The present invention relates to a process for preparing a pharmaceutical starting compound compound by hydrolyzing a compound of the general formula (II): Wherein R.sup.1 is protected carboxy, R.sup.2 is lower alkoxy or higher alkoxy, A.sup.1 is an aromatic bivalent group, heterocyclic bivalent group or cyclo (lower) alkane bivalent group, and A.sup.2 is an aromatic bivalent group, heterocyclic bivalent group or cyclo (lower) alkane bivalent group, with aqueous potassium hydroxide and by treating with hydrochloric acid. ##STR00001##
