GB2168972A - Cephalosporin antibiotics - Google Patents

Abstract

Compounds of general formula (I'> <IMAGE> (wherein Y<1> represents an acetoxy group, a group of formula -O.CO.NHR<1> wherein R<1> represents a hydrogen atom or a C1-4 alkyl group optionally substituted by one to three halogen atoms or the group -O.CO.NHR<2> where R<2> is an N-protecting group; B is -S- or -SO- (???- or ???-); R<3> represents hydrogen or a carboxyl blocking group; and R<4> is an amino or protected amino group) and salts thereof are disclosed. Processes for their preparation and pharmaceutical compositions which comprise as active ingredient one or more cephalosporin antibiotics of general formula (I') are also disclosed.

Description

SPECIFICATION Cephalosporin antibiotics This invention relates to improvements in or relating to cephalosporins. More particularly it relates to new cephalosporin compounds and derivatives thereof having valuable antibiotic activity.

The cephalosporin compounds in this specification are named with reference to "cephem" after jAmer. Chem. Soc., 1962, 84, 3400, the term "cepham" referring to the basic cepham structure with one double bond.

Cephalosporin antibiotics are widely used in the treatment of diseases caused by pathogenic bacteria in human beings and animals, and are especially useful in the treatment of diseases caused by bacteria which are resistant to other antibiotics such as penicillin compounds, and in the treatment of penicillin-sensitive patients. In many instances it is desirable to employ a cephalosporin antibiotic which exhibits activity against both Gram-positive and Gram-negative microorganisms, and a significant amount of research has been directed to the development of various types of broad spectrum cephalosporin antibiotics.

Thus, for example, in our British Patent Specification No. 1399086, we describe a novel class of cephalosporin antibiotics containing a 7P-(a-etherified oximino)-acylamido group, the oximino group having the syn configuration. This class of antibiotic compounds is characterised by high antibacterial activity against a range of Gram-positive and Gram-negative organisms coupled with particularly high stability to p-lactamases produced by various Gram-negative organisms.

The discovery of this class of compounds has stimulated further research in the same area in attempts to find compounds which have improved properties, for example against particular classes of organisms. This interest is reflected in the very large numbers of patent applications which have been filed relating to cephalosporin antibiotics having particular oxyimino etherifying groups in combination with particular substituents both on the 7ss-acylamido side chain and at the 3-position of the cephalosporin nucleus.

British Patent No. 1604971 generically defines a wide range of cephalosporin antibiotics in which the 73-position side-chain may be selected from interalia a syn 2-(2-aminothiazol-4-yl)-2-(etherified oxyimino)acetamido group in which the etherifying group may be a substituted methyl group, although the preferred etherifying group is an unsubstituted methyl group. The 3-position group may also be selected from a large number of alternatives and a possible 3-substituent according to the generic definition is an acetoxymethyl group or an optionally substituted carbamoyloxymethyl group.

British Patent Specification No. 1576625 contains a generic definition of cephalosporin antibiotics having a 7(3-(a-etherified oxyimino)acetamido side chain wherein the etherifying group, amongst very many possible meanings, may be an alkyl group substituted by a heterocyclic group, which side chain is further a-substituted by a group which interalia may be an aminothiazolyl group. The aromatic thienyl group is the only heterocyclic substituent of the oxime etherifying group exemplified. The 3-position group may also be selected from a large number of alternatives and a possible 3-substituent within the generic definition is an acetoxymethyl or an optionally substituted carbamoyloxymethyl group.

We have now discovered that by the selection of a (Z)-2-(2-aminothiazol-4-yl)-2-(etherified oxyimino)acetamido group at the 7P-position in combination with certain particular groups as herein defined at the 3-position, and by the selection of a thiiranylmethoxyimino group as the etherified oxyimino grouping, cephalosporin compounds having a particularly advantageous profile of activity (described in more detail below) against a wide range of commonly encountered pathogenic organisms may be obtained.

Accordingly, we provide cephalosporin antibiotics of general formula (I)

[wherein Y represents an acetoxy group or a group of formula -O.CO.NHR1 wherein R1 represents a hydrogen atom or a C1.4 alkyl group optionally substituted by one to three halogen atoms], non-toxic salts and non-toxic metabolically labile esters thereof.

R1, when present, preferably represents a hydrogen atom or a methyl, ethyl or 2-chloroethyl group.

The compounds according to the invention are syn isomers. The syn isomeric form is defined by the configuration of the

group with respect two the carboxamido group. In this Specification, the syn configuration is denoted structurally as

It will be understood that since the compounds according to the invention are geometric isomers, some admixture with the corresponding anti isomer may occur. It will further be appreciated that in the thiiranylmethyl group, the carbon atom of the thiiranyl ring adjacent to the methyl group is chiral and may therefore exist in either R or S configuration.The invention includes within its scope all individual enantiomeric forms ofthe compounds of formula (I) as well as mixtures (including racemic mixtures) thereof. Itwill be understood that all intermediates possessing athiiranylmethyl group used in the preparation of compounds of formula (I) may exist either as separate enantiomers or as mixtures.

The invention also includes within its scope the solvates (especially the hydrates) of the compounds of formula (I) and of their non-toxic salts. It also includes within its scope non-toxic salts and solvates of metabolically labile esters of the compounds of formula (I). It will be appreciated that the solvates should be pharmacologically acceptable.

The compounds according to the present invention may exist in tautomeric forms (for example in respect of the 2-aminothiazoiyl group) and it will be understood that such tautomeric forms, e.g. the 2iminothiazolinyl form, are included within the scope of the invention.

The compounds according to the invention exhibit broad spectrum antibiotic acitvity both in vitro and in vivo. They have high activity against both Gram-positive and Gram-negative organisms, including many ,3-lactamase producing strains. The compounds also possess high stability to p-lactamases produced by a range of Gram-negative and Gram-positive organisms.

Compounds according to the invention have been fond to exhibit high activity against a broad range of Gram-positive organisms, e.g. strains (including penicillinase-producing strains) of Staphylococcus aureus, Staphylococcus epidermidis and Streptococcus species. This is coupled with high activity against various members of the Enterobacteriaceae (e.g. strains of Escherichia coli, Klebsiella pneumoniae, Citrobacter diversus, Enterobactercloacae, Serratia marcescens, Proteus mirabilis and indole-positive Proteus organisms such as Proteus vulgaris, Proteus morganiiand Providence species), strains of Haemophilus influenzae, and Acinetobacter calcoaceticus as well as good activity against Pseudomonas species (e.g.

Pseudqmonas aeruginosa). This combination of high activity against Gram-positive organisms with high activity against Gram-negative organisms possessed bythecompounds of the invention is unusual and particularly advantageous.

Non-toxic salt derivatives which may be formed by reaction of the carboxyl group present in the compounds of formula (I) include inorganic base salts such as alkali metal salts (e.g. sodium and potassium salts) and alkaline earth metal salts (e.g. calcium salts); amino acid salts (e.g. lysine and arginine salts); organic base salts (e.g. procaine, phenylethylbenzylamine, dibenzylethylenediamine, ethanolamine, diethanolamine and N-methylglucosamine salts). Other non-toxic salt derivatives include acid addition salts, e.g.

formed with hydrochloric, hydrobromic, sulphuric, nitric, phosphoric, formic and trifluoroacetic acids. The salts may also be in the form of resinates formed with, for example, a polystyrene resin or cross-linked polystyrene divinylbenzene copolymer resin containing amino or quaternary amino groups or su Iphonic acid groups, or with a resin containing carboxyl groups, e.g. a polyacrylic acid resin. Soluble base salts (e.g.

alkali metal salts such as the sodium salt) of the compounds of formula (I) may be used in therapeutic applications because of the rapid distribution of such salts in the body upon administration. Where, however, insoluble salts of compounds (I) are desired in a particular application, e.g. for use in depot preparations, such salts may be formed in conventional manner, for example with appropriate organic amines.

Non-toxic metabolically labile ester derivatives which may be formed by esterification of the carboxyl group in the parent compound of formula (I) include acyloxyalkyl esters, e.g. lower alkanoyloxy-methyl or -ethyl esters such as acetoxy-methyl or -ethyl or pivaloyloxymethyl esters. In addition to the above ester derivatives, the present invention includes within its scope the compounds of formula (I) in the form of other physiologically acceptable equivalents, i.e. physiologically acceptable compounds which, like the metabolically labile esters, are converted in vivo into the parent antibiotic compound of formula (I).

These and other salt and ester derivatives such as the salts with toluene-p-sulphonic and methanesulphonic acids or the esters with t-butyl or diphenylmethyl esterifying groups may be employed as intermediates in the preparation and/or purification of the present compounds of formula (I), for example in the processes described below.

A preferred compound according to the invention is (6R, 7R)-7-[ (Z)-2-(2-aminothiazol-4-yl(-2 (thiiranylmethoxyimino)acetamido]-3-carbamoyIoxymethyl-ceph-3.em-4carboxyIic acid, together with the non-toxic salts and non-toxic metabolically labile esters thereof.

The compounds of the invention may be used for treating a variety of diseases caused by pathogenic bacteria in human beings and animals, such as respiratory tract infections and urinary tract infections.

According to another embodiment of the invention we provide a process for the preparation of an antibiotic compound of general formula (I) as herein before defined or a non-toxic salt or non-toxic metabolically labile ester thereof which comprises forming a compound offormula (I')

[wherein Y1 is the group Y as defined above or the group -O.CO.NHR2 where R2 is an N-protecting group, e.g. a labile group such as an acyl group, especially a lower alkanoyl group such as acetyl, a halo-substituted lower alkanoyl group such as mono-, di- ortrichloro-acetyl, a chlorosulphonyl or bromosulphonyl group, or a halogenated alkoxycarbonyl group such as 2,2,2-trichloroethoxycarbonyl;B is -S- or -SO- (a- or ss-); R3 represents hydrogen or a carboxyl blocking group, e.g. the residue of an ester-forming aliphatic or araliphatic alcohol or of an ester-forming phenol, silanol or stannanol (the said alcohol, phenol, silanol or stannanol preferably containing 1 to 20 carbon atoms) or a symmetrical or mixed anhydride blocking group derived from an appropriate acid; and R4is an amino or protected amino group] or a salt thereof, by (A) acylating a compound of the formula (II)

(wherein B, y1 and R3 are as defined above) or a salt, e.g. an acid addition salt (formed with, for example, a mineral acid such as hydrochloric, hydrobromic, sulphuric, nitric or phosphoric acid or an organic acid such as methanesulphonic or toluene-p-sulphonic acid) or a 7-N-silyl derivative thereof, with an acid of formula (111)

(wherein R4 is an amino or protected amino group), or a salt thereof or with an acylating agent corresponding thereto; or (B) reacting a compound of formula (IV)

(wherein R3, R4 and B are as hereinbefore defined) or a salt thereof, with an acylating agent serving to form the group -CH2Y1 (wherein Y1 is as defined above) at the 3-position; whereafter, if necessary and/or desired in each instance, any of the following reactions, in any appropriate sequence, are carried out: i) reduction of a compound wherein B is -SO- to form a compound wherein B is -S-, ii) conversion of a carboxyl group into a non-toxic metabolically iabile ester function, iii) formation of a non-toxic salt function, iv) removal of any carboxyl blocking and/or N-protecting groups, and v) resolution, where the initial product is a mixture of enantiomers.

The above reactions i) to v) may be carried out in conventional manner.

In the processes according to the invention, preferred carboxyl blocking and N-protecting groups R2, R3 and R4 are groups which may subsequently be removed under mild conditions (i.e. those which do not cause cleavage of the thiirane or ss-lactam ring: see for example Thedora W. Greene, "Protective Groups in Organic Synthesis" (John Wiley and Sons, 1981)).

Other reagents and conditions used in the processes according to the invention should be chosen such that they do not cause significant degradation of the thiirane ring.

In the above-described process (A), the starting material of formula (II) is preferably a compound wherein Bis -S-.

Acylating agents which may be employed in the preparation of compounds of formula (I) include acid halides, particularly acid chlorides or bromides. Such acylating agents may be prepared by reacting an acid (Ill) or a salt thereof with a halogenating agent e.g. phosphorus pentachloride, thionyl chloride or oxalyl chloride.

Acylations employing acid halides may be effected in aqueous and non-aqueous reaction media, convenientlyattemperatures of from -SOto +500C, preferably -40to +30"C, preferably in the presence of an acid binding agent. Suitable reaction media include aqueous ketones such as aqueous acetone, aqueous alcohols such as aqueous ethanol, esters such as ethyl acetate, halogenated hydrocarbons such as methylene chloride, amides such as dimethylacetamide, nitriies such as acetonitrile, or mixtures of two or more such solvents.Suitable acid binding agents include tertiary amines (e.g. triethylamine or dimethylaniline), inorganic bases (e.g. calcium carbonate or sodium bicarbonate), and oxiranes such as lower 1,2-alkylene oxides (e.g. ethylene oxide or propylene oxide) which bind hydrogen halide liberated in the acylation reaction.

Acids offormula (lli) may themselves be used as acylating agents in the preparation of compounds of formula (I). Acylations employing acids (III) are desirably conducted in the presence of a condensing agent, for example a carbodiimide such as N,N'-dicyclohexylcarbodiimide or N-ethyl-N'-z-dimethylaminopropyl- carbodiimide; a carbonyl compound such as carbonyldiimidazole; or an isoxazolium salt such as N-ethyl-5-phenylisoxazolium perchlorate.

Acylation may also be effected with other amide-forming derivatives of acids of formula (III) such as, for example, an activated ester, a symmetrical anhydride or a mixed anhydride (e.g. formed with pivalic acid or with a haloformate, such as a lower alkylhaloformate). Mixed anhydrides may also be formed with phosphorus acids (for example phosphoric or phosphorous acids), sulphuric acid or aliphatic or aromatic sulphonic acids (for example toluene-p-sulphonic acid). Acylations using anhydrides may conveniently be effected in the presence of an acid binding agent such as those described above for acylation using acid halides. An activated ester may conveniently be formed in situ using, for example, 1 -hydroxybenzotriazole in the presence of a condensing agent as set out above. Alternatively, the activated ester may be preformed.

Acylation reactions involving the free acids or their above-mentioned amide-forming derivatives are desirably effected in an anhydrous reaction medium, e.g. methylene chloride, tetrahydrofuran, dimethylformamide or acetonitrile.

An alternative method of activation is, for example, by reacting an acid of formula (III) with a solution or suspension preformed by adding a carbonyl halide, in particular oxalyl chloride or phosgene, or a phosphoryl halide such as phosphorus oxychloride to a solvent such as a halogenated hydrocarbon, for example methylene chloride, containing a lower acyl tertiary amide such as N,N-dimethylformamide.The activated form of the the acid of formula (Ill) may then be reacted with a 7-amino compound of formula (II) in a suitable solvent or mixture of solvents for example alcohols such as an alkanol, e.g. ethanol or industrialmethylated spirits; halogenated hydrocarbons, e.g. methylene chloride; ethers, e.g. tetrahydrofuran or dioxan; esters, e.g. ethyl acetate; ketones, e.g. acetone; amides, e.g. dimethylacetamide; nitriles, e.g.

acetonitrile; water; and mixtures thereof. The acylation reaction may conveniently be effected at temperatures of from -50" to +50 C, preferably -40"to +30"C, if desired in the presence of an acid binding agent, for example as described above (e.g. triethylamine).

If desired, the above acylation reactions may be carried out in the presence of a catalyst such as 4-dimethylaminopyridine.

The acids of formula (III) and acylating agents corresponding thereto may, if desired, be prepared and employed in the form of their acid addition salts. Thus, for example, acid chlorides may conveniently be employed as their hydrochloride salts, and acid bromides as their hydrobromide salts.

Carbamoylation of 3-hydroxymethyl compounds of formula (IV) may be effected by conventional methods using suitable acylating (i.e. carbamoylating) agents. Suitable carbamoylating agents include isocyanates of formula RS.NCO (wherein R5 is a labile substituent group or the group R1 as defined above), to give a compound containing a 3-position substituent having the formula -CH2O.CoNHR5 (wherein R5 has the above defined meaning).The carbamoylation reaction may desirably be effected in the presence of a solvent or solvent mixture selected from hydrocarbons (e.g. aromatic hydrocarbons such as benzene and toluene), halogenated hydrocarbons (e.g. dichloromethane), amides (e.g. formamide or dimethylformamide), esters (e.g. ethyl acetate), ethers (e.g. cyclic ethers such as tetrahydrofuran and dioxan), ketones (e.g. acetone), sulphoxides (e.g. dimethylsulphoxide) and mixtures of these solvents. The reaction may conveniently be carried out at a temperature of between -80 C and the boiling temperature of the reaction mixture, for example up to 100 C, preferably between -20 C and +300C. The labile group R5 may subsequently be cleaved, e.g. by hydrolysis, to form a 3-carbamoyloxymethyl group.Examples of labile groups R5 which are readily cleavable upon subsequent treatment include those labile groups hereinbefore given as examples of the group R2. Such labile groups may generally be cleaved by acid or base catalysed hydrolysis (e.g. by base catalysed hydrolysis using sodium bicarbonate). Halogenated groups such as chlorosulphonyl, dichlorophosphoryl, trichloroacetyl and 2,2,2-trichloroethoxycarbonyl may also be cleaved reductively, while groups such as chloroacetyl may also be cleaved by treatment with thioamides such as thiourea.

The carbamoylating agent is desirably used in excess (for example at least 1.1 moles relative to the compound of formula (IV)). The carbamoylation may be assisted by the presence of base, e.g. a tertiary organic base such as a tri-(lower alkyl) amine (e.g. triethylamine) or by employing the compound (IV) in the form of an alkali metal (e.g. sodium) salt, although such assistance may not be necessary in the case of more active isocyanates, e.g. compounds wherein R5 is a strongly electron-withdrawing group such as chlorosulphonyl ortrichloroacetyl. Carbamoylations involving reaction of a free acid of formula (IV) with excess isocyanate wherein R5 is a group such as chlorosulphonyl ortrichloroacetyl are thus of particular practical advantage by virtue of the simplicity of the reaction conditions, since there is no need for temporary blocking and subsequent deblocking of the 4-position carboxy group of the cephalosporin and since the electron-withdrawing R5 group in the resulting N-protected 3-carbamoyloxymethyl cephalosporin product is readily removed by, for example, hydrolysis with aqueous sodium bicarbonate.

It should be noted that it may be convenient to retain or even introduce an N-substituting group R5 during transformations of intermediate 3-carbamoyloxymethyl compounds in order to minimise unwanted side reactions involving the carbamoyloxymethyl group.

Another useful carbamoylating agent is cyanic acid, which is conveniently generated in situ, for example, from an alkali metal cyanate such as sodium cyanate, the reaction being facilitated by the presence of an acid, e.g. a strong organic acid such as trifluoroacetic acid. Cyanic acid effectively corresponds to the isocyanate compounds mentioned above wherein R5 is hydrogen and therefore converts compounds of formula (IV) directly to their 3-carbamoyloxymethyl analogues.

Alternatively, carbamoylation may be effected by reaction of the compound of formula (IV) with phosgene or carbonyldiimidazole followed by ammonia or the appropriate substituted amine, optionally in an aqueous or non-aqueous reaction medium.

Acetylation of 3-hydroxymethyl compounds of formula (IV) may be effected by conventional methods, for example in an analogous manner to that described in British Patent Specification No. 1141293, i.e. by blocking the 4-carboxy group, acetylating the 3-hydroxymethyl group of the protected compound and subsequently removing the blocking group.

3-Hydroxymethyl starting materials of formula (IV) are novel compounds and form a further feature of the invention. They may be prepared by methods analogous to those described in British Patent No. 1474519 and U.S. Patent No.3976546. Alternatively they may be prepared by acylating the corresponding 7-amino-3-hydroxymethyl compounds, for example, analogously to process (A) above.

The reaction product may be separated from the reaction mixture, which may contain, for example, unchanged cephalosporin starting material and other substances, by a variety of processes including recrystallisation, ionophoresis, column chromatography and use of ion-exchangers (for example by chromatography on ion-exchange resins) or macroreticular resins.

Where a compound is obtained in which B is -SO- this may be converted into the corresponding sulphide by, for example, reduction of the corresponding acyloxysulphonium or alkoxysulphonium salt prepared in situ by reaction with e.g. acetyl chloride in the case of an acetoxysulphonium salt, reduction being effected by, for example, sodium dithionite or by iodide ion as in a solution of potassium iodide in a solvent e.g. acetic acid, acetone, tetrahydrofuran, dioxan, dimethylformamide or dimethylacetamide. The reaction may be effected at a temperature of from - 20 to + 50"C.

Metabolically labile ester derivatives of the compounds of formula (I) may be prepared by reacting a compound of formula (I) or a salt or protected derivative thereof with the appropriate esterifying agent such as an acyloxyalkyl halide (e.g. iodide) conveniently in an inert organic solvent such as dimethylformamide or acetone, followed, where necessary, by removal of any protecting groups.

Base salts of the compounds of formula (I) may be formed by reacting an acid of formula (I) with an appropriate base. Thus, for example, sodium or potassium salts may be prepared using the respective 2-ethylhexanoate or hydrogen carbonate salt Acid addition salts may be prepared by reacting a compound of formula (I) or a metabolically labile ester derivative thereof with the appropriate acid.

Where a compound of formula (I) is obtained as a mixture of isomers, the syn isomer may be obtained by, for example, conventional methods such as crystallisation or chromatography.

Mixtures of enantiomers, including racemic mixtures, of compounds according to the invention or intermediates therefor may be resolved using conventional means; see for example "Stereochemistry of Carbon Compounds" by E.L. Eliel (McGraw Hill, 1962) and "Tables of Resolving Agents" by S.M. Wilen.

For use as starting materials for the preparation of compounds of general formula (I) according to the invention, compounds of general formula (III) the amide forming derivatives thereof such as acid halides and anhydrides corresponding thereto in their syn isomeric form or in the form of mixtures of the syn isomers and the corresponding anti isomers containing at least 90% of the syn isomer are preferably used.

Acids offormula (III) and their derivatives are themselves novel compounds and form a further feature of the present invention. They may be prepared by etherification of a compound of formula (V)

(wherein R4 is as hereinbefore defined and R6 represents hydrogen or a carboxyl blocking group) or a salt thereof, by selective reaction with a compound of general formula (VI)

(wherein T is a halogen atom, such as chloro, bromo or iodo; sulphate; or a sulphonate group, such as tosylate and mesylate), followed by removal of any carboxyl blocking group R6: The carboxyl blocking group R6 used is preferably a group which may subsequently be removed under mild conditions.For example, a p-nitrobenzyl group may be employed in which case removal of the blocking group may for example be effected using sodium bicarbonate and sodium dithionite in the presence of aqueous tetrahydrofuran.

Separation, including resolution, of isomers may be effected either before or after such etherification. The etherification reaction is conveniently carried out in the presence of a base, e.g. potassium carbonate or sodium hydride, and is preferably conducted in an organic solvent, for example dimethylsulphoxide, a cyclic ether such as tetrahydrofuran or dioxan, or an N,N-disubstituted amide such as dimethylformamide. Under these conditions the configuration of the oxyimino group is substantially unchanged by the etherification reaction. When the compound of formula (V) is employed in the form of a free acid or a salt with a base, the etherification reaction is generally carried out in the presence of a strong base, e.g., potassium t-butoxide, sufficient base being added to form a dianion.Furthermore, the reaction should be effected in the presence of a base if an acid addition salt of a compound of formula (V) is used, the amount of base being sufficientto neutralise rapidly the acid in question.

The acids offormula(lll) may be converted into the corresponding acid halides and anhydrides and acid addition salts by conventional methods, for example as described hereinabove, and optionally with or without previous purification.

The compounds offormulae (Vl), employed as starting materials, may be prepared by conventional methods e.g. by reaction with thiourea in methanol, (see for example, C.C.J. Culvenor, W. Davies and LH.

Pausacker; J. Chem. Soc 1946, 1050). If desired these compounds may be purified, e.g. by distillation, before further reaction.

It should be appreciated that in some of the above transformations it may be necessary to protect any sensitive groups in the molecule of the compound in question to avoid undesirable side reactions. For example, during any of the reaction sequences referred to above it may be necessary to protect the NH2 group of the aminothiazolyl moiety, for example by tritylation, acylation (e.g. chloroacetylation or formylation), protonation or other conventional method. The protecting group may thereafter be removed in any convenient way which does not cause breakdown of the desired compound. The thiirane grouping in the oxime portion of the compounds of formulae (III) and (IV) is susceptible to cleavage for example by strong acids or bases, and it is therefore desirable to employ N-protecting groups which can be removed under mild conditions.For example, a trityl group may be removed by using an optionally halogenated carboxylic acid, e.g. acetic acid, formic acid, chloroacetic acid or trifluoroacetic acid or mixtures of such acids, optionally in the presence of methyl phenyl ether (anisole), or, in the case of a chloroacetyl group, by treatment with thiourea.

Carboxyl blocking groups used in the preparation of compounds of formula (I) or in the preparation of compounds of formula (I) or in the preparation of necessary starting materials are desirably groups which may readily be split off at a suitable stage in the reaction sequence, conveniently at the last stage. It may, however, be convenient in some instances to employ non-toxic metabolically labile carboxyl blocking groups such as acyloxy-methyl or -ethyl groups (e.g. acetoxy-methyl or -ethyl or pivaloyloxymethyl) and retain these in the final product to give an appropriate ester derivative of a compound of formula (I).

Suitable carboxyl blocking groups are well known in the art, a list of representative blocked carboxyl groups being included in British Patent No. 1399086. Preferred blocked carboxyl groups are those which may be deblocked without the use of strongly acidic conditions, for example aryl lower alkoxycarbonyl groups such as p-methoxybenzyloxycarbonyl, p-nitrobenzyloxycarbonyl and diphenylmethoxycarbonyl. The carboxyl blocking group may subsequently be removed by any of the appropriate methods disclosed in the literature; thus, for example, mild acid or base catalysed hydrolysis is applicable in many cases, as are enzymically-catalysed hydrolyses.

The antibiotic compounds of the invention may be formulated for administration in any convenient way, by analogy with other antibiotics and the invention therefore includes within its scope pharmaceutical compositions comprising one or more antibiotic compounds in accordance with the invention adapted for use in human or veterinary medicine. Such compositions may be presented for use in conventional manner with the aid of any necessary pharmaceutical carriers or excipients.

The antibiotic compounds according to the invention may, for example, be formulated for injection and may be presented in unit dose form, in ampoules, or in multi-dose containers, if necessary with an added preservative. The compositions may also take such forms as suspensions, solutions, or emulsions in oily or aqueous vehicles, and may contain formulatory agents such as suspending, stabilising and/or dispersing agents. Alternatively the active ingredient may be in powder form for reconstitution with a suitable vehicle, e.g. sterile, pyrogen-free water, before use.

If desired, such powder formulations may contain an appropriate non-toxic base in order to improve the water-solubility of the active ingredient and/or to ensure that when the powder is reconstituted with water, the pH of the resulting aqueous formulation is physiologically acceptable. Alternatively the base may be present in the water with which the powder is reconstituted. The base may be, for example, an inorganic base such as sodium carbonate, sodium bicarbonate or sodium acetate, or an organic base such as lysine or lysine acetate. The antibiotic compounds may also, for example, be formulated as suppositories e.g.

containing conventional suppository bases such as cocoa butter or other glycerides.

Compositions for veterinary medicine may, for example, be formulated as intramammary preparations in either long acting or quick-release bases.

The compositions may contain from 0.1% upwards, e.g. 0.1-99% of the active material, depending on the method of administration. When the compositions comprise dosage units, each unit will preferably contain 100-3000 mg of the active ingredient e.g. 200-2000 mg. The daily dosage for adult human treatment will preferably range from 200 to 12000 mg e.g. 1000-9000 mg per day, depending inter alia on the nature of the infection and the route and frequency of administration. In general, intravenous or intramuscular administration will be employed, for example using 400 to 4000 mg per day of the active ingredient in adult human treatment. In treating Pseudomonas infections higher daily doses may be required.It will be appreciated that in some circumstances, for example, in the treatment of neonates, smaller dosage units and daily dosages may be desirable.

The antibiotic compounds according to the invention may be administered in combination with other therapeutic agents such as antibiotics, for example penicillins or other cephalosporins.

The following-Examples illustrates the invention. All temperatures are in "C; DMSO is dimethylsulphoxide; EtOH is ethanol.

Intermediate 1 4-Nitrobenzyl (Z)-2-hydroxyimino-2-(2-tritylaminothiazol-4-yl)-acetate A mixture of sodium (Z) -2-hydroxyimino-2-(2-tritylaminothiazol-4-yI)-acetate (63.6g) and 4-nitrobenzyl bromide (33.5g) in N,N-dimethylformamide (500ml) at room temperature was stirred for 1 hour and allowed to stand for 4 days. The reaction mixture was added to water (2.5 1) and ethyl acetate (1.5 1). The aqueous phase was acidified to pH 1 with dilute hydrochloric acid and the two phases separated. The organic phase was cooled in an ice bath and petroleum ether (1.5 1) added. The product precipitated out of solution and filtration afforded the title compound (65.89).

Vmax (CHBr3) 3550, 3400, 1740, 1610, 1600, 1523,1348cm1; XmaX (EtOH) 261.5nm, E11c1ni 342; 229nm, E1icm 484, 264nm, E1 / m 340, 270nm, E jcYom 324.

Intermediate 2 Preparation 1 4-Nitrobenzyl (Z)-2- Thllran ylm eth ox yim in o-2-(2-tritylamin othiazol-4-yl)acetate A mixture of chloromethyl thiirane (see C.C.J. Culvenor, W. Davies and K.H. Pausacker, J. Chem. Soc. 1946 1050) (I.954g), Intermediate 1 (3.9859) and potassium carbonate (4.159) in dimethylsulphoxide (75ml) was stirred at room temperature for 26 hours. The reaction mixture was diluted with ethyl acetate (400ml) and washed successively with water, sodium hydrogen sulphate solution, water, saturated sodium chloride solution and dried with magnesium sulphate. The solvent was removed under reduced pressure. The crude product was purified by flash chromatography on silica gel to afford the title compound (2.7g).

T (CDC13) includes 3.48 (thiazole proton), 5.73 (t,J 6Hz) 6.83 (m), 7.4-7.9(m).

Preparation 2 4-Nitrobenzyl 2-thiEranylmethoxyimino-2-{2-tritylaminothiazo/-4yl)acetate 2-Chloromethylthiirane (see C.C.J. Culvenor,W. Davies and K.H. Pausacker, J. Chem. Soc. 1946, 1050) (5.04ml) and potassium carbonate (89) were added to a solution of Intermediate 1 (89) in dimethylsulphoxide (40ml). The resultant mixture was stirred at ambient temperature for 1.75 hours when it was poured into ethyl acetate (800ml) and water (100ml) and the two phases were separated.The organic phase was washed with water (100ml, 2 x 50ml), 10% sodium hydrogen sulphate solution (2 x 100ml), water (100ml) and saturated brine (100ml). The ethyl acetate solution was finally dried over anhydrous magnesium sulphate and evaporated under reduced pressure to an oil. This was dried in vacuo at room temperature to yield 9.2g of the title compound.

A sample of the above foam (29) was dissolved in ethyl acetate (5my) and diluted 1:1 with 40/60 petroleum ether. This solution was applied to a 6 x 10cm column of Kieselgel 60 (ART9385,110g) packed under pressure in ethyl acetate/40:60 petroleum ether (1:3). The column was eluted under slight nitrogen pressure with the same solvent mixture. The fractions containing the purified compound were collected and concentrated under reduced pressure to give 1.399 of the title compound.

vmax (CHBr3) 3400 (NH), 1746 (COOR), 1528 + 1349 (Ar-NO2), 754 (Ph) cam~1.

values (CDCI3) include 1.81 and 2.44 (d,d.J=9Hz, phenyl protons); 2.75 (trityl); 3.10-(N-H); 3.50 (aminothiazol proton); 4.60 (COOCH2-); 5.72 (t, J=6Hz, O-CH2); 6.83 (m, thiiranyl methylene proton), 7.4- 7.9 (thiiranyl methine proton).

Intermediate 3 Preparation 1 (2)-2-Thiiranylmethoxyimino-2-(2-tritylaminothiazol-4-yl)acetic acid A mixture of Intermediate 2 (0.89g) and sodiumdithionite (2.869) in water (24ml), saturated aqueous sodium hydrogen carbonate (12ml) and tetrahydrofuran (36mull was stirred at room temperature for 1.75 hours. The reaction mixture was added to ethyl acetate (250ml) and washed successively with sodium hydrogen sulphate solution, saturated sodium chloride solution and dried with magnesium sulphate.

Removal of solvent under vacuum afforded the title compound in quantitative yield.

T (d6-DMSO) includes 3.09 (thiazole proton), 5.62-6.2 (m) 6.84 (q, J 7Hz) 7.4-7.8(m).

Preparation 2 {Z)-2-ThiEranylmethoxyimino-2-62-tritylaminothiazol-4yl)acetic acid Water (140ml) and saturated sodium bicarbonate solution (70ml) were added to a solution of Intermediate 2 (5.2g) in tetrahydrofuran (210ml) under nitrogen. Sodium dithionite (1 6.7g) was added and the mixture was stirred at ambient temperature (21-22") for 1.5 hours. The reaction was partitioned between a stirred mixture of ethyl acetate (750ml) and 10%wlwsodium hydrogen sulphate solution (300ml).The separated aqeuous phase was extracted with further ethyl acetate and the bulked organic fractions were washed with 10% w/w sodium hydrogen sulphate (75ml) and 1:1 10% sodium hydrogen sulphate solution/-saturated brine (100ml) before drying over anhydrous magnesium sulphate. The solution was concentrated under reduced pressure to a pale yellow solid which was dried in vacuo at ambient temperature to give 4.719 of the title compound.

A 1.6g aliquot of the title compound was adsorbed onto a column of silica (100g) from solution in dichioromethane: methanol 8:1 v/v. Elution with the same solvent mixture allowed the isolation of a purified version of the title compound (1.1 g).

values (DMSO-d6) include 1.37 (N-H); ca 2.75 (triphenylmethyl H); 3.28 (aminothiazole H); 5.75-6.45 (-CH2-); 6.89 (thiirane ring methine H); approx. 7.357.9 (thiirane ring methylene, ABq, 6Hz).

EXAMPLE 1 a) Diphenylmethyl (6R,7R)-7-[(Z)-2-thiiranylmethoxyimino-2-(2-tritylaminothiazol-4-yl)acetamido]-3- carhamoyloxymethyl-ceph-3-em-4-carboxylate A solution of oxalyl chloride (183mg) in methylene chloride (2ml) was added to a solution of N,N-dimethylformamide (0.34ml) in methylene chloride (3ml) at -20"C. The reaction mixture was stirred in an ice bath for 20 minutes before recooling to -20"C. A solution of Intermediate 3 (659mg) in methylene chloride (5ml) was added.The resultant mixture was stirred at -20 C for 20 minutes and then in an ice bath for 20 minutes before recooling to- -20"C. It was then added to a stirred solution of N,N-dimethylaniline (0.36ml) and diphenyl methyl (6R,7R)-7-amino-3-carbamoyloxymethylceph-3-em-4-carboxylate (577mg) in methylene chloride (5ml) at -20 C. The reaction mixture was stirred in an ice bath for 70 minutes, diluted with methylene chloride (150ml), washed successively with water, sodium hydrogen sulphate solution, sodium hydrogen carbonate solution, saturated sodium chloride solution and dried with magnesium sulphate.Removal of solvent under vacuum gave the crude product which was purified by flash chromatography on silica gel to afford the title compound (671 mg).

T (CDCI3) includes 3.26 and 3.28 (thiazole proton), 4.06 (dd, J 5,8Hz), 4.98 (d,J 5Hz), 4.97 and 5.24 (ABq, J 14Hz), 6.45 and 6.63 (ABq, J 18Hz); Vmax (CHBr3) 3450 and 3405 (NH and NH2), 1789 (p-lactam), 1729 (carbamate), 1685 and 1515 (amide), 1580 (NH carbamate).

b) (6R,7R)-7-HZ)-2-(2-Aminothiazol-4-yl)-2-(thifranylmethoxyimino)acetamidoj-3-carbamoyloxymethyl-ceph- 3-em -4-ca rb oxylic acid, trifluoroacetate salt.

A solution of the product of stage a (530mg) in anisole (2ml) and trifluoroacetic acid (8ml) was stirred at room temperature for 50 minutes. The reaction mixture was added to water (50ml) with stirring. Diethyl ether (50ml) was added. The two phases were separated and the organic phase extracted with water. The combined aqueous extracts were washed with ether before being freeze dried to give the title compound (89.5mg).

T (d6-DMSO) includes 0.56 (d, J8, Hz amide NH), 3.16 (thiazole proton) 4.19 (dd, J 8,5HZ), 4.92 (d, J 5Hz), 5.10 and 5.36 (ABq, J 14Hz), 5.6-6.2 (m) 6.39 and 6.54 (ABq J 18Hz), 6.85 (m) 7.3-7.7 (m).

#max(EtOH)237.5nm,E11cm/1%128;#inf247nm,E1Cm120,292nm,E1cm/1%63,322nm,E1%1cm/36.

EXAMPLE 2 a) /6R, 7R)-7-[Z)-2-f2- Tritylamin othiazol-4-yl)-2-thifran ylmeth ox yim in oacetamido]-3- (carbamoyloxymethyl)ceph-3-em-4-carboxyllc acid A solution of oxalyl chloride (0.96ml) in methylene chloride (4ml) was added to a stirred solution of N,N-dimethylformamide (2.53ml) in methylene chloride (1 Oml) at less than -5" over 5 minutes. The mixture was stirred at less than -5" for 20 minutes when Intermediate 3 (5.1 2g) was added and the solution stirred at -5" for 30 minutes.The solution was then cooled to -10 and added to a solution of (6R,7R)-7-amino-3 (carbamoyloxymethyl)ceph-3-em-4-carboxylic acid (2.6g) in industrial methylated spirits (25ml) and water (7ml) containing triethylamine (4.38ml) at - 10' with vigorous stirring. The solution was stirred in an ice bath for 30 minutes. It was then washed with water (80ml) and the aqueous phase back extracted with methylene chloride. The bulked organic liquors were layered with water (50ml) and the pH adjusted to 3.0 with 2N hydrochloric acid. After separation and back extraction of the aqueous layer with methylene chloride, the bulked organic liquors were dried over anhydrous magnesium sulphate and concentrated under reduced pressure to a brown foam.This was dissolved in methylene chloride (20ml) and added to diisopropyl ether (50ml) with stirring over 60 minutes. The solid was collected by filtration, washed with 2:1 diisopropyl ether/methylene chloride and finally diisopropyl ether and dried in vacuo at ambienttemperatureto give the title compound (7.049).

A 4g aliquot of this material was adsorbed on a column of silica gel (1009) from a solution in dichloromethane. Elution with a mixture of dichloromethane and industrial methylated spirits gave a purified title compound (1.29).

T values (DMSO-ds) include 0.44 (d, 6Hz; CONH); 1.16 (C-NH): approx. 2.4-2.8 (triphenylmethyl); 3.18 (aminothiazole H); 3.42 (OCONH2); 4.35 (d,d, 8,3Hz; C-7 H); 4.93 (d, 5Hz; C-6 H); 5.07 + 5.19 (ABq, 12Hz; -CH2OCONH2); 6.46 + 6.66 (C-2 H2) approx. 5.6-6.2 (-O-CH2-); 6.76 (thiirane methane H); approx. 7.3-7.7 (thiirane methylene H).

b) (6R,7R)-7-[(Z)-2-(2-aminothiazol-4-yl)-2-thiiranylmethoxyiminoacetamido]-3-(carbamoyloxy-methyl)ceph- 3-em-4-carboxylic acid hydrochloride The product of stage a) (39) was stirred in formic acid (12ml) for 5 minutes. Water (3ml) was added and the mixture was stirred at 22-25 for 21/2 hours. The precipitated trityl carbinol was removed by filtration and washed with formic acid (3ml). The filtrate and wash were evaporated to a solid by rotary evaporation at reduced pressure at 25 . The residue was slurried in acetone (14ml) and concentrated hydrochloric acid (0.5ml) was added. The mixture was stirred at ambient temperature for 2 hours. The solid was collected by filtration and washed with acetone.The crystalline solid was dried in vacuo to give 1.559 of the title compound.

Excess diethyl ether was added to bulked liquors resulting from unsuccessful attempts to recrystallise the crude title compound from dimethsulphoxide, water, dichloromethane, ethyl acetate, ethanol and acetone.

The resulting flocculent, crystalline precipitate was isolated by suction filtration, washed with diethyl ether, then dried in vacuo to give the title compound (0.1 5g).

Vmax (Nujol) 3380,3300 (NH,NH2), 2600, 1708 (CO2H), 1764 (p-lactam carbonyl), 1708 (OCONH2), 1660 + 1548 (CONH) cm-1.

T values (DMSO-d6) 0.24 (IH,d,J8Hz,CONH); 3.04(1 H,s,aminothiazole H); 3.42 (2H,CONH2); 4.18 (1H,dd,J8,5 Hz,C-7 H); 4.79(1H,d,J5Hz,C-6H 4.79 (1H,d,J5Hz,C-6H); 5.07 + 5.34(2H,ABq,J13Hz,CH20CONH2); 5.63 + 5.96 (2H,ABq,J13Hz,NOCH2); 6.35 + 6.52 (2H,ABq,J18Hz, C-2); 6.69 (1 H, thiirane methine); 7.34 + 7.48 (2H, thiirane methylene).

Claims (17)

1. Compounds of general formula (I')

(wherein y1 represents an acetoxy group, a group of formula -O.CO.NHR' wherein 131 represents a hydrogen atom or a C1.4 alkyl group optionally substituted by one to three halogen atoms or the group -O.CO.NH132 where R2 is an N-protecting group; B is-S- o -SO- (oi- or (3-); R3 represents hydrogen or a carboxyl blocking group; and 134is an amino or protected amino group) and salts thereof.

2. Compounds as claimed in claim 1 having the general formula (I)

[wherein Y represents an acetoxy group or a group of formula -O.CO.NHR1 wherein R1 represents a hydrogen atom or a C1-4 alkyl group optionally substituted by one to three halogen atoms], non-toxic salts, non-toxic metabolically labile esters, and solvates thereof.

3. Compounds as claimed in claim 2 wherein Y is a group of formula -O.CO.NHR1 in which R1 represents a hydrogen atom or a methyl, ethyl or 2-chloroethyl group, non-toxic salts, non-toxic metabolically labile esters and solvatesthereof.

4. (6R,7R)-7-[(Z)-2-(2-aminothiazol-4-yl (-2-(thiiranylmethoxyimino)acetamido]-3- carbamoyloxymethylceph-3-em-4-carboxylic acid, non-toxic salts, non-toxic metabolically labile esters and solvates thereof.

5. A process for the preparation of a compound as claimed in claim 1 which comprises either (A) acylating a compound of formula (II)

(wherein B, Y' and R3 are as defined in claim 1) or a salt or a 7-N-silyl derivative thereof, with an acid of formula (III)

(wherein R4 is an amino or protected amino group) or a salt thereof or with an acylating agent corresponding thereto; or (B) reacting a compound of formula (IV)

(wherein R3, R4 and B are as defined in claim 1), or a salt thereof, with an acylating agent serving to form the group -CH2Y1 (wherein Y1 is as defined in claim 1) atthe3-position; whereafter, if necessary and/or desired in each instance, any of the following reactions, in any appropriate sequence, are carried out: i) reduction of a compound wherein B is -SO- to form a compound wherein B is -S-, ii) conversion of a carboxyl group into a non-toxic metabolically labile ester function, (iii) formation of a non-toxic salt function, iv) removal of any carboxyl blocking and/or N-protecting groups, and v) resolution, where the initial product is a mixture of enantiomers.

6. A process as claimed in claim 5 wherein an acid of formula (III), a salt thereof or an acylating agent corresponding thereto is employed in the syn isomericform or in the form of a mixture of the syn isomer and the corresponding anti-isomer containing at least 90% of the syn isomer.

7. A process as claimed in claim 5 wherein carbamoylation of a compound of formula (IV) is effected using an isocyanate of formula R5.NCo (wherein R5 is a labile substituent group or the group R1 as defined in claim 1), or cyanic acid; or by reaction with phosgene or carbonyldiimidazole followed by ammonia or the appropriate substituted amine.

8. Compounds of formula (IV) as defined in claim 5, and salts thereof.

9. Acids of formula (Ill) as defined in claim 5, salts thereof and derivatives thereof.

10. A process for the preparation of an acid of formula (Ill) or a salt or a derivative thereof as claimed in claim 9 which comprises etherification of a compound of formula (V)

(wherein R4 is an amino or protected amino group and 135 represents hydrogen or a carboxyl blocking group) or a salt thereof, by selective reaction with a compound of formula (VI)

(wherein T is a halogen atom, sulphate or a sulphonate group), followed by removal of any carboxyl blocking group R6.

11. A process as claimed in claim 5 or claim 6 which further comprises formation of an acid of formula (III) or a salt thereof by a process as claimed in claim 10.

12. Pharmaceutical compositions which comprise as active ingredient at least one compound as claimed in claim 2 in association with one or more pharmaceutical carriers and/or excipients.

13. A process as claimed in claim 5 substantially as hereinbefore described.

14. A process as claimed in claim 5 substantially as herein before described with reference to the Examples.

15. A process as claimed in claim 10 substantially as hereinbefore described.

16. A process as claimed in claim 10 substantially as hereinbefore described with reference to the Examples.

17. A pharmaceutical composition as claimed in claim 12 substantially as hereinbefore described,