CA1112643A

CA1112643A - 3,5-diamino-6-phenyl-1,2,4-triazines

Info

Publication number: CA1112643A
Application number: CA353,081A
Authority: CA
Inventors: Martin G. Baxter; David A. Sawyer; Alistair A. Miller; Albert R. Elphick
Original assignee: Wellcome Foundation Ltd
Current assignee: Wellcome Foundation Ltd
Priority date: 1979-06-01
Filing date: 1980-05-30
Publication date: 1981-11-17
Also published as: JPH0144179B2; ATA289680A; CZ384891A3; EP0021121B1; JPH0144706B2; BG60427B2; FI801758A7; PL224633A1; MY8500062A; ES8104993A1; DK153787C; EP0021121A1; PL124029B1; AU530999B2; HU182086B; IE801126L; UA5576A1; NL950007I2; AT370097B; IL60201A

Abstract

ABSTRACT OF THE DISCLOSURE
The present invention provides compounds of the formula (III):

Description

2~3 The present invention relates to a group of novel compounds which are useful in the treatment of CNS disorders, such as epilepsy, to pharmaceutical compositions containing them, and to methods for their preparation.
U~K. Patent No. 759,014 discloses compounds of the formula (I~:

NH

~2~ ~ ~ y (I) wherein X and Y are hydrogen and/or halogen atoms, as having activity against bacterial and malarial infections in animals. This patent specifically discloses those com-pounds wherein X~and Y are both hydrogen atoms, wherein X
is a hydrogen atom and Y is a 4-chloro atom, and wherein X is a 4-chloro atom and Y is a 2-chloro and 3-chloro atom, respectively.
Rees et al, J. Med. Chem., 1972 15, 859, have shown that these compounds, and in particular the 4-chlorophenyl and the 3,4-dichlorophenyl compounds are active against the malaria organism Plasmodium berghei in mice. However, these two compounds ~ere also shown to be toxic at curative doses and presumably were not investi-gated further because of their low therapeutic ratio in this context. The 2,4-dichlorophenyl compound had only slight antimalarial activity. The therapeutic ratio of the compounds were such as to prevent their use in human medicine for the treatment or prophylaxis of malaria and they were not progressed further.

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6~3 U.S. Patent No. 3,637,688 discloses compounds of the formula (II~:

~ = 4=~ R2 N - N / ~ (II) wherein Rl is hydrogen or fluorine, and R , R3 and R4 are hydrogen, fluorine or trifluoromethyl provided that at least one of Rl, R , R and R is fluorine or tri-fluoromethyl, as being useful in the treatment of malaria.
In the Rees article re~erred to above, the 4-trifluoro~
methylphenyl compound (E, R =CF3, R =R =R =H) was claimed to be less toxic than the chlorophenyl compounds whilst still being active against malaria. The other fluoro and trifluoromethyl compounds referred to in the article were substantially less active than the 4-trifluoromethyl-phenyl compound.
Rosenburg and Bottiroli Proc. Soc. exp. Biol., 1964, 115, 410, described a series of tests in which three anti-malarial agents, quinacrine, chloroquine and hydroxychloro~uine, were tested as anticonvulsants. Only hydroxychloroquine possessed a favourable activity profile.
It has now been discovered that a group of novel 3,5-diamino-6-(substituted phenyl)-1,2,4-triazines are active in the treatment of CNS disorders, such as psychiatric and neurological disorders, and are parti-cularly useful as anticonvulsants, for example in the treatment of epilepsy. Furthermore, these triazines are '1.

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6~3 believed to be nondepressant at likely therapeutic dose levels and therefore are advantageous as compared with depressant anti-epileptics such as phenobarbitone.
Accordingly the present invention provides a compound of the formula (III~:

R R
2 ~ ~ R8 ~-N ~
6 / \ (III) or an acid addition salt thereof, wherein R6 is chlorine, bromine, iodine, Cl 4 alkyl or trifluoromethyl; R7 is hydrogen, halogen Cl 4 alkyl or trifluoromethyl or R6 and R form a -CH=CH~CH=CH- group optionally substituted by a halogen atom or a Cl 4 alkyl or trifluoromethyl group, R is hydrogen, bromine, iodine, Cl 4 alkyl or trifluoromethyl, R9 is hydrogen, halogen, Cl_4 alkyl or trifluoromethyl, R10 is hydrogen, methyl, or fluorine and R 1 is an amino, Cl 10 acylamino or di-substituted aminomethyleneamino group provided that, at most, only two of R -R10 are other ~han hydrogen -and that R7-R10 are not all hydrogen when R6 is chlorine.
I Suitably the Cl 4 alkyl group is a methyl group.
Sùitably R is a chlorine or bromine atom or a methyl or trifluoromethyl group or i5 linked to'R7 to form a -CH=CH-CH=CH- group and preferably R is a chlorine or bromine atom or linked to R to ~orm a -CH=CH-CH=CH- group.

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7 ~ 3 Preferably R and R are each hydrogen, chlorine or bromine atom~.
Preferably R8 is a hydrogen or bromine atom.
Suitable substituents for the aminomethylene-amino group are Cl 4 alkyl groups or a -(CH2)2X(CH2)n~ :~
group wherein X.is O, S, NH or CH2 group and n is the integer 1 or 2.
Suitably Rll is an amino, acetamido or dimethyl-aminomethyleneamino group and preferably R is an amino group.
When three of the substituerlts R6-R10 are other than hydrogen, it is preferred that R and R10 are hydrogen and that R , R7 and R9 are those halogen atoms previously defined and in particular chlorine atoms~
Preferred compounds of the formula (III) include:

3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazine ;' 3,5-diamino-6-~2,5-dichlorophenyl)-1,2,4-triazine 3,5-diamino-6-(4-bromo-2-chlorophe,nyl)-1,2,4-triazine 3,5-diamino-6-.(5-bromo-2-chlorophenyl)-1,2,4-triazine 3,5 diamino-6-(2,3,5-trichlorophenyl)-1,2,4-triazine ' 3,5-diamino-6-(2-chloro-6-fluorophenyl)-1,2,4-triazine 3,5-diarnino-6-(2-methylphenyl)-1,2,4-triaæine 3,5-diamino-6-~2-trifluoromethylphenyl)-1,2,4-triazine 3,5-diamino-6 (2-bromophenyl)-1,2,4-triazine 3,5-diarnino-6-(2-iodophenyl)-1,2,4-triazine 3,5-diamino-6-(2-bromo-5-chlorophenyl)-1,2,4-triazine 3,5-diarnino-6-(1-naphthyl)-1,2,4-triazine 5-acetamido-3-amino-6-(2,3-dichlorophenyl)-1,2,4-triazine 3-amino-6-(2,3-dichlorophenyl)-5-dimethylarninomethylene-amino-1~2~4-triazine ~, :- : , " ., , .:

L;26~3 3,5-diamin~-6-(2-methyl-1-naphthyl)-1,2,4-triazine 3,5-dlamino-6-(3-chloro-1-naphthyl)-1,2,4-triazine The present invention also provides the first practicable medical use of the compounds of the formula (III), as hereinbefore defined. Preferably this will be for the treatment of CNS disorders, and in particular epilepsy, in humans.
In a further aspect, the present invention pro-vides pharmaceutical formulations comprising a compound of the formula lIII) in admixture with a pharmaceutically ~cceptable carrier. Suitable acid addition salts of the --- compounds of formula (III) include those formed with both organic and inorganic acids. Such acid addition salts will normally be pharmaceutically acceptable. Thus, preferred salts include those formed from hydrochloric, sulphuric, citric, tartaric, phosphoric, lactic, pyruvic, acetic, succinic, oxalic,, fumaric, maleic, oxaloacetic, methane-sulphonic, ~-toluenesulphonic and benzenesulphonic acids.
The compounds of the formula (III) will be pre-~ent in the compositions of the present invention in an effective unit dosage fbrm, that is to say in an amount sufficient to!be effective against CNS disorders in vivo.
The pharmaceutically acceptable carriers present in the compositions of this invention are materials recom-mended for the purpose of administering the medicament.
These may be liquid or solid materials, which are other-wise inert or medlcally acceptable and are compatible with the active ingredients.

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', These pharmaceutical compositions may be given orally or parenterally, used as a suppository, or applied topically as an ointment, cream or powder. However, oral and parenteral administration of the compositions are preferred.
For oral administration, fine powders or granules will contain diluting, dispersing and~or surface active agents, and may be present in a draught, in water or in a syrup, in capsules or sachets in the dry state or in non-aqueous suspension wherein suspending agents may be included, or in a suspension in water or syrup. Where desirable or necessary, ~lavouring, preserving, suspend-ing, thickening or emulsifying agents can be included.
When a suspension is prepared in water accord-ing to the present invention at least one of such agents will be present.
For parenteral administration, the compounds may be presented in sterile aqueous injection solutions which may contain anti-oxidants or buffers.
As stated above, the free base or a salt `
thereof may be administered in its pure form unassociated with other additives in which case a capsule or sachet is the preferred carrier.
Alternatively the active compound may be pre-sented in a pure form as an effective unit dosage, for instance, compressed as a tablet or the like.

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Other compounds which may be included are, for example, medically inert ingredients, e.g. solid and liquid diluents such as lactose, starch, or calcium phosphate for tablet or capsules; olive oil or ethyl oleate for soft capsules; and water or vegetable oil for suspensions or emulsions; libricating agents such as talc or magnesium stearate; gelling agents such as colloidal clays, thickening agents such as gum tragacanth or sodium alginate; and other therapeutically acceptable accessary ingredients such as humectants, preservatives, buffers, and antioxidants which are useful as carriers in such formulations.
Tablets or other forms of presentation provided in discrete units may conveniently contain an amount of ~ compound of the formula (III) which is effective at such ; dosage or as a multiple of the same, for instance, units containing 5 mg to 500 mg, usually around 10 mg to 250 mg.
The pharmaceutical compositions of the present invention will be prepared by the admixture of a compound of the formula (III) with a pharmaceutically acceptable carrier. Conventional pharmaceutical excipients may be admixed as required~
The present invention provides a method of treat-ment of convulsions in mammals, and particularly epilepsy in humans by the administration of a non-toxic anticon-vulsant effective amount of a compound of the formula (III) .-~
or a pharmaceutically acceptable salt, or a composition as hereinbefore defined.
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As indicated above, the compounds of the formula (III) are generally useful in treating such disorders by oral administration or injection (1.~. or s.c).
The compounds of the formula (III) are normally administered orally at a dose of from 0.1 mg/kg. to 30 mg~kg. per day. The dose range for adult humans is generally from 8 mg. to 2,400 mg/day and preferably 35 to 1,050 mg/day. Due to the fact that the compounds of the formula (III) are extremely long acting, it may often be advantageous to administer an initial dose of 70 to 2,400 mg. the first day then a lower dose of 20 to 1,200 mg. on subsequent days.
The present invention also provides a process for the preparation of compounds of the formula (III) which comprises the cyclisation of a compound of the formula (IV): R Rl ~H
\~ 11 'CNH2 R ~ - CCN (IV) wherein R -Rl are as hereinbefore defined; and thereafter, where desired substituting the amino group adjacent-to the phenyl ring to give a group Rll wherein Rll is as herein-before defined other than amino, by conventional methods.
This cyclisati~n reaction i5 normally c~rried out by refluxing in an alkanol, preferably a Cl 4 alkanol such as methanol or ethanol, in the presence of a strong base such as potassium hydroxide.

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: ~ ' ': ' , , ! , The compounds of the formula (I~) are novel intermediates and as such form a further important part of the present invention.
The preparation of the compounds of the formula (IV) is analogous to that de~scribed in the literature, i.e.
U.S. Patent No. 3,637,688, for structurally related com-pounds The following examples illustrate the preparation of the compounds of the invention and their CNS activity.

Preparation of 3,5-diamino-6-(2,3-dichlorophenyl)~1,2,4-triazine.
2,3-~ichlorobenzo-ic Acid A solution of 2,3-dichloroiodobenzene (37.3 g, 0.14M) in sodium dried ether (300 mls) was added dropwise to magnesium turnings (3.65g, 0.15gm Atm) and a crystal of iodine with warming so as-to form a Grignard reagent.
The mixture was stirred and refluxed for 2 hours then cooled and transferred dropwise, under nitrogen, into a stirred mixture of sodium dried ether (250 mls) containing solid carbon dioxide (ca. lOOg). The mixture was stirred for 2 hours, left overnight to warm to room temperature, then treated with ice (ca. 150g) and 2 ; aqueous hydrochloric acid (75 mls), and the product extracted with ether (200, 100 and 50 mls). The combined ether extracts were washed with water (2 ~ 40 mls) then repeatedly extracted with 2N aqueous sodium hydroxide (100, 50 and 50 mls3. These basic solutions were com-bined, stirred with activated charcoal (3 g) for 10 minutes, , .,' ~'~
g _ i: , '~ :
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~%6~3 filtered and the cooled filtrate was acidified with con-centrated hydrochloric acid t25 mls) at 10C. The resultant solid was filtered off, washed with water (2 x 20 mls) and dried in vacuo~ Yield 20.76g (77.6%), m.p. 167-169C (uncorrected).
2,3-Dichlorobenzoyl Chlorlde A mixture of 2,3-dichlorobenzoic acid (39.4g 0.2M) and thionyl chloride (100 mls) was heated to reflux for 2-1/2 hours. The cooled solution was evaporated down ln vacuo ànd distilled under nitrogen. Yield 35.5 g (85%), b.p. 146-148C at 31mm of mercury pressure.
2,3-Dichlorobenzo~yl Cyanide ~ mixture of cuprous cyanide (36.9g, 0.41M), potassium iodide (68.5g, 0.41M) and xylene (400 mls) was refluxed in an atmosphere of nitrogen under a Dean and Stark trap for 24 hours so a.s to remove all trace of water. I
A solution of 2,3-dichlorobenzoyl chloride (35.5g, 0.17M) in sodium dried xylene (130 mls) was added dropwise to the above mixture of dry cuprous cyanide and xylene. ~he resulting mixture was stirred and heated to reflux for a furt~er 72 hours. The cooled mixture was filtered and the solid washed well with sodium dried xylene (200 mls). The filtrate ~ld washings were com-hined and evaporated down in vacuo to give an oil.
Yield 32g (94%~
,, , "- I

3,5-Diamino-6-(2,3-dichlorophenyl)-1,2,~-triazlne A solution of 2,3-dichlorobenzoyl cyanide (32g, 0.16M) in dimethylsulphoxide (80 mls) was added dropwise to a stirred suspension of aminoguanidine bicarbonate ~81.67g, 0.6M) which had been treated with 8N aqueous nitric acid (400 mls) at a temperature o~ ca 25C. The mixture was stirred for 3 hours, then left to stand at room temperature for 7 days. The cooled mixture was stirred and basified with 0.880 aqueous ammonia (400 mls) at 20C, then stirred with ice cooling for 30 minutes, filtered and th~ resulting solid washed thoroughly with water and finally dried in vacuo.
~he above solid was added to a 10% solution of potassium hydroxide pellets in methanol (400 mls) and the solution heated to refluxed for 1-1/2 hours. When cool the solution was evaporated down in vacuo, treated with ice water (800 mls) then stirred for 30 minutes and ~ filtered. The residue was dried and recrystallised from ; isopropanol to give 3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazine. Yield 6.8g (15.6%), m.p. 216-218C
(uncorrected).

By a method analogous to that described in Example 1 the compounds listed in Tables 1 and 2 were prepared:---J,~

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Tabl _ V~ =N~2) m.p. (uncor- % Yield rected) (from Acid) _ _ _ ~ .
2,5-C12 228-230C
2-Cl,4-Br 223~225C 6 2-Cl,5-Br 238-240aC 2 2-CF3 177-178C 0.4 2-C1,6-F 226-228C 14.5 2-Me 181-183C 25 2-Br 204-207C 34 2-Br,5-Cl 255-./56~C 1.2 Table 2 , . ~
. VI, R m.p. (uncor- % Yield . ~ rected) (from Acid) .. . _ 215-216C 7.5 2-Me 131-134C 0.3 ~` 3-Cl /85-2860C L l o ., :

.~ , .,~ , , , ,,: , . ' Preparation of 3,5-diamino-6-(2,3,5-trichlorophen~l)-~=~
2 3 5-Trichlorobenzoic Acid Powdered sodium nitrite (37.0 g, 0.54M) was added portionwise to concentrated sulphuric acid (270 ml) which was stirred under an atmosphere of nitrogen. The temperature of the mixture was not allowed to rise above 70. Meanwhile 3-amino-2,5-dichlorobenzoic acid (100 g, 0.45M) was dissolved in hot glacial acetic acid (1,200 ml), the resultant ~olution was cooled rapidly to room temperature and added dropwise to the above stirred and cooled nitrous acid mixture so that the internal temperature did not rise above 30. The solution formed after the addition was left at room temperature for 2 hours then was slowly added to a stirred solution of cuprous chloride (97 g, 0.97M) in concentrated hydro-chloric acid (970 ml). The resultant mixture was stirred until the nitrogen evolution had ceased and was then left ; 20 overnight. The solid was filtered off, washed well with water and dried ln vacuo. Yield 90.1 g t89%) m.p.
; 164-165C (uncorrected).
2,3,5- richlorobenzoyl Chloride A mixture of 2,3,5-trichlorbenzoic acid ~90 g, 0.4M) and dimethylformamide (1 ml) in thionyl chloride (200 ml) was heated to reflux for 2 hours. The cooled solution was evaporated down ln vacuo and the residue distilled under nitrogen. Yield 89.2 g (90%), b.p. 158-160C at the pressure of 30 mm of mercury.

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.

2,3,5-Trichlorobenzoyl Cyanide A mixture o-f cuprous cyanide (89 g, O.9M), potassium iodide (150.5 g, 0.9M) and xylene (800 ml) was heated -to reflux in an atmosphere of nitrogen under a Dean and Stark trap for 24 hours.
A solution of 2,3,5-trichlorobenzoyl chloride (89 g, 0.36M) in sodium dried xylene (100 ml) was added to the above suspension. The resulting mixture was stirred and heated to reflux for a further 72 hours.
The cooled mixture was filtered and the solid was washed well with sodium dried xylene (200 ml). m e filtrate and washings were combined and evaporated in vacuo to give an oil. Yield 76 g (96%).
3,5-Diamino-6-(2,3,5-trichlorophenyl)-1,2,~-triazine A solution of 2,3,5-trichlorobenzoyl cyanide (38.5 g, 0.16M) in dimethylsulphoxide (80 ~1) was added dropwise to a stirred suspension of aminoguanidine bi-carbonate (65.76 g, 0.32M) which had been treated with 8N aqueous nitric acid (560 ml). The mixture was stirred ,1~ , . .
for 3 hours and then was-left to stand at room temperature for 21 days. ~he solid was filtered off, washed with .~;
water (2 x lOO ml) a~d drled in vacuo. A suspension of the dried solid in a 10% solution of potassium hydroxide .
pellets in meth-anol (320 ml) was heated to reflux for 1 hour, the mixture was cooled and evaporated down in vacuo.
~ The residue was treated with ice/water (200 ml), the resultant solid was filtered off and dried in vacuo.

-: , .: . .... ..

: ., ~L~ 2643 This dried solid was put on top of a dry column (25 mm diameter, 200 g of MFC silica gel) and eluted with a solution of ethyl acetate/methanol/acetic acid (90:2.5:2.5).
Fractions 50 to 80 (900 drops per fraction) were collected, combined and evaporated down in vacuo. The resultant solid was recrystallised from isopropanol to give 3,5-diamino-6-(2,3,5-trichlorophenyl)-1,2,4-triazine.
Yield 0.77g. (1.6%), m.p. 232-235C (uncorrected).

Preparation_of 5-Acetamido-3-amino-6-(2,3-dichlorophenyl)-1 2 4-triazine '~
. _ ' A solution of 3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazine (2 gm, 8mM) and acetic anhydride (10 mls) in acetic acid (20 mls~ was stirred and heated to reflux for 2 hours. The solution was then cooled and evaporated down in vacuo. ~he residue was treated with aqueous 0.880 ammonia (100 mls~ and the resultant mixture was I stirred for 2 hours. The solicl was separated by filtration, dried then recrystallized -from isopropanol to give 5-acetamido-3-amino-6-(2,3-dichlorophenyl)-1,2,4-triazine.
Yield 1.0 gms (42%), m.p. 250-252V (uncorrected).
;~ EXAMPLE-5 Preparation of 3-Amino-6-~2,3-dichlorophenyl)-5 dimethyl aminomethYleneamino-ll2l4-triazine oxalate.
Dimethylfo~namide dimethyl acetal (1 ml) was added dropwise to a stirred mixture o~ 3,5-diamino-6 (2,3-dichloropheny])-1,2,4-triazine (1 g, 4mM) in dry dimethylformamide (20 mls) in a nitrogen atmosphere.

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.

' The mixture was stirred and heated at 120 for 2 hours, and the resultant solution was cooled and evaporated down in vacuo. The residual oil was washed once with water (20 mls) then dissolved ~ a solution of oxalic acid (1 gm) in methanol (20 mls). Ether (100 mls) pre-cipitated an oil ~hich slowly crystallized. The residue was recrystallized from aqueous isopropanol to give 3-amino-6-(2,3-dichlorophenyl)-5-dimethylaminomethyIene-amino-1,2,4-triazine oxalate. Yield 0.19 gms (14%), m.p.
172-175C Dec. (u~corrected)~
EX~MPLE 6 ; : , Pharmacoloqical Activity of Compounds of the Present Invention Tables 3 and 4 ~ , ~ The anticonvulsant activity of certain compounds S of the present invention was determined by a standard maximal electroshock test, that described by L. A. Woodbury ` and V. D. Davenport, Arch. Int. Pharmacody_.: 1952, 92, ~ 97.
,:

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VH; Rl VH,R ~ 50~ S ,~
Mice, mg ~ g, p.o.
, 2,3-C12 ~I2 2.4 I

2,5-C15 NH2 3.3 2-Me NH2 15.0 2-Cl, 4-Br NH2 12.8 I:
2-Cl, 5-Br NH2 6.0 2-CF3 NH2 20.0 ~. 2-Cl, 6-F ~M2 12.2 ,.
;~ 10 2,3,5-C13 NH2 0.65 :
. 2-Br NH2 8.5 2-I ~H2 11.8 l:
. 2-Br, 5-Cl NH2 4.6 2,3-C12 NHCOCH3 5 ~' 2,3-C12 N-CH~Me2 5 ~`"' VIII, R 50~ S ~
.mice, mgjkg, p.o. ~:

H 2.9 ; 2-Me 16.5 ; 10 3-Cl 6.5 , . . . . . .
.

6~3 The LD50,s (expressed in mg/kg, p.o.) of 3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazine and 3,5 diamino-6-(2,5-dichlorophenyl)-1,2,4-triazine were determined in mice and rats. The LD50 described is the dose for which 50% of the animals survive 10 days after administration of the compound.

VIII, R Mice Rats . ... _ __ __ 2,3-C12 ~H2 250 640 ` 2___ _ 2 Tablet Formulation 3,5-Diamino-6-(2,3-dichlorophenyl)-~` 1,2,4-triazine 150 mg) Lactose 200 mg) Maize Starch50 mg) Contents per Polyvinylpyrrolidone4 mg) Tablet Magnesium Stearate 4 mg) The drug was mixed with the lactose and starch and granu-lated with a solution of the polyvinylpyrrolidone in water.
The resultant granules were dried, mixed with magnesium stearate and compressed to gi~e tablets of average weight ; 20 408 mg.

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In this specification the formulae (V), (VI), (VII) and (VIII) are as follows: .

2 (V) and (VII) R/
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Claims

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

1. A process for the preparation of a compound of the formula (III) (III) or an acid addition salt thereof, wherein R6 is chlorine, bromine, iodine, C1-4 alkyl or trifluoromethyl; R7 is hydrogen, halogen, C1-4 alkyl or trifluoromethyl or R6 and R7 form a -CH=CH-CH=CH- group unsubstituted or sub-stituted by a halogen atom or a C1-4 alkyl or trifluoro-methyl group; R8 is hydrogen, bromine, iodine, C1-4 alkyl or trifluoromethyl; R9 is hydrogen, halogen, C1-4 alkyl or trifluoromethyl; R10 is hydrogen, methyl or fluorine and R11 is amino, C1-4 acylamino or di-substituted amino-methyleneamino, provided that at most only two of R7, R8, R9 and R10 are other than hydrogen and that R7, R8, R9 and R10 are not all hydrogen when R6 is chlorine, which comprises:
cyclising a compound of the formula (IV):

(IV) wherein R6, R7, R8, R9 and R10 are as defined above to produce a compound of formula (III) in which R11 is amino and thereafter, when desired, substituting the amino group R11 to give a different group R11, as defined above, and, when desired converting a product of formula (III) obtained to a corresponding acid addition salt.

