Process for epimerizing beta-lactam antibiotic compounds by means of an acid quench

The process of epimerizing a compound having the formula ##STR11## wherein the symbol indicated as a curved broken line represents the following:

• ##STR12## wherein R.sub.1 is an easily removable ester blockingg group;
• R' is hydrogen, halo, loweralkanoyloxy, carbamoyloxy, furyl, thiazolyl, thiazolyl, thiadiazolyl, pyrrolyl, or tetrazolyl;
• each of which can be substituted with a lower alkyl substituent of 1-6 carbon atoms;
• R" is phenyl, furyl, thienyl, thiazolyl, thiadiazolyl, pyridyl, pyrazolyl, or tetrazolyl;
• R'" is loweralkanoyl;
• R.sup.5 is loweralkyl;
• and Y is PO(OH).sub.2 (OR.sup.4), SO.sub.2 (OH) or SO.sub.2 NH.sub.2 in which R.sup.4 is loweralkyl;
• a. which comprises reacting the compound above with an aromatic or aliphatic aldehyde or ketone to yield an intermediate of the formula ##STR13## wherein the broken curved line is as defined, and R.sup.2 is lower-alkyl or phenyl and R.sup.3 is hydrogen, loweralkyl or phenyl;
• b. and treating the latter intermediate with a base sufficiently strong to convert the aldimino compound to its anionic form said treatment conducted in the presence of an aprotic solvent and the optional presence of a dipolar aprotic co-solvent, followed by addition of a molecular excess of acid, a carboxylic acid having from 1-5 carbon atoms;
• c. and reacting the compound thereby produced with acid in the optional presence of an amine, and recovering the product, ##STR14## wherein the curved broken line is as defined above.