CA1067068A - 3-CARBAMOYLOXYMETHYL-7-(.alpha.-(1-CARBOXYCYCLOBUT-1-OXYIMINO)-.alpha.-(FUR-2-YL) ACETAMIDO) CEPH-3-EM-4-CARBOXYLIC ACID - Google Patents

Abstract

A B S T R A C T
This invention relates to a process for the preparation of an antibiotic compound of the formula (I) or a non-toxic derivative thereof, said compound being a syn isomer or existing as a mixture of syn and anti isomers containing at least 90% of the syn isomer, wherein (A) a compound of the formula (II) (wherein B is > S or > S ? O; R1 represents hydrogen or a carboxyl blocking group; and the dotted line bridging the 2-, 3- and 4- positions indicates that the compound is a ceph-2-em or ceph-3-em compound) or an acid addition salt or an N-silyl derivative thereof, is condensed with an acylating agent corresponding to an acid of formula (III) (wherein R2 is a carboxyl blocking group) or (B) a compound of the formula (IV) (wherein B and the dotted line are as defined above; and each R1 may in-dependently represent hydrogen or a carboxyl blocking group) is reacted with a carbamoylating agent serving to form a carbamoyloxymethyl or N-protected carbamoyloxymethyl group at the 3-position; whereafter, if necessary and/or desired in each instance, any of the following reactions (C), in any appropriate sequence, are carried out:- i) conversion of a .DELTA.2 isomer into the desired .DELTA.3 isomer, ii) reduction of a compound wherein B is > S ? O to form a compound wherein B is > S, and iii) removal of any carboxyl blocking and/or N-protecting groups; and finally (D) recovering the desired compound or a non-toxic derivative thereof, if necessary after separation of isomers.
It also relates to the products of the process which are useful as broad spectrum antibiotics having particularly high activity against gram-negative microorganisms.

Description

1067Q6r3 Tis application is a divisional of our copending Patent Application Serial NoO 216,571 filed December 20J 19740 This invention is concerned with improvements in or relating to cephalosporin compounds, and is more particularly concerned with a cephalosporin compound possess-ing valuable antibiotic propertiesO
The cephalosporin compounds in this specification are named with reference to "cepham" after J.AmerOChemO
SocO, 1962, 84, 3400, the term "cephem" referring to the basic cepham structure with one double bondO
Cephalosporin antibiotics are widely used in the treatment of diseases caused by pathogenic bacteria in ; human beings and animals, for example 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 patientsO In many in-: stances it is desirable to employ a cephalosporin anti-biotic 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 antibioticsD
Considerable interest is currently being direct-ed to the development of broad spectrum cephalosporin anti-biotics which possess high activity against gram negative i

- 2 -.

organisms, Existing commercially available ~-lactam antibiotics tend to exhibit comparatively low activity against certain gram negative organisms such as Proteus organisms, which are an increasingly common source of infection in humans, and are also generally substantially inactive against Pseudomonas organisms, Several Pseudomonas organisms are resistant to the majority of existing commercially available antibiotic compounds, and the practical therapeutic applications of aminoglycoside antibiotics such as gentamicin which do exhibit Pseudomonas activity tend to be lim~ed or complicated by the high . toxicity of these antibiotics, It is well known that cephalosporin antibiotics normally exhibit low toxicity I . in man, sothat the development of broad spectrum cephalosporin antibiotics possessing high activity against gram negative organisms such as strains of Proteus and Pseudomonas fulfils a significant need in chemotherapy, The present invention provides a cephalosporin antibiotic of the formula .,'' ~

.

.

~067068 1~
H H
C.CO.NH
Il , ,o~ ~d~ CH20cONH2 ~ .C.COOH COOH
:~>
. (I) and non-toxic derivatives thereof, the compounds.
- being ~yn isome~ or existing as mixtures of syn and anti isomers containing at least 9~/O of the syn isomer, 5 The compoundsexhibit broad spectrum antibiotic activity characterised by particularly high activity against gram negative microorganisms., including those which produce ~-lactamases, and also possess very high stability to ~-lactamases produced by a range . . 10 of gram negative organisms, A characteristic feature of the compoundsistheir high in vitro activity against gram-negative organisms such as Enterobacter cloacae, Serratia marcesce~s and 1~5~ oUS_ es~
. .
. The compounds.have particularly high activity .
_ ~

~.t i, against strains of Escherichia coli,Haemophilus influenzae and Prote;us organisms, e,g, strains of Proteus morganii . ~
, . . .
and Proteus mirabilis, The compoundsh ve.also shown `~ ~, unusually high.activity against Pseudomonas organisms, for S~: example straing of Pseudomonas aeruginosa.
~.,, , ~ .
The compoundbof the~invention are defined as having the syn lsomeric form as-regards the configuration of : the group ~ . -. ::
O.C,COOH ~ ~

with respect.to the carboxamido group,. In this specification ~,., ~. ~ . . : .
~the syn configuration ls denoted structurally as . O .CONH- -N
. .C C ON

. this configuration being as:signed on the basis of the .
work of Ahmad and Spenser reported in Can,~ Ll 1961, 39, 1340, As indicated above, the compoundsmay exist as mixtures of syn and anti isomers provided . 15 that such mixtures contain at least 9~/0 of the syn : - 5 -.

.

isomer, We prefer, however, the compoundsto be svn isomers essentially free from the corresponding anti isomer, By "non-toxic derivatives" is meant those derivatives which are physiologically acceptable in the dosage at which they are administered, Such derivatives may include, for example, salts, biologically acceptable esters, l-oxides and solvates (especially hydrates), It will be appreciated that derivatives such as salts and esters may be formed by reaction of either or both of the carboxyl groups present in the compound of formula(I2.
Non-toxic salt derivatives which may be formed from the compound of general 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), and organic base salts (e.g. procaine, phenylethylbenzylamine, dibenzylethylenediamine, ethanolamine, diethanolamine, triethanolamine and N-methylglucosamine salts).

~067068 The salts may also be in the form of resinates formed with, for example, a polystyrene resin or cross-linked polystyrene divinylbenzene copolymer resincontaining amino or quaternary amino groups. Use of highly soluble base salts (e,g, alkali metal salts such as the sodium salt) of the compound of formula(I)is generally advantageous in therapeutic applications because of the rapid distribution of such salts in the body upon administrationO Where, however, insoluble salts of the compound (I) are desired in a ~articular application, e g for use in depot preparations, such salts may be formed in conventional manner, for example with appropriate organic amines, Biologically acceptable, metabolically labile ester derivatives which may be formed fromthe compounds of formula O include, for example, acyloxymethyl esters, e g lower alkanoyloxymethyl esters such as acetoxymethyl or pivaloyloxymethyl esters, .
_ 7 _ .

1067~68 tnpounds The e~Ywu*~ according to the invention may be prepared by any convenient method, for example by techniques analogous to those described in Canadian Patent No, 19 027~554 Thus according to one embodiment of the invention we provide a process for the preparation of the antibiotic compound of formula (~ (as defined above~
or a non-toxic derivative thereof, said compound being a ~y~ isomer or existing as a mixture of syn and anti 0 isomers containing at least 9~/0 of the syn isomer, wherein (A) a compound of the formula B
H2N ~/ ~

0 ~ \ ~ 1CH20CNH2 COOR
(II) . - 8 -.

Iwherein B is ~S or ~S-~ 0 (~- or ~ ); Rl represents hydrogen or a carboxyl blocking group, e,g, the residue of an ester-forming aliphatic or araliphatic alcohol or an ester-forming phenol, silanol or stannanol (the said alcohol, phenol, silanol or stannanol preferably containing 1-20 carbon atoms) or a symmetrical or mixed anhydride group derived from an appropriate acid; and the dotted line bridging the 2-, 3- and 4-positions indicates that the compound may be a ceph-2-em or ceph-3-em compound~ or an acid addition salt such as a hydrochloride, hydrobromide, sulphate, nitrate, phosphate, methane sulphonate or p-toluenesulphonate or an N-silylated derivative thereof, is condensed with an acylating agent.corresponding to an acid of formula ~; ~L C . COOH
N

O. C. COOR2 ( I:EI) ' <>

~ ' :

(wherein R2 is a carboxyl blocking group, e,g, a group as hereinbefore defined in connection with Rl );

or ~B) a compound of the formula H H

. . ~ ~ C.CO.NH ~ B ~
O N . ~ ~ CH20H
.C.COORl COOR
<>
(IV) (wherein B and the dotted line are as hereinbefore defined; and each Rl may independently represent hydrogen or a carboxyl blocking group) is reacted wlth a carbamoylating agent serving to form a carbamoyloxymethyl .
or.N-protected carbamoyloxymethy,l group at the 3-position;
whereafter, if necessary and/or desired in each instance, l~ any of the following reactions (C) in any appropriate sequence, are carried out:- ' i) conversion of a Q2 isomer into the desired ~3 isomer, ii) reduction of a compound wherein B is ~S-~O to form - a compound wherein B is ~S, and .

~067~)68 iii) removal of any carboxyl blocking and/or N
protecting groups; and finally (D) recovering the desired compound of formula (I) or a non-toxic derivative thereof, if necessary after separation of isomers.
Non-toxic derivatives of the compounds of formula (I) may be formed in any convenient way, for example according to methods well known in the art. Thus, for example, sodiu~
and potassium salts may be formed by reaction of the cephalosporin acid with sodium 2-ethylhexanoate or potassium 2-ethylhexanoate, Biologically acceptable ester derivatives may be formed using conventional esterifying agents, l-Oxides may be formed by treatment of the corresponding cephalosporin sulphide with an appropriate oxidising agent, for example with a peracid such as metaperiodic acid, peracetic acid, monoperphthalic acid or m-chloroperbenzoic acid, or with t-butyl hypochlorite, this last reagent conveniently being employed in the presence of a weak base such as pyridine, ~ 67 0 ~ 8 Acylating agents which may be employed in the preparation of the compound of formula(~ include acid halides, particularly acid chlorides or bromides, Such acylating agents may be prepared by reacting an acid . (III3 or a salt thereof with a halogenating agent e,g, phosphorus pentachloride, thionyl chloride or oxalyl chloride, Treatment of the sodium, potassium or triethylammonium salt of the acid (III) with oxalyl chloride is advantageous in that under these conditions isomerisation is minimal, Acylations employing acid halides may be effected in aqueous and non-aqueous reaction media, conveniently at temperatures of from -50 to +50C, preferably -20 to +300C, if desired in the presence of an acid binding agent, Suitable reaction media include aqueous ketones .
:

such as aqueous acetone, esters such as ethyl acetate, halogenated hydrocarbons such as methylene chloride, amides such as dimethylacetamide, nitriles such as . acetonitrile, or mixtures of two or more such solvents, Suitable acid binding age~ 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 of formula (III) may themselves be used as acylating agents in the preparation of the compound of formula.~4, Acylations employing acids (III) are desirably conducted in the presence of a condensation agent, for example a carbodiimide such as N,N'-diethyl-, - dipropyl- or diisopropylcarbodiimide, N,N'-dicyclohexyl-carbodiimide or N-ethyl-N'-y-dimethylaminopropylcarbo~
diimide; a carbonyl compound such as carbony~;imidazole;
or an isoxazolinium salt such as N-ethyl-5-phenylisoxaz-olinium perchlorate, Acylation reactions of this type are desirably effected in an anhydrous reaction medium, . e,g, methylene chloride, dimethylformamide or acetontrile, Acylation may also be effected with other amide-.

