GB1566261A - 1,3 - diaza - bicyclo(o,2,0)heptane derivatives - Google Patents

Abstract

The novel compounds of the general formula I, in which R<2> and R<4> have the meaning given in Claim 1, are valuable antibiotics. In order to prepare them, a compound of the general formula VIII is reacted with an acyl halide of the formula R<4>-Hal. <IMAGE>

Description

(54) 1,3-DIAZA-BICYCLO[3,2,0]HEPTANE DERIVATIVES (71) We, SMITHKLINE CORPORATION, of 1500 Spring Garden Street, Philadelphia, Pennsylvania 19101, United States of America, a corporation organized under the laws of the Commonwealth of Pennsylvania, one of the United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention concerns 1,3-diazabicyclo[3.2.0] heptan-7-ones which have antibacterial activity.

The basic penicillin nucleus is a 4-thia-1-azabicyclo [3.2.0]heptan-7-one ring system having the skeletal structure:

Compounds having this ring system have been the object of intense research and numerous scientific articles and patents over the past two decades.

Within the last few years, attention has been directed to the synthesis of corn pounds having analogous ring systems. Among these penicillin analogs are 1-azabicyclo [3.2.0lheptane-7-one systems [Moll et at., Z. Nattarforsch B 24:942 (1969); Earle et al., 7. Chem. Soc. C 2093 (1969) and Lowe et at., 7. Chem. Soc. Chem. Comm. 328 (1973)]; 4-oxa-1-azabicyclo[3.2.0]heptan-7-one systems [Deshpande et al., 7. Chem.

Soc. C 1241 (1%6); Wolfe et at., Can. 7. Chem. 50:2902 (1972); Golding et at., 7. Chem. Soc. Chem Comm. 293 (1973); German Offenlegungschriften 2,219,601, 2,356,862 and 2,411,856; Japanese Patent Specification 9,007,263 and Netherlands Patent Specification 7,313,896]; 1,4-diazabicyclo[3.2.0]heptan-7-one systems [Bose et al., 7. Org. Chem. 38:3437 (1973) and German Offeniegungsschrift 2,219,601] and a 3-thia-1-azabicydo[3.2.0]heptan-7-one system [Bose et al., 7. Chem. Soc. C 188 (1971)].

The present invention provides 1,3-diazabicyclo [3.2.0] heptan-7-one penicillin analogs which arc represented by the formula: in which:

R1 is hydrogen or

R2 is phenyl; phenoxymethyl; benryl; eaminobenzyl; ahydroxybenzyl; ecar- boxybenzyl; phenyl substituted with lower alkyl of from one to four carbon atoms, lower alkoxy of from one to four carbon atoms, trifluoromethyl, halo or hydroxy; or benzyl substituted on the phenyl ring with lower alkyl of from one to four carbon atoms, lower alkoxy of from one to four carbon atoms, trifluoromethyl, halo or hydroxy; RS is hydrogen or an easily removable ester-forming protecting group, for example 2,2,2-trichloroethyl, t-butyl, benzyl, benzhydryl, benzyloxymethyl, tnitrophenyl, pmethoxyphenyl, pnitrobenzyl or p-methoxybenzyl; and R" is alkanoyl of from one to five carbon atoms, e.g. acetyl or propionyl; alkoxy carbon of from two to five carbon atoms, e.g. ethoxycarbonyl; haloacetyl; dihaloacetyl; beiizoyl; benzoyl substituted with lower alkyl of from one to four carbon atoms, lower alkoxy of from one to four carbon atoms, trifluoro methyl or halo, e.g. panisoyl or p-toluoyl; phenylacetyl; phenylacetyl sub stituted on the phenyl ring with lower alkyl of from one to four carbon atoms, lower alkoxy of from one to four carbon atoms, trifluoromethyl or halo; methanesulfonyl; ethanesulfonyl; benzenesulfonyl; benzylsulfonyl or ptoluenesulfonyl; and non-toxic, pharmaceutically acceptable salts thereof.

It will be recognized that the 2-carboxylic acid group of the compounds of formula I, when R3 is hydrogen, can be readily converted into a non-toxic pharma ceutically acceptable salt, for example a salt formed with the alkali metals such as sodium or potassium, the alkaline earth metals such as calcium, or with the ammonium cation. These salts can be prepared by standard methods.

The expression "easily removable ester-forming protecting group" is one which has acquired a definite meaning within the penicillin, cephalosporin and peptide arts.

Many such groups are known which are used to protect the carboxyl group during subsequent chemical reactions and are later removed by standard methods to give the free carboxylic acid. Known ester-forming protecting groups include 2,2,2-trichloroethyl, C-C6-tertiary alkyl, C,--tertiary alkenyl, CK7-tertiary alkynyl, Ct alkanoylmethyl, phthalimidomethyl, benzoylmethyl, naphthoylmethyl, furoylmethyl, thienoylmethyl, nitrobenzoylmethyl, halobenzoylmethyl, methylbenzoylmethyl, methane suffonylbenzoylmethyl, phenylbenzoylmethyl, benzyl, nitrobenzyl, methoxybenzyl, benzyloxymethyl, nitrophenyl, methoxyphenyl, benzhydryl, trityl, trimethylsilyl and triethylsilyl. The choice of an ester-forming protecting group is well within the ability of one skilled in the art. Factors which are considered include the subsequent reaction conditions the group must withstand and the conditions desired for removing the protecting group. Because the novelty of this invention lies within the new bicyclic nucleus, the choice of a protecting group is not critical to the invention.

The compounds of formula I are prepared as shown in Scheme 1 below in which R2 and R are defined as above, R' is an easily removable amine protecting group, X is halogen, preferably chloro, and R3 is an easily removable ester-forming protecting group. The compounds VI, VIa, VII and VIIa of Scheme 1, and processes for their preparation, are described and claimed in our Application 17327/79 (Serial No.

1,566,262).

The expression "an easily removable amine protecting group" is a well known term which includes many groups known and used in the penicillin, cephalosporin or peptide synthesis art. These groups include trityl, t-butoxycarbonyl, trichioroethoxy- carbonyl, benzyloxycarbonyl and 1-methoxycartoonyl-2-propenyl. Divalent amine protecting groups include phthaloyl and imine-forming groups. The choice of the protecting group depends on various factors including the subsequent chemical reaction conditions and the conditions desired for removing the protecting group. The choice of the protecting group to be used is within the ordinary ability of one skilled in the art.

Scheme 1

According to Scheme 1, when the imine resulting from the condensation of methyl glyoxalate and 2,4-dimethoxybenzylamine is allowed to react with a mixed anhydride of azidoacetic acid, azetidinone II is obtained. Hydrogenation of this compound gives the corresponding amino derivative which can be protected with an amine protecting group by standard methods to give compound III. Treatment of III with potassium persulfate results in removal of the dimethoxybenzyl group to give compound IV which upon reduction, for example with sodium borohydride, gives V. Reaction of the tosylate derivative of V with an azide such as sodium azide gives the corresponding azidomethyl compound VI. The amine protective group is removed, for example by treatment of VI with trifluoroacetic acid, and the resulting amino compound VI-a is acylated according to standard procedures to give VII. Reduction of VII with subsequent reaction of the aminomethyl compound VII-a thus formed with a glyoxalic acid derivative, the carboxylic acid function being suitably protected with an easily removable ester-forming protecting group, gives compound VIII. Treatment of VIII with an acyl halide (R4-X) gives the 1,3-diazabicyclo compounds of formula I where Rl is R2CO- and R3 and is an easily removable ester-forming protecting group. When R4 is formyl, the corresponding compounds of formula I where R1 is R2CO- and R3 is an easily removable ester-forming protecting group are also prepared by treatment of VIII with N-formyl-imidazole in the presence of a catalytic amount of imidazole hydrochloride.

Cleavage of the ester-forming protecting group gives the compounds of formula I where R1 is R2CO- and R3 is hydrogen.

When the amine protective group selected is itself a group desired as a Gsub- stituent in the final product, viz. one of the formula R2CO-- where R2 is defined as above, the steps of deblocking of the amine function and subsequent acylation can be eliminated from the reaction sequence depicted in Scheme 1.

When R1 is hydrogen, the corresponding compounds of formula I are, preferably, prepared by removal of the amine and carboxylic acid protective groups from a 3-substituted - 68 - benzyloxycarbonylamino - 7 - oxo - 1,3 - diazabicyclo [3.2.O]heptane - 2 - carboxylic acid benzyl ester, for example by hydrogenolysis. The 3 - substituted 6 benzyloxycarbonylamino - 7 - oxo - 1,3 - diazabicsclo[3.2.0]heptane - 2 - carboxylic acid benzyl esters are prepared by the methods ascribed above.

Alternatively, the 3-azido-azetidinone II can be converted into a 3-amino-2tosyloxymethyl derivative by cleavage of the 2P-dimethoxybenzyl group, followed by reduction of the ester function, conversion of the product hydroxymethyl compound into the tosylate and reduction of the azide moiety, all as described above. The resulting 3-amino-azetidinone can then be acylated or protected as required and converted to the desired 1,3-diazabicyclo[3.2.0]heptane compound.

The starting materials, in particular compounds of formula VII-a, for the compounds of this invention can be prepared as described and claimed in our Application 17327/79 (Serial No. 1,566,262).

It is recognized that, due to asymmetric carbon atoms both in the bicyclic PjAactam ring system and in some acyl side chains, stereoisomers will exist. All of these isomers, including separated isomers and mixtures thereof, are included within the scope of this invention.

The compounds of formula I are useful as antibacterial agents. For example, the compound 3 - acetyl - 7 - oxo - 613 - phenoxyacetylamino - 1,3 - diazabicyclo[3.2.0]heptane - 2 - carboxylic acid exhibited activity against Staahylococcus aureus, B.

subtiiis and other bacteria in in retro testing. In addition, the compounds of formula I where R1 is hydrogen are useful as chemical intermediates in the preparation of novel bicyclic,B-lactams which have antibacterial activity.

The invention further provides pharmaceutical compositions having antibacterial activity which comprise a pharmaceutical carrier containing an active but non-toxic quantity of a compound of formula I or a non-toxic, pharmaceutically acceptable salt thereof, as well as methods of combatting bacterial infections by administering a compound of formula I or a non-toxic, pharmaceutically acceptable salt thereof to a nonhuman infected host in a non-toxic amount sufficient to combat such infections. The preferred route of administration is by parenteral injection, such as subcutaneously, intramuscularly or intravenously, of suitably prepared sterile solutions or suspensions containing an effective, non-toxic amount of a cephalosporin compound of the invention.

The compounds of formula I can be formulated and administered in the same manner as other cephalosporins. The dosage regimen comprises administration, preferably by injection, of an active but non-toxic quantity of a compound of formula I. The precise dosages are dependent upon the age and weight of the subject and on the infection being treated, and they can be determined by those skilled in the art based on the data disclosed herein compared with that available to the art attained with known cephalosporins.

The following Examples illustrate the invention but are not to be construed as limiting the scope thereof. All temperatures are in degrees Centigrade ("C.) unless otherwise indicated.

PREPARATION 1 Methyl cs-3-azido- 1-(2,4-dimethoxybenzyl)-4-oxoazetidine-2-carboxylate To a mixture containing 16.82 g (0.101 mole) of 2,4-dimethoxybenzylamine and anhydrous magnesium sulfate in 150 ml of methylene chloride at 25 was added a solution of 10.05 g (0.114 mole) of methyl glyoxalate in 20 ml of methylene chloride.

The reaction mixture was stirred at room temperature overnight (15 hours) and then was filtered and the solvents were removed in vaciw to afford the imine of Scheme 1 as a dark orange gum.

To a solution of 15.1 g (0.149 mole) of azidoacetic acid in 130 ml of anhydrous methylene chloride at 0 (ice bath) was added dropwise 21.0 ml (0.15 mole) of trifluoroacetic anhydride. This mixture was stirred at 0 for 15 min and then 20.8 ml (0.15 mole) of triethylamine was added dropwise. Stirring was continued for an additional 45 min and then the entire reaction mixture was transferred under argon into an addition funnel which was cooled externally by dry ice. The addition funnel was attached to a flask containing the imine from above, 200 ml of anhydrous methylene chloride and 20.8 ml (0.15 mole) of triethylamine. The solution of the mixed anhydride obtained was added dropwise from the addition funnel to the solution of imine at 00.

Stirring was continued at 0 for 1 hour and then the dark reaction mixture was transferred to a separatory funnel and washed with water, aqueous sodium bicarbonate and brine and dried over anhydrous magnesium sulfate. The solvents were removed in vacuo and the residue was chromatographed on 300 g of silica gel (70--230 mesh) affording an off-white solid which was further purified by trituration with ether to give the title compound as a white solid; tlc: bemene: ethyl acetate (1:1), silica gel GF, Rf=0.64; mp 8284 (ethyl acetatehexane).

PREPARATION 2 Methyl cis-4-oXo-3-phenoxyacetylaminoazetidine-2-carboxylate A mixture containing 10.0 g (0.0312 moIe) of methyl cis-3-azido-1-(2,4dimeth- oxybenzyl)A-oxoazetidine-2-carboxylate, 1.0 g of 10% palladium on carbon and 200 ml of ethanol was hydrogenated at 60 psi of hydrogen at 4045 for 2 hours. The reaction mixture was allowed to cool to 25 and was filtered through Celite (registered Trade Mark). After removing the solvents in vacua there remained a clear, yellow gum.

The crude amine was taken up in 100 ml of anhydrous methylene dichloride and was cooled to 0 in an ice bath. To this solution was added 4.32 ml (0.0312 mole) of triethylamine, followed by the slow addition of a solution of 5.32 g (0.0312 mole) of phenoxyacetyl chloride in 40 ml of methylene dichloride. The mixture was stirred at 0" for 1 hour, then extracted successively with water, aqueous hydrochloric acid, aqueous sodium bicarbonate and brine and was dried over anhydrous magnesium sulfate. Filtration, followed by removal of the solvent in vacuo, afforded a yellow solid. This material was partially dissolved in ether, cooled to --25" and filtered to give methyl cis - 1 - (2,4 - dimethoxybenzyl) - 4 - oxo - 3 - phenoxyacetylaminoazetidine - 2 - carboxylate as a white solid; tlc: benzene: ethyl acetate (1:1), silica gel, Rf=0.38; mp 115.5--116.0" (ethyl acetate-hexane).

To 900 ml of acetonitrile, which had been thoroughly degassed with argon, was added 30.0 g (0.070 mole) of methyl cis-1-(2A-dimethoxybenzyl)A-oxo-3-phenoxy- acetylaminoazetidine-2-carboxylate and the solid was rinsed into the reaction vessel with an additional 50 ml of degassed acetonitrile. This solution was heated to 78" under argon and to it was added a degassed solution of 75.6 g (0.28 mole) of potassium persulfate and 37.5 g (0.14 mole) of sodium monohydrogen phosphate in 1400 ml of water. Addition of the aqueous solution was made in six portions of 250 ml over a period of 1 hour while maintaining the external temperature between 78" and 82".

After cooling the reaction mixture, the acetonitrile was removed by evaporation.

Sodium chloride was added to the concentrated reaction mixture and it was extracted four times with ethyl acetate. The combined ethyl acetate extracts were dried (MgSO), filtered and concentrated in vacuo to approximately 100--200 ml. Addition of ether (ca. 300 ml) followed by low temperature (--25"C) crystallization, afforded the title compound; tlc: silica gel GF, ethyl acetate, Rf=0.44; ethyl acetate: benzene (1:1), RF=0.21; mp 140141 (ethyl acetate-hexane).

PREPARATION 3 cis-2-Hydroxymethyl4-oxo-3 -phenoxyacetylaminoazetidine To a solution of 13.5 g (0.049 mole) of methyl cis-4-oxo-3-phenoxyacetylaminoazetidine-2-carboxylate in 975 ml of tetrahydrofuran and 100 ml of water 0 (ice bath) was added a cold solution of 3.75 g (0.099 mole) of sodium borohydride in 250 ml of water over a period of 10 min. The solution was stirred at 0 for 40 min and then glacial acetic acid was added dropwise until hydrogen evolution ceased. Solid sodium bicarbonate and sodium chloride were added and this mixture was extracted five times with 250 ml portions of ethyl acetate. After drying the combined extracts (MgSO4), the solvent was removed in vacua. The resulting residue was dissolved in ethyl acetate, clarified with Norit (registered Trade Mark) and allowed to crystallize to give the title compound; tlc: ethyl acetate, silica gel GF, Rf=0.10; mp 153 -154" (ethyl acetate).

PREPARATION 4 cis-2-Azidomethyloxo-3-phenoxyacetylaminoazetidine To a solution of 4.30 g (0.022 mole) of 98% ptoluenesuifonyl chloride in 24 ml of anhydrous pyridine at 0 (ice bath) was added 2.64 g (0.011 mole) of cis-2-hydroxy methylXoxo-3-phenoxyacetylaminoazetidine in one portion. The solution was stirred at 0 for 3 hours, then was stored at --25" overnight. After warming to 0 , 1.0 ml of 85% lactic acid was added and stirring was continued for 1 hour. The reaction mixture was poured into ethyl acetate and extracted successively with water, dilute aqueous hydrochloric acid, aqueous sodium bicarbonate and brine and was dried (MgSO4).

Filtration, followed by removal of the solvent in vacua, resulted in a yellow solid.

Clarification of a hot solution of this material in ethyl acetate (375 ml), followed by the addition of hexane (200 ml) and recrystallization, afforded cis4-oxo-3-phenoxy- acetylamino-2-toluenesulfonyloxymethylazetidine, tlc: ethyl acetate, silica gel GF, Rf=0.47; mp 136 (dec.).

A mixture containing 1.131 g (2.8 mmole) of cis-4-oxo-3-phenoxyacetylamino-2- FtoluenesuLfonyloxymethylazetidine, 0.961 g (14.8 mole) of sodium azide and 25 ml of anhydrous N,N-dimethylformamide was heated under argon at 40 for 6 hours, then at ambient temperature for 24 hours. The reaction mixture was poured into ethyl acetate and was washed with water. The combined aqueous washes were extracted once with ethyl acetate and the ethyl acetate fractions were combined and extracted with brine. After drying the ethyl acetate solution (MgSO4) and filtering, the solvent was removed in vacuo to afford a yellow semi-crystalline residue. This residue was slurried in methylene chloride and chromatographed on 25 g of silica gel (70--230 mesh). The 1:1 ethyl acetate: methylene dichloride fractions afforded the title compound; tlc: ethyl acetate, silica gel GF, Rf=0.38; mp 142--143" (dec) (ethyl acetate-hexane).

PREPARATION 5 cis-2-Azidomethyl-3-t-butoxycarbonylamino-4-oxoazetidine A mixture containing 10.0 g (0.0312 mole) of methyl cis-3-azido-1-(2,4-dimeth oxybenzyl)9-oxoazetidine-2-carboxylate, 1.0 g of 10% palladium on carbon and 200 ml of ethanol was hydrogenated for 2 hours at 4045 and 60 psi of hydrogen. The reaction mixture was allowed to cool to 25 and was filtered through a filter-aid. After removing the solvents in vacuo there remained methyl cir-3-amino-1-(2,4-dimethoxy- benzyl)-4-oxoazetidine-2-carboxylate.

A solution of 5.5 g (18.8 mole) of methyl cis-3-amino-1-(2,4-dimethoxybenzyl)- 4-oxoazetidine-2-carboxylate in 100 ml of dry toluene was cooled to --78" and 2.5 ml (18.8 mole) of triethylamine was added followed by rapid addition of 35 ml (42 mmole) of a 12% solution of phosgene in benzene. The mixture was stirred for 15 min at 780, and 3 hours at 450 (acetonitrile-dry ice), then warmed to room temperature and concentrated to half volume in vacua. To the resulting solution was added 50 ml of t-butanol and the mixture was stirred at room temperature overnight. The solvents were removed in vcnnre and the residue diluted with ethyl acetate and filtered.

The filtrate was transferred to a separatory funnel and washed with 5% aqueous sodium bicarbonate, 5% hydrochloric acid and brine, dried (MgSO4) and evaporated to dryness. Recrystallization of the crude, crystalline product from ether gave methyl cis - 3 - t - butoxycarbonylamino - 1 - (2,4 - dimethoxybenzyl) - 4 - oxoazetidine - 2 - carboxylate, mp 1341350.

A solution of 10.5 g (26.7 mmole) of methyl 3-t-butoxycarbonylamino-1-(2,4-di- methoxybenzyl)-4-oxoazetidine-2-carboxylate in 500 ml of acetonitrile was degassed with argon and warmed to 80". A degassed solution of 15 g (55.5 mmole) of potassium persulfate and 7.5 g (28 mmole) of sodium monohydrogen phosphate in 150 ml of water was added in five portions over 1 hour. The reaction mixture was stirred at 8085 under argon for 2-3 hours until all starting material had disappeared (tlc).

The reaction mixture was cooled, concentrated in vacua and shaken with ethyl-acetate water. The organic phase was washed with dilute hydrochloric acid, aqueous sodium bicarbonate solution and brine; dried (MgSO4) and evaporated to dryness. The residue was chromatographed on silica gel with 1:1 benzene:ethyl acetate to afford pure product which crystallized from ethyl acetate-hexane to give methyl cis-3-t-butoxy carbonylamino-4-oxoazetidine-2-carboxylate, mp 140144 .

Sodium borohydride reduction of methyl cis-3-t-butoxycarbonylamino-4-oxou azetidine-2-carboxylate as described in Preparation 3, followed by conversion of the 2-hydroxymethylazetidine product to the p-toluenesulfonate derivative, mp 160162 (d), and reaction of the derivative with sodium azide as described in Preparation 4 gives the title compound.

PREPARATION 6 cis-3-Amino-2-azidomethyl-4-oxoazetidine cis - 2 - Azidomethyl - 3 - t - butoxycarbonylamino - 4 - oxoazetidine (ca. 1 g) is dissolved in 2 ml of methylene chloride and the solution is cooled to 0 and treated with 0.5 ml of trifluoroacetic acid for 30 minutes at 0 . The solution is washed with 5% aqueous sodium bicarbonate and extracted with dilute hydrochloric acid. The aqueous phase is neutralized and extracted with ethyl acetate. Evaporation of the solvent gives the title compound.

PREPARATION 7 cis-3-Amino-4-oxo-2-p-toluenesulfonyloxymethylazetidine A degassed solution of 3.8 g (0.012 mole) of methyl cis-3-azido-1-(2,4-dimethoxy- benzyl)4-oxoazetidine-2-carboxylate was treated with potassium persulfate and sodium monohydrogen phosphate as described in Preparation 2 to give methyl cis-3-azido-4oxoazetidine-2-carboxylate which was purified by chromatography on silica gel with benzene-ethyl acetate as eluant.

Methyl cis-3-azido-4-oxoazetidine-2-carboxylate was reduced with sodium borohydride as described in Preparation 3 and the product was chromatographed on silica gel with ethyl acetate as eluant to give cis-3-azido-2-hydroxymethyl4-oxoazetidine.

cis - 3 - Azido - 4 - oxo - 2 - p - toluenesuffonyloxymethylazetidine was prepared from cis-3-azido-2-hydroxymethyl4-oxoazetidine according to the procedure of Preparation 4.

Zinc dust (2.0 g, 0.03 mole) was slowly added with cooling to a solution of 5.0 g (0.011 mole) of cis-3-azido-4-oxo-2-p-toluenesulfonyloxymethylazetidine in 50 ml of 50% aqueous acetic acid. The reaction mixture was stirred for 30 minutes and filtered.

The solids were washed with water and the filtrate was saturated with hydrogen sulfide, filtered and concentrated to near dryness. The residue was dissolved in ethyl acetate-water and the pH was adjusted to 8.0 by addition of sodium carbonate and sodium hydroxide solutions. The layers were separated and the aqueous phase was extracted twice with ethyl acetate. The extracts were combined, dried (MgSO4) and evaporated to dryness to give the title compound.

PREPARATION 8 cis-2-Aminomethyl-4-oxo-3-mandeloylaminoazetidine When cis-3-aminoW4-oxo-2-pWtoluenesulfonyloxymethylazetidine is reacted with O-benzylmandeloyl chloride according to the procedure described in Preparation 2 and the product is subsequently converted to the corresponding 2-azidomethyl compound which is subsequently reduced with zinc and acetic acid as described in Example 2, cis - 2 - aminomethyl - 3 - (a - benzyloxyphenylacetylamino) - 4 - oxoazetidine is obtained.

A suspension of 14 mg of 10% palladium on carbon and 0.06 mole of cis-2-amino methyl-3-(ebenzyloxyphenylacetylamino)-4-oxoazetidine in ca. 2 ml of anhydrous ethyl acetate is hydrogenated at room temperature and atmospheric pressure. The reaction mixture is filtered and the filtrate is evaporated to dryness to give the title compound.

PREPARATION 9 Reaction of cis-3-amino-4-oxo-2-pWtoluenesulfonyloxymethylazetidine with a halide of an acid listed below, suitably protected as necessary: benzoic acid ptoluic acid 4ethylbenzoic acid 4-íbutylbenzoic acid msanisic add 4- > butoxybenzoic acid 2-chlorobenzoic acid 4-bromobenzoic acid 4-hydroxybenzoic

PREPARATION 11 Reduction of a 2-azidomethyl-3-substitutedXoxoazetidine listed in Preparation 9 according to the procedures described in Preparation 8 or Preparation 10 gives the following 2-aminomethyl compounds: cis-2-aminomethy1-3-benzoylamincoxoazetidine cis-2-aminomethylSoxo-3 -(p-toluoylamino)azetidine cis-2-aminomethyl-3 -(4-ethylbenzoylamino)-4-oxoazetidine cis-2-aminomethyl-3-(4-t-butylbenzoylamino)-4-oxoazetidine cis-2-aminomethyl-3 -(m-anisoylamino)-4-oxoazeudine cis-2-aminomethyl-3-(4-n-butoxybenzoyiamino)-oxoazetidine cis2-aminomethyl-3-(2-chlorobenzoy1amino)A-oxoazetidine cis-2-aminomethyl-3-(4-bromobenzoylamino)-4-oxoazetidine cis-2-aminomethyl-3-(4-hydroxybenzoylamino)-4-oXoazetidine cis-2-aminomethylffioxo-3-(3 -trifluoromethylbenzoylamino)azetidine cis-2-aminomethyl-4-oxo -3 -phenylacetylaminoazetidine cis-2-aminomethyl-3-(eaminophenylacetylamino-4-oxoazetidine cis-2-aminomethyl-3-(carboxyphenylacetylamino)-4-oXoazetidine cis-2-aminomethyl-3-(4-fluorophenylacetylamino)-4-oxoazetidine cis-2-aminomethyl-3 -(3-hydroxyphenylacetyl amino)A-oxoazetidine cis-2-aminomethyl-4-oxo-3-(4-trifluoromethylphenylacetylamino)azetidine.

PREPARATION 12 cis-2-Azidomethyl-3-(4,5-diphenyl-2-oxo-4-oxazolin-3-yl)-4-oxoazetidine To a mixture containing 16.82 g (0.101 mole) of 2,4-dimethoxybenzylamine and anhydrous magnesium sulfate in 150 ml of methylene chloride at 25 is added a solution of 10.05 g (0.114 mole) of methyl glyoxalate in 20 ml of methylene chloride.

The reaction mixture is stirred at room temperature overnight (15 hours) and then is filtered. The solvents are removed in sacio to afford methyl N-(2,4-dimethoxybenzyl)iminoacetate as a dark orange gum.

A mixture of 4,5-diphenyl-2-oxo-4-oxazolin-3-ylacetic acid (2.1 g, 7.1 mole) [J. Org. Chem., 38, 3034 (1973)], 5 ml of thionyl chloride and 20 ml of methylene chloride is refluxed for 2.5 hours. After cooling to room temperature the solvent is removed in uacuo and the resulting oil crystallizes on standing. The product is triturated with ether-hexane to give 4,5-diphenyl-2-oxo-P-oxazolin-3-ylacetic acid chloride, mp 10X112 .

Methyl N-(2,4-dimethoxybenzyl)iminoacetate (1.43 g) is dissolved in 13 ml of dry methylene chloride and 1 ml of triethylamine and cooled in an ice bath. A solution of 4,5-:liphenyl-2-oxo-4-oxazolin-3-ylacetic acid chloride (2.0 g, 6.4 mmole) in 10 ml of methylene chloride is added over a 10 minute period. After one hour, the mixture is washed with water and 5 % aqueous sodium bicarbonate, then dried and evaporated to give a red oil which is chromatographed on silica gel to give methyl cSs-1-(2,4-di- methoxybenzyl)-3-(4,5-diphenyl-2-oxo-4-oxazolin-3-yl)-4-oxoazetidine-2-carboxylate.

Methyl cis - 1 - (2,4 - dimethoxybenzyl) - 3 - (4,5 - diphenyl - 2 - oxo - 4 oxazolin - 3 - yl) - 4 - oxoazetidine - 2 - carboxylate is treated with potassium persulfate and sodium monohydrogen phosphate as described in Preparation 5 to give methyl cis - 3 - (4,5 - diphenyl - 2 - oxo - 4 - oxazolin - 3 - yl) - 4 - oxoazetidine 2 - carboxylate.

Sodium borohydride reduction of methyl cis-3-(4,5-diphenyl-2-oxo-4-oxazolin-3- yl)4-oxoazetidin2-carboxylate as described in Preparation 3, followed by conversion of the 2-hydroxymethylazetidine product to the p-toluenesulfonate derivative and reac tion of this derivative with sodium azide as described in Preparation 4 gives the title compound.

PREPARATION 13 When pmethoxybenzyl alcohol, isoborneol, benzyl alcohol or 2,232-trichloroethanol is substituted for t-butanol in Preparation 5 in the reaction with methyl cis-3-amino 1-(2,4Zimethoxybenzyl)4-oxoazetidine-2-carboxylate, methyl cis-1-(2,4-dirnethoxybenzyl)-3-(p-methoxybenzyloxycarbonylamino)-4-oxoazetidine-2-carboxylate, methyl as- 1 - (2,4 - dimethoxybenzyl) - 3 - isobornyloxycarbonylamino - 4 - oxoazetidine - 2 carboxylate, methyl cis-3-benzyloxycarbonylamino- 1-(2,4-dimethoxybenzyl)-oxo- azetidine-2-carboxylate or methyl cis-1-(2,4 dimshoxybenzyl)4Oxo-3-(2,2,2-trichloro- ethoxycarbonylamino)-azetidine-2-carboxylate is obtained, respectively.

Methyl 3 - isobornyloxycarbonylamino - 1 - (2,4 - dimethoxybenzyl) - 4 - oxoazetidine - 2 - carboxylate can also be prepared by treating the 3-amino compound with isobornyloxycarbonyl chloride in the presence of base according to standard procedures; Chem. Pham Bull., 20, 1017 (1972).

Treatment of the methyl cis-l-(2,4-dimetaoxybenzyl)-3-(substituted oxycarbonylamino)4-oxoazetidine-2carboxylates mentioned above with potassium persulfate and sodium monohydrogen phosphate as described in Preparation 5 gives the following compounds, respectively: methyl cis-3-(methoxybenzyloxycarbonylamino)A-oxoazetidine-2-carboxylate methyl ris-3-isobomyloxycarbonylaminoA-oxoazetidin2-carboxylate methyl cis-3-benzyloxycarbonylaminoA-oxoazetidine-2-carboxylate methyl cis-4-oxo-3-(2,2,2-trichloroethoxycarbonylamino)azetidine-2-carboxylate.

Sodium borohydride reduction of a methyl cis-3-(substituted oxycarbonylamino)4-oxoazetidine-2-carboxylate listed above as described in Preparation 3, followed by conversion of the 2-hydroxymethylazetidine product thus formed to the p-toluenesulfonate derivative and reaction of this derivative with sodium azide as described in Preparation 4 gives the following compounds, respectively: cis-2-azidornethyl-3-(p-methoxybenzyloxycarbonylamino)4-oxoazetidine cis-2-azidomethyl-3-isobornyloxycarbonylamino-4-oxoa tidine cis-2-azidomethyl-3-benzyloxycarbonylamino4-oXoazetidine cis-2-azidomethyl-4-oxo-3-(2,2,2-trichloroethoxycarbonylamino)azetidine.

EXAMPLE 1 3-Acetyl-7-oxo-6tR-phenoxyacetylamino-1,3-diazabicyclo [3.2.0] heptane 2-carboxylic acid A suspension of 0.499 g (1.81 mmole) of cis-2-azidomethyl-4-oxo-3-phenoxy acetylammoazetidine and 0.189 g of 10% palladium on carbon in 25 ml of absolute ethanol was hydrogenated at atmospheric pressure and at 40 for 1 hour. The solution was filtered through Celite and the solvent was removed in vacua to afford a colorless gum which was dissolved in 15 ml of methylene dichloride. Anhydrous magnesium sulfate was added, followed by addition of a solution of 0.314 g (1.91 mmole) of benzyl glyoxalate in 10 ml of methylene dichloride. The reaction mixture was stirred at room temperature under argon for 2.5 hours, then was allowed to stand at 0" overnight.

After filtering the reaction mixture, the solvents were removed in vacuo to give a semicrystalline residue which was recrystallized from ethyl acetate-hexane to give N-(cis4-oxo-3-phenoxyacetylamino-2-azetidinylmethyl)iminoacetic acid benzyl ester as a colorless solid.

To a solution of 50 mg (0.13 mmole) of N-(cisA-oxo-3-phenoxyacetylamino-2- azetidinylmethyl)iminoacetic acid benzyl ester in 1.8 ml of anhydrous methylene dichloride at 0 under argon was added 16 Sal (0.20 mole) of anhydrous pyridine, followed by 14 sLI (0.20 mmole) of acetyl chloride. After the reaction mixture had been stirred at 0 for 1 hour, ethyl acetate was added and the resulting mixture was rapidly suction filtered through a sintered glass funnel containing 1.0 g of silica gel. The solvents were removed in vacuo to afford a semi-crystalline yellow gum which was recrystallized from ether-methanol to give 3-acetyl-7-oxGG'phenoxyacetylamino- 1,3- diazabicyclo[3.2.0]heptane-2-carboxylic acid benzyl ester as a mixture of G2 epimers; tlc: ethyl acetate, silica gel GF, Rf=0.55; mp 148-150'.

A suspension of 14 mg of 10% palladium on carbon and 28 mg (0.064 mmole) of 3 - acetyl - 7 - oxo - - phenoxyacetylamino - 1,3 - diazabicyclo[3.2.0]heptane - 2 - carboxylic add benzyl ester in ca. 2 ml of anhydrous ethyl acetate was hydrogenated at room temperature and atmospheric pressure for 1 hour. The reaction mixture was filtered through Celite and the solvents were removed in vacua to afford the title compound; tlc: 90:8:2 methylene chloride: methanol : acetic add, silica gel GF, Rf=0.31.

EXAMPLE 2 3-Acetyl-6uT-amino-7sxo-1,3-diazabicyclo [3.2.0]heptane-2 carboxylic acid Reaction of cis-3-arninoXoxo-2-p-toluenesulfonyloxymethylazeudine with benzyl chioroformate according to the general acylation conditions described in Preparation 2 gives cis - 3 - benzyloxycarbonylamino - 4 - oxo -2 - p - toluenesulfonylmethylazetidine.

cis - 3 - Benzyloxycarbonylamaio - 4 - oxo - 2 - p - toluenesulfonyloxymethylazetidine is converted to cis-2-azidomethyl-3-benzyloxycarbonylamino-4-oXoazetidine as described in Preparation 4.

cis-2-Azidomethyl-3-benzyloxycarbonykmino-4-oxoazetidine is treated with zinc dust in 50% aqueous acetic acid as described in Preparation 7. Reaction of the crude reduction product with benzyl glyoxalate in methylene chloride as described in the procedure of Example 1 gives N-(cis-3-benzyloxycarbonylamino -4-oxo-2-azetidinyl- methyl)iminoacetic acid benzyl ester which, when treated with acetyl chloride accord ing to the procedure of Example 1, gives 3-acetyl-6 -benzyloxycarbonylamino-7-oxo- 1,3-diazabicyclo [3.2.0.]heptane-2-carboxylic acid benzyl ester.

Hydrogenolysis of 3-acetylo -benzyloxycarbonylamino-7-oxo-1,3-diazabicyclo- [3.2.0]heptane-2-carboxylic acid benzyl ester as described in Example 1 gives the title compound.

EXAMPLE 3 3-Acetyl-6S -mandeloylamino-7-oxo-1,3-diazabicyclo [3.2.0] -heptane 2-carboxylic acid When cis-2-aminomethyl-3-(&alpha;-benzyloxyphenylacetylamino)-4-oxoazetidine is re acted with benzyl glyoxalate and the product is treated with acetyl chloride, all as described above, 3-acetyl4 -(ebenzyloxyphenylacetylamino)-7-oxo-1,3-diazabicyclo- [3.2.0]heptane-2-carboxylic acid benzyl ester is obtained. Hydrogenolysis of the benzyl protective groups as previously described gives the title compound.

EXAMPLE 4 When propionyl chloride is substituted in the procedure of Example 1 for acetyl chloride in the reaction with N-(cis-4-oxo-3-phenoxyacetylamino-2-azetidinylmethyl)- iminoacetic acid benzyl ester, the following compound of this invention is obtained: 3 - (p - anisoyl) - 7 - oxo - 6/? - phenoxyacetylamino - 1,3 - diazabicyclo[3.2.0]- heptane - 2 - carboxylic acid benzyl ester IR: 5.57 GB-lactam); 5.7,u (ester); ca.

