preferably, bicarbonate, in an aqueous or aqueous-organic medium, followed by ~ 5 ~7 isolation of the salt by methods known per se.
When a mixture of products is obtained in any of the abovementioned processes they may be separated by the application or adaptation of methods known per se, e.g. chromatography.
Compounds of the general formula shown in Figure III may be prepared by the application or adaptation of methods known per se, for example methods described by Shealy et al., J. Org. Chem.
(1961), 26, 2396, and Cheng et al., J. Pharm. Sci.
(196&), 57, 10447 and methods described hereinafter in the Reference Examples.
By the term 'methods known per se' as used in the present specification is meant methods heretofore 1~ used or described in the literature.

~L'~

The following Examples illustrate the preparation of compounds of general formula I according to the present invention, and the Reference Examples illustrate the preparation of intermediates.

Compound A
Sodiu~ nitrite (0.44g) was dissolved in aqueous acetic acid (2M; lOml) at 0C and the solution was stirred at 0C and treated with finely ground 5-amino-imidazole-4-N-benzyl-N-phenylcarboxamide hydrochloride (0.7g; prepared as described in Reference Example 1) in small portions. After 10 minutes the resulting gummy solid was extracted with eth~l acetate (2 x 20ml). The combined ethyl acetate extracts were washed with water and dried over magnesium sulphate.
The resulting solution of 5-diazoimidazole-4 N-benzyl-N-phenylcarboxamide was treated with methyl isocyanate (5ml) and the mixture was stirred at room temperature in the dark for 24 hours. The solution was then evaporated to low volume and the residue was subjected to medium pressure column chromatography, eluting with ethyl acetate, to give 8-(N-benzyl-N-phenylcarbamoyl)-3-methyl-L3H]-imidazo[5,1-d]-1,2,3,5-tetrazin-4-one (0.22g), in the form of a white, crystalline solid, m.p. 168-170C (with decomposition) LElemental analysis~ 62~6;H~4~41;N~22~3V/o; calculated:
C,63.32;H,4.47;N,23.32%; I.R. (K~r disc): 3100, 1735, 1620cm~l; N~IR (in DMSO-d6):- singlets at 3.75, 5.10 and 8.55ppm, multiplet at 7.0-7.4ppm; m/e 360 S (~+) ] -Com~und ~
Sodium nitrite (3.7g) was dissolved in aqueousacetic acid (2M; 35ml) at 0C and the solution was 10 stirred at 0C and treated with a solution of 5-amino-imidazole-4 N-benzyl-N-(4-methoxybenzyl)carboxamide hydrochloride (2.2g; prepared as described in Reference Example 2) in 1,2-dimethoxyethane (lOml), dropwise. A reddish gum separated which was extracted 15 with ethyl acetate (2 x 20 ml). The combined ethyl acetate extracts were washed with water and with saturated aqueous sodium chloride solution, and dried over sodium sulphate.
The .esulting solution of 5-diazoimidazole-4-20 N-benzyl-N-(4-methoxybenzyl)carboxamide was treated with 2-chloroethyl isocyanate (2ml) and the mixture was allowed to stand at room temperature in the dark for 24 hours. The solution was then evaporated to low volume and the residue was subjected to medium 25 pressure column chromatographyJ eluting with ethyl acetate, to give crude 8-[N-benzyl-N-(4-methoxybenzyl)-carbamoyl]-3-(2-chloroethyl)-L3~]-imidazoL5,1-d]-1,2,3,5-tetrazin-4-one (1.5g) in the form of a brown oil.

Compound C
8-LN-Benzyl-N-(4-methoxybenzyl)carbamoyl]-3-(2-chloroethyl)-L3H]-imidazoL5,1-d]-1,2,3,5-tetrazin-4-one (1.5g; crude material prepared as described in Example 2) and anisole (0.5ml) were dissolved together in trifluoroacetic acid (20ml) and allowed to stand at room temperature for 18 hours. The mixture was then evaporated to dryness and the residue was subjected to medium pressure column chromatography, eluting with a mixture (2:1 v/v) of ethyl acetate and petroleum ether (b.p. 60-80C), to give 8-(N-benzylcarbamoyl)-3-(2-chloroethyl)-L3H]-imidazoL5,1-d]-1,2,3,5-tetrazin-4-one (0.34g), in the form of a colourless solid, m.p.
153-155C (recrystallised from diethyl ether).
LElemental analysis: C~49~5;H~3~92;N~24~4;Cl~10~4~/o;
calculated: C~50~53;H~3~94;N~25~26;C1~10~65~/o; I.R.
(KBr disc) 3370, 3150, 1755 and 1660cm~l; NMR (in D~SO-d6): singlets at 7.3 and 8.9ppm, doublet at

4.4ppm and triplets at 4.0, 4.6 and 9.05ppm].

- L~ -Compound_D
Sodium nitrlte (0.61g) was dissolved in water (lOml) and the solution was stirred at 0C and treated with a solution of crude 5-aminoimidazole-4-~-(4-methoxybenzyl)-N-phenylcarboxamide (2.5g; prepared as described in Reference Example 3) in hydrochloric acid (2M; 9ml) and l,~-dimethoxyethane (15ml), dropwise.
AEter 20 minutes the solution was extracted with ethyl acetate (3 x 50ml) and the combined extracts were dried over magnesium sulphate and evaporated, to give

5-diazoimidazole-4-N-(4-methoxybenzyl)-N-phenyl-carbo;amide (2.8g), in the form of an orange oil.
This oil was dissolved in ethyl acetate (40ml) and treated with 2-chloroethyl isocyanate (8ml). The mixture was allowed to stand in the dark for 5 days.
The solution was evaporated to low volume and the resulting residue was subjected to medium pressure column chromatography, eluting with ethyl acetate, to give 3-(2-chloroethyl)-8-[N-(4-methoxybenzyl)-N-phenylcarbamoyl]-L3H]-imidazoL5,1-d]-1,2,3,5-tetrazin-4-one (1.5g) in the form of a glass, m.p.
55C [NMR (in D~SO-d6):- singlets at 3.6, 5.0 and 8.5ppm, triplets centred at 3.9 and 4.5ppm, multiplet at 6.6-7.2ppm; I.R. (KBr disc) 1740 and 1640cm 1].

~ ~5 - 2~ -Compound E
3-(2-Chloroethyl)-8- LN- (~-methoxybenzyl)-M-phenylcarbamoyl~-[3H]-imidazo~5~l-d~ 2~3~5-tetrazin-4-one (l.Og; prepared as described in Example 4) and anisole (0.2ml) were dissolved together in trifluoroacetic acid (lOml) and the solution was allowed to stand at room temperature for 1~ hours.
The mixture was then evaporated to dryness and the residue was triturated with diethyl ether, to give 3-(2-chloroethyl)-8-(N-phenylcarbamoyl)-L3H~-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one (0.43g), in the form of a tan solid, m.p. 166C (with decomposition) (after recrystallisation from ethyl acetate) LElemental L5 analysis: C,48.4jH,3.22jN,26.0~/o; calculated:
C~48~99jH~3~48;N~26~37~/o; I.R. (KBr disc): 3390, 1735 and 1680 cm 1, NMR (in DMSO-d6):- singlets at 8.9 and 10.3ppm, doublet centred at 7.8ppm, triplets centred at 4.0 and 4.6ppm, multiplet at 7.0-7.9ppm].
EXA~PLE 6 Compound F
Sodium nitrite (2.&g) was dissolved in aqueous acetic acid (2M; 84ml) and the solution was stirred at 0C and treated with finely ground 5-aminoimidazole-4-N-benzyl-N-phenylcarboxamide hydrochloride (2.8g;
prepared as described in Reference Example 1) in small portions. After 10 minutes the resul~ing gummy-solid was extracted with ethyl aceta~e (3 x 80ml) and the combined extracts were washed with water, and then with saturated aqueous sodium chloride solution, and then dried over magnesium sulphate.
The resulting solution of 5-diazoimidazole-4-N-benzyl-N-phenylcarboxamide was trea~ed with 2-chLoroethyl isocyanate (9ml) and the mixture was allowed to stand in the dark at room temperature for 4 lG days. The solution was then evaporated to low volume and the residue was subjected to medium pressure column chromatography, eluting with ethyl acetate, to give 8-(N-benzyl-N-phenylcarbamoyl)-3-(2-chloroethyl)-[3H]-imidazoL5,1-d]-1,2,3,5-tetrazin-4-one (l.Og), in the form of a glass [Elemental analysis: C,59.3;H,4.57;
N,19.9;Cl,8.5V/o; calculated: C,58.75;H,4.15;N,20.56;
Cl,8.67%; I.R. (KBr disc): 1740 and 1640cm~l; NMR
(in DMSO-d6):- singlets at 5.2, 7.1, 7.3 and 8.6ppm, triplets centred at 4.0 and 4.6ppm].

Compound G
A solution of sodium nitrite (llg) in water (50ml) was cooled to 0C and treated with a solution of 5-aminoimidazole-4-N-methyl-N-phenylcarboxamide hydrochloride (4.0g; prepared as described in Reference Example 4) in aqueous acetic acid solution (2M; 40ml), dropwise. After 10 minutes the resulting mixture was extracted with ethyl acetate (4 x lOOml), and the combined extracts were filtered, and dried over magnesium sulphate.
The resulting solution of 5-diazoimidazole-4-N-methyl-N-phenylcarboxamide was treated with 2-chloroethyl isocyanate (llml) and the mixture was allowed to stand in the dark at room temperature overnight. The solution was then evaporated to low volume and the residue was subjected to medium pressure column chromatography, eluting with ethyl acetate, to give a solid (5.75g). This solid was triturated with diisopropyl ether, and then with dichloromethane. The insoluble residue was recrys~allised from a mixture of petroleum ether (b.p. 60-80C~ and ethyl acetate and then from a mixture of ethyl acetate and diisopropyl ether, to give 3-(2-chloroethyl)-8-(N-methyl-N-phenyl-carbamoyl)-[3H]-imidazo-[5,1-d~-1,2,3,5-tetrazin-4-one (0.8g), in the form of a colourless solid, m.p.
130-132 [Elemental analysis C,50.4jH,3.91;N,24.9;
Cl,10.6a/o; calculated: C,50.53;H,3.94;N,25.26;
Cl,10.65V/o; I.R. (KBr disc): 1750 ana 1640cm~l; NMR
(in DMS0-d6):- singlets at 3.4, 7.2 and 8.65ppm, triplets centred at 3.~5 and 4.6ppm].

EXAMPLE 8 -~
Compound H
A stirred suspension of S-diazo-2-methylimidazole-4-carboxamide (1.54g; prepared as described in Reference Example 5) in ethyl acetate (45ml) was treated with 2-chloroethyl isocyanate (6.33g) and the mixture was stirred at ambient temperature for 5 days in the dark. The mixture was then diluted with diethyl ether and the resulting solid was filtered off, washed with diethyl ether and dried in vacuo at ambient temperature, to give 8-carbamoyl-3-(2-chloro-ethyl)-6-methyl [3H]~imidazoL5,1-d]-1,2,3,5-tetrazin-4-one (2.00g), m.p. 170C (with decomposition) LElemental analysis: C,37.0;H,3.49;N,32.8;C1,13.3~/o;
calculated: C,37.44;H,3.54;N,32.75;C1,13.82%].
EXA~lPLE
Compound I
A solution of 5-diazoimidazole-4-(N,N-dimethyl-sulphonamide) (0.55g; prepared as described in Reference Example 6) in dry ethyl acetate (40ml) was treated with 2-chloroethyl isocyanate (3ml) and the mixture was stirred in the dark for 48 hours. The mixture was then evaporated in vacuo at below 40C to about 15ml volume and diluted with dry diethyl ether.
The resulting solid was filtered off, to give 3-(2-chloroethyl)-8-(N,N-dimethylsulphamoyl)-[3H]-~2 - ~4 -imidazoL5,1-dJ-1,2,3,5-tetrazin-4-one (0.68g), in ~he form of greyish needles, m.p. 15S-156C. LElemental analysis: C~30~4;H~3~35;N,26~8;C1~ 8~o; calculated:
C,31.3;H,3.62;N,27.4;Cl,11.6%; I.R. 1755cm~l; NMR
(in DMSO-d6): singlets at 2.80, 8.9Gppm, triplets at 3.99, 4.62ppm].

Compound J
A suspension of 5-diazoimidazole-4-(N-methyl-sulphonamide) (0.7g; prepared as described in Reference Example 7) in ethyl acetate (40ml) was treated with 2-ehloroethyl isocyanate (3ml) and the mixture was stirred in a stoppered flask in the dark for 48 hours. The mixture was then evaporated in vacuo at below 35C to approximately half its volume, an~ was diluted with diethyl ether. The resulting solid was filtered off and washed with diethyl ether, to give 3-(2-chloroethyl)-8-(N-methylsulphamoyl)-[3H]-imidazo-L 5,1-dJ-1,2,3,5-tetrazin-4-one (0.32g), in the form of shining buff plates, m.p. 147-148C LElemental analysis: C~28.5;H~2.~0;N~28~7~/o; calculated:
C,28.7;H,3.08;N,28.7%; I.R. 1745cm~l; NMR (in DMso-d6) doublet at 2.58ppm, triplets at 3.98, 4.61ppm, quartet at 7.~4ppm, singlet at &.84ppm].

s~
- ~5 -Compound K
A solution of 5-diazo-4-methylsulphonyli~idazole (0.65g; prepared as described in Reference Example 8) in dry ethyl acetate (50ml) was treated with 2-chloroethyl isocyanate (3ml) and the mixture was stirred at room temperature in the dark for 48 hours.
The mixture was then evaporated in vacuo and the oily residue was triturated with petroleum ether (b.p.
60-80C). The resulting solid was filtered off and subjected to medium pressure chromatography, eluting with ethyl acetate, and the white solia product was triturated with petroleum ether and filtered off, to give 3-(2-chloroethyl)-&-methylsulphonyl-L3H~-imidazo-L5,1-d]-1,2,3,5-tetrazin-4-one (0.72g), m.p.
154-155C. LElemental analysis: C,30.3jH,2.85;N,25.0;
Cl~ 5~/o; calculated: C,30.28;H,2.90;N,25.22;
Cl~ 55~/o]~
EXA~PLE 12 Compound L
A solution of 5-diazo-4-methylsulphonylimidazole (0.65g; prepared as described in Reference Example 8) in dry ethyl acetate (60ml) was treated with methyl isocyanate (3.5ml) and was left to stand at room temperature in the dark for 3 days. A further quantity of methyl isocyanate (3.5ml) was added and s~

the mixture was warmed at 40C ~or 2 days and then was left to stand at room temperature for 3 days. The~
mixture was then evaporated in vacuo to a volume o~
between lO and 15ml, and was subjected to medium S pressure chromatography, eluting with ethyl acetate, to givP 3-methyl-8-methylsulphonyl-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one (0.17g), in the form of a white crystalline solid, m.p. 185-186C (with decomposition). LElemental analysis: C,31.2;H,2.89;
N~30~3V/o; calculated: C,31.44;H,3.08;N,30.56%].

