Synthesis of Some Heterofunctionalized Penicillanic Acid Derivatives and Investigation of Their Biological Activities

6‐Substituted amino‐penicillanic acid esters were synthesized starting with 6‐apa. The compounds containing a 1,3‐thiazole‐ or 1,3‐thiazolidinone nucleus linked to the penicillanic acid skeleton via a hydrazino linkage were obtained from 6‐apa. The treatment of carbonylamino and carbonothioylamino compounds with 4‐chlorophenacyl bromide or ethyl bromoacetate gave 6‐bis{4‐[1,3‐thiazol(idinone)amino]benzoyl}amino derivatives of 6‐apa. Benzyl derivatives were synthesized in several steps, starting with 4‐aminobenzoyl chloride. The treatment of 4‐{[3‐benzyl‐4‐oxo‐1,3‐thia(oxa)zolidin‐2‐ylidene]amino}benzoyl chlorides with 6‐apa in ethanolic solution produced the 6‐[bis(4‐{[3‐benzyl‐4‐oxo‐1,3‐thiazolidin‐2‐ylidene]amino}benzoