| abstract |
A compound represented by the formula (II) epimerizes by the action of a base and the product is precipitated for shifting the equilibrium to yield the corresponding epimer represented by the formula (I). ##STR1## wherein Ar is an optionally substituted aryl or heterocyclic group; n Tet is an optionally substituted tetrazolyl group and n B 1 and B 2 are each ester forming group in the field of penicillin or cephalosporin chemistry. |