Compound M
A solution of 5-diazoimidazol~-4-~N-(4-methoxy-benzyl)sulphonamide] (0.3g; prepared as described in Reference Example 9) in dry ethyl acetate (25ml) was treated with 2-chloroethyl isocyanate (1.5g) and the mixture was stirred at room temperature for 4~ hours~
The resulting dark solution was filtered and evaporated to dryness. The resulting brown solid was triturated with petroleum ether, filtered off and subjected to medium pressure chromatography, eluting with ethyl acetate, to give a white solid that was triturated with petroleum ether, filtered off and dried at 70C/lOmmHg for 1 hour, to give 3-(2-chloro-ethyl)-8-~N-(4-methoxybenzyl)sulphamoyl]-L3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one (0.2g), m.p. 155-156C

3~ h~

(with decomposition) L~;~.R. 1745cm~1; Elemental analysis: C~41~9;H~3~72;N~20~5~/o; calculated: C,42.16;
H,3.79;N,21.07%].

Compound N
3-(2-Chloroethyl)-8-LN-(4-methoxybenzyl)sulphamoyl]-[3H]-imidazo-[5,1-d] 1,2,3,5-tetrazin-4-one (O.lg;
prepared as described in Example 13) was dissolved in trifluoroacetic acid (l.Oml) and anisole (3 drops) and the solution was allowed to stand at room temperature for two hours. The mixture was then evaporated in vacuo and the residue was triturated with diethyl ether, to give a yellow solid, which was subjected to medium pressure chromatography, using a mixture of petroleum ether (b.p. 60-80C) and ethyl acetate (1:1 v/v) as eluent, to give 3-(2-chloroethyl)-8-sulphamoyl-[3H]-imidazo[5,1-d]-1,2,3,5-tetrazin-4-one (50mg), in the form of a white solid, m.p. 183C (with decomposition) LI.R. 1750cm~l; NMR (in DMSO-d6):
singlets at 8.8, 7.8ppm, triplets at 4.58, 3.95ppm].

Compound O
A stirred suspension of 3-diazopyrazole-4-carboxamide (5.9g; prcpared as described by Cheng et al., op. cit.) in ethyl acetate (150ml) was treated with 2-chloroethyl isocyanate (24ml) and stirred at ambient temperature for 7 days in the dark; The mixture was diluted with diethyl ether and the resulting solid was filtered off and washed with diethyl ether, to give a mixture in the form of a cream solid (8.36g), m.p. 173-174C (with decompos-ition).
A solution of a sample of the said mixtu~e (l.Og) in dimethyl sulphoxide (20ml) was heated at 60C
overnight. Tbe solution was then evaporated to dryness (at below 60C and at pressures down to O.lmmHg) and the residue was triturated with a mixture of dichloromethane and diethyl ether. The resulting solid was collected and dissolved in boiling acetonitrile (approximately 50ml). The resulting solution was treated with deactivated silica gel (3g containing 20% water) and the mixture was evaporated to dryness. The residue was loaded onto a column of silica gel and subjected to medium pressure chromatography, eluting with ethyl acetate, and recrystallising the product from acetonitrile, to give 8-carbamoyl-3-(2-chloroethyl)-L3H]-pyrazolol5,1-d]-1,2,3,5~tetrazin-4-one (0.25g), in the form of colourless needles, m.p. 203-204C ~with decomposition) LElemental analysis: C,34.8;H,2.92;
N,34.7;C1,14.6~/o; calculated: C,34.65;H,2.91;N,34.64;
Cl,14.61%].

M~
- 2~ -EXAMPL~ 1 Compound P
A stirred suspension of 3-diazopyrazole-4-carboxamide (1.6g; prepared as described by Cheng et al., opu cit.) in dichloromethane (49ml) and N-methylpyrrolid-2-one (2.5ml) was treated with methyl isocyanate (6ml) and stirred in the dark for 7 days.
The mixture was then diluted with diethyl ether and the resulting solid was filtered off, to give a mixture in the form of a cream solid (2.24g), m.p.
179-L81C (with decomposition).
A solution of a sample of this solid (l.Og) in dimethyl sulphoxide (lOml) was treated with deactivated silica gel (8g; containing 20% water) and the mixture was evaporated to dryness (at 60C/O.lmmHg). The residue was loaded onto the top of a column of silica gel and subjected to medium pressure chromatography, eluting with ethyl acetate.
The product was triturated with a small amount of 20 saturated aqueous sodium bicarbonate solution and quickly filtered, to give 8-carbamoyl-3-methyl-[3H]-pyrazolo[S,l-d]-1,2,3,5-tetrazin-4-one (41mg), in the form of a colourless solid, m.p. 170C (with decomposition). [NMR (in DMSO-d6): singlets at 3.95, 7.45, 7.55, 8.50ppm; I.R. (KBr disc): 3400, 3160, 1750 and 1680cm~l~.

Compound~Q
A solution of sodium nitrite (0.79g) in water (6ml) was treated with a solution oE crude 4-amino-5-piperidinocarbonylimidazole hydrocbloride (2.lg; prepared as described in Reference Example 10) in aqueous acetic acid (lM;17ml), dropwise with stirring, at 5-10C during 5 minutes. The solution was extracted with ethyl acetate (4 x 45ml) and the combined extracts were dried over magnesium sulphate and evaporated at 30C/O.lmmHg. The residue was dried in a desiccator over phosphorus pen~oxide for 45 minutes, to give 4-diazo 5-piperidinocarbonylimidazole (1.73g) in the form of red crystals, pure enough for use in the next stage.
A solution of crude 4-diazo-5-piperidinocarbonyl-imidazole (1.73g; prepared as described above) in dry ethyl acetate (53ml) was treated with 2-chloroethyl isocyanate (5.9ml) and the mixture was stirred in the dark for 2 days. The solution was then evaporated at 30C/O.lmmHg and the residue was subjected twice to medium pressure chromatography on silica gel, eluting with a mixture of ethyl acetate and acetonitrile (88:12 v/v). The appropriate fractions were combined and evaporated and the residue was tri~urated with petroleum ether (b.p. 40-60C), to give 3-(2-chloro-ethyl)-8-piperidinocarbonyl-L3H]-imi~azoL5,1-d~-1,2,3,5-tetrazin-4-one (1.46g), in the form of light purple crystals, m.p. 92-94C LElemental analysis: C,45.3;
H,4.98;N,26.1%; calculated: C,46.4;H,4.87;N,27.1%;
N~ (in D~lSO-d6): singlet at 8.7ppm, triplets at 4.6 and 4.0ppm, multiplets at 3.2-3.4 and 1.5-1.8ppm; I.R.
(KBr disc): 1750, 1630cm~l].

Co~pound R
A stirred solution of sodium nitrite (1.61g) in water (5ml) was cooled and maintained at 5-10C and treated dropwise with a solution of 5-amino-2-butylimidazole-4-carboxamide hydrochloride (1.61g;
prepared as described in West German Patent Specification No. 2358509j in hydrochloric acid (lM;
17.7ml) during 5 minutes to give a yellow precipitate, which was filtered off and dried in a desiccator over phosphorus pentoxide, to give 2-butyl-5-diazoimidazole-4-carboxamide (0.47g), in the form of a yellow solid, m.p. 109-111C (with decomposition), pure enough for use in the next stage.
A solution of crude 2-butyl-5-diazoimidazole-4-carboxamide (0.47g; prepared as described above) in ethyl acetate (14ml) was treated with 2-chloroethyl isocyanate (1.5ml) and left to stand in the dark for 24 hours. The resulting fawn solid was filtered off and recrystallised from a mixture of ethyl acetate and acetonitrile, to give 6-butyl-&-carbamoyl-3-(2-chloro-ethyl)-[3H]-imidazo~5,1-d~-1,2,3,5-tetrazin-4-one (0.49g), in the form of colourless crystals, m.p.
165-167C (with decomposition) [Elemental analysis:
C,43.9;H,4.90;N,27.9;C1,12.0%; calculated: C,44.2;
H~5~06;N~28~1;Cl~ 9~/o~

Compound S
A stirred solution of sodium nitrite (0.44g) in water (3.7ml) was cooled and maintained at 5-10C and treated dropwise with a solution of 5-amino-2-cyclohexylimidazole-4-carboxamide hydrochloride (l.lg;
prepared as described in West German Patent Specification No. 2358509) in aqueous acetic acid (2~;
28ml) during 5 minutes. The resulting orange precipitate was filtered off and dried in a desiccator over phosphorus pen~oxide for 1 hour, to give crude 2-cyclohexyl-5-diazoimidazole-4-carboxamide (0.86g), in the form of an orange solid, pure enough for use in the next stage.
A solution of the crude 2-cyclohexyl-5-dLazo-imidazole-4-carboxamide (0.86g; prepared as described above) in ethyL acetate (17ml) was treated with 2-chloroethyl isocyanate (2.Oml) and left to stand in the dark for 24 hours. The resul~ing solid was filtered off and recrystallised from ethyl acetate, to give 8-carbamoyl-3-(2-chloroethyl)-6-cyclohexyl-[3H]-imidazoL5,1-d~ 1,2,3,5-tetrazin-4-one (0.23g), in the form of colourless crystals, m.p. 245-248C (with decomposition) [Elemental analysis: C,47.6;H,5.16i N,25.6;Cl,10.8%; calculated: C,48.1;H,5.28;N,25.9;
Cl,10.5V/o].

Compound T
A stirred solution of sodium nitrite (0.58g) in water (4.7ml) was cooled and maintained at 5-10C and treated dropwise with a solution of 5-amino-2-phenethylimidazole-4-carboxamide hydrochloride (1.8g;
prepared as described in Reference Example 11) in aqueous acetic acid (2~; 18ml) during 5 minutes. The resulting yellow precipitate was filtered off and dried in a desiccator over phosphorus pentoxide for 1 hour, to give crude 5-diazo-2-phenethylimidazole-4-carboxamide (2.0g), in the form of a yellow solid, pure enough for use in the next stage.
A suspension of crude 5-diazo-2~phenethylimidazole-4-carboxamide (2.0g; prepared as described above) in ethyl acetate (29ml) was treated with 2-chloroethyl isocyanate (3.4ml) and stirrea in the dark for 24 hours. The resulting solid was filtered off and recrystallised twice from ethyl acetate, to give ~'5 8-carbamoyl-3-(2-chloroethyl)-6-phenethyl-L3H]-imidazo[5,1-d]-1,2,3,5-t:etrazin-4~one (0.44g), in the form of colourless crystals, m.p. 17~-1&1C (with decomposition) [Elemental analysis: C,51.8;H,4.1g;
N~24~2;Cl~10~2%; calculated: C,52.0;H,4.36;N,24.2;
Cl,10.2%].
~XAMPLE 21 Compound U
A solution of 2-benzyl-5-diazoimidazole-4-10 carboxamide (2.4g; prepared as described in Reference Example 12) in dry ethyl acetate (150ml) was treated with 2-chloroethyl isocyanate (lOml) and the reaction mixture was left to stand at room temperature in the dark for 20 hours. The reaction mixture was then 15 evaporated to dryness and the residue was triturated witb petroleum ether (b.p. 60-80C; 2 x 30ml) to remove excess 2-chloroethyl isocyanate. The remaining residue was then triturated with dichloromethane (2 x 50ml) to extract the desired product from insoluble 20 1,3-bis(2-chloroethyl)urea byproduct. The combined dichloromethane extracts were evaporated to dryness and subjected to medium pressure chromatography on silica gel, eluting with ethyl acetate. The appropriate fractions were combined, evaporated an~
25 recrystallised from ethyl acetate, to give 6-benzyl-8-carbamoyl-3-(2-chloroethyl)-L3H~-imidazo[5,1-d]-1,2,3,5-tetrazin-4-one (0.7g), m.p. 161-163C (with decomposition) LElemental analyais: C,$0.4;~l,3.96;
N,25.4;Cl,10.8V/o; calculated: C,50.53;H,3.g4;N,25.26;
Cl,10.66U/o; I.R. 1740cm 1].

Comp~und V
A solution of 5-diazo-2-isopropylimidazole-4-carboxamide (1.2g; prepared as described in Reference Example 13) in dry ethyl acetate (75ml) was treated with 2-chloroethyl isocyanate (5ml) and the mixture was left to stand in the dark at room temperature for 5 days. The resulting crystalline solid was filtered off and was washed with petroleum ether (b.p.
60-80C), to give 8-carbamoyl-3-(2-chloroethyl)-6-isopropyl-[3H]-imidazo[5,1-d]-1,2,3,5-tetrazin-4~one (0.2g), m.p. 189-190C (with decomposition) [Elemental analysis: C,42.0;H,4.64;N,29.5%; calculated: C,42.19;
H,4.60;N,29.5%; I.R. 1740cm~lJ.
EXA~lPLE 23 Compound W
A solution of sodium nitrite (0.7g) in water (6ml) was added to a solution of 5-amino-2-propylimida~ole-4-carboxamide (1.37g; prepared as described in West German Patent Specification No 2358509) in aqueous acetic acid (2M; 22ml) at 0-5C, dropwise, during 5 minutes. The resulting precipitate was filtered off S~
- 3~ -and dried in a desiccator over phosphorus pentoxide, to give 5-diazo-2-propylimidazole-4-carboxamide (0.56g), in the form of a yellow solid, pure enough for use in the next stage.
A solution of crude 5-diazo-2-propylimidazole-4-carboxamide (0.56g; prepared as described above) in dry ethyl acetate (14ml) was treated with 2-chloro-ethyl isocyanate (1.6ml) and stirred in the dark for 24 hours. The resulting precipitate was filtered off and washed with ethyl acetate, to give 8-carbamoyl-3-(2-chloroethyl)-6-propyl-[3H]-imidazo~5,1-d~-1,2,3,5-tetrazin-4-one (0.48g), in the form of a buff solid, m.p. 145-148C (with decomposition) [Elemental analysis: C,41.1;H,4.4;N,28.5V/o; calculated: C,42.2;
H,4.60;N,29. 5'/0; NMR (in DMS0-d6): singlet at 7.7ppm;
triplets at 4.6, 4.0, 3.2 and l.Oppm, multiplet at 1.8ppm; I.R. (KBr disc): 1750, 1695cm 1].

Compound X
A stirred solution of sodium nitrite (0.44g) in water (3.8ml) was added to a solution of 5-amino-2-ethylimidazole-4-carboxamide (0.80g; prepared as described in West German Patent Specification No 2358509) in aqueous acetic acid (2M; 14ml) at 0-3C, dropwise, during 5 minutes. The resulting precipitate was filtered off and dried in a desiccator over ~z~

phosphorus pentoxide for 1 hour, to give 5-diazo-2-ethylimidazole-4-carboxamide (0.62g), in the form of a yellow solid, m.p. 139C ~with decomposition), pure enough for use in the next stage.
A solution of crude 5-diazo-2-ethylimidazole-4-carboxamide (0.62g; prepared as described above) in dry ethyl acetate (22ml) was treated with 2-chloroethyl isocyanate (2.4ml) and stirred in the dark for 24 hours. The resulting precipitate was filtered off and washed with ethyl acetate, to give 8-carbamoyl-3-(2-chloroethyl)-6-ethyl-L3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one (0.59g), in the form of pale grey crystals, m.p. 172-174C (with decomposition) [Elemental analysis: C,39.7;H,3.98;N,31.0;Cl,13.1%;
calculated: C,39.9;H,4.10;N,31.0;Cl,13.1].

Compound Y
Dry ethyl acetate (lOOml) was treated with 5-diazo-4-(4-methoxybenzyl)sulphamoyl-2-methylimidazole (2.45g; prepared as described in Reference Example 14), followed by 2-chloroethyl isocyanate (3ml) and the reaction mixture was stirred in the dark at room temperature for 56 hours. The mixture was then treated with a further quantity of 2-chloroethyl isocyanate (3ml) and stirred in the dark at room temperature for a further period of 24 hours. The >

reactioo mixture was tnen evaporated to dryness and the residue was triturated with petroleum ether (b.p. 60-80C; 3 x 25ml) to remove excess 2-chloro-ethyl isocyanate. The remaining residue was then triturated with dichloromethane (2 x 50ml) to extract the desired product from insoluble 1,3-bis(2-chloro-ethyl)urea byproduct. The combined dichloromethane extracts were evaporated to dryness and subjected to medium pressure chromatography on silica gel, eluting with ethyl acetate, to give 3-(2-chloroethyl)-8-(4-methoxybenzyl)sulphamoyl-6-methyl-L3H]-imidazo-~S,l-d]-1,2,3,5-tetrazin-4-one (1.5g), m.p. 159-160C
(with decomposition) [I.R. 1760cm~l~.

Compound Z
A solution of 3-(2-chloroethyl)-8-(4-methoxy-benzyl)sulphamoyl-6-methyl-[3H]-imidazo[5,1-d~-1,2, 3,5,-tetrazin-4-one (1.5g; prepared as described in Example 25) in trifluoroacetic acid (lOml) and anisole (10 drops) was left to stand at room ~emperature overnight. The reaction mixture was evaporated in vacuo and the residue was triturated with diethyl ether. The resulting pale brown solid was filtered off and recrystallised from acetone, to give 3-(2-chloroethyl)-6-methyl-8-sulphamoyl-[3H~-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one (0.55g), m.p. 199-200C

~,~d"~

~ - 3~ -(with decomposition) [Elemental analysis: C,29.1;
H~3~02;N~28~8;C1~12~1;S~10~6%; calculated: C,28.12;
H~3~10;N~28~71;Cl~12~11;S~10~95~/o; I.R. 1760, 3310cm~l~ .

Compound AA
A solution of 5-diazo-4-dimethylsulphamoyl-2-methylimidazole (1.8g; prepared as described in Reference Example 15) in dry ethyl acetate (lOOml) was treated with 2-chloroethyl isocyanate (4ml) and the mixture was left to stand for 2 days at room temperature. The mixture was then treated with a further quantity of 2-chloroethy' isocyanate (4ml) and left to stand at room temperature for a further period of 6 days. The reaction mixture was then evaporated in vacuo and the residue was triturated with petroleum ether (b.p. 60-80C; 2 x 25ml). The remaining solid was dissolved in ethyl acetate and subjected to medium pressure chromatograpny on silica gel, eluting with ethyl acetate. The appropriate fractions were combined, evaporated to dryness, and triturated with petroleum ether (b.p. 60-80C), to give 3-(2-chloro-ethyl)-8-dimethylsulphamoyl-6-methyl-[3H]-imldazo [5,1-d~-1,2,3,5-tetrazin-4-one (2.17g), m.p. 137-138C
[Elemental analysis: C,33.8;H,3.91;N,25.8;Cl,11.2;

- ~o -S~9~7%; calculated: C,33.7;H,4.0g;N,26.20;C1,11.05;
Sl 10~0%~ ~

Compound BB
A solution of 5-diazo-2-methyl-4-methylsulphonyl-imidazole (0.4g; prepared as described in Reference Example 16) in dry ethyl acetate (30ml) was treated with 2-chloroethyl isocyanate (2ml) and left to stand at room temperature, in the dark, for 4 days. The mixture was then evaporated to dryness and the residue was triturated with petroleum ether (b.p. 60-80C; 2 x 25ml) to remove excess 2-chloroethyl isocyanate. The remaining residue was dissolved in ethyl acetate and subjected to medium pressure chromatography on silica gel, eluting wit~ ethyl acetate, to give 3-(2-chloroethyl)-6-methyl-8-methylsulphonyl-L3H]-imidazo[5,1-d]-1,2,3,5-tetrazin-4-one (0.22g), m.p.
149-150C [Elemental analysis: C,33.0;H,3.35;N,23.8;
Cl,12.7%;S,10.7%; calculated: C,32.94;H,3.46;N,24.01;
Cl,12.15;S,10.99V/o; I.R. 1745cm~l].

Compound CC
A suspension of 3-diazopyrazole-4-(N,N-dimethyl-carboxamide) hydrochloride (0.92g; prepared as described in Reference Example 17) in dry dichloro-methane (50ml) was treated with 2-chloroethyl ~2~ rj~r7~i~

isocyanate (2.5ml) and the stirred suspension was then treated with 1,~-diazobicycloL5,4,0]undec-7-ene (0.7g).
The resulting solution was stirred at room ~emperature in the dark overnigh~. The dichloromethane was evaporated off and the resulting gum was tritura~ed with petroleum ether (b.p. 60-&0C). The insoluble residue was subjected to medium pressure chromatography, eluting with ethyl acetate. The appropriate fractions were combined, evaporated to dryness and the residue was recrystallised from ethyl acetate, to give 3-(2-chloroethyl)-8-(dimethylcarbam-oyl)-[3H]-pyrazoloL5,1-d~-1,2,3,5-tetrazin-4-one (0.38g) in the form of colourless crystals, m.p.
116-118C (with decomposi~ion) [Elemental analysis:
C,35.7;H,3.96;N,30.9;C1,13.1%; calculated: C,3g.93;
H,4.10;N,31.05;C1,13.1V/o; I.R. (KBr disc): 1770, 1630cm~l; NMR (in acetone-d6): singlets at 3.25 and &.40ppm, triplets at 4.25ppm and 4.95ppm].

Compound DD
Stirred concentrated sulphuric acid (2.5ml) was treated with 8-carbamoyl-3-(2-chloroethyl)-L3H]-imidazoL571-d~-1,2,3,5-tetrazin-4-one (0.24g; prepared as described in British Patent Specification No.
2104522). The mixture was cooled to 0C and treated ~ 42 -dropwise with concentrated nitric acid (d = 1~42; lml).
The solution was maintained at 4C for 1 hour and then was poured on to ice. The precipitated solid was collected, washed with water, and recrystallised from aqueous acetone, to give 3-(2-chloroethyl)-8-(N-nitro-carbamoyl) [3H]-imidazoL5,1-d]-1,2,3,5-tetrazin-4-one ~0.2~g) in the form of colourless crystals, m.p.
160 161C (with decomposition) LElemental analysis:
C,28.6;H,1.89,Cl,12.0;N,33.6%; calculated: C,29.23;
H,2.10;Cl,12.33;N,34.09%; I.R. (KBr disc): 3200, 1750, 1720 and 1620 cm~l; NMR (DMS0-d6) triplets at 4.05ppm (J = 6Hz) and 4.70ppm (J = 6Hz), singlet at 9.05~pm, broad singlet at 8.25ppm; m/e 287/289 (M+)].

Compounds EE, FF, GG, HH and II
By proceeding in a manner similar to that described in Examples 1, 2, 4, 6 to 13, 15 to 25 and 27 to 29 and using the appropriate diaæo compounds as intermediates (prepared by the application or adaptation of methods described in the following Reference Examples), there were prepared:-3-methyl-8-methylsulphonyl-l3H]-pyrazolo[5,1-d]-1,2,3,5-tetrazin-4-one, in the form of a colourless solid, m.p. 182-184C;
3-(2-chloroethyl)-8-methylsulphonyl-[3H]-pyrazolo-[5,1-d]-1,2,3,5-tetrazin-4-one, in the form of a colourless solid, m.p. 166-171C ;
3-(2-chloroethyl)-6-methyl-8-methylsulphinyl-L3H]-imidazoL5,1-d~-1,2,3,5-tetraziD_4_one, in the form of a yellow solid, m.p. 118-120C;
3~(2-chloroethyl)-8-ethylsulphonyl-6-methyl-[3H]-imidazoL5,1-d]-1,2,3,5-tetrazin-4-one, m.p.
146-147C; and 3-(2-chloroethyl)-6-methyl~8-propylsulphonyl-[3H]-imidazo[5,1-d~-1,2,3,5-tetrazin-4-one, in the form of a white crystalline solid, m.p. 85-86C.

~L~

REFER~NCE ~XAMPL~ 1 (i) An intimate mixture o~ 5 nitroimidazole-4-carboxylic acid (2.0 ~) and phosphorus pentachloride (~.67 g) was stirred and heated in an oil bath at 120C for 1 hour. The resul~ing yellow slurry was evaporated at 60C/O.lmmHg for 30 minutes, to give l,6-dinitro-5h,10H-diimidazoL1,5-a:1',5'-d]pyrazine-5,10-dione (1.90 g) in the form of a yellow solid, m.p. 24~-251C (with decomposition). LI.R. (KBr disc):
1750 cm~l; m/e 278 (~+)].
LWindaus, Ber., 1923, 56, 6&4 and Gireva, Chem. Abs., 59, 1622e, using the same method, describe their products as "5-nitroimidazole-4-carbonyl chloride"].
(ii) A mixture of 1,6-dinitro-5H,lOH-diimidazo-Ll,5-a:1',5'-dlpyrazine-5,10-dione (5.&g), N-benzyl-aniline (15g) and tetrahydrofuran (250ml) was heatea at reflux for 6 hours. The tetrahydrofuran was evaporated off in vacuo and the residual gum was partitioned between dilute hydrochloric acid (2N;l litre) and ethyl acetate (1 litre). Insoluble N-benzylaniline hydrochloride was removed by filtration, and the ethyl acetate layer was separated. The aqueous phase was extracted twice more with ethyl acetate and the combined organic phases were washed with dilute hydrochloric acid (2N), and ~ 45 ~

then with water, dried over magnesium sulphate, and evaporated to dryness to ~ive an orange gUM. The gum was triturated twice with boiling diethyl ether, to give a colourless solid, which was crystallised from isopropanol, to give 5-nitroimidazole-4-N-benzyl-N-phenylcarboxamide (4.0g), in the form of colourless flakes, m.p. 237-240C LElemental analysis:
C,62.3;H,4.28;N,17.3~/o; calculated: C,63.35;H;4.38;
N, 17~38%; I.R. (KBr disc): 1665c~ 1~.
(iii3 A solution of 5-nitroimidazole-4-N-benzyl-N-phenylcarboxamide (4.0g) in dry ethanol (450ml) was hydrogenated at 26C and 3 atmospheres pressure, using a Raney nickel catalyst. When hydrogen absorption was complete (after 4 hours 50 minutes), the mixture was filtered, treated with concentrated hydrochloric acid (3.6ml) and evaporated to dryness below 40C.
Trituration of the residue with diethyl ether gave 5-aminoimidazole-4-N-benzyl-N-phenylcarboxamide hydrochloride (3.82g), in the form of a pale yellow solid, m.p. 190-193C (with decomposition) LNMR (in DMS0-d6): singlets at 5.05, 7.1-7.2 and 8.4ppm; I.R.
(KBr disc): 1640cm~l; m/e 292 (~+)J.

(i) A mixture of N-benzyl-N-~4-methoxybenzyl)amine [21.9g; Annalen, (1931), 490, 185J, 1,6-dinitro-SH,lOH-diimidazo[5,1-a:1',5'-d~pyrazine-5,10-dione (6.7g;
prepared as described in Reference Example 1)) and dry tetrahydrofuran (200ml) was heated at reflux for 18 hours. The tetrahydrofuran was evaporated off in vacuo and the residual oily solid was partitioned between dilute hydroehloric acid (2N, 500ml) and ethyl acetate (5~0ml). Insoluble N-benzyl-N-(4-methoxy-benzyl)amine hydrochloride was removed by filtration, and the ethyl acetate layer was separated. The aqueous phase was extracted twice more with ethyl acetate and the combined organic phases were washed with dilute hydrochloric acid (2N), then with water, and then with saturated aqueous sodium chloride solution, and then it was dried over sodium sulphate and evaporated to dryness. The residual gum was subjected to medium pressure column chromatography, eluting with ethyl acetate, to give 5 nitroimidazole-4-N-benzyl-N-(4-methoxybenzyl)carboxamide (2.9g) in the form of a tan solid, m.p. 167-170C [after crystallisation from a mixture of petroleum ether (b.p. 60-80C) and isopropanol] [Elemental analysis:
C,61.3;H,4.93;N,15.3%; calculated: C,62.29;
H,4.95; N,15.25Vlo; I.R. (KBr disc): 3100-2&00, 1640, 1510, 1450 and 1370 cm 1. N~R (in DMSO-d6 at 120C): singlets at 3.76, 4.5, 4.6, 7.3 and 7.8ppm, ~ 47 -doublets centred at 6~5 and 7.Zppm (The NMR
spectrum at room temperature is complicated because of doubling of signals caused by hinaered rotation about the bond linking the amide carbonyl group to the amide nitrogen atom).
(ii) A solution of 5-nitroimidazole-4-N benzyl-N-(4-methoxybenzyl)carboxamide (2.2g) in dry ethanol (200ml) was hydrogenated at room temperature and 3 atmospheres pressure using a Raney nickel catalyst.
When hydrogen absorption was complete (after 2 hours 48 minutes), the mixture was filtered, treated with hydrogen chloride gas, and evaporated to dryness below 40C. Trituration with a mixture of isopropanol and diethyl ether gave 5-aminoimidazole-4-N-benzyl-N-(4-methoxybenzyl)carboxamide hydrochloride (2.2g), in theform of a gummy solid, which decomposed above 70C
[I.R. (KBr disc): 3400-2800, 1640cm~l; NMR (in methanol-d4): singlets at 3.7, 4.4, 4.5, 7.2 and 8.3ppm, doublets centred at 6.7 and 6.9ppm (signals broadened because of hindered rotation about the bond linking the amide carbonyl group to the amide nitrogen atom).