forming derivatives of acids of formula(lII)such as, for example, a symmetrical anhydride or a mixed anhydride - (e.g. with pivalic acid or formed with a haloformate such as a lower alkylhaloformate). The mixed or symmetrical anhydride may be generated in situ; thus~
for example, a mixed anhydride may be genera~ed using N-ethoxycarbonyl-2-ethoxy-l, 2-dihydroquinoline~ 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 e~e ~_Sc~ o~C
tolucne~ onlc acid).
Carbamoylation of 3-hydroxymethyl compounds (IV) may be effected by conventional methods~ Thus, for example, a 3-hydroxymethyl cephalosporin may be reacted with an isocyanate of formula R .NC0 (wherein R represents a labile substituent group) to give a compo~nd containing a 3-position substituent having the formula -CH20.CONHRa (wherein Ra has the above defined meaning). The labile N-protecting substituent is subsequently cleaved~ e.g. by hydrolysis, to form a 3-carbamoyloxymethyl group. Labile groups R` which are readily cleavable upon subsequent treatment include chlorosulphonyl and bromosulphonyl;

':

~067068 halogenated lower aIkanoyl groups such as dichloroacetyl and trichloroacetyl; and halogenated lower alkoxycarbonyl groups such as 2,2,2-trichloroethoxycarbonyl. These labile Ra groups may generally be cleaved by a~id or base catalysed hydrolysis (e.g. by base catalysed hydrolysis using sodium bicarbonate).
Another carbamoylating agent of use in the carbamoylation of 3-hydroxymethyl cephalosporins is cyanic acid, which is conveniently generated in situ from, for example~ 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 a compound of formula Ra~NCO wherein Ra is hydrogen, and therefore converts 3-hydroxymethyl cephalosporin compounds directIy to their 3-carbamoyloxymethyl analogues.

3-Hydroxymethyl cephalosporins (I~) for use in the above carbamoylation reactions may~ for example, be prepared by the methods described in British Patent No.
1,121,308 and Canadian Patents Nos~ 1,027,554 and 1,021,280.

~2-Cephalosporin ester derivatives obtained in accordance with the process of the invention may be converted into the corresponding ~3 derivative by, for example, treatment of the ~2 ester with a base~
S Ceph-2-em reaction products may also ~e oxidised to yield the corresponding ceph-3-em l-oxide~ for example by reaction with a peracid as mentioned previously; the resulting sulphoxide may, if desired, subsequently be reduced as described hereinafter to yield the corresponding ceph-3-em sulphide.
- Where a compound is obtained in which B is >S~ 0 this may be converted to the corresponding sulphide by~
for example, reduction of the corresponding acyloxy-sulphonium or alkyloxysulphonium salt prepared in situ by reaction with e.g~ acetyl chloride in the case of an acetoxysulphonium salt, reduction being eff-ected by~ for example, sodium dithionite or by iodide ion as in a solution of potassium iodLde in a water miscible solvent e.g. acetic acid, tetrahydrofuran, dioxan, dimethyl-formamide ar dimethylacetamide. The reaction may be . ' , ' .
~16 -~.o6~068 effected at a temperature of -20 to +50C.
Where the compound ~ 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. Syn and anti isomers may be distinguished by appropriate techniques, e.g. by their ultraviolet spectra, by thin layer or~ paper chromatography or by their proton magnetic resonance spectra. Thus, for example5 the p m.r. spectra of DMS0-d6 solutions of syn compounds of formula(I)exhibit the doublet for the amide NH at a lower field than do similar solutions of the corresponding anti-isomers. These factors may be employed in monitoring reactions.
Starting materials of formula (III) may be prepared - 15 in an analogous manner to that described in our copending Application Serial No. 216571~ for example~ as described in the Preparation belowO
Carboxyl blocking groups R and, where appropriate~
R used in the preparation of the compound of ~rmula (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 as the last stage. It may, however, be convenient in some ~ 17 -instances to employ biologically acceptable, metabolically labile carboxyl blocking groups such as acyloxymethyl groups (e.g. pivaloyloxymethyl) and retain these in the final product to give a biologically acceptable ester derivative of the compound of formula~I).
Suitable carboxyl blocking groups are well known in the art, a list of representative blocked carboxyl groups being included in Canadian Patent No~ 1,027,554. Preferred blocked carboxyl groups include aryl lower alkoxycarbonyl groups such as ~-methoxybenzyloxycarbonyl~ ~-nitro-benzyloxycarbonyl and diphenylmethoxycarbonyl; lower alkoxycarbonyl groups such as t-butoxycarbonyl; and lower haloalkoxycarbonyl groups such as 2,2,2-trichloroethoxy-carbonyl.~ The carboxyl blocking group may subsequently be removed by any of the appropriate methods disclosed in the literature; thus~ for example, acid or base catalysed hydrolysis is applicable in many cases, as are enzymically-catalysed hydrolyses.
The antibiotic compounds of the invention~ i.e. the compound of form~la(I)and non-toxic derivatives thereof, may be formulated for administration in any convenient way, by analogy wLth other antibiotics and the invention therefore includes within its scope pharmaceutical .

