GB1582960A

GB1582960A - Chemical synthesis of -lactam derivatives

Info

Publication number: GB1582960A
Application number: GB26788/77A
Authority: GB
Original assignee: Eli Lilly and Co
Current assignee: Eli Lilly and Co
Priority date: 1976-07-01
Filing date: 1977-06-27
Publication date: 1981-01-21
Also published as: DE2728578A1; BE856288A; NL7707302A; IL52144A; JPS535194A; ES460338A1; IL52144A0; FR2356653A1; FR2356653B1

Description

(54) CHEMICAL SYNTHESIS OF ss-LACTAM DERIVATIVES (71) We, ELI LILLY AND COMPANY, a corporation of the State of Indiana, United States of America, having a principal place of business at 307 East McCarty Street, City of Indianapolis, State of Indiana, 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 relates to the chemical synthesis of ss-lactam derivatives and more particularly to a process whereby p-nitrobenzyl, trihaloethyl, phenacyl and substituted phenacyl esters of penicillins and cephalosporins are reductively cleaved with zinc in an inert solvent to provide the de-esterified penicillin or cephalosporin as the free acid.

Cephalosporin and penicillin esters are commonly employed intermediates in the synthesis of cephalosporin and penicillin antibiotics. Ester derivatives are used to block or protect the carboxylic acid function of the molecule while reactions at other sites in the molecule are carried out. For example. in the well-known penicillin sulfoxide ring expansion process for the preparation of desacetoxy-cephalosporins (U.S. Patent 3,275,626), the carboxyl group of the penicillin sulfoxide is protected by esterification.

Likewise the synthesis of 3'-methyl substituted cephalosporin antibiotics is generally carried out on a cephalosporin ester. The acylation of a 7-aminocephalosporin or 6-aminopenicillin nucleus is often carried out on an amino nucleus ester compound.

Particularly useful ester groups which have been employed extensively as carboxylic acid blocking groups are the p-nitrobenzyl ester group and the 2,2,2-trichloroethyl ester group.

The p-nitrobenzyl ester group has been found to be especially useful in the penicillin sulfoxide ring expansion process as described in U.S. Patent Nos. 3.632,850 and 3,781,282.

The usefulness of the trichloroethyl ester group is illustrated in U.S. Patent No. 3.828,023.

The phenacyl ester group is also a useful carboyxlic acid protecting group which has been employed previously in the penicillin and cephalosporin art. Each of these ester groups and in particular the p-nitrobenzyl and the 2,2,2-trichloroethyl ester groups have achieved wide acceptance because of the ease with which they can be removed to provide the final product.

Each of the above mentioned ester groups can be removed by chemical reduction means, for example, with zinc in a mineral acid. for example. hydrochloric acid, and in addition the p-nitrobenzyl ester group can be removed by catalytic hydrogenolysis in the presence of a hydrogenation catalyst, preferably palladium supported on carbon.

In view of the importance of these ester groups in the synthesis of 13-lnctam antibiotics, alternative methods for the cleavage of these ester groups would be of value to the synthetic chemist. This invention provides an alternative process for the cleavage of p-nitrobenzyl, trihaloethyl, phenacyl. and substituted phenacyl esters. In particular this invention provides a process for the reductive cleavage of these esters from the penicillin and cephalosporin molecule to provide the free acid compound.

The present invention provides a process for the preparation of a ss-lactam acid of the formula

wneretn Y Is

or

R is H2N-, H3N, phthalimido, succinimido, an acylam)no group of the formula

wherein R' is hydrogen, C1-C4 alkyl, or cyanoacetyl; an acylamino group of the formula

wherein R" is phenyl or phenyl substituted by C1-C4 alkyl, C1-C4 alkoxy, halogen, hydroxy, amino. or aminomethyl; an acylamino group of the formula

wherein R" has the same meanings as defined above; an acylamino group of the formula

wherein R"' is R" as defined above or is 2-thienyl. 3-thienyl. 2-furyl. or l-tetrazolyl; or an a-substituted acylamino group of the formula

wherein R"" is R" or is 2-thienyl, 3-thienyl, or 2-furyl and Q is -OH, -NH,. -NH3, -COOH. or -SORH: which process comprises reacting a l3-lactam ester of the formula

wherein R and Y are as defined above. and R@ is p-nitrobenzyl. 2,2,2-trihaloethyl, phenacyl or phenacyl substituted bV C,-C, alkyl. C1-C4 alkoxy. halogen or nitro: R2 is hydrogen.

C1-C4 alkyl. C1-C4 alkoxy, phenyl. C1-C4 alkoxymethyl, C1 -C4 alkylthiomethyl. chloro, or bromo; or a heterocyclic-thiomethyl group of the formula -CH2-S-R4 Ix wherein R4 is

wherein Z and Z' are independently hydrogen, phenyl or C,-C4 alkyl, with between 3 and 4 moles of zinc per mole of ester in an inert solvent, in the presence of between 7 and 10 moles per mole of ester of an organothiol of the formula R3SH II wherein R3 is C1-C12 alkyl, CsC7 cycloalkyl, or C1-C4 alkyl substituted by hydroxy, carboxy, C1-C4 alkoxycarbonyl, C1-C4 alkoxy, or amino; phenyl or phenyl substituted by C1 -C4 alkyl, halogen, or C,-C, alkoxy; naphthyl or naphthyl substituted by C1 -C4 alkyl, halogen, or C1-C4 alkoxy; C1-C4 alkyl substituted by phenyl or naphthyl, or phenyl or naphthyl substituted by Cl-C4 alkyl, C-C4 alkoxy, halogen, amino or carboxy; or Rl is pyridine, quinoline, pyrimidine, imidazole, benzimidazole, oxazole, thiazole, benzoxazole, benzothiazole, tetrazole, triazole, oxadiazole, or thiadiazole, or such a heterocyclic group substituted with C1-C3 alkyl or phenyl.

When R in the above formula represents an acylamino group, examples of such groups include acetylamino, phenylacetylamino, phenoxyacetylamino, ahydroxyphenylacetylamino. a-aminophenylacetylamino, 2-thienylacetylamino, 2furylacetylamino, benzoylamino, and 2,6-diinethoxybenzoylamino. The acylamino group R can be any of the known penicillin and cephalosporin side chain groups which are derived from carboxylic acids and which are generally prepared by acylating a 6-amino or 7-amino nucleus with an active derivative of a carboxylic acid.

Examples of groups represented by R2 include for example hydrogen, chloro, methoxy, methoxymethyl, methylthiomethyl, ethoxymethyl, C1-C4 alkyl and phenyl.

A preferred group of 3-lactam esters of Formula VIII within the above definition are the cephalosporin esters wherein Y is the 3-substituted-3-cephem group (b) or the 3exomethylenecepham group (c).

When in the above definition of the starting materials of Formula VIII, R is H2N-, the 7-amino-3-cephem esters are described and examples of such 7-amino esters are p-nitrobenzyl 7-amino-3-methyl-3-cephem-4-carboxylate, p-nitrobenzyl 7-amino-3exomethylenecepham-4-carboxylate. 2.2,2-trichloroethyl 7-amino-3-methyl-3-cephem-4carboxylate ,p-nitrobenzyl 7-amino-3-methoxy-3-cephem-4-carboxylate. benzoylmethyl (phenacyl) 7-amino-3-methoxymethyl-3-cephem-4-carboxylate, 2,2,2-trichloroethyl 7amino-3-cephem-4-carboxylate. p-nitrobenzyl 7-amino-3-cephem-4-carboxylate, pnitrobenzyl 7-amino-3-chloro-3-cephem-4-carboxylate and 2.2,2-tribromoethyl 7-amino-3methoxymethyl-4-carboxylate. + When in the above formula VIII, R is HN- the acid addition salt forms of the 7-amino nucleus compounds are represented. Suitable acid addition salts of these 7-amino compounds can be formed with the mineral acids such as hydrochloric acid and hydrobromic acid, and with the organosulfonic acids, for example methanesulfonic acid, benzenesulfonic acid. 4-chlorobenzenesulfonic acid, and o- or p-toluenesulfonic acid.

When in the above formula VIII, R' is hydrogen. the acylamino group represented is the 7-formamido group and representative compounds thus described include p-nitrobenzyl 7-formamido-3-methyl-3-cephem-4-carboxylate, p-nitrobenzyl 7-formamido-3methoxymethyl-3-cephem-4-carboxylate. 2 .2,2-trichloroethyl 7-formamido-3-cephem-4carboxylate, and p-nitrobenzyl 7-formamido-3-methoxy-3-cephem-4-carboxy When in the above formula Vlll. R' is C-Ct alkyl. examples of compounds represented thereby are p-nitrobenzyl 7-acetylamino-3-methyl-3-cephem-4-carboxylate. 2.2.2trichloroethyl 7-acetylamino-3-methoxymethyl-3-cephem-4-carboxylate. and p-nitrobenzyl 7-acetylamino-3-methoxy-3-cephem-4-carboxylate.

Examples of cephalosporin esters represented by the above formula Vile. when R is of Formula IV, are p-nitrobenzyl 7.benzoylamino-3-methyl-3-cephem-4-carboxylate, p-nitrobenzyl 7-(2,6-dimethoxybenzoylamino)-3-methoxy-3-cephem-4-carboxylate, 2,2,2trichloroethyl 7-(4-chlorobenzoylamino )-3-methoxymethyl-3-cephem-4-carboxylate, phe nacyl 7-benzoylamino-3-cephem-4-carboxylate, p-nitrobenzyl 7-(2 aminomethylbenzoylamino)-3-methyl-3-cephem-4-carboxylate, 2,2,2-tribromoethyl 7-(4 hydroxybenzoylamino).3.ethoxymethyl-3-cephem-4-carboxylate and p-nitrobenzyl 7-(4aminobenzoylamino)-3-methyl-3-cephem-4-carboxylate.

Examples of starting materials of the above formula VIII, when R is of Formula V, are p-nitrobenzyl 7.phenoxyacetylamino-3-methyl-3-cephem-4-carboxylate, 2,2,2trichloroethyl 7.phenoxyacetylamino-3-methoxymethyl-3-cephem-4-carboxylate, pnitrobenzyl 7-phenoxyacetylamino-3-chloro-3-cephem-4-carboxylate, phenacyl 7-(4 chlorophenoxyacetylamino)-3.methyl-3-cephem-4-carboxylate, p-nitrobenzyl 7-phenoxyacetylamino-3-cephem-4-carboxylate, p-nitrobenzyl 7-phenoxy-acetylamino-3 exomethylenecepham-4-carboxylate, p-nitrobenzyl 7-(4-hydroxyphenoxyacetylamino)-3 methoxy-3-cephem-4-carboxylate, p-nitrobenzyl 7-phenoxyacetylamino-3-bromo-3cephem-4-carboxylate, 2,2,2-tribromoethyl 7.phenoxyacetylamino-3-methyl-3-cephem-4- carboxylate, and p-nitrobenzyl 7-(3 ,4-dimethylphenoxyacetylamino)-3-( l-methyl-1H- tetrazol-5.ylthiomethyl).3.cephem-4-carboxylate.

Examples of esters of the above formula VIII, when R is of Formula VI are p-nitrobenzyl 7.phenylacetylamino-3-methyl-3.cephem-4.carboxylate, p-nitrobenzyl 7 phenylacetylamino-3-methoxymethyl-3-cephem-4-carboxylate, 2,2,2-trichloroethyl 7 phenylacetylamino-3.methyl-3-cephem-4-carboxylate, p-nitrobenzyl 7-phenylacetylamino 3-methoxy-3-cephem-4-carboxylate, p-nitrobenzyl 7-phenylacetylamino-3-chloro-3cephem-4-carboxylate, p-nitrobenzyl 7-[2-(2-thienyl)acetylamino -3-methyl-3-cephem-4- carboxylate, 2,2,2,-trichloroethyl 7-[2.(2.thienylacetylamino -3-methoxy-methyl-3- cephem-4-carboxylate, p-nitrobenzyl 7-[2.(2.thienyl)acetylamino].3.bromo-3.cephem-4- carb oxylate, p-nitrobenzyl 7-[2-(2-furyl)acetylamino]-3-cephem-4-carboxylate, p nitrobenzyl 7-[(5-methyl- 1H-tetrazol-1-yl)acetylamino]-3-methyl-3-cephem-4-carboxylate, and phenacyl 7-(3,4-dichlorophenylacetylamino)-3-isopropoxymethyl-3-cephem-4- carboxylate.

Starting materials where in the above formula VIII, R is of Formula VII are illustrated by the following examples: p-nitrobenzyl 7-(D-a-amino-2-phenylacetylamino)-3-methyl-3- cephem-4-carboxylate. p-nitrobenzyl 7-( D-a.amino-a-4-hydroxyphenylacetylamino)-3- methyl-3-cephem-4-carboxylate, 2,2,2-trichloroethyl 7-(D-a.amino.a.phenylacetylamino)- 3-methoxymethyl-3-cephem-4-carboxylate, p-nitrobenzyl 7-(D-a-amino-a phenylacetylamino)-3.cephem-4.carboxylate, p-nitrobenzyl 7-(D-a-amino-aphenylacetylamino)-3-chloro-3-cephem-4-carboxylate, p-nitrobenzyl 7-(D-a-amino-aphenylacetylamino)-3-(1,2.3-triazol-5-ylthiomethyl)-3-cephem-4-carboxylate, 2,2,2trichloroethyl 7-(D-a-amino-a-4-hydroxyphenylacetylamino)-3-(1,2,3-triazol-5- ylthiomethyl)-3-cephem-4-carboxylate. p-nitrobenzyl 7-(D-a-amino-o-phenylacetylamino)- 3-methoxy-3-cephem-4-carboxylate. 2.2.2-trichloroethyl 7.[D-a-amino-a-(2- thienyl)acetylamino]-3-methyl-3-cephem-4-carboxylate, phenacyl 7-[D-a-amino-a-(3thienyl)acetylamino]-3-ethoxymethyl-3-cephem-4-carboxylate, p-nitrobenzyl 7-[a-amino α-(3-chloro-4-hydroxyphenyl)acetylamino]-3-methoxy-3-cephem-4-carboxylate, 2,2,2tribromoethyl 7-(a-sulfo-a-phenylacetylamino)-3-methyl-3-cephem-4-carboxylate. p nitrobenzyl 7-(α-carboxy-α;-phenylacetylamino)-3-(1-methyl-1H-tetrazol-5-ylthiomethyl)- 3-cephem-4-carboxylate, and p-nitrobenzyl 7-[ct.amino-a-(2-furyl)-acetylamino -3- methoxymethyl-3-cephem-4-carboxylate.

An especially preferred group of esters of Formula VIII useful in the process of the invention are represented by the following formula

wherein R is H2N -. H?N-. 2-thienylacetylamino, phenylacetylamino, phenoxyacetylamino, or phenylglycylamino and R6 is methyl. methoxymethyl. chloro or methoxy. Another group of especially preferred esters are those wherein R is R5. R, is the pNB group, and Y is the group

The cephalosporin acids of Formula I obtained as products of the de-esterification process of this invention are all known cephalosporin antibiotics.The cephalosporins unsubstituted in the 3-position, the 3-H-cephem compounds, are described in British Patent No. 1,377,762. 3-Methyl-3-cephem antibiotics, the desacetoxycephalosporins, are described in U.S. Patent No. 3,275,626 wherein 3-exomethylenecephams are also disclosed.

Desacetoxycephalosporins are also described in U.S. Patent 3,507,861. 3-Phenyl and 3-alkyl substituted 3-cephem compounds are described in British Patent No. 1,405,757. The 3-methoxy-3-cephem antibiotics are described in U.S. Patent Nos. 3,917,587 and 3,917,588.

3-Alkoxymethyl-3-cephem antibiotics are described in U.S. Patent Nos. 3,790,567 and 3,665,003. 3-Heterocyclicthiomethyl-substituted-3-cephem antibiotics are described, for example, in U.S. Patent No 3,641,021, 3,516,997, 3,759,904 and 3,766,175.

As noted previously, the cephalosporin esters which can be de-esterified in the process of this invention can be substituted in the 3-position of the cephem ring with any group inert to the reaction conditions described above. The above described 3- and 7-position substituents are exemplary of such groups. Likewise cephalosporin esters substituted in the 2-position by reaction-inert groups such as the 2-methyl-3-cephem esters and the 2,2-dimethyl-3cephem esters can be de-esterified to the acid antibiotic form in this process.

A further embodiment of the process of this invention comprises the de-esterification of a penicillin ester of Formula VIII wherein Y is the group

+Preferred penicillanic acid esters are represented when R is amino (-NH2) or ammonium (no3) by, for example, p-nitrobenzyl 6-aminopenicillanate (6-APA pNB ester), 2,2,2trichloroethyl 6-aminopenicillanate. phenacyl 6-amino-penicillanate, 4-nitrophenacyl 6aminopenicillanate, p-nitrobenzyl 6-aminopenicillanate hydrochloride, p-nitrobenzyl 6aminopenicillanate p-toluenesulfonate, and p-nitrobenzyl 6-aminopenicillanate benzenesulfonate.

Examples of 6-acylaminopenicillanic acid esters which can be de-esterified in the process of this invention are the p-nitrobenzyl esters of 6-formamidopenicillanic acid, 6acetamidopenicillanic acid. 6-propionamidopenicillanic acid, 6-cyanoacetamidopenicillanic acid, 6-benzamidopenicillanic acid, 6-(2,6-dimethoxybenzamido)penicillanic acid, 6phenylacetamidopenicillanic acid (penicillin G pNB ester), 6phenoxyacetamidopenicillanic acid (penicillin V pNB ester), 6-(4chlorophenoxyacetamidopenicillanic acid, 6-[2-(2-thienyl)acetamido]penicillanic acid, 6-[2 (2-furyl)acetamido]penicillanic acid, 6-(D-2-amino-2-phenylacetamido)penicillanic acid (ampicillin pNB ester), 6-[D-2-amino-2-(2-thienyl)acetamido]penicillanic acid, 6-(D-2carboxy-2-phenylacetamido)penicillanic acid (carbenacillin pNB ester), 6-[D-2-amino-2-(4hydroxyphenyl)acetamido]penicillanic acid, the trichloroethyl esters of 6acetamidopenicillanic acid. 6-benzamidopenicillanic acid, 6-(2,6dimethoxybenzamido)penicillanic acid, 6-phenylacetamidopenicillanic acid, 6phenoxyacetamidopenicillanic acid, 6-l2-(2-thienyl)acetamido]penicillanic acid, 6-(D-2 amino-2-phenylacetamido)penicillanic acid. 6-(D-2-carboxy-2- phenylacetamido)penicillanic acid. 6-phthalimidopenicillanic acid, 6-(D-2-hydroxy-2phenylacetamido)penicillanic acid, and the phenacyl and substituted phenacyl esters of 6-phenylacetamidopenicillanic acid, 6-phenoxyacetamidopenicillanic acid. 6-(2,6- dimethoxybenzamido)penicillanic acid, 6-phthalimidopenicillanic acid, 6-(D-2-amino-2phenylacetamido)penicillanic acid, 6-[2-(2-furyl)acetamido]-penicillanic acid, thienyl)acetamido penicillanic acid and 6-( D-2-carboxy-2-phenylacetamido )penicillanic acid.

Especially preferred penicillin esters of Formula VIII in the de-esterification process are the p-nitrobenzyl esters of 6-aminopenicillanic acid, 6-(D-2-amino-2-phenylacetamido)penicillanic acid (ampicillin), penicillin V and penicillin G.

According to the de-esterification method of this invention an ester of Formula VIII is reacted in an inert solvent with metallic zinc in the presence of an organic thiol of Formula I1 until de-esterification is complete or substantially complete and the cephalosporin free acid compound is recovered from the reaction mixture by conventional procedures.

The metallic zinc employed in the process is preferably of small particle size, for example in the form of a fine dust. Between 3 and 4 moles of zinc per mole of ester is used. The stoichiometric amount of zinc is consumed during the reaction and if a greater molar excess is employed the unreacted zinc can be filtered from the reaction product mixture following completion of the de-esterification.

Solvents which can be employed in the process are selected from the commonly available organic solvents which are inert under the reaction conditions employed. Examples of such solvents include the amide solvents such as dimethylformamide (DMF) and dimethylacetamide (DMAC); organonitriles such as acetonitrile and propionitrile; ether solvents such as tetrahydrofuran, dioxane, and the ethers derived from glycols, for example the dimethyl ether of ethyleneglycol. Preferred solvents in the process of this invention are DMAC and DMF. The reaction need not be carried out under strictly anhydrous conditions and accordingly the solvents employed need not be rigorously dried before use.

The reaction is preferably carried out at a temperature between 20 and 75"C., particularly at a temperature between 45 and 60"C. The de-esterification reaction is exothermic and occasionally the rise in temperature is preceded by a short induction period. It is preferred that the initial temperature is the ambient temperature.

Illustrative of thiols of Formula II which can be used in the process are the Cl-Ct, alkyl thiols which can be straight or branched chain such as methanethiol, ethanethiol, 1-propanethiol, 2-propanethiol, 1-butanethiol, 2-butanethiol, 2-methyl-1-propanethiol, 2-methyl-2-propanethiol, 1-pentanethiol, 3-methyl- 1-butanethiol, 2-methyl-2-butanethiol, 1-hexanethiol, 1-heptanethiol, 2-ethyl-1-hexanethiol, 1-nonanethiol, 1-decanethiol and 1-dodecanethiol. C5-C7-cycloalkylthiols include, for example, cyclopentanethiol, cyclohexanethiol and cycloheptanethiol.

Examples of substituted C1-C4 alkylthiols are 2-hydroxyethanethiol, 3hydroxypropanethiol, 4-hydroxybutanethiol, 3-aminopropanethiol, 2-aminoethanethiol, mercaptoacetic acid, 2-mercaptopropionic acid, 4-mercaptobutyric acid, 4methoxycarbonylbutanethiol, 3-ethoxycarbonylpropanethiol, 2-methoxyethanethiol, 3ethoxypropanethiol, 4-methoxybutanethiol, and related hydroxy, carboxy, alkoxycarbonyl, lower alkoxy, and amino substituted C,-C4 lower alkylthiols.

Examples of thiols represented when R3 is phenyl, substituted phenyl, naphthyl, or substituted naphthyl, are benzenethiol, 4-chlorobenzenethiol, 3,4-dichlorobenzenethiol, 3-bromobenzenethiol, 4-methylbenzenethiol, 4-methoxybenzenethiol, 2,4,dimethylbenzenethiol. 3,4-dimethoxybenzenethiol. 4-t-butylbenzenethiol, 3carboxybenzenethiol. 4-aminobenzenethiol, 4-fluorobenzenethiol, 4-chloro-3hydroxybenzenethiol, 2 ,4-dichlorobenzenethiol. 1-naphthylenethiol, 2-napthylenethiol, 4-methyl-1-napthylenethiol, 8-methyl-2-naphthylenethiol and 4-bromo-1-naphthylenethiol.

Examples of heterocyclic thiols include, for example, 2-pyridinethiol, 4-pyridinethiol, 2-quinolinethiol, 4-methyl-2-quinolinethiol. 1-methyl-lH-tetrazol-5-ylthiol, 1-phenyl-lH- tetrazol-5-ylthiol. 2-methyl-l .3.4-thiadiazol-5-ylthiol, 2-ethyl-i ,3,4-oxadiazol-5-ylthiol, 1,2 ,3-triazol-5-ylthiol. 2-ethyl- 1.3 ,4-oxadiazol-5-ylthiol, 1 ,2,3-triazol-5-ylthiol, 1,3-oxazol2-ylthiol, 1 .3-thiazol-2-ylthiol. 1 -methyl- 1,3 ,4-triazol-2-ylthiol, pyrimidin-2-ylthiol, 2mercaptobenzothiazole. 2-benzimidazolethiol and 2-benzoxazolethiol.Examples of phenyl and naphthyl substituted C,-CA alkylthiols are benzylthiol, 1-naphthylmethanethiol, 1-phenylethanethiol. 2-phenylethanethiol. 4-chlorobenzylthiol, 4-methylbenzylthiol, 4hydroxyphenylethanethiol. 4-phenylbutanethiol, 3-phenylbutanethiol and 2phenylpropanethiol.

Benzenethiol and the substituted benzenethiols. for example 4-chlorobenzenethiol, are preferred thiols in the present process. since consistently higher yields of the cephalosporin and penicillin free acid compounds are obtained with their use. l-Methyl-1H-tetrazol-5- ylthiol is also a preferred thiol.

As described above the process is useful for the de-esterification of the p-nitrobenzyl ester group. the trihaloethyl ester group. or the phenacyl(benzoylmethyl) ester group from a ss-lactam compound of Formula VIII. The term trihaloethyl ester group refers to the 2,2,2-trichloroethyl and the 2.2 .2-tribromoethyl ester groups. Substituted phenacyl ester groups which can be employed in the process include 4-chlorophenacyl. 4-methylphenacyl, 3,4-dimethoxyphenacyl, 3-hydroxyphenacyl. 3-chloro-4-hydroxyphenacyl and related esters. The process of this invention affords the highest yields of the free acid compounds when the starting ester is p-nitrobenzyl ester (pNB).

The stoichiometry of the de-estcrification of the pNB ester is shown in the following reaction diagram wherein A represents the acylamino or amino cephalosporin or penicillin to which the ester group is attached at the 3- or 4-position and R3 is as defined above.

As the stoichiometry of the de-esterification process shows, for complete deesterification at least 3 moles of zinc and at least 7 moles of thiol are required. The reaction is preferably carried out with between 3 and 4 moles of zinc and with between 7 and 10 moles of thiol per mole of starting ester. Amounts of zinc and thiol in excess of these preferred molar ratios can be used, however large excesses may complicate the recovery of the product.

The stoichiometry of the reduction of the trihaloethyl and phenacyl or substituted phenacyl esters has not been fully determined, however, it varies from that described above for the p-nitrobenzyl ester group. However the molar ratios of thiol and zinc used with the pNB ester group are likewise applicable in the de-esterification of the trihaloethyl and phenacyl esters.

The de-esterification process of this invention is advantageously carried out as follows.

The cephalosporin or penicillin ester of Formula VIII is dissolved in the inert solvent, for example, DMF, and between 7 and 10 moles of the organothiol of Formula II per mole of ester is added to the solution. With stirring, between 3 and 4 moles of zinc dust per mole of ester is then added to the reaction solution. Generally, the reaction is initiated immediately as indicated by a sharp rise in temperature. With the more acidic thiols, for example benzenethiol, the temperature rises rapidly to between 70 and 75"C., however, with less acidic thiols the temperature increase is slower reflecting a more sluggish reaction. After the reaction has subsided as indicated by a drop in the temperature, the temperature of the reaction mixture is preferably maintained between 45 and 60"C. by means of external heating.In some instances the reaction is complete after the initial exothermic temperature rise as indicated by a thin-layer chromatogram of a small portion of the reaction mixture. In the more sluggish reactions the reaction mixture may be heated to 45 to 650C. for some 2 to 6 hours after the initial exothermic reaction.

The course of the reaction can be followed by chromatographic analysis of a small portion of the reaction mixture withdrawn from time to time during the progress of the de-esterification. Thin-layer chromatography carried out on silica gel plates is a convenient chromatographic technique.

During the course of the reaction the stoichiometric amount of zinc is digested and any excess remains in suspension in the mixture. The reaction mixture may be filtered to remove the insoluble zinc and generally a filter aid is used to clarify the reaction mixture.

When the ss-lactam ester starting material is a pNB ester the aniline side product (as shown in the above stoichiometry diagram) can be separated from the product by diluting the filtrate with water, adding a water-immiscible solvent such as ethyl acetate in which the penicillin or cephalosporin free acid is soluble, washing the organic layer with dilute acid such as 5% hydrochloric acid to remove the aniline side product, further washing the organic layer with water, drying the organic layer over a suitable drying agent such as sodium sulfate, and finally evaporating the dried organic extract to obtain the penicillin or cephalosporin free acid compound. The product can be further purified by recrystallization.

When the free acid product is a 7-amino compound or a 7-acylamino compound having an amino group in the side chain. e.g.. the phenylglycyl side chain, the cephalosporin or penicillin acid can be selectively precipitated from the filtered. water-diluted reaction mixture by adjusting the pH to the isoelectric point of the free amino acid compound.

A preferred embodiment of this invention comprises the de-esterification of the p-nitrobenzyl ester group of the antibiotic cephalexin. In this embodiment the p-nitrobenzyl ester of cephalexin as the p-toluenesulfonic acid salt is dissolved in DMF and benzenethiol is added to the solution in 10 molar excess. The solution is agitated at room temperature and excess zinc dust is added. After the exothermic reaction has subsided the mixture is stirred for 1-2 hours and is filtered. The filtrate is diluted with water and the pH adjusted to 6.5 by the addition of a basic organic amine such as triethylamine. Cephalexin crystallizes from the diluted filtrate as the bis-DMF solvate of the zwitterionic form. This crystalline form of cephalexin is described in U.S. Patent No. 3.781.282.

In another preferred embodiment of this invention p-nitrobenzyl 7-amino-3-methyl-3cephem-4-carboxylate hydrochloride (the pNB ester of 7-ADCA) is dissolved in DMF and benzenethiol is added to the solution. With stirring at room temperature excess zinc dust is added to the solution. The reaction is stirred for about one hour and is filtered. The filtrate is diluted with water and acidified to pH 1.8 with hydrochloric acid. The pH is readjusted to 4.0 with triethylamine and on standing the product. 7-ADCA. slowly crystallizes.

In a further embodiment of this invention. the p-nitrobenzyl ester of 6-APA is reacted in acetonitrile with 1-methyl-I H-íetrazol-5-ylthiol and zinc dust while maintaining the temperature below 5()"C. The reaction mixture is filtered to remove excess zinc and the filtrate diluted with water. The pH is adjusted to the isoelectric point of 6 with triethylamine and the precipitated 6-APA is recovered by filtration.

In another embodiment of this invention. the p-nitrobenzyl ester of ampicillin is reacted in DMF with zinc and benzenethiol to provide ampicillin.

The penicillin esters of Formula VIII which can be de-esterified in the process of this invention have been previously described in the patent literature and are prepared by known methods.

The yields of ss-lactam acid obtained with various thiols (R3SH) in the de-esterification of the pNB ester group are illustrated in Table I below. The ester employed was the pNB ester of cephalexin in the form of the p-toluene-sulfonic acid salt. The preferred solvent, DMF, was used in each case.

The molar ratio of RRSH/pNB ester was 10:1, and of zinc dust/pNB ester was 3 to 3.1:1.

TABLE I De-esterification of ceplialexiti tosylate p-nitrobenzyl ester R3SH Percent Yield benzenethiol 93.8 2,5-dichlorobenzenethiol 86.0 4-methoxybenzenethiol 88.3 1-methyl-lH-tetrazol-5-ylthiol 93.0 n-propylthiol 65.9 2-hydroxyethanethiol 72.7 1/ Yields are corrected for DMF solvates The following examples are provided to further illustrate the process of this invention.

Example 1 To a stirred solution of 6.55 g. (10 mM) of the p-toluenesulfonic acid salt of p-nitrobenzyl 7-(D-a-amino-a-phenylacetylamino)-3-methyl-3-cephem-4-carboxylate and 10.2 ml. (100 mM) of benzenethiol in 50 ml. of N,N-dimethyl-formamide (DMF) were added 1.95 g. (30 mM) of zinc dust. The temperature of the reaction mixture rose from ambient to 750C. in ten minutes and nearly all of the zinc had dissolved. After one hour the mixture was filtered through a filter aid pad to remove traces of undissolved zinc and the filter was washed with 25 ml. of DMF. The filtrate and wash were diluted with 10 ml. of water and the pH was adjusted to 6.5 with triethlyamine.Cephalexin (7-(D-cr-amino-2-phenylacetylamino)-3- methyl-3-cephem-4-carboxylic acid) crystallized from the solution as the bis-DMF solvate and was filtered. washed with DMF and ethyl acetate, and dried under vacuum. The yield of pure. snow-white crystals was 4.33 g (9()'7Xy of theory).

Example 2 To a stirred suspension of 1.95 g (30 mM) of zinc dust and 10.2 ml. (100 mM) of benzenethiol in 50 ml. of DMF was added a solution of p-nitrobenzyl 7-amino-3-methyl-3cephem-4-carboxylate hydrochloride. The temperature of the reaction mixture rose from ambient to 68"C. in two minutes. After ten minutes the reaction mixture was virtually clear except for some undissolved zinc and on cooling the product began to crystallize. After the reaction had cooled to room temperature 5.5 ml. of water were added and the pH was adjusted to 1.8 with concentrated hydrochloric acid. All of the crystallized product redissolved as the hvdrochloride salt and the light yellow solution was filtered to remove excess zinc. The filtrate (ca 9() ml.) was diluted with 4 ml. of water and the pH adjusted to 4.0 with triethylamine.The solution was seeded with 7-aminodesacetoxycephalosporanic acid and the product was allowed to slowly crystallize. The crystalline precipitate was filtered to yield 2.02 g. (94 36/ of theory) of 7-amino-3-methyl-3-cephem-4-carboxylic acid as a light cream-colored solid.

Example 3 To a stirred solution of 3.69 g. (1() mM) of phenacyl 7-amino-3-methyl-3-cephem-4carboxylate hydrochloride and 10.2 ml. of benzenethiol in 50 ml. of DMF were added 2.03 g of zinc dust. The temperature of the mixture rose from ambient to 43.5"C. and after it began to drop the mixture was heated to 55-6() C. for 30 minutes. The reaction mixture was filtered to remove excess zine and the light yellow filtrate was diluted with water (approximately 10% by volume). The pH of the filtrate was adjusted to 4.0 with triethylamine and was seeded with crvstals of 7-ADCA hydrochloride. When the product failed to crystallize the pH was adjusted up to pH 5.8.When the product failed to precipitate at the higher pH the solution was acidified to pH 1.5 with hydrochloric acid and was then adjusted to pH 4.0 with triethylamine. After reseeding the solution 10 ml. of water were added whereupon the product crystallized slowly. The solution was diluted with another 10 ml. of water and was then stirred for 2 hours at about room temperature to complete crystallization. The product was filtered and washed with DMF and ethyl acetate and was dried. The dry weight of product was 0.34 g. (16% yield) of 7-amino-3-methyl-3cephem-4-carboxylic acid. TLC of the filtrate showed additional product remained in solution.

Example 4 To a stirred solution of 5.18 g. (10 mM) of 2,2,2-trichloroethyl 7-amino-3-methyl-3cephem-4-carboxylate p-toluenesulfonate and 10.2 ml. (100 mM) of benzenethiol in 50 ml.

of DMF were added 2.03 g. (31 mM) of zinc dust. The temperature of the reaction mixture rose from ambient to 47.5"C. in 2 minutes. After 30 minutes the reaction mixture was heated to a temperature between 50 and 58"C. for 15 minutes and was then stirred for 2 hours at room temperature. The reaction mixture was filtered and the filtrate diluted with a volume of water about equal to 10% of the filtrate volume. The pH was adjusted to 4.0 with triethylamine and seeded with crystalline 7-ADCA. When the product failed to crystallize the pH was adjusted to 5.0. The product precipitated, was filtered and dried to yield 1.49 g.

(69.6% yield) of 7-amino-3-methyl-3-cephem-4-carboxylic acid as an off-white crystalline solid.

Example 5 To a stirred solution of 0.30 g. (0.5 mM) of p-nitrobenzyl 7-phenoxyacetylamino-3-(1 methyl-lH-tetrazol-5-ylthiomethyl)-3-cephem-4-carboxylate and 0.51 ml. of benzenethiol (5 mM) in 2.5 ml. of DMF were added 0.1 g. of zinc dust. After an induction period of several minutes the temperature of the mixture rose from ambient to about 50"C. in 10 minutes. Stirring was continued for 30 minutes and the light yellow reaction mixture was treated with 25 ml. of ethyl acetate and filtered. The filtrate was washed 3 times with 25 ml.

portions of dilute hydrochloric acid and twice with 50 ml. portions of water. The washed filtrate was evaporated to a syrup which was dissolved in 3 ml. of ethyl acetate. A solution of 0.05 g. of lithium acetate dihydrate in 0.25 ml. of methanol was added to the ethyl acetate solution. The product, 7-phenoxyacetylamino-3-(1-methyl-lH-tetrazol-5-ylthiomethyl)-3- cephem-4-carboxylic acid, precipitated as 0.5 g. of the lithium salt.

The following Table II contains additional examples of the de-esterification process which can be carried out by employing the molar ratios of thiol and zinc dust to cephalosporin ester employed in Example 1.

TABLE II Example No. R R1 R2 R3 6 H2N pNB1 -OCH3 phenyl 7 phenylglycylamino pNB -OCH3 phenyl 8 phenoxyacetylamino TCE2 -CH2O-CH3 4-chlorophenyl 9 phenylacetylamino TBE3 H 4-methoxyphenyl 10 acetylamino pNB -CH3 4-bromophenyl 11 mandeloylamino TCE -CH2-O-C2H5 1-phenyl-lH tetrazol-2-yl 12 tetrazole-1- pNB -OCH3 n-butyl acetylamino 13 H2N pNB Cl phenyl 14 phenylglycylamino TCE 5-methyl- 2-hydroxyethyl 1,3,4 oxadiazol 2-ylthiol 15 H2N TCE H phenyl 16 phenoxyacetylamino pNB -CH3 phenyl 17 phenoxyacetylamino phenacyl -CH3 phenyl 18 phenoxyacetylamino 4-chloro- -CH3 4-methylphenyl phenacyl 1/ p-nitrobenzyl 2/ 2,2,2-trichloroethyl 3/ 2,2,2-tribromoethyl Example 19 To a stirred solution of 1.20 g. (2.95 mM) of p-nitrobenzyl 7-amino-3-chloro-3-cephem-4carboxylate in 15 ml. of dimethylformamide were added 3.3 g. (20 mM) of benzenethiol and 590 mg. of zinc dust. The temperature of the reaction mixture increased on addition of the zinc. After the temperature subsided the mixture was stirred for one hour while the temperature was maintained slightly above room temperature with a warm water bath. The reaction mixture was then cooled and the product crystallized from the reaction mixture.

The product was filtered. washed with acetone. and dried iti vacuo to yield 560 mg. (81% yield) of 7-amino-3-chloro-3-cephem-4-carboxylic acid. The product was contaminated with a small amount of zinc dust.

Example 20 By following the procedures described in Example 1. p-nitrobenzyl 7-(D-a-amino-aphenylacetylamino)-3-chloro-3-cephem-4-carboxylate is reacted in DMF with benzenethiol and zinc dust and 7-( D-a-amino-a-phenylacetylamino)-3-chloro-3-cephem-4-carboxylic acid is isolated.

Example 21 By following the procedures described in Example 5. p-nitrobenzyl 7phenoxyacetylamino-3-exomethylenecepham-4-carboxylate is reacted in acetonitrile with benzenethiol and zinc dust and 7-phenoxyacetylamino-3-exomethylenecepham-4- carboxylic acid is isolated.

Example 22 To a solution of p-nitrobenzvl 7-amino-3-exomethylenecepham-4-carboxylate in tetrahy drofuran are added 4 equivalents of zinc dust and 7 equivalents of benzenethiol and the mixture is stirred for 2 hours. The mixture is filtered, the filtrate diluted with water and 7-amino-3-exomethylenecepham-4-carboxylic acid is precipitated by adjusting the pH to about 3.5-4.5 with triethylamine with cooling.

Example 23 By following the procedures described by Example 1, the p-nitrobenzyl ester of ampicillin is reduced to provide ampicillin.

Example 24 By following the procedure described by Example 4, 2,2,2-trichloroethyl 6aminopenicillanate is de-esterified to provide 6-APA.

WHAT WE CLAIM IS: 1. A process for the preparation of a P-lactam acid of the formula

wherein Y is

or

R is H2N-, H7N, phthalimido, succinimido, an acylamino group of the formula

wherein R" is phenyl or phenyl substituted by C1-C4 alkyl, Co-C4 alkoxy, halogen, hydroxy, amino. or aminomethyl; an acylamino group of the formula

wherein R"' is R" as defined above or is 2-thienyl, 3-thienyl, 2-furyl, or l-tetrazolyl; or an a-substituted acylamino group of the formula

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. drofuran are added 4 equivalents of zinc dust and 7 equivalents of benzenethiol and the mixture is stirred for 2 hours. The mixture is filtered, the filtrate diluted with water and 7-amino-3-exomethylenecepham-4-carboxylic acid is precipitated by adjusting the pH to about 3.5-4.5 with triethylamine with cooling. Example 23 By following the procedures described by Example 1, the p-nitrobenzyl ester of ampicillin is reduced to provide ampicillin. Example 24 By following the procedure described by Example 4, 2,2,2-trichloroethyl 6aminopenicillanate is de-esterified to provide 6-APA. WHAT WE CLAIM IS:

1. A process for the preparation of a P-lactam acid of the formula

wherein Y is

or

R is H2N-, H7N, phthalimido, succinimido, an acylamino group of the formula

wherein R"" is R" or is 2-thienyl, 3-thienyl, or 2-furyl and Q is -OH, -NH2, N$, -COOH, or -SO3H; which process comprises reacting a ss-lactam ester of the formula

wherein R and Y are as defined above, and R1 isp-nitrobenzyl, 2,2,2-trihaloethyl, phenacyl or phenacyl substituted by C1 -C4 alkyl, C1 -C4 alkoxy, halogen or hitro; R2 is hydrogen, Cl-C4 alkyl, Cl-C4 alkoxy, phenyl, C1-C4 alkoxymethyl, C1-C4 alkylthiomethyl, chloro, or bromo; or a heterocyclic-thiomethyl group of the formula -CH2-S-R4 IX wherein R4 is

wherein Z and Z' are independently hydrogen, phenyl or C9-C4 alkyl, with between 3 and 4 moles of zinc per mole of ester in an inert solvent in the presence of between 7 and 10 moles per mole of ester of an organothiol of the formula R3SH II wherein Rl is C1 -C12 alkyl, C5-C7 cycloalkyl, or C1-C4 alkyl substituted by hydroxy, carboxy, C1-C4 alkoxycarbonyl, C1-C4 alkoxy. or amino; phenyl or phenyl substituted by C1-C4 alkyl, halogen or C1-C4 alkoxy; naphthyl or naphthyl substituted by C1-C4 alkyl, halogen or C1-C4 alkoxy; C1-C4 alkyl substituted by phenyl or naphthyl, or phenyl or naphthyl substituted by Ct-C4 alkyl, C1-C4 alkoxy, halogen, amino or carboxy; or R3 is pyridine, quinoline. pyrimidine, imidazole, benzimidazole, oxazole, thiazole, benzoxazole, benzothiazole, tetrazole. triazole, oxadiazole or thiadiazole, or such a heterocyclic group substituted with C1-C3 alkyl or phenyl.

2. The process of claim 1 wherein Y is

and R2 is as defined in claim 1.

3. The process of claim 2 wherein R1 is p-nitrobenzyl.

4. The process of claim 2 wherein R1 is 2,2,2-trichloroethyl.

5. The process of claim 2 wherein R1 is phenacyl.

6. The process of any one of claims 2 - 5 wherein R3 is phenyl or phenyl substituted by C1-C4 alkyl. C1-C4 alkoxy or halogen.

7. The process of claim 6 wherein R3 is phenyl.

8. The process of any one of claims 2 - 7 wherein R2 is methyl, methoxy, chloro, or methoxymethyl.

9. The process of claim 8 wherein R is H2N- or HRN-.

10. The process of claim 9 wherein p-nitrobenzyl 7-amino-3-methyl-3-cephem-4carboxylate hydrochloride is de-esterified.

11. The process of claim 9 wherein p-nitrobenzyl 7-amino-3-chloro-3-cephem-4carboxylate is de-esterified.

12. The process of claim 9 wherein 2,2,2-trichloroethyl 7-amino-3-methyl-3-cephem-4carboxylate p-toluenesulfonate is dc-esterified.

13. The process of claim 9 wherein phenacyl 7-amino-3-methyl-3-cephem-4-carboxylate hydrochloride is de-esterified.

14. The process of claim 8 wherein R is an acylamino group+ of Formula VII.

15. The process of claim 9 or 14 wherein Q is H2N- or' N-.

16. The process of claim 15 wherein p-nitrobenzyl 7-(D-a-amino-a phenylacetylamino)-3-methyl-3-cephem-4-carboxylate p-toluenesulfonate is de-esterified.

17. The process of any of claims 1 to 16 wherein the inert solvent is dimethylformamide or dimethylacetamide.

18. The process of claim 6 wherein R is an acylamino group of Formula V.

19. The process of claim 18 wherein p-nitrobenzyl 7-phenoxyacetylamino-3-methyl-3cephem-4-carboxylate is de-esterified.

20. The process of claim 6 wherein R is an acylamino group of Formula VI.

21. The process of claim 20 wherein R is 2-thienylacetylamino or phenylacetylamino.

22. The process of claim 1 wherein Y is

23. The process of claim 22 wherein p-nitrobenzyl 6-(D-a-amino-aphenylacetamido)penicillanate is de-esterified.

24. The process of claim 22 wherein p-nitrobenzyl 6-aminopenicillanate is de-esterified.

25. The process of claim 1 wherein Y is

R is H2N-, H.N-, phenylacetylamino, phenoxyacetylamino, or 2-thienylacetylamino, R1 is p-nitrobenzyl.

26. The process of claim 25 wherein p-nitrobenzyl 7-amino-3-exomethylenecepham-4carboxylate is de-esterified.

27. The process of claim 25 wherein p-nitrobenzyl 7-phenoxyacetylamino-3exomethylenecepham-4-carboxylate is de-esterified.

28. The process of claim 2 wherein p-nitrobenzyl 7-phenoxyacetylamino-3-(1-methyllH-tetrazol-5-ylthiomethyl)-3-cepthem-4-carboxylate is de-esterified.

29. The process of any one of claims 2, 10, 12, 13, 16 or 28 wherein the compound of Formula II is benzenethiol.

30. The process of claim 29 wherein the solvent is dimethylformamide.

31. The process of claim 29 or 30 when dependent On claim 10 wherein the temperature is from the ambient temperature to 68"C.

32. The process of claim 24 or 25 when dependent on claim 12 wherein the temperature is from the ambient temperature to 58"C.

33. The process of claim 24 or 25 when dependent on claim 13 wherein the temperature is from the ambient temperature to 60"C.

34. The process of claim 25 when dependent on claim 16 wherein the temperature is from the ambient temperature to 75"C.

35. The process of claim 29 or 30 when dependent on claim 28 wherein the temperature is from the ambient temperature to 50"C.

36. The process of claim 16 wherein the compound of Formula 11 is 2,4dichlorobenzenethiol.

37. The process of claim 16 wherein the compound of Formula II is 4methoxybenzenethiol.

38. The process of claim 16 wherein the compound of Formula Il is 1-methyl-lH- tetrazol-5-ylthiol.

39. The process of claim 16 wherein the compound of Formula Il is n-propylthiol.

40. The process of claim 16 wherein the compound of Formula ll is 2hydroxyethanethiol.

41. The process of any of claims 36-4() wherein the solvent is dimethylformamide.

42. The process of any of claims 36-40 wherein the initial temperature is the ambient temperature.

43. The process as claimed in claim 1 substantially as hereinbefore described with particular reference to any one of the examples.

44. A process according to any one of claims 1 to 43 wherein treatment of the ester is effected at a temperature in the range from 20"C to 75 C.

45. A process according to claim 44 wherein the temperature is in the range from 45"C to 60 C.

46. A ss-lactam acid of Formula I as defined in claim 1 whenever prepared by a process according to any one of claims 1 to 45.