(i) A mixture of 1,6-dinitro-5H,10H-diimidazo-[1,5-a:1',5'-d]pyrazine-5,10-dione (5.5g; prepared as described in Reference Example l),N-(4-methoxybenzyl)-aniline [14.5g; Zechmeister et al, Ber., (1530), 63B, ~ 48 2883] and tetrahydrofuran (250ml) was heated at reflux for 12 hours. The tetrahydrofuran was then evaporated off in vacuo and the residual dark oil was partitioned between dilute hydrochloric acid (2M; lOOOml) and ethyl acetate (lOOOml). The organic layer was separated, washed with water, dried over magnesium sulphate and evaporated to dryness. The resulting solid was triturated with diethyl ether, to give 5-nitroimidazole-4-N-(4-methoxybenzyl)-N-phenyl-carboxamide (3.1~g), in the form of a peach-coloured solid, m.p. 212-215C (after recrystallisation from isopropanol). [Elemental anaylsis: C,60.4;H,4.41;
N~16~0%; calculated: C,61.37;H,4.58;N,15.91%; N~R (in DMSO-d6): singlets at 3.7, 5.0 and 7.7ppm, multiplet at 6.7-7.3ppm; I.R. (KBr disc) 1660cm 1].
(ii) A solution of 5-nitroimidazole-4-N-(4-methoxybenzyl)-N-phenylcarboxamide (2.lg) in dry ethanol (200ml) was hydrogenated at 25C and 3 atmospheres pressure, using a Raney nickel catalyst.
When hydrogen absorption was complete (after 5 hours), the mixture was filtered, and evaporated to dryness.
The residue was triturated with diethyl ether, to give 5-aminoimidazole-4-N-(4-methoxybenzyl)-N-phenyl-carboxamide (1.9g), in the form of a gum.

- ~9 -lA portion of this gum was characterised as its picrate:- 5-aminoimidazole-4-N-(4-methoxybenzyl~-N-phenylcarboxamide (0.15g) was dissolved in dry 1,2-dimethoxyethane (3ml) and treated with a solution 5 of picric acid (0.25g) in 1,2-dimethoxyethane (5ml).
The resulting crystals were filtered off and washed with diethyl ether, to give 5-aminoimidazole-4-N-(4-methoxybenzyl)-N-phenylcarboxamide picrate (0.07g), in the form of a yellow solid, m.p. 20ioC (with decomposi~ion) [Elemental analysis: C,49.1;H,3.64;
N,l6-5%;c~4H2lN7o9 2H20 requires: C,49.1;H,4.29;
N,16.69%3~ .
REFERENCE EXAI~PLE 4 (i) A mixture of 1,6-dinitro-5H,lOH-diimidazo-[1,5-a:1',5'-d]pyrazine-5,10-dione (8.08g; prepared as described in Reference Example 1), N-methyl-aniline (12.44g) and tetrahydrofuran (400ml) was heated at reflux for 24 hours. The tetrahydrofuran was then evaporated off in vacuo and the residual dark solid was treated with boiling diethyl ether. The remaining, undissolved solid was subjected to medium presure column chromatography, eluting with a mixture of ethyl acetate and methanol (1:1 v/v), to give 5-nitroimidazole-4-N-methyl-N-phenylcarboxamide (4.68g), in the form of a white solid, m.p. lg3C
LElemental analysis: C,52.5;H,3.95;N,22.2%;
calculated: C,53.66;H,4.09;N,22.76V/o; I.R. 1660cm~l~.

(ii) A-solution of 5-nitroimidazole-4-N~methyl-N-phenylcarboxamide (l.Og) in dry ethanol (llOml) wa~
hydrogenated at 23C and 3 atmospheres pressure, using a Raney nickel catalyst. When hydrogen absorption was complete (after 1 hour 39 minutes), the mixture was filtered and treated with dry hydrogen chloride gas.
The solution was then evaporated to dryness, to give 5-aminoimidazole-4-N-methyl-N-phenylcarboxamide hydrochloride (0.9g), in the form of an off-white solid, m.p. 100C (with decomposition).
{ This compound was characterised as its picrate:-A solution of 5-aminoimidazole-4-N~methyl-N-phenyl-carboxamide hydrochloride (0.25g) in water (2ml) was treated with a solution of picric acid (0.25g) in 1,2-dimethoxyethane (2ml). The precipitate was filtered off and washed with 1,2-dimethoxyethane, to give 5-aminoimidazole~4-N-methyl-N-phenylcarboxamide picrate (0.12g), in the form of a yellow solid, m.p.
237-238C (with decomposition) [Elemental analysis:
C,45.3;H,3.26;N,21.8%; calculated: C,45.85;H,3.39;
N,22.02%; I.R. (KBr disc): 1640cm 1]~.

REFERENCE EXA~lPL~ S
A stirred solution of sodium nitrite (l.Og) in water (8ml) was cooled to 0C and treated with a solution of 4-amino-2-methylimidazole~5-carboxamide hydrochloride (2.0g; prepared as described in West German Patent Specification No. 2358505) in aqueous acetic acid (2N; 24ml), maintaining the temperature at between -2C and 0C. When the addition was compLete the resulting yellow solid was filtered off and dried in vacuo over phosphorus pentoxide, to give 5-diazo-2-methylimidazole-4-carboxamide (1.26g), m.p. 175C
(explodes).

(i) A stirred aqueous solution of dimethylamine (30% w/w; 35ml), cooled in a cold water bath, was treated with 5-nitroimidazole-4-sulphonyl chloride (4.15g of damp material, freshly prepared from 3.33g of 5-nitroimidazole-4-thiol ammonium salt by the method of Fisher et al, Can. J. Chem., 39, 501), in portions. The mixture was stirred for a further 20 minutes ana was then evaporated in vacuo at below 40C to reduce the volume by half. The mixture was then made strongLy acidic by treatment with concentrated hydrochloric acid and the resulting pale yellow solid was filtered off and recrystallised from dimethylformamide, to give 5-nitroimidazole-4-(N,N-dimethylsulphonamide) (2.73g), in the form of brownish plates, m.p. 282-283C (with decomposition) ~Elemental analysis: C,27.3;H,3.65;N,25.4;S,14~2V/o; calculated:
C~27~3;~3~66;N~25~4;S~14~6J/o]~
(ii) A solution of 5-nitroimidazole-4-(N,N-5 dimethylsulphonamide) (l.Og) in dry ethanol (lOOml) was hydrogenated at 24C and 3 atmospheres using a Raney nickel catalyst. The mixture was then filtered and immediately diluted with diethyl ether (200ml) and treated with dry hydrogen chloride gas until it was 10 slightly acidic. The mixture was then evapora~ed in vacuo at below 30C. The residual solid was dissolved in hot dry ethanol (20ml) and the solution was treated with charcoal, filtered, evaporated to 15ml volume, treated with dry diethyl ether (60ml) and allowed to 15 crystallise. The resulting solid was filtered off, to give 5-aminoimidazole-4-(N,N-dimethylsulphonamide) hydrochloride (0.8g) in the form of pinkish-buff needles, m.p. 188-189C (with decomposition) LElemental analysis: C,26.1;H,4.80;N,23.6;Cl,15.g;
S~l3.9%;C5HloN402S:HCl requires C,26.5;H,4.85;
N~24~7;Cl~15~6;S~14~15//o~
(iii) A stirred solution of sodium nitrite (0.31g) in water (5ml), cooled in an ice-bath, was treated dropwise with a solution oi: 5-aminoimidazole-4-(N,N-dimethylsulphonamide) hydrochloride (0.7g) in dilute hydrochloric acid (2N;3.1ml). The resulting ~ 53 solid was filtered off an~ washed with ice-ccld water, to give 5-diazoimidazole-4-(N,N-dimethylsulphonamide) (0.3&g~, m.p. 10~C (with decompositon). ~I.R. 21&0, 2210cm~l] .
A further portion (0.21g) of slightly less pure product was obtained by extraction of the aqueous liquors at 0C with ethyl acetate, drying the extract over magnesium sulphate and evaporation in vacuo (i) A stirred aqueous solution of methylamine (25% w/w; 35ml), cooled in a cold water-bath, was treated with 5-nitroimidazole-4-sulphonyl chloride (4.15g of damp material, freshly prepared from 3.33g of 5-nitroimidazole-4-thiol ammonium salt according to the method of Fisher et al., ~ cit.), in portions.
The mixture was stirred for a further 15 minutes and was then evaporated in vacuo at below 40C to reduce the volume by half. The mixture was then made strongly acidic by treatment witn concentrated hydrochloric acid and the resulting solid was filtered off and recrystallised from water, to give 5-nitro-imidazole-4-(N-methylsulphonamide) (2~07g)~ in the form of pale yellow blades, m.p. 260-263C (with decomposition) LElemental analysis: C~23~1;H~2~87;
N~27~4;S~15~4~/o; calculated: C~23.3;H~2.~3jN~27.2;
S,15.55%].

~2~r~t;~

(ii) A solution of 5-nitroimidazole-4-(N-methyl-sulphonamide) (l.Og) in dry ethanol (lOOml) was hydrogenated at 24C and 3 atmospheres using a Raney nickel catalyst. The mixture was then filtered and immediately diluted with diethyl ether (200ml) and ~reated with dry hydrogen chloride gas until it was slightLy acidic. The mixture was then evaporated in vacuo at below 30C. The residual solid was dissolved :
in a minimum volume of hot ethanol and the solution was treated with charcoal, ~iltered and diluted with diethyl ether. The resulting solid was filtered off, to give 5-aminoimidazole-4-(N methylsulphonamide) hydrochloride (0.63g), m.p. 178-180C (with decomposition) LElemental analysis: C,22.3;H,4.13;
N,25.5;Cl,16.9%;C4H&N402S:HCl requires C~22~6;H~4~26;N~26~35;Cl~16~7V/o~ ~
(iii) A stirred solution of sodium nitrite (0.285g) in water (4ml), cooled in an ice-bath, was treated d~opwise with a solution of 5-aminoimidazole-4-(N-methylsulphonamide) hydrochloride (0.55g) in dilute hydrochloric acid (2N; 2.8ml). The resul~ing solid was filtered off and washed with ice-cold water, to give 5-diazoimidazole-4-(N-methylsulphonamide) (0.36g), m.p. 150C (with decomposition). LElemental analysis: C,25.2;~,2.47;N,37.0U/o; calculated: C,25.7;
H,2.69;N,37.4~/o; I.R. 2210cm 1].

$ 2~

A further portion (0.07g) of product was obtained by extraction of the aqueous liquors at 0C
with ethyl acetate, drying the extract over magnesium sulphate and evaporation in vacuo.

A solution of sodium nitrite (0.5g) in water (5ml), maintained at 0C, was treated dropwise with a solution of 5-amino-4-methylsulphonylimidazole hydrochloride ~l.Og; prepared as described by Bennett et al, J.A.C.S., 7~(3~, 2188-2151! (1557)] in dilute hydrochloric acid (2N; 5ml). The solution was stirred for a further 15 minutes and was then extractea with ethyl acetate (5 x 20ml). The combined extracts were dried over sodium sulphate and evaporated in vacuo to leave a yellow oil that crystallised on standing, to give 5-diazo-4-methylsulphonylimidazole (0.74g), m.p.
12~-130C [I.R. 2125cm lJ.

(i) A stirred solution of p-methoxybenzylamine (lOg) in water (30ml) was treated with 5-nitro-imidazole-4-sulphonyl chloride (6.8g of damp material, freshly prepared from 6.0g of 5 nitroimidazole-4-thiol ammonium salt by the method of Fisher et al., ~
cit.). The mixture soon set solid, whereupon it was treated with isopropanol (20ml) and triturated, and allowed to stand overnight. The resulting solid was filtered off, washed with ice-cold wa~er, and ~hen it was suspended in water (L50ml) and treated carefully with dilute hydrochloric acid (2N) until the suspension just attained pH2. The resulting yellow solid was filtered off and washed with a little ice-cold water to give 5-nitroimidazole-4- LN- (4 methoxybenzyl)sulphonamide~ (7.42g), m.p. 269-270C
(with decomposition).
(ii) A solution of 5-nitroimidazole-4-LN-(4-methoxybenzyl)sulphonamide] (l.Og) in dry ethanol(lOOml) was hydrogenated for 6 hours at 3 atmosphees using a Raney nickel catalyst (50%). The catalyst was quickly filtered off with the aid of diatomaceous earth and the filtrate was immediately treated with concentrated hydrochloric acid (20ml). The mixture was evaporated to dryness and the resulting residue was triturated with diethyl ether. The solid was filtered off and washed with diethyl ether, to give 5-aminoimidaæole-4- LN- (4-methoxybenzyl)sulphonamide]
(0.25g), m.p. 154-155C.
(iii) A solution of sodium nitrite (0.14g) in water (5ml) was treated dropwise with a solution of 5-aminoimidazole-4- LN- (4-methoxybenzyl)sulphonamide]
(0.5g) in dilute hydrochloric acid (2N; lOml), maintaining the temperature at 0C. The mixture was stirred at 0C for a further 15 minutes and then the solid was filtered off, washed with water and dried over phosphorus pentoxide, to give 5-diazoiimidazole-4-LN-(4-methoxybenzyl)sulphonamide (0.3g), m.p.
144-146C (with decomposition) ~I.R. 2180cm 1].

(i) A solution of piperidine (6.4ml) in dry tetrahydrofuran (92ml) was treated with 1,6-dinitro-diimidazo[l,5-a:1',5'-d~pyrazine-5,10-dione (4.59g;
prepared as described in Reference Example 1) and stirred at room temperature for 1 hour. The mixture was then evaporated and the residue was dissolved in dilute hydrochloric acid (2N; ~2ml). The solution was extracted with ethyl acetate (3 x 200ml) and the combined extracts were dried over magnesium sulphate and evaporated. The residue was subjected to medium pressure chromatography on silica gel, eluting with a mixture of chloroform and methanol (9:1 v/v). The appropriate fractions were combined and evaporated and the residue was washed with diethyl ether, followed by ethyl acetate, to give 4-nitro-5-piperidinocarbonyl-imidazole (2~72g), in the form of a yellow solid, m.p.149-150C. LElemental analysis: C,48.2;H,5.33;N,25.1~/o;
calculated: C,48.2;H,5.39;N,25.0%].

(ii) A solution of 4-nitro-5-piperidinocarbonyl-imidazole (2.68g; prepared as described above) in methanol (27ml) and dimethylformamide (27ml) was treated with platinum oxide (0.27g) and the shaken mixture was hyarogenated at room temperature and atmospheric pressure. When hydrogen uptake was complete, the mixture was fil~ered and the filtrate was evaporateà in vacuo. The residue was dissolved in dilute hydrochloric acid (2N; 50ml), the solution was filtered and tne filtrate was evaporated in vacuo.
The resulting residue was washed witn acetone, to give 4-amino-5-piperi~inocar~onylimidazole nydrochloride (2.1g), in thé form of a pale green solid, m.p.
175-177C, pure enough for use in the next stage.

(i) A stirred solution of 2-cyanoethylbenzene (5.0g) and benzyl mercaptan (&.Og) in dly dioxan (~Omlj was treated with hydrogen chloride gas until saturated (3 hours), an~ left to stand at room temperature for 5 days. The mixture was then treated witb diethyl ether and the resulting precipitate was filtered off and washed with diethyl ether, to give S-benzyl 3-phenylpropionothioimidate hydrochloride (9.7g), in the form of a colourless solid, m.p.
15&-160C, pure enough for use in the next stage.
(ii) A solution of ~-amino-.~-cyanoacetamide (3.3g) in ethanol (20ml) was treate~ with crude S-benzyl-3-phenylpropionothioimidate hydrochloride (9.7g; prepared as described above) and the mixture was heated at reflux for 15 minutes. The mixture was : /
- 5~ -cooled and the resulting solid was filtéred o~f and recrystallised from methanol, to give 5-amino-2-phenethylimidazole-4-carboxamide hydrochloride (2.3g), in the form of colourless crystals, m.p. 270-274C
LElemental analysis: C,53.8;H,5.55;N,21. l~/o;
C12H14N40:HCl requlres: C~54.0;H~5.67;N~21.0~/o].
REFERENCE EXA~PLE 12 A solution of sodium nitrite (0.5g) in water (15ml~ maintained at 0-5C was treatea dropwise with a solution of 5-amino-2-benzyl-4-carbamoylimidazole (1.26g; prepared as described in West German Patent Specification No 2358509~ in dilute hydrochloric acid (2N;15ml). The mixture was stirred at 0C for a further period of 30 minutes and the resulting pale yellow solid was filtered o~, washed with water and dried in a desiccator over phosphorus pentoxide, to give 2-benzyl-5-diazoimidazole-4-carboxamide (O.&g), m.p. 121-122C (with decomposition) LI.R. 2180cm~l~.

(i) A solution of isobutyronitrile (6.9g) and benzyl mercaptan (20ml) in dry dioxan (lOOml) was treated with dry hydrogen chloride gas for 3 hours at 0-10C. The mixture was then alLowed to warm to room temprature and the vessel was closed and allowed to stand at room temperature for 14 days. The mixture was then poured onto diethyl ether (1 litre) and the

- 6~ -resulting ~hite precipitate was filtered off and washea with diethyl ether, to give S-benzyl isobutylthi imidate hydrochloride (20.3g), mOp. 165-16~C
[Elemental analysis: C,57.1;H,7.0;N,5.9;Cl,15.7;
S~13.5/o;C11~15NS:HCl requires: C,57.5;H,7.02;
N~6.l;cl~l5.43;sJl3.~6vlo] .
(ii) A solution of~-amino-c~-cyanoacetamide (5.0g) and S-benzyl isobutylthioimidate hydrochlvride (11.5g; prepared as described above) in ary 2-ethoxyethanol (150ml) was heated at reflux for 30 minutes. The solvent was evaporated. The resulting dark oil was triturated with a mixture o~ chloroform and methanol (4:1 v/~; lOOml) and the insoluble material was filtered OLf and discarded. The filtrate was subJectea to medium pressure chromatography on silica gel, eluting with a mixture of chloroform ana methanol (4:1 v/v). The appropriate fractions (identified with ninhydin spray on a sample, which gave an intense yellowish brown colour) were combined and evaporated, to give 5-amino-2-isopropylimidazole-4-carboxamide hydrochloride (4.44g) in the form of a gummy solid, pure enough for use in the next stage.
(iii) A solution o~ sodium nitrite (0.5g) in water (5ml) maintained at 0C was treated dropwise with a solution of crude 5-amino-2-isopropylimidazole-4-carboxamide hydrochloride (l.lg; prepared as descriDed above) in aqueous acetic acid (2N; 20ml). The ~ Z,~ 3~
, ' _ 61 mixture was then stirred for a further period of S
minutes at 0C anc1 then was extracted with ethyl acetate (3 x 2Gml). The combined extracts were dried -over magnesium sulphate, concentrated ln vacuo to a volume of 20ml, and subjectea to medium pressure chromatography on siLica gel, eluting with ethyl acetate. The appropriate fractions (iaenti~ied with 2-naphthol spray on a sample, which gave a deep red colour) were combined ana evaporated to dryness, to give 5-diazo-2-isopropylimidazole-4-carboxamide (0.43g), m.p. 120C (with decomposition) LI.R.
2170cm~l].
REF~RENCE EXA~L~ 14 -(i) A cooled, stirred solution of 2-methyl-5-nitroimidazole (127g) in aqueous sodium hydroxide solution (52 w/v; 1500ml) was treated with bromine (160g), maintaining the temperature at 15-~0C. The mixture was stirred at room temperature for 5.5 hours and the solid which had precipitated was redissolved by treatment of the mixture with aqueous sodium hydroxide solution (2N). Traces of insoluble material were filtered off and the filtrate was acidified to pHl ~y treatment witn concentrated hydrochloric acid.
The resulting white solid was filtered off, recrystallised from ethanol and dried in a desiccator over phosphorus pentoxide, to give 4-bromo-2-methyl-5-~ nitroimidazole (151g), in the forrrl of a white crystalline solid, m.p. 267-26~C.
(ii) A stirred solution o~ 4-bromo-2-methyl-5 - nitroimidazole (20.6gms; prepared as described above) in aqueous ammonia solution (5N; 180ml) was warmed at 45C and treated with a steady stream of hydrogen sulphide gas for 40 minutes. A yellow crystalline solid was slowly ~ormed. Yhe mixture was coolea in ice and the solid was filtered o~, washed with ice-water, and dried in a desiccator over phosphorus pentoxide, to give 4-mercapto-2-methyl-S-nitroimidazole ammonium salt (14.6g), darkens without melting below 300C LElemental analysis: C,27.2;H,4.41;N,31.6;
S,l~.2/o;c4H4o2N3s:NH4 requires: C,27.27;
H,4.58;N,31.8;S,1&.2V/o~.
(iii) An ice-cooled, vigorously stirred solution of 4-mercapto-2-metnyl-5-nitroimidazole ammonium salt (3.51g; prepared as described above) in dilute hydrochloric acid (lN; 120ml) was treated with chlorine gas until a white solid had been formed. The mixture was stirred for a further period of 30 minutes at 0C and then the solid was filtered off, washed with water and dried in a desiccator over phosphorus pentoxide, to give 4-chlorosulphonyl-2-methyl-5-nitroimidazole (3.0g); m.p. 160-162C (with decomposition) LElemental analysis: C,2U.&;~,1.73;

- 6~5 ~

N~18~3;C1~15~7;S~14~6~/o; calculated: C,21.25;H,1.7~;
N~18~63;Cl~15~72;S~14~21V/o~ ~
(iv) A cooled solution o~ 4-methoxybenzylamine (5.48g) in dry absolute ethanol (20ml~ was treated with 4-chlorosulphonyl-2-methyl-5-nitroimidazole (2.25g; prepared as described above) and the mixture was stirred at room temperature for 3 hours. The yellow soli~ which precipitated was filtered off, washed with ethanol and discarded as 4-methoxybenzyl-amine hydrochloride. The combined filtrate and washings were evaporated to dryness and the resulting residue was suspended in wa~er (50ml), acidified to pHl by treatment with concentrated hydrochloric acid, and extracted with ethyl acetate (3 x 20ml). The combined extracts were dried over magnesium sulphate and evaporated to dryness, to give 4-(4-metnoxy-benzylsulphamoyl)-2-methyl-5-nitroimidazole (2.77g), in the form of an o~f-white solid, m.p. 167-170C
Lelemental analysis C~44~2;H~4~32;N~17~2;S~9~5V/o;
calculated: C,44.17;H,4.32;N,17.17;S,5.83%].
(v) A solution of 4-(4-methoxybenzyl-sulphamoyl)-2-methyl-5-nitroimidazole (4.5g; prepared as described above) in dry ethanol (120ml) was hydrogenated at 3 atmospheres pressure over a Raney nickel catalyst for 30 minutes. The catalyst was filtered off and washed with dry ethanol (lOml) and the combined filtrate and washings were acidified to pHl by treatme~t with concentrated hydrochloric acid and evaporated to dryness. The resulting residue was triturated with diethyl ether, to give 5-amino-4-(4-methoxybenzylsulphamoyl)-2-methylimidazole hydrochloride (3.25g); m.p. 183-185C.
(vi) A solution of sodium nitrite (0.3g) in water (5ml) maintained at 0-5C was treated dropwise with a solution of 5 amino-4-(4-methoxybenzyl-sulphamoyl)-2-methylimidazole hydrochloride (l.Og;
prepared as described above) in dilute hydrochloric acid (2N; lOml). The mixture was stirred for a further period of 5 minutes at 0-5C and the resulting orange solid was filtered off, washed with water and dried in a desiccator over phosphorus pentoxide, to give 5-diazo-4-(4-methoxybenzylsulphamoyl)-2-methyl-imidazole (0.75g), m.p. 140C ~with decomposition) [I.R. 2200cm~l~.

(i) An ethanolic solution of dimethylamine (33U/o w/v; lOml) was cooled and stirred and treated portionwise with 4-chlorosulphonyl-2-methyl-5-nitro-imidazole (2.25g; prepared as described in Reference Example 14) and stirred at room temperature for a further period of 45 minutes. The solution was acidified to pHl by treatment with concentrated hydrochloric acid and the resulting white solid was filtered off and washed wit~ cold water, to give ~ ~5 4-dimethylsulphamoyl-2-methyl-5-nitroimidazole ~ g), m.p. 240-241C lElemental analysis: C,30.5;H,4.24;
N~23~8;S~13~8~/o; calculated: C,30.77;H,4.3;N,23.~2;
S,13.69~/o; NM~ (in D~SO-d6): singlets at 2.30 and 2.80ppm~.
(ii) A solution of 4-dimethylsulphamoyl-2-methyl-5-nitroimidazole (12g; prepared as described above) in dry ethanol (300ml) was hydrogenated at 3.5 atmospheres pressure over a Raney nickel catalyst for 1 hour. The catalyst was filtered off and the filtrate was acidified to pHl by treatment with concentrated hydrochloric acid and evaporated to dryness. The resulting orange residue was triturated with diethyl ether, to give 5-amino-4-dimethyl-sulphamoyl-2-methylimidazole (8.9g), m.p. 215-217C
(with decomposition).
~ iii) A solution of sodium nitrite (l.Og) in water (15ml) was maintained at 0C and treated dropwise with a solution of 5-amino-4-dimethyl-sulphamoyl-2-methylimidazole (2.4g) in dilute hydrochloric acid (2N; 30ml), and stirred for a further period of 10 minutes at 0C. The mixture was extracted with ethyl acetate (5 x 30ml) and the combined extracts were dried over magnesium sulphate, evaporated to dryness and triturated with petroleum ether (b.p. 60-80C), to give 5-diazo-4-dimethyl-~ 5 - sulpnamoyl-2-methylimidazole (l.~g), ~I.p. 85-~7UC
(with decompositon) LI.~, 21&0cm~l~.
R~FEX~NCE ~XAMPLE 16 (i) A solution of 4-mercapto-2-methyl-5-nitro-imidazole ammonium salt (10.5g; prepared as described in Reference Example 14) in methanolic sodium met~oxide solution Lprepared by carefuily dissolving sodium (2.3g) in dry methanol (250ml)~ was treated with methyl iodide (10.7g) and heated at reflux for 2 hours. The mixture was then evaporated to dryness and the residue was suspended in aqueous sodium hydroxide solution (2N; lOOml). The suspension was filtered and tne fil~rate was acidified to pHl by treatment with concentrated hydrochloric acia, to give 2-methyl-4-methylthio-5-nitroimidazole (9.Og), in the rorm of a yellow solid, m.p. 236-237C (with decomposition) [Elemental analysis: C,34.7;H,4.04;N,24.3jS,18.5V/o;
calculated: C~34.67;H~4.07;N,24.26;S~L8.51J/o]~
(ii) A solution o~ 2-methyl-~-methylthio-5-nitroimidazole (3.46g; prepared as described above) in glacial acetic acid (35ml) was heated at 60C and treated dropwise with aqueous hydrogen peroxide solution (30% w/v; 35ml). The mixture was then heated at 100C for 15 minutes, coolea to room temperature and treated with suf~icient sodium sulphite to destroy the excess of hydrogen peroxide (detected by testing a sample with starch and potassium iodide). The mixture v was then subjected to continous liquid-liquid extraction with ethyl aceta~e for 20 hours. The extract was evaporated and the remaining white solid was triturated with petroleum ether (b.p. ~0-&0C) and filtered off, to give 2-methyl-4-methylsulphonyl-5-nitroimidazole (3.6g), m.p. 222-224C Lelemental analysis: C,29.8;H,3.28;N,20.6;S,15.7V/o; calculated:
C~25~27;H~3~44;N~20~48;S~15~63~/o]~
(iii) A solution of 2 methyl-4-methyl-sulphonyl-5-nitroimidazole (4.9g; prepared as described above) in dry ethanol (400ml) was hydrogenated at 3.5 atmospheres pressure over a Raney nickel catalyst for 30 minutes. The catalyst ws filtered off and the filtrate was acidified to pH 1 ~y treatment with concentrated hydrochloric acid and evaporated to dryness and the resulting residue was triturated with diethyl ether containing a trace of ethanol to give a purple solid which was filtered off and washed with diethyl ether, to give 5-amino-2-methyl-4-methylsulphonylimidazole hydrochlori~e (4.1g), m.p. above 300C ~Elemental analysis: C,27.3;
H,4.51;N,l9.9;C1,17.9;S,13.7V/o; calculated: C,28.37;
H,4.76;N,19.8;Cl,16.75;S,15.15%].
(iv) A solution of sodium nitrite (0.25g) in water (5ml), maintained at 0C, was treatea dropwise with a solution of 5-amino-2-methyl-4-methylsulphonyl-~d~

imidazole hydrochloride (0.53g; prepare~ as aescribed above). The mixture was stirred Eor a furtner period of 15 minutes at 0C and was ex~racted with ethyl acetate (5 x 15ml). The comDined extracts were dried over magnesium sulphate and evaporated to dryness.
The resulting oil was ~riturated with petroleum ether (b.p. 60-80C) to give 5-diazo-2-methyl-4-methyl-sulphonylimidazole (0.4g), m.p. 1~0C (with decomposition) LI.R. 21&5cm~l].

(i) A mixture of ~-cyano-N,N-dimethylacetamide (~.2g; prepared as described by Bowman et al., J. Chem Soc., 1954, 1171), acetic anhydride (21ml) and triethyl orthoformate (21ml) was heated at 160-170C
in a flask fitted with a McIntyre head for 90 minutes, during which time 26ml of ethyl acetate distillate was collected. The reaction mixture was concentrated in vacuo to give a dark oil, which was treated with ethanol (lOml) and concentrated in vacuo again. The residue was distilled at 160-170C/0.5mmHg and then subjected to medium pressure chromatography on silica gel, eluting with ethyl acetate, to give 2-cyano-3-ethoxy-N,N-dimethylpropenamide (5.3g) in the form of an off-white, oily solid, pure enough for use in the next stage.

~ ,3 _ 69 (ii) A solution ot crude 2-cyano-3-ethoxy-N,~I-dimethylpropenamide (5.3g; prepared as describe~
above) in dry ethanol (SOml) was treated dropwise with hydrazine hydrate (1.58g). After the addition was complete the mixture was heated at re~lux for 6 hours and then was evaporated to dryness. The residue was substituted to medium pressure chromatography on silica gel, eluting with a mixture of chloroform and methanol (17:3 v/v) and the appropriate fractions were combined and evaporated to dryness. The resulting residue was dissolved in hot isopropanol (5ml) and treated with concentratea hydrochloric acid (4ml) and the resulting crystalline precipitate was collected, to give 3-aminopyrazole-4-(N,N-dimethylcarboxamide) hydrochloride (1.3~g), in the form of colourless crystals, m.p. 195C. LElemental analysis: C,37.8;
H~5~82;N~29~0;C1~18~3~/o; calculated: C,37.8;H,5.82;
N,29.39;Cl,1&.6%; I.R. (K~r disc): 3500, 3400, 3000-2200, 1655cm~l; NMR (in DMSO-d6): singlets at 3.0 and 8.lppm and broad singlet at 7.2ppmj.
(iii) A saturated solution of dry hydrogen chloride in dry methanol (70ml) was treated with 3-aminopyrazole-4-(N,N-dimethylcarboxamide) hydro-chloride (1.3~g; prepared as described above). The stirred mixture was cooled to 0C and treated with amyl nitrite (2.55g), dropwise during 15 minutes, _ 70 maintaining the temperature at 0C. The resulting solution was left to stand at 2-4C for 1 hour an~ was then poured into diethyl ether (800al1). The resulting solid was collected and washed with diethyl etner, to give 3-diazopyrazole-4-(N~N-dimethylcarboxamide) hydrochloride (0.92g), in the form of colourless crystals, m.p. 150C (explodes). LElementaL analysis:
C,35.3;H,3.79jN,34.3%;C6H70N5Cl;HCl requires:
C~35~74;H~4~00;N~34~74~/o; I.R. (KBr disc): 3000-2100, 2280, 1630cm~l~.

The present invention includes within its scope pharmaceutical compositions which compriset as active ingredient, at least one compound of the general formula shown in Figure I, together with a pharmaceutical carrier or coating. In clinical practice the compounds of the general formula shown in Figure I will normally be administered orally, rectally, parenterally, for example intraperitoneally or intravenously, e.g. by infusion, or vaginally.
~ethods of presentation o~ pharmaceutically active compounds are well known in the art and a suitable vehicle may be determined by the physician or pharmacist, depending upon such factors as the effect sought, the size, age, sex and condition of the patient and on the properties of the active compound.
The compositions may also contain, as is usual in the art, such materials as solid or liquid diluents, wetting agents, preservatives, flavouring and colouring agents and the like.
Solid compositions for oral administration include compressed tablets, pills, dispersible powders, and granules. In such solid compositions one or more of the active compounds is, or are, admixed with at least one inert diluent such as calcium carbonate, potato starch, alginic acid, or lactose. The compositions may also comprise, as is normal practice, additional - 72 _ substances other than inert diluents, e.g. lubricating agents, such as magnesium stearate. Liqui~
compositions for oral administration include pharmaceutically~acceptable emulsions, solutions, suspensions, syrups and elixirs containing inert diluents commonly used in the art, such as water and liquid paraffin. Besides inert diluents such compositions may also comprise adjuvants, such as wetting and suspending agents, e.g. polyvinyl-pyrrolidone, and sweetening, flavouring, perfuming andpreserving agents. The compositions according to the invention, for oral administration, also include capsules of absorbable material such as gelatin containing one or more of the active substances with or without the addition of diluents or excipients.
Solid compositions for vaginal administration include pessaries formulated in manner known ~ se and containing one or more of the active compounds.
Solid compositions for rectal administration include suppositories formulated in manner known per se and containing one or more of the active compounds.
Preparations according to the invention for parenteral administr~tion incLude sterile aqueous or non-aqueous solutions, suspensions, or emulsions.
Examples of non-aqueous solvents or suspending media are polyethylene glycol, dimethyl sulphoxide, vegetable oils such as olive oil, and injectable

- 7~ -organic esters such as ethyl oleate. These compositions may also include adjuvants such as preserving, wetting, emulsifying and dispersing agents. They may be sterilised, for example, by filtration through a bacteria-re~aining filter, by incorporation of sterilising agents in the compositions, or by irradiation. They may also be manufactured in the form of sterile solid compositions, which can be dissolved in sterile water or some other sterile injectable medium immediately before use.
The percentage of active ingredient in the compositions of the invention may be varied, it being necessary that it should constitute a proportion such that a suitable dosage for the therapeutic effect desired shall be obtained. Obviously several unit dosage forms may be administered at about the same time. In general, the preparations should normally contain at least 0.025% by weight of active substance when rquired for administration by injection, including administration by infusion; for oral administration the preparation will normally contain at least 0.1% by weight of active substance. The dose employed depends upon the desired therapeutic effect, the route of administration and the duration of the treatment.

The tetrazine derivatives of general formula I ar~
useful in the treatment of malignant neopLasms, for example carcinomas, melanomas, sarcomas, lymphomas and leukaemias, at doses which are generally between 0.1 and 200, preferably between 1 and 20, mg/kg body weight per day.
The following Composition Examples illustrate pharmaceutical compositions according to the presen~
invention.
COMPO~SITION EXAMPLE 1 A solution suitable for parenteral administration was prepared from the following ingredients:-

8-(N-benzyl-N-phenylcarbamoyl)-3-methyl-[3H]-imidazol5,1-d]-1,2,3,5-tetrazin-4-one 1.0 g dimethyl sulphoxide 10 ml by dissolving the 8-(N-benzyl-N-phenylcarbamoyl)-3-methyl-[3H]-imidazoL5,1-d]-1,2,3,5-tetrazin-4-one in the dimethyl sulphoxide. The resulting solution was divided, under aseptic conditions, into ampoules at an amount of 1.1 ml per ampoule. The ampoules were sealed, to give 10 ampoules each containing 100 mg of 8-(N-benzyl-N-phenylcarbamoyl)-3-methyl-[3H]-imidazo-L5,1-d]-1,2,3,5-tetrazin-4-one.
Similar ampoules containing solutions suitable for parenteral administration may be prepared by proceeding in a similar manner but replacing the 3~ b~

8-(N-benzyl-N-phenylcarbamoyl-3-methyl-~3H]-imidazo-[5,1-d~-1,2,3,5-tetrazin-4-one by another col-npound of the general formula shown in Eigure I.
COMPOSITLON ~XAMPLE 2 A solution suitable for parenteral administration was prepared from the following ingredients:-3-(2-chloroethyl)-8-(N-methylsulphamoyl)-L3H3-imiàazo[5,1-d~-1,2,3,5-tetrazin-4-one 1.0 g dimethyl sulphoxide 10 ml 10 arachis oil 90 ml by dissolving the 3-(2-chloroethyl)-8-(N-methyl-sulpbamoyl)-~3~j-imidazoL5,1-dj-1,2,3,5-tetrazin-4-one in the dimethyl sulphoxide and adding the arachis oil. The resulting solution was divided, under aseptic conditions, into ampoules at an amount of 10 ml per ampoule. The ampoules were sealed, to give 10 ampoules each containing 100 mg of 3-(~-chloro-ethyl)-8-(N-methylsulphamoyl)-L3H]-imidazoL5,1-d]-1,2,3,5-tetrazin-4-one.
Similar ampoules containing solutions suitable for parenteral administration may be prepared by proceeding in a similar manner but replacing the 3-(2-chloroethyl)-8-(N-methylsulphamoyl)-[3H]-imiaazo-L5,1-d~-1,2,3,5-tetrazin-4-one by another compound of the general formula shown in Figure I.

7~ ~
COMPOSITION EXAM~LE 3 Capsules suitable for oral administration were preparea by placing 3-(2-chloroethyl)-8-(N-methyl-sulphamoyl)-[3H]-imidazoL5,1-d]-1,2,3,5-tetrazin-4-one into gelatin shelLs of number 2 size at a rate of 10 m8 per capsule.
Similar capsules may be prepared by using another compound of the general formula shown in Figure I or any other conveniently sized capsule shells.

s~
--i 77 _ R2 ~1 1 ~N ;~

zl \~ N ~ N~

FIG. I FIG. II

R12 ~2~ /~\~

FIG. III FIG. V

~ R A~Z\N\Rl FIG. VI FIG. VII

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Process for the preparation of tetrazine derivatives of the general formula:

(I) [wherein R1 represents a cycloalkyl group containing 3 to 8 carbon atoms, or a straight- or branched-chain alkyl, alkenyl or alkylnyl group containing up to 6 carbon atoms, each such alkyl, alkenyl or alkylnyl group being unsubsti-tuted or substituted by from one to three substituents selected from the group consisting of halogen atoms, straight- or branched-chain alkoxy, alkylthio, alkylsulphi-nyl and alkylsulphonyl groups containing up to 4 carbon atoms, and phenyl groups (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group); A1 represents a nitrogen atom or a group -CR3 =
wherein R3 represents a hydrogen atom or a substituent R4 wherein R4 represents a halogen atom, or a straight- or branched-chain alkyl or alkenyl group, containing up to 6 carbon atoms, which may carry up to 3 substituents selected from the group consisting of halogen atom, phenyl group, phenyl group substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, straight-or branched-chain alkoxy, alkylthio and alkylsulphonyl groups containing up to 3 carbon atoms, or R4 represents a cycloalkyl group containing 3 to 8 carbon atoms, a cyano, hydroxy, nitro, phenoxy group or phenoxy group substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, or a group of the forrnula -COR5 (wherein R5 represents an alkyl or alkoxy group of up to 4 carbon atoms, a hydroxy group, a phenyl group or a phenyl group substi-tuted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group) or an alkanoylamino group containing up to 6 carbon atoms, or R4 represents a group of the formula -S(O)nR6, -SO2NR7R8 or -CZ2NR7R8 (wherein n represents 0, 1 or 2, R6 represents a straight- or branched-chain alkyl or alkenyl group, containing up to 4 carbon atoms, which may carry a phenyl substituent (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group), a cycloalkyl group containing 3 to 8 carbon atoms or a phenyl group(unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group) R7 and R8, which may be the same or different, each represents a hydrogen atom or a straight- or branched-chain alkyl or alkenyl group, containing up to 4 carbon atoms, which may carry a phenyl substituent (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group) or a cycloalkyl group containing 3 to 8 carbon atoms or a phenyl group (unsubstituted or substi-tuted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group) or the group -NR7R8 represents a 5,6 or 7 membered heterocyclic ring which may contain a further heteroatom selected from the group consisting of nitrogen, oxygen and sulfur, said heterocyclic ring being unsubsti-tuted on substituted by one or two substituents selected from the group consisting of straight- or branched- chain alkyl substituents each containing up to 4 carbon atoms, and Z2 represents an oxygen or sulphur atom) A2 represents a nitrogen atom or, when A1 represents a nitrogen atom, A2 represents a nitrogen atom or a group -CR3= wherein R3 is as hereinbefore defined, Z1 represents an oxygen or sulphur atom; and R2 represents a group of the formula -S(O)nR6, -SO2NR7R8, -CSNR7R8, -CONR7R9 or -CZ2NHNO2, wherein n, R6, R7, R8 and Z2 are as hereinbefore defined, and the group -NR7R9 represents a 5,6 or 7 membered heterocyclic ring which may contain a further heteroatom selected from the group consisting of nitrogen, oxygen and sulfur, said heterocyclic ring being unsubstituted or substituted by one or two substituents selected from the group consisting of straight- or branched-chain alkyl substituents each containing up to 4 carbon atoms, or R7 is as hereinbefore defined and R9 represents a straight- or branched-chain alkyl or alkenyl group containing up to 4 carbon atoms which carries a phenyl substituent (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group) or a phenyl group (unsubstituted or substi-tuted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group) or, when A1 represents a nitrogen atom or a group -CR4= wherein R4 is as hereinbefore defined and Z1 and Z2 are as hereinbefore defined or, when A1 represents a group -CH= and Z1 represents a sulphur atom and Z2 is as hereinbefore defined, R2 represents a group of the formula -S(O)nR6, -SO2NR7R8, -CZ2NR7R8 or CZ2NHNO2 wherein n, R6, R7,R8 and Z2 are as hereinbefore defined] and, when R2 and/or R3 represents a sulphamoyl or monosubstituted sulphamoyl group and/or R3 represents a carboxy group;
pharmaceutically acceptable salts thereof; excluding the derivatives of formula (I) in which A1 represents a group -CR3= wherein R3 represents a hydrogen atom, A2 represents a nitrogen atom and either R1 represents a straight- or branched-alkyl, alkenyl or alkynyl group containing up to 6 carbon atoms, each such alkyl, alkenyl or alkynyl group being unsubstituted or substituted by from 1 to 3 substi-tuents selected from the group consisting of halogen atoms, straight-or branched-alkoxy, alkylthio, alkylsulfinyl and alkylsulfonyl groups containing up to 4 carbon atoms and phenyl group (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group), or R1 represents a cycloalkyl group containing 3 to 8 carbon atoms and R2 represents a carbamoyl group which is substituted on the nitrogen atom i) by two groups selected from the group consisting of phenyl group, phenyl group substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, phenylalkyl group and phenylalkyl group substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group; or ii) a phenyl group substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, or a phenylalkyl group substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, or iii) a phenyl group (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group) or a phenylalkyl group substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, and a straight- or branched- alkyl group containing up to 4 carbon atoms; which comprises:
(A) in the case of a tetrazine derivative of general formula (I) wherein R2 is other than a sulphamoyl, monophenylcarba-moyl, monophenylcarbamoyl substituted on the phenyl moiety by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, monophenylthiocarbamoyl, monophenylthio-carbamoyl substituted on the phenyl moiety by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, nitrocarbamoyl or nitrothiocarbamoyl group, and R1, A1, A2 and Z1 are as hereinbefore defined, reacting a compound of the general formula:

(III) (wherein A1 and A2 are as hereinbefore defined and R12 represents a group within the abovementioned definition of R2 in relation to general formula (I) other than a sulphamoyl, monophenylcarbamoyl, monophenylcarbamoyl substituted on the phenyl moiety by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, monophenylthiocarbamoyl, monophenylthiocarbamoyl substituted on the phenyl moiety by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, nitrocarbamoyl or nitrothiocarbamoyl group, with a compound of the general formula:

R1NCZ1 (IV) wherein R1 and Z1 are as hereinbefore defined, or (B) in the case of a tetrazine derivative of general formula (I) wherein R2 represents a monophenylcarbamoyl, a monophenylcarbamoyl substituted on the phenyl moiety by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, a monophenylthiocarbamoyl, a monophenylthiocarbamoyl substituted on the phenyl moiety by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, and R1, A1, A2 and Z1 are as hereinbefore defined in relation to that formula, the debenzylation of a compound of the general formula:

(VIII) (wherein R7 is as hereinbefore defined, R13 represents benzyl group or a benzyl group sustituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, and Z2 is as hereinbefore defined) by the application or adaptation of methods known per se for the replacement of a benzyl group or a benzyl group substituted on the phenyl-moiety by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, by a hydrogen atom, or (C) in the case of a tetrazine derivative of general formula (I) wherein R1, A1, A2 and Z1 are as hereinbefore defined in relation to that formula and R2 represents a group of the formula -CZ2NHNO2, Z2 being as hereinbefore defined, the nitration of a corresponding compound of the general formula:

(VA) (wherein Z2, R1, A1, A2 and Z1 are as hereinbefore defined in relation to general formula (I)), to convert the grouping -CZ2NH2 to -CZ2NHNO2, or, (D) in the case of a tetrazine derivative of general formula (I) wherein R1, A1, A2 and R2 are as hereinbefore defined in relation to that formula and Z1 represents a sulphur atom, reacting a compound of the general formula:

(VI) (wherein R1, A1 and R2 are as hereinbefore defined in relation to general formula (I), and R15 represents a group of the formula -S(O)nR6, -SO2NR7R8, -CZ2NR7R8 or -CZ2NHNO2, R6, R7, R8, n and z being as hereinbefore defined in relation to general formula (I)) with phosphorus penta-sulphide to convert the moiety to , or (E) in the case of a tetrazine derivative of general formula (I) wherein R1, A1, A2 and Z1 are as hereinbefore defined in relation to that formula and R2 represents a group of the formula -CSNR7R8 wherein R7 and R8 are as hereinbefore defined in relation to general formula (I), reacting a corresponding compound of the general formula:

(VIIA) (wherein R1, A1, A2, Z1, R7 and R8 are as hereinbefore defined in relation to general formula (I)) with phosphorus pentasulphide to convert the grouping -CONR7R8 to -CSNR7R8, and optionally, when the tetrazine product obtained is a compound of general formula I wherein R2 and/or R3 represent a sulphamoyl or mono-substituted sulphamoyl group and/or R3 represents a carboxy group, converting by a method known per se the product into a pharmaceutically acceptable salt.

2. Process according to claim 1, wherein the salt thus obtained is an alkali metal salt.

3. Process for the preparation of a tetrazine derivative of general formula (I) as defined in claim 1, wherein R2 is other than a sulphamoyl, monophenylcarbamoyl, monophenylcarbamoyl substituted on the phenyl moiety by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, monophenylthiocarbamoyl, monophenylthiocarbamoyl substituted on the phenyl moiety by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, nitrocarbamoyl or nitrothiocarbamoyl group, and R1, A1, A2 and Z1 are as defined in claim 1, which comprises reacting a compound of the general formula:

(III) wherein A1 and A2 are as defined in claim 1 and R12 represents a group within the above-mentioned definition of R2, with a compound of the general formula:

R1NCZ1 (IV) wherein R1 and Z1 are as hereinbefore defined, to obtain the desired compound.

4. Process for the preparation of a tetrazine derivative of general formula (I) as defined in claim 1, wherein R2 represents a monophenylcarbamoyl, a monophenyl-carbamoyl substituted on the phenyl moiety by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up -to 4 carbon atoms and nitro group, a monophenylthiocarbamoyl or a monophenylthiocarbamoyl substituted on the phenyl moiety by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, and R1, A1, A2 and Z1 are as defined in claim 1 in relation to that formula, which comprises the debenzylation of a compound of the general formula:

(wherein R7 is as defined in claim 1, R13 represents a benzyl group or a benzyl group substituted on the phenyl moiety by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, and Z2 is as defined in claim 1) by the application or adaptation of methods known per se for the replacement of a benzyl group or a benzyl group substituted on the phenyl moiety by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, by a hydrogen atom, to obtain the desired compound.

5. Process for the preparation of a tetrazine derivative of general formula (I) as defined in claim 1, wherein R1, A1, A2 and Z1 are as hereinbefore defined in claim 1 in relation to that formula and R2 represents a group of the formula -CZ2NHNO2, Z2 being as defined in claim 1, which comprises the nitration of a corresponding compound of the general formula:

(VA) (wherein Z2, R1, A1, A2 and Z1 are as defined in claim 1 in relation to general formula (I)), to convert the grouping -CZ2NH2 to -CZ2NHNO2.

6. Process for the preparation of a tetrazine derivative of general formula (I) as defined in claim 1, wherein R1, A1, A2 and R2 are as defined in claim 1 in relation to that formula and Z1 represents a sulphur atom, which comprises reacting a compound of the general formula:

(VI) wherein R1, A1 and R2 are as defined in claim 1, and R15 represents a group of the formula -S(O)nR6, -SO2NR7R8, -CZ2NR7R8 or -CZ2NHNO2, R6, R7, R8, n and Z2 being as defined in claim 1, with phosphorus pentasulphide to convert the moiety to .

7. Process for the preparation of a tetrazine derivative of general formula (I) as defined in claim 1, wherein R1, A1, A2 and Z1 are as hereinbefore defined in claim 1 in relation to that formula and R2 represents a group of the formula -CSNR7R8 wherein R7 and R8 are as defined in claim 1 in relation to general formula (I), which comprises reacting a corresponding compound of the general formula:

(VIIA) wherein R1, A1, A2, Z1, R1 and R8 are as defined in claim 1, with phosphorus pentasulphide to convert the grouping -CONR7R8 to -CSNR7R8.

8. Process according to claim 4 or 5, which further comprises converting the resulting product of formula (I) wherein R2 and/or R3 represent a sulphamoyl or mono-substituted sulphamoyl group and/or R3 represents a carboxyl group, by a method known per se into a pharmaceu-tically acceptable salt thereof.

9. Process according to claim 6 or 7, which further comprises converting the resulting product of formula (I) wherein R2 and/or R3 represent a sulphamoyl or mono-substituted sulphamoyl group and/or R3 represents a carboxyl group, by a method known per se into a pharmaceu-tically acceptable salt thereof.

10. Process according to claim 1, in which the cycloalkyl group referred to is cyclohexyl.

11. Process for the preparation of 8-(N-benzyl-carbamoyl)-3-(2-chloroethyl)-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one, which comprises reacting 8-[N-benzyl-N-(4-methoxybenzyl) carbamoyl]-3-(2-chloroethyl)-[3H]-imidazo [5,1-d]-1,2,3,5-tetrazin-4-one with anisole to form the desired compound.

12. Process for the preparation of 8-carbamoyl-3-(2-chloroethyl)-6-methyl-[3H]-imidazo-[5,1-d]-1,2,3,5-tetra-zin-4-one, which comprises reacting 5-diazo-2-methyl-imidazole-4-carboxamide with 2-chloroethyl isocyanate to form the desired compound.

13. Process for the preparation of 3-(2-chloro-ethyl)-8-(N,N'-dimethylsulphamoyl)-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one, which comprises reacting 5-diazo-imidazole-4-(N,N-dime-thylsulphonamide) with 2-chloroethyl isocyanate to form the desired compound.

14. Process for the preparation of 3-(2-chloro-ethyl)-8-(N-methylsulphamoyl)-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one, which comprises reacting 5-diazoimidazole-4-(N-methylsulphonamide) with 2-chloroethyl isocyanate to form the desired compound.

15. Process for the preparation of 3-(2-chloro-ethyl)-8-methylsulphonyl-[3H]-imidazo-[5,1-d]-1,2,3,5-tetra-zin-4-one, which comprises reacting 5-diazo-4-methylsulpho-nylimidazole with 2-chloroethyl isocyanate to form the desired compound.

16. Process for the preparation of 3-(2-chloro-ethyl)-8-methylsulphonyl-[3H]-imidazo-[5,1-d]-1,2,3,5-tetra-zin-4-one, which comprises reacting 5-diazo-4-methylsulpho-nylimidazole with 2-chloroethyl isocyanate to form the desired compound.

17. Process for the preparation of 3-methyl-8-methylsulphonyl-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one, which comprises reacting 5-diazo-4-methylsulphonylimidazole with methyl isocyanate to form the desired compound.

18. Process for the preparation of 3-(2-chloro-ethyl)-8-[N-(4-methoxybenzyl)-sulphamoyl]-[3H]-:imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one, which comprises reacting 5-diazoimidazole-4-[N-(4-methoxybenzyl)sulphonamide] 2-chloro-ethyl isocyanate to form the desired compound.

19. Process for the preparation of 3-(2-chloro-ethyl)-8-sulphamoyl-[3H]-imidazo-[5-1-d]-1,2,3,5-tetrazin-4-one, which comprises reacting 3-(2-chloroethyl)-8-[N-(4-methoxybenzyl)sulphamoyl]-[3H]-imidazo[5,1-d]-1,2,3,5-tetra-zin-4-one with anisole to form the desired compound.

20. Process for the preparation of 8-carbamoyl-3-(2-chloroethyl-[3H]-pyrazolo-[5,1-d]-1,2,3,5-tetrazin-4-one, which comprises reacting 3-diazopyrazole-4-carboxamide with 2-chloroethyl isocyanate to form the desired compound.

21. Process for the preparation of 3-(2-chloro-ethyl)-8-piperidinocarbonyl-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one, which comprises reacting 4-diazo-5-piperi-dinocarbonylimidazole with 2-chloroethyl isocyanate to form the desired compound.

22. Process for the preparation of 6-butyl-8-carbamoyl-3-(2-chloroethyl)-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one, which comprises reacting 2-butyl-5-diazoimidazole-4-carboxamide with 2-chloroethyl isocyanate to form the desired compound.

23. Process for the preparation of 8-carbamoyl-3-(2-chloroethyl)-6-propyl-[3H]-imidazo-[5,1-d]-1,2,3,5-tetra-zin-4-one, which comprises reacting 5-diazo-2-propyl-imidazole-4-carboxamide with 2-chloroethyl isocyanate to form the desired compound.

24. Process for the preparation of 8-carbamoyl-3-(2-chloroethyl)-6-ethyl-[3H]- imidazo-[5,1-d]-1,2,3,5-tetra-zin-4-one, which comprises reacting 5-diazo-2-ethylimi-dazole-4-carboxamide with 2-chloroethyl isocyanate to form the desired compound.

25. Process for the preparation of 3-(2-chloro-ethyl)-6-methyl-8-sulphamoyl-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one, which comprises reacting 3-(2-chloroethyl)-8-(4-methoxybenzyl)sulphamoyl-6-methyl-[3H]-imidazo[5,1-d]-1,2,3,5-tetrazin-4-one with anisole to form the desired compound.

26. Process for the preparation of 3-(2-chloro-ethyl)-8-dimethylsulphamoyl-6-methyl-[3H]imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one, which comprises reacting 5-diazo-4-dimethylsulphamoyl-2-methylimidazole with 2-chloroethyl isocyanate to form the desired compound.

27. Process for the preparation of 3-(2-chloro-ethyl)-6-methyl-8-methylsulphonyl-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one, which comprises reacting 5-diazo-2-methyl-4-methylsulphonylimidazole with 2-chloroethyl iso-cyanate to form the desired compound.

28. Process for the preparation of 3-(2-chloro-ethyl)-8-(dimethylcarbamoyl)-[3H]-pyrazolo-[5,1-d]-1,2,3,5-tetrazin-4-one, which comprises reacting 3-diazopyrazole-4-(N,N-dimethylcarboxamide) hydrochloride with 2-chloroethyl isocyanate and 1,8-diazobicyclo [5,4,0]undec-7-ene to form the desired compound.

29. Process for the preparation of 3-(2-chloro-ethyl)-8-(N-nitrocarbamoyl)-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one, which comprises reacting a mixture of concentrated sulphuric acid and 8-carbamoyl-3-(2 chloroethyl)-[3H]-imidazor[5,1-d]-1,2,3,5-tetrazin-4-one with concentrated nitric acid to form the desired compound.

30. Tetrazine derivatives of the general formula:

(I) [wherein R1 represents a cycloalkyl group containing 3 to 8 carbon atoms, or a straight- or branched-chain alkyl, alkenyl or alkylnyl group containing up to 6 carbon atoms, each such alkyl, alkenyl or alkylnyl group being unsubsti-tuted or substituted by from one to three substituents selected from the group consisting of halogen atoms, straight- or branched-chain alkoxy, alkylthio, alkylsulphi-nyl and alkylsulphonyl groups containing up to 4 carbon atoms, and phenyl groups(unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group); A1 represents a nitrogen atom or a group -CR3 =
wherein R3 represents a hydrogen atom or a substituent R4 wherein R4 represents a halogen atom, or a straight- or branched chain alkyl or alkenyl group, containing up to 6 carbon atoms, which may carry up to 3 substituents selected from the group consisting of halogen atom, phenyl group, phenyl group substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, straight-or branched-chain alkoxy, alkylthio and alkylsulphonyl groups containing up to 3 carbon atoms, or R4 represents a cycloalkyl group containing 3 to 8 carbon atoms, a cyano, hydroxy, nitro, phenoxy group or phenoxy group substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, or a group of the formula -COR5 (wherein R5 represents an alkyl or alkoxy group of up to 4 carbon atoms, a hydroxy group, a phenyl group or a phenyl group substi-tuted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group) or an alkanoylamino group containing up to 6 carbon atoms, or R4 represents a group of the formula -S(O)nR6, -SO2NR7R8 or -CZ2NR7R8 (wherein n represents 0, 1 or 2, R6 represents a straight- or branched-chain alkyl or alkenyl group, containing up to 4 carbon atoms, which may carry a phenyl substituent (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group), a cycloalkyl group containing 3 to 8 carbon atoms or a phenyl group (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group) R7 and R8, which may be the same or different, each represents a hydrogen atom or a straight- or branched-chain alkyl or alkenyl group, containing up to 4 carbon atoms, which may carry a phenyl substituent (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group) or a cycloalkyl group containing 3 to 8 carbon atoms or a phenyl group (unsubstituted or substi-tuted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group) or the group -NR7R8 represents a 5,6 or 7 membered heterocyclic ring which may contain a further heteroatom selected from the group consisting of nitrogen, oxygen and sulfur, said heterocyclic ring being unsubsti-tuted on substituted by one or two substituents selected from the group consisting of straight- or branched- chain alkyl substituents each containing up to 4 carbon atoms, and Z2 represents an oxygen or sulphur atom); A2 represents a nitrogen atom or, when A1 represents a nitrogen atom, A
represents a nitrogen atom or a group -CR3= wherein R3 is as hereinbefore defined, Z1 represents an oxygen or sulphur atom; and R2 represents a group of the formula -S(O)nR6, -SO2NR7R8, -CSNR7R8, -CONR7R9 or -CZ2NHNO2, wherein n, R6, R7, R8 and Z2 are as hereinbefore defined, and the group -NR7R9 represents a 5,6 or 7 membered heterocyclic ring which may contain a further heteroatom selected from the group consisting of nitrogen, oxygen and sulfur, said heterocyclic ring being unsubstituted on substituted by one or two substituents selected from the group consisting of straight- or branched-chain alkyl substituents each containing up to 4 carbon atoms, or R7 is as hereinbefore defined and R9 represents a straight- or branched-chain alkyl or alkenyl group containing up to 4 carbon atoms which carries and phenyl substituent (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group) or a phenyl group (unsubstituted or substi-tuted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group) or, when A1 represents a nitrogen atom or a group -CR4= wherein R4 is as hereinbefore defined and Z1 and Z2 are as hereinbefore defined or, when A1 represents a group -CH= and Z1 represents a sulphur atom and Z2 is as hereinbefore defined, R2 represents a group of the formula -S(O)nR6, -SO2NR7R8, -CZ2NR7R8 or CZ2NHNO2 wherein n, R6, R7,R8 and Z2 are as hereinbefore defined] and, when R2 and/or R3 represents a sulphamoyl or monosubstituted sulphamoyl group and/or R3 represents a carboxy group;
pharmaceutically acceptable salts thereof; excluding the derivatives of formula (I) in which A1 represents a group -CR3= wherein R3 represents a hydrogen atom, A2 represents a nitrogen atom and either R1 represents a straight- or branched-alkyl, alkenyl or alkynyl group containing up to 6 carbon atoms, each such alkyl, alkenyl or alkynyl group being unsubstituted or substituted by from 1 to 3 substi-tuents selected from the group consisting of halogen atoms, straight-or branched-alkoxy, alkylthio, alkylsulfinyl and alkylsulfonyl groups containing up to 4 carbon atoms and phenyl group (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group), or R1 represents a cycloalkyl group containing 3 to 8 carbon atoms and R represents a carbamoyl group which is substituted on the nitrogen atom i) by two groups selected from the group consisting of phenyl group, phenyl group substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, phenylalkyl group and phenylalkyl group substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, or ii) a phenyl group substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, or a phenylalkyl group substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, or iii) a phenyl group (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group) or a phenylalkyl group substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, and a straight- or branched- alkyl group containing up to 4 carbon atoms.

31. Tetrazine derivatives according to claim 30, wherein R1 is as defined in claim 30, R2 represents a car-bamoyl group unsubstituted or substituted on the nitrogen atom by one or two groups selected from straight- and branched-chain alkyl and alkenyl groups, containing up to 4 carbon atoms, and cycloalkyl groups containing 3 to 3 carbon atoms, Al represents a group -CR4= wherein R4 represents a straight- or branched-chain alkyl or alkenyl group containing up to 6 carbon atoms, which may carry up to 3 substituents selected from halogen atoms, phenyl group and phenyl groups substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group, or R4 represents a cycloalkyl group containing 3 to 8 carbon atoms, A represents a nitrogen atom, and Z1 represents an oxygen atom.

32. Tetrazine derivatives according to claim 30, wherein R1 is as defined in claim 30, R2 represents a group of the formula -S(O)nR6 or -SO2NR7R8, wherein n represents 0, 1 or 2, R6 represents a straight- or branched-chain alkyl or alkenyl group, containing up to 4 carbon atoms, which may carry a phenyl substituent (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group), a cycloalkyl group containing 3 to 8 carbon atoms, or a phenyl group (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group), R7 and R8, which may be the same or different, each represents a hydrogen atom or a straight- or branched-chain alkyl or alkenyl group, containing up to 4 carbon atoms, which may carry a phenyl substituent (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group), or a cycloalkyl group containing 3 to 8 carbon atoms, or a phenyl group (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group), A1 represents the group =CH-, A2 represents a nitrogen atom, and Z1 represents an oxygen atom.

33. Tetrazine derivatives according to claim 30, wherein R1 is as defined in claim 30, R2 represents a group of the formula -S(O)nR6, -SO2NR7R8 or -CZ2NR7R8 (wherein n represents 0, 1 or 2, R6 represents a straight- or branched-chain alkyl or alkenyl group, containing up to 4 carbon atoms, which may carry a phenyl substituent (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group), a cycloalkyl group containing 3 to 8 carbon atoms, or a phenyl group (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group)), R7 and R8, which may be the same or different, each represents a hydrogen atom or a straight- or branched-chain alkyl or alkenyl group, containing up to 4 carbon atoms, which may carry a phenyl substituent (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group), or a cycloalkyl group containing 3 to 8 carbon atoms or a phenyl group (unsubstituted or substituted by one or more substituents selected from the group consisting of halogen atoms, alkyl group containing up to 4 carbon atoms, alkoxy group containing up to 4 carbon atoms and nitro group), A1 represents a nitrogen atom, A2 represents a group -CR3=, wherein R3 represents a hydrogen atom, or a substituent R4 as defined in claim 30, and Z1 represents an oxygen or sulphur atom.

34. Tetrazine derivatives according to claim 30, in which the cycloalkyl group referred to is cyclohexyl.

35. Tetrazine derivatives according to claim 30, which have one or more of the following features:
(i) R1 represents a methyl or 2-haloethyl group;
(ii) R2 represents a group of the formula -SOR6, -SO2R6 -SO2NR7R8, -CONR7R8 or -CONHNO2, wherein R6, R7 and R8 are as defined in claim 30;
(iii) one of A1 and A2 represents a nitrogen atom and the other represents a group -CR3=
wherein R3 is as defined in claim 30;
(iv) R3 represents a substituent R4 wherein R4 represents an alkyl group containing up to 6 carbon atoms;
(v) A represents a nitrogen atom;
(vi) Z1 represents an oxygen atom; and/or (vii) Z2 represents an oxygen atom.

36. Tetrazine derivatives according to claim 35, wherein R1 represents the 2-chloroethyl group.

37. Tetrazine derivatives according to claim 35, wherein R2 represents a group -SOR6, -SO2R6, -SO2NR7R8, -CONR7R8 or -CONHNO2 wherein R6 represents an alkyl group containing up to 4 carbon atoms, R7 represents a hydrogen atom or an alkyl group containing up to 4 carbon atoms, and R8 represents a hydrogen atom, an alkyl group containing up to 4 carbon atoms, a benzyl group or a benzyl group substituted by an alkoxy group containing up to 4 carbon atom.

38. Tetrazine derivatives according to claim 35, wherein R3 represents a butyl, propyl, ethyl or methyl group.

39. Tetrazine derivatives according to claim 30, which have one or more of the following features:
(i) R1 represents a methyl or 2-haloethyl group;
(ii) R2 represents a group of the formula -SOR6, -SO2R6, -SO2NR7R8, -CONR7R8 or -CONHNO2, wherein R6, R7 and R8 are as defined in claim 30;
(iii) one of A1 and A2 represents a nitrogen atom and the other represents a group -CR3=
wherein R3 is as defined in claim 30;
(iv) R3 represents a methyl group;
(v) A2 represents a nitrogen atom;
(vi) Z1 represents an oxygen atom; and/or (vii) Z2 represents an oxygen atom.

40. Tetrazine derivatives according to claim 30, which have one or more of the following features:
(i) R1 represents the 2-chloroethyl group;
(ii) R2 represents a group of the formula -SOR6, -SO2R6 -SO2NR7R8, -CONR7R8 or -CONHNO2, wherein R6, R7 and R8 are as defined in claim 30;
(iii) one of A1 and A2 represents a nitrogen atom and the other represents a group -CR3=
wherein R3 is as defined in claim 30;
(iv) R3 represents a methyl group;
(v) A2 represents a nitrogen atom;
(vi) Z1 represents an oxygen atom; and/or (vii) Z2 represents an oxygen atom.

41. 8-(N-Benzylcarbamoyl)-3-(2-chloroethyl)-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one.

42. 8-Carbamoyl-3-(2-chloroethyl)-6-methyl-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one.

43. 3-(2-Chloroethyl)-8-(N,N'-dimethylsulpha-moyl)-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one.

44. 3-(2-Chloroethyl)-8-(N-methylsulphamoyl)-[3H]-imidazo-[5-1,d]-1,2,3,5-tetrazin-4-one.

45. 3-(2-Chloroethyl)-8-methylsulphonyl-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one.

46. 3-(2-Chloroethyl)-8-methylsulphonyl- [3H]-imidazo-[5,1-d] -1,2,3,5-tetrazin-4-one.

47. 3-Methyl-8-methylsulphonyl-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one.

48. 3-(2-Chloroethyl)-8-[N-(4-methoxybenzyl)-sulphamoyl]-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one.

49. 3-(2-Chloroethyl)-8-sulphamoyl-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one.

50. 8-Carbamoyl-3-(2-chloroethyl)-[3H]-pyrazolo-[5,1-d]-1,2,3,5-tetrazin-4-one.

51. 3-(2-Chloroethyl)-8-piperidinecarbonyl-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one.

52. 6-Butyl-8-carbamoyl-3-(2-chloroethyl)-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one.

53. 8-Carbarnoyl-3-(2-chloroethyl)-6-propyl-[3H]-imidazo-[-5,1-d]-1,2,3,5-tetrazin-4-one.

54. 3-(2-Chloroethyl)-6-methyl-8-sulpllarnoyl-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one.

55. 3-(2-Chloroethyl)-8-dimethylsulphamoyl-6-methyl-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one.

56. 3-(2-Chloroethyl)-6-methyl-8-methylsulphonyl-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one.

57. 3-(2-Chloroethyl)-8-(dimethylcarbamoyl)-[3H]-pyrazolo-[5,1-d]-1,2,3,5-tetrazin-4-one.

58. 3-(2-Chloroethyl)-8-(N-nitrocarbamoyl)-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one.

59. 8-(N-Benzyl-N-phenylcarbamoyl)-3-methyl-[3H]-imidazo[5,1-d]-1,2,3,5-tetrazin-4-one,8-[N-benzyl-N-(4-methoxybenzyl) carbamoyl]-3-(2-chloroethyl)-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one, 3-(2-chloroethyl)-8-[N-(4-methoxybenzyl)-N-phenylcarbamoyl]-[3H]-imidazo[5,1-d]-1,2,3,5-tetrazin-4-one, 3-(2-chloroethyl)-8-(N-phenylcarba-moyl)-[3H]-imidazo[5,1-d]-1,2,3,5-tetrazin-4-one, 8-(N-benzyl-N-phenylcarbamoyl)-3-(2-chloroethyl)-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one,3-(2-chloroethyl)-8-(N-methyl-N-phenylcarbamoyl)-[3H]-imidazo[5,1-d]-1,2,3,5-tetrazin-4-one, 8-carbamoyl-3-methyl-[3H]-pyrazolo[5,1-d]-1,2,3,5-tetrazin-4-one, 8-carbamoyl-3-(2-chloroethyl)-6-cyclohexyl-[3H]-imidazo[5,1-d]-1,2,3,5-tetrazin-4-one, 8-carbamoyl-3-(2-chloroethyl)-6-phenethyl-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-9-one, 6 benzyl-8-carbamoyl-3-(2-chloroethyl)-[3H]-imidazo[5,1-d]-1,2,3,5-tetrazin-4-one, 8-carbamoyl-3-(2-chloroethyl)-6-isopropyl-[3H]-imidazo [5,1-d]-1,2,3,5-tetrazin-4-one, 3-(2-chloroethyl)-8-(4 methoxybenzyl)sulphamoyl-6-methyl-[3H]-imidazo[5,1-d]-1,2,3,5-tetrazin-4-one, 3-methyl-8-methylsulphonyl-[3H]-pyrazolo-[5,1-d]-1,2,3,5-tetrazin-4 one, 3-(2-chloroethyl)-8-methylsulphonyl-[3H]-pyrazolo[5,1-d]-1,2,3,5-tetrazin-4-one, 3-(2-chloroethyl)-6-methyl-8-methylsulphinyl-[3H]-imidazo[5,1-d]-1,2,3,5-tetrazin-4-one, 3-(2-chloroethyl)-8-ethylsulphonyl-6-methyl-[3H]-imidazo[5,1-d]-1,2,3,5-tetrazin-4-one and 3-(2-chloroethyl)-6-methyl-8-propylsul-phonyl-[3H]-imidazo-[5,1-d]-1,2,3,5-tetrazin-4-one.

60. Pharmaceutical composition, characterized in that it comprises in association with a pharmaceutically acceptable carrier, at least one of tetrazine derivatives described in claim 30.