2. A process according to claim 1, wherein R6 is a chlorine or bromine atom, R7 is a hydrogen, chlorine or bromine atom or R6 is linked to form a -CH=CH-CH=CH-group, R9 is a hydrogen, chlorine or bromine atom, R8 is a hydrogen bromine atom and R11 is an amino group.

3. A process according to claim 1, comprising cyclising said compound of formula (IV) to produce a com-pound of formula (III), in which R11 is amino.

4. A process according to claim 1, including a step of converting a compound obtained of formula (III), in which R11 is amino to a compound of formula (III), in which R11 is C1-4 acylamino or disubstituted aminomethylene-amino.

5. A process according to claim 1, including a step of C1-4 acylating a compound obtained of formula (III), in which R11 is amino to produce a corresponding compound in which R11 is C1-4 acylamino.

6. A process according to claim 1, including a step of converting a compound of formula (III) obtained to a corresponding acid addition salt.

7. A process according to claim 1, including a step of converting a compound of formula (III) obtained to a corresponding pharmaceutically acceptable acid addition salt, with an inorganic or organic acid.

8. A process according to claim 1, for preparing 3,5-diamino-6-(2,3-dichlorophenyl)-1,2,4-triazine, which comprises cyclising a compound of said formula (IV) in which R6 and R7 are both chlorine and R8, R9 and R10 are hydrogen.

9. A process according to claim 8, which comprises reacting 2,3-dichlorobenzoyl cyanide with aminoguanidine to produce said compound of formula (IV).

10. A process according to claim 8, wherein said cyclising comprises refluxing said compound of formula (IV) in a C1-4 alkanol, in the presence of a strong base.

11. A compound of the formula (III):

(III) or an acid addition salt thereof, wherein R6 is chlorine, bromine, iodine, C1-4 alkyl or trifluoromethyl; R7 is hydrogen, halogen, C1-4 alkyl or trifluoromethyl or R6 and R7 form a -CH=CH-CH=CH- group unsubstituted or sub-stituted by a halogen atom or a C1-4 alkyl or trifluoro-methyl group; R8 is hydrogen, bromine, iodine, C1-4 alkyl or trifluoromethyl; R9 is hydrogen, halogen, C1-4 alkyl or trifluoromethyl; R10 is hydrogen, methyl or fluorine and R11 is amino, C1-4 acylamino or disubstituted amino-methyleneamino, provided that at most only two of R7, R8, R9 and R10 are other than hydrogen and that R7, R8, R9 and R10 are not all hydrogen when R6 is chlorine, whenever prepared by the process of claim 1, or by an obvious chemical equivalent.

12. A compound of the formula (III), as defined in claim 1, wherein R6 is a chlorine or bromine atom, R7 is a hydrogen, chlorine or bromine atom or R6 is linked to form a -CH=CH-CH=CH- group, R9 is a hydrogen, chlorine or bromine atom, R8 is a hydrogen bromine atom and R11 is an amino group, whenever prepared by the process of claim 2, or by an obvious chemical equivalent.

13. A compound of formula (III), as defined in claim 1, wherein R11 is amino, whenever prepared by the process of claim 3, or by an obvious chemical equivalent.

14. A compound of formula (III), as defined in claim 1, wherein R11 is C1-4 acylamino or disubstituted amino-methyleneamino, whenever prepared by the process of claim 4, or by an obvious chemical equivalent.

15. A compound of formula (III), as defined in claim 1, wherein R11 is C1-4 acylamino, whenever prepared by the process of claim 5, or by an obvious chemical equivalent.

16. An acid addition salt of a compound of formula (III), as defined in claim 1, whenever prepared by the process of claim 6, or by an obvious chemical equivalent.

17. A pharmaceutically acceptable acid addition salt of a compound of formula (III), as defined in claim 1, whenever prepared by the process of claim 7, or by an obvious chemical equivalent.

18. 3,5-Diamino-6-(2,3-dichlorophenyl)-1,2,4-triazine, whenever prepared by the process of claim 8, 9 or 10, or by an obvious chemical equivalent.