6.00, (amides).

Removal of the benzyl ester protecting group as previously described or by other standard methods gives 7-oxo-6?-phenoxyacetylamino-3-propionyl- 1,3-diazabicyclo- [3.2.0] heptane-2-carboxylic acid.

Similarly, 3-propionyl, butyryl and valeryl derivatives of the 7-oxo-1,3-diaza bicyclo[3.2.0]-heptane-2-carboxylic acid compounds disclosed herein are prepared.

EXAMPLE 5 Substitution of ethyl chloroformate in the procedure of Example 1 in place of acetyl chloride in the reaction with N-(cis-4-oxo-3-phenoxyacetylamino-2-azetidinyl- methyl)iminoacetic acid benzyl ester gives 3-ethoxycarbonyl-7-oxo-6 -phenoxyacetyl- amino-1,3-diazabicyclo [3.2.0]heptane-2-carboxylic acid benzyl ester IR:5.56y tB-lac- tam); 5.66 (ester); 5.85 and S.90jt (amides and carbonate).

Removal of the benzyl ester protecting group as previously described or by other standard methods gives 3 ethoxycarbonyl-7-oxo-6 -phenoxyacetylamino-1,3-diaza- bicyclo[3.2.0]heptane-2-carboxylic add.

In like manner, 3-alkoxycarbonyl derivatives of the other 7-oxo-1,3-diazabicyclo [3.2.0]heptane-2-carboxylic acid compounds described above are prepared.

EXAMPLE 6 Substitution of pctoluoyl chloride or fanisoyl chloride in the procedure of Example 1 in place of acetyl chloride in the reaction with N-(cis-4-oxo-3-phenoxyacetyl amino-2-azetidinylmethyl)iminoacetic acid benzyl ester gives the following compounds of this invention: 7 - oxo - - phenoxyacetylamino - 3 - (p - toluoyl) - 1,3 - diazabicyclo[3.2.0]- heptane - 2 - carboxylic acid benzyl ester IR: 5.58} lactam); 5.70ju (ester); 5.90, 5.96, 6.10 (amides).

3 - (p - anisoyl) - 7 - oxo - 6f3 - phenoxyacetylamino - 1,3 - diazabicyclo[3)2.0] heptane - 2 - carboxylic acid benzyl ester; mp 148--150".

Removal of the benzyl ester protecting group as previously described or by other standard methods gives the carboxylic acid compounds of this invention listed below: 7 - oxo - - phenoyxacetylamino - 3 - (p - toluoyl) - 1,3 - diazabicyclo[3.2.0]heptane - 2 - carboxylic acid 3 - (p - anisoyl) - 7 oxo - 6,$ - phenoxyacetylamino - 1,3 - diazabicyclo[3.2.0]heptane - 2 - carboxylic acid.

Similarly, the other 7-oxo-1,3-diazabicyclo[3.2.0]heptane-2-carboxylic acid esters disclosed herein may be acylated with a benzoyl chloride to give the corresponding compounds of this invention.

EXAMPLE 7 When methanesulfonyl chloride is reacted with N-(cisA-oxo3-phenoxyacetyl- amino-2-azetidinylmethyl)-iminoacetic acid benzyl ester according to the procedure described in Example 1, 3-methanesulfonyl-7-oxoz phenoxyacetylamino-1,3-diaza- bicyclo[3.2.0]heptane-2-carboxylic acid benzyl ester; mp 117120 is prepared.

Removal of the benzyl ester protecting group as previously described or by other standard methods gives 3-methanesulfonyl-7-oxo-6f?-phenoxyacetylamino-1,3-diaza- bicyclo [3.2.0] heptane-2-carboxylic acid.

Similarly, 3-substituted sulfonyl derivatives of the other 7-oxo-1,3-diazabicyclo [3.2.0] heptane-2-carboxylic acids disclosed herein are prepared.

WHAT WE CLAIM IS: 1. A compound of the formula:

in which: R1 is hydrogen or

R2 is phenyl; phenoxymethyl; benzyl; vaminobenzyl; ehydroxybenzyli a-car- boxybenzyl; phenyl substituted with lower alkyl of from one to four carbon atoms, lower alkoxy of from one to four carbon atoms, trifluoromethyl, halo or hydroxy; or benzyl subsrituted on the phenyl ring with lower alkyl of from one to four carbon atoms, lower alkoxy of from one to four carbon atoms, trifluoromethyl, halo or hydroxy; R3 is hydrogen or an easily removable ester-forming protecting group; and Rz is alkanoyl of from one to five carbon atoms; alkoxycarbonyl of from two to five carbon atoms; haloacetyl; dihaloacetyl; benzoyl; benzoyl substituted with lower alkyl of from one to four carbon atoms, lower alkoxy of from one to four carbon atoms, trifluoromethyl or halo; phenylacetyl; phenylacetyl sub stituted on the phenyl ring with lower alkyl of from one to four carbon atoms, lower alkoxy of from one to four carbon atoms; trifluoromethyl or halo; methanesulfonyl; ethanesulfonyl; benzenesulfonyl; benzylsulfonyl or p toluenesulfonyl; and non-toxic, pharmaceutically acceptable salts thereof.

2. A compound as claimed in claim 1 in which R3 is an easily removable esterforming protecting group.

3. A compound as claimed in claim 1 in which RS is hydrogen.

4. A compound as claimed in claim 2 in which R is 2,2,2-trichloroethyl, C,--C,- tertiary alkyl, C5-Cr-tertiary alkenyl, C 47-tertiary alkynyl, C1C,;-alkanoylmethyl, phthalimidomethyl benzoylmethyl, naphthoylmethyl, furoylmethyl, thienoylmethyl, nitrobenzoylmethyl, halobenzoylmethyl, methylbenzoylmethyl, methanesulfonylbenzoyl- methyl, phenylbeazoylmethyl, benzyl, nitrobenzyl, methoxybenzyl, benzyloxymethyl, nitrophenyl, methoxyphenyl, benzhydryl, trityl, trimethylsilyl or triethylsilyl.

5. A compound as claimed in claim 4 in which R3 is 2,2,2-trichloroethyl, t-butyl, beazyl, benzhydryl, benzyloxymethyl, pnitrophenyl, pmethoxyphenyl, p-nitrobenzyl or pmethoxybenzyl.

6. A compound as claimed in claim 5 in which R' is acetyl, propionyl, ethoxycarbonyl, panisoyl, p-toluoyl or methanesulfonyl.

7. A compound as claimed in claim 6 in which R1 is hydrogen.

8. A compound as claimed in claim 6 in which Rt is

9. A compound as claimed in claim 8 in which R2 is phenoxymethyl.

10. A compound as claimed in claim 9 being the compound 3-acetyl-7-oxo-6 & phenoxyacetylamino-1,3-diazabicyclo [3.2.0] heptane-2-carboxylic acid benzyl ester.

11. A compound as claimed in claim 3 in which Rl is acetyl, propionyl, ethoxycarbonyl, p-anisoyl, p-toluoyl or methanesulfonyl.

12. A compound as claimed in claim 11 in which R1 is hydrogen.

13. A compound as claimed in claim 11 in which R' is

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (23)

**WARNING** start of CLMS field may overlap end of DESC **. standard methods gives 3-methanesulfonyl-7-oxo-6f?-phenoxyacetylamino-1,3-diaza- bicyclo [3.2.0] heptane-2-carboxylic acid. Similarly, 3-substituted sulfonyl derivatives of the other 7-oxo-1,3-diazabicyclo [3.2.0] heptane-2-carboxylic acids disclosed herein are prepared. WHAT WE CLAIM IS:

1. A compound of the formula:

in which: R1 is hydrogen or

R2 is phenyl; phenoxymethyl; benzyl; vaminobenzyl; ehydroxybenzyli a-car- boxybenzyl; phenyl substituted with lower alkyl of from one to four carbon atoms, lower alkoxy of from one to four carbon atoms, trifluoromethyl, halo or hydroxy; or benzyl subsrituted on the phenyl ring with lower alkyl of from one to four carbon atoms, lower alkoxy of from one to four carbon atoms, trifluoromethyl, halo or hydroxy; R3 is hydrogen or an easily removable ester-forming protecting group; and Rz is alkanoyl of from one to five carbon atoms; alkoxycarbonyl of from two to five carbon atoms; haloacetyl; dihaloacetyl; benzoyl; benzoyl substituted with lower alkyl of from one to four carbon atoms, lower alkoxy of from one to four carbon atoms, trifluoromethyl or halo; phenylacetyl; phenylacetyl sub stituted on the phenyl ring with lower alkyl of from one to four carbon atoms, lower alkoxy of from one to four carbon atoms; trifluoromethyl or halo; methanesulfonyl; ethanesulfonyl; benzenesulfonyl; benzylsulfonyl or p toluenesulfonyl; and non-toxic, pharmaceutically acceptable salts thereof.

2. A compound as claimed in claim 1 in which R3 is an easily removable esterforming protecting group.

3. A compound as claimed in claim 1 in which RS is hydrogen.

4. A compound as claimed in claim 2 in which R is 2,2,2-trichloroethyl, C,--C,- tertiary alkyl, C5-Cr-tertiary alkenyl, C 47-tertiary alkynyl, C1C,;-alkanoylmethyl, phthalimidomethyl benzoylmethyl, naphthoylmethyl, furoylmethyl, thienoylmethyl, nitrobenzoylmethyl, halobenzoylmethyl, methylbenzoylmethyl, methanesulfonylbenzoyl- methyl, phenylbeazoylmethyl, benzyl, nitrobenzyl, methoxybenzyl, benzyloxymethyl, nitrophenyl, methoxyphenyl, benzhydryl, trityl, trimethylsilyl or triethylsilyl.

5. A compound as claimed in claim 4 in which R3 is 2,2,2-trichloroethyl, t-butyl, beazyl, benzhydryl, benzyloxymethyl, pnitrophenyl, pmethoxyphenyl, p-nitrobenzyl or pmethoxybenzyl.

6. A compound as claimed in claim 5 in which R' is acetyl, propionyl, ethoxycarbonyl, panisoyl, p-toluoyl or methanesulfonyl.

7. A compound as claimed in claim 6 in which R1 is hydrogen.

8. A compound as claimed in claim 6 in which Rt is

9. A compound as claimed in claim 8 in which R2 is phenoxymethyl.

10. A compound as claimed in claim 9 being the compound 3-acetyl-7-oxo-6 & phenoxyacetylamino-1,3-diazabicyclo [3.2.0] heptane-2-carboxylic acid benzyl ester.

11. A compound as claimed in claim 3 in which Rl is acetyl, propionyl, ethoxycarbonyl, p-anisoyl, p-toluoyl or methanesulfonyl.

12. A compound as claimed in claim 11 in which R1 is hydrogen.

13. A compound as claimed in claim 11 in which R' is

14. A compound as claimed in claim 12 being the compound 3-acetyl-6"e-amino- 7 < xo-1,3-diazabicyclo [3.2.o] -heptane-2-carboxylic acid.

15. A compound as claimed in claim 13 in which R2 is phenoxymethyl.

16. A compound as claimed in claim 15 being the compound 3-acetyl-7-oxo-6ss; phenoxyacetylamino-1,3-diazabicyclo[3.2.0]heptane-2-carboxylic acid.

17. A compound as claimed in claim 1, as described in any one of Examples 1 to 7.

18. A process for preparing a compound according to claim 1 where R1 is R2-C, which comprises reacting a compound of formula:

(where R2 is as defined in claim 1 and R3 is an easily removable ester-forming protecting group) with an acyl halide of formula R4X (where R4 is as defined in claim 1 and X represents a halogen), cleaving the ester-forming protecting group R3 when a cora- pound of formula I where R3 is hydrogen is required, and, if desired, converting the product into a salt thereof.

19. A process for preparing a compound according to claim 1 (where R4 is formyl and R1 is R2HO), which comprises reacting a compound of formula VIII (as defined in claim 18) with N-formyl-imidazole (in the presence of a catalytic amount of imidazole hydrochloride) and if desired converting the product into a salt thereof.

20. A process for preparing a compound as claimed in claim 1, substantially as described in any one of Examples 1 to 7.

21. A compound according to claim 1) when prepared by a process according to any one of claims 18 to 20.

22. A method of treating a bacterial infection of a non-human animal which comprises administering an effective amount of a compound as claimed in claim 1.

23. A pharmaceutical composition comprising a compound of formula I as defined in claim 1, or a non-toxic, pharmaceutically acceptable salt thereof, and a pharmaceutical carrier.