~,o67~6~

compositions comprising an antibiotic compound 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 be formulated for injection and may be presented in unit dose form in ampoules, or in multi-dose containers with an added preservative. The compositions may 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.
The antibiotic compounds may also be presented in a form suitable for absorption by the gastro-inte~tinal tract.
Tablets and capsules for oral administration may be in unit dose presentation form, and may contain conventional excipients such as binding agents~ for example syrup, acacia, gelatin, sorbitol, tragacanth or polyvinylpyrrolidone; fillers for example lactose~ sugar, - 19 ~

~067068 maize-starch, calcium phosphate, sorbitol or glycine;
lubricants, for example magnesium stearate, talc, polyethylene glycol or silica; disintegrants, for example potato starch; or acceptable wetting agents such as sodium lauryl sulphate~ The tables may be coated according to methods well known in the art. O~al liquid preparatio~ may be in the form of~ for example, aqueous or oily suspensions, solutions~ emulsions, syrups or elixirs, or may be presented as a dry product for reconstitutior with water or other suitable ve~icle before use. Such liquid preparatio~ may contain conventional additives such as suspending agents, for example sorbitol syrup, methyl cellulose, glucose/sugar syrup, gelatin, hydroxy-ethylcellulose, carboxymethyl cellulose, aluminium sterate gel or hydrogenated edible fats; emulsifying agents, for example lecithin~ sorbitan mono-oleate or acacia9 non-aqueous vehicles (which may include edible oils), for example almond oil, fractionated coconut oil, oily esters~ propylene glycol or ethyl alcohol; and preservatives~ for example methyl or propyl p-hydroxy-benzoates or sorbic acid. The antibiotic compounds may also be formulated as suppositories,e.g. containing conventional suppository bases such as cocoa butter .

106'7068 or other glyceride~
~7 e~,c,~e Compositions for veterinary mcdici may, for example~ be formulated as intrammary preparations in either long acting or quick-release bases.
The compositions may contain from 0.1% upwards~ e.g~
0.1-99%, preferably from 10-60% of the active material, depending on the method of administration. When the compositions comprise dosage units, each unit will preferably contain 50-1500mg of the active ingredient.
The dosage as employed for adult human treatment will preferably range from 500 to 5000 mg per day, depending on the route and frequency of administration, although in treating Pseudomonas infections higher daily doses may ~e required.
The antibiotic compounds according to the invention may be administered in combination with other therapeutic agents such as antibiotics, for example penicillins, tetracyclines or other cephalosporins.
The following examples iIlustrate the invention. All temperatures are in C. The structure of the products U)~S
-wer~ verified by p.m.r. spectroscopy and i.r. spectroscopy.

_ 21 -11~67068 PREPARATION
2-(1-t-ButoxYcarbonYlcyclobut-l-oxyimino~-2-(fur-2-yl~
acetic acid (sYn-isomer) A solution of 2-(fur-2-yl)-2-hydroxyimino acetic acid S (syn-isomer) (7.05g) in dimethylsulphoxide (lOOml) was added dropwise, over 30 minutes, to a stirred solution of potassium t-butoxide (11.2g) in dimethylsulphoxide (200ml) under an atmosphere of dry nitrogen. Stirring was con-tinued for a further 30 minutes and then a solution of t-butyl l-bromocyclobutanecarboxylate (12.1g~ in dimethyl-sulphoxide (25ml) was added over 30 minutes to the reaction mixture at room temperature. After addition was complete the resulting solution was stirred for a further hour at 650. The reaction mixture was poured on to ice and acidified to pH 1.5 under ether. The two layers were separated and the aqueous layer was q~racted with more ether. The combined ether extracts were washed once with water, then extracted with aqueous sodium bicarbonate ~ solution. The combined alkaline extracts were acidified under methylene chloride to pH 1.6 with concentrated hydrochloric acid and the acid solution was extracted further with methylene chloride. The combined organic extracts were washed (water and saturated brine), dried - and concentrated to give a solid which was crystallised from carbon tetrachloride to ~ive the title compound m.p. 113-114C and ~ max (pH6 buffer) 278nm (~17~200).

.

106'706B
Example (6R.7R)-3-carbamoyloxymethYl-7-c2-(l-carboxycyclobut l-oxyimino)-2-(fur-2-Yl)-acetamido]ceE~h-3-em-4-carbox~lic acid (svn-isomer) A solution of 2-(1-t-butoxycarbonylcyclobut-1-oxyimino)-2-(fur-2-yl) acetic acid (syn isomer) (0.93g) in methylene chloride containing a few drops of N,N-dimethylformamide and triethylamine (0.75ml) was treated with oxalyl chloride (0.30ml) at 0-5 for ca.
1 hour. The mixture was then evaporated to dryness.
The residue was suspended or dissolved in 25ml acetone and added to a stirred, ice-cold solution of (6R,7R)-7-amino-3-carbamoyloxymethyl-ceph-3-em-4-carboxylic acid (0.90g) in a mixture-of acetone and water containing sodium hydrogen carbonate (0.83g). The reaction mixture was stirred for 45 minutes, allowing the temperature to rise to room temperature, whereafter the acetone was - removed under reduced pressure.

.

~C~67068 The pH was adjusted to 1.5 - 2~0 and the product extracted into ethyl acetate (alternatively ether or methylene chloride may b~ used). The organic layer was washed with water and/or saturated brine) dried and evaporated to give (6R~7R)-3-carbamoyloxymethyl-7-~2-(~buto~ycarbonyl-cyclobut-l-oxyimino)~-(fur-~2-yl)-acetamido~ceph-3-em-4-carboxylic acid (sYn-isomer~ which was characterised by optical rotation and/or by spectroscopy.
The t-butyl ester ~1.13g) was deprotected by treating with trifluoracetic acid containing anisole at room temperature for at least 5 minutes. The reaction mixture was evaporated in vacuo and the product isolated by tri~uration or by .
distributing between ethyl acetate (or ether) and an aqueous solution of sodium hydrogen carbonate~ separating the aqueous extracts, acidifying these extracts under ethyl acetate and isolating the title dicarboxylic acid,(0.99g) Ca~26(DMSO); ~ max (pH 6 phosphate buffer) 277.5 nm (~15~100)~ ~ max (N-yol- Trade Mark) 1788 cm 1; ~ (d6-DMSO) values include 0.34 (NH)j 4.12 (7-H~ and 7.56 ànd 8.10 (cyclobutyl protons).

.

Claims (16)

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

1. A process for the preparation of an antibiotic compound of the formula (I) or a non-toxic derivative thereof, said compounds being syn isomers or existing as a mixture of syn and anti isomers containing at least 90% of the syn isomer, wherein (A) a compound of the formula (II) (wherein B is > S or >S? O; R1 represents hydrogen or a carboxyl blocking group; and the dotted line bridging the 2-, 3- and 4- positions indicates that the compound is a ceph-2-em or ceph-3-em compound) or an acid addition salt or an N-silyl derivative thereof, is condensed with an acylating agent corresponding to an acid of formula (III) (wherein R2 is a carboxyl blocking group) or (B) a compound of the formula (IV) (wherein B and the dotted line are as defined above; and each R1 may independently represent hydrogen or a carboxyl blocking group) is reacted with a carbamoylating agent serving to form a carbamoyloxymethyl or N-protected carbamoyloxymethyl group at the 3-position; whereafter, if necessary and/or desired in each instance, any of the following reactions (C), in any appropriate sequence, are carried out:-i) conversion of a .DELTA.2 isomer into the desired .DELTA.3 isomer, ii) reduction of a compound wherein B is >S ? O to form a compound wherein B is >S, and iii) removal of any carboxyl blocking and/or N-protecting groups;
and finally (D) recovering the desired compound or a non-toxic derivative thereof, if necessary after separation of isomers.

2. A process according to claim 1 wherein the compound of formula (I)or a non-toxic derivative thereof is recovered as the syn isomer essentially free from the anti isomer.

3. A process according to claim 1 wherein a compound (II) or an acid addition salt or N-silyl derivative thereof is condensed with an acid halide corresponding to the acid (III)

4. A process according to claim 3 wherein the condensation is effected in the presence of an acid binding agent comprising a tertiary amine, an inorganic base or an oxirane.

5. A process according to claim 1 wherein a compound (II) or an acid addition salt or N-silyl derivative thereof is condensed with an acid (III) in the presence of a condensation agent comprising a carbodiimide, carbonyldiim-idazole or an isoxazolinium salt.

6. The compound of formula (I) or a non-toxic derivative thereof whenever prepared by a process as claimed in any of claims 1, 2 or 5, or by an obvious chemical equivalent thereof.

7. A process according to claim 1 for the preparation of the compound of formula I wherein a compound of formula II (wherein B is >S, R1 represents hydrogen or, a carboxyl blocking group, and the dotted line indicates a ceph-3-em compound.) or an acid salt thereof, is condensed with an acylating agent corresponding to an acid of formula III (as defined in claim 1) whereafter any carboxyl blocking groups are removed.

8. A process according to claim 7 wherein the compound of formula II or an acid addition salt thereof is condensed with an acid halide of formula III in the presence of an acid binding agent comprising an inorganic base.

9. The compound of formula I (as defined in claim 1) whenever prepared by a process according to claim 7 or claim 8, or by an obvious chemical equivalent thereof.

10. A process according to claim 1 in which the resulting compound of formula I is converted into a non-toxic salt thereof.

11. Non-toxic salts of the compound of formula I whenever prepared by a process as claimed in claim 10.

12. A process according to claim 10 in which the resulting compound of formula I is converted into the sodium or potassium salt thereof.

13. A process according to claim 12 wherein the compound of formula I is converted into the sodium or potassium salt thereof by reaction with respectively sodium or potassium 2-ethylhexanoate.

14. Sodium and potassium salts of the compound of formula I (as defined in claim I) whenever prepared by a process according to claim 12 or claim 13 or by an obvious chemical equivalent thereof.

15. A process according to claim 1 wherein the resulting alkanoyloxy compound of formula I is converted into a lower alkanoyloxymethyl ester thereof.

16. Lower alkanoyloxymethyl esters of the compound of formula I whenever prepared by a process according to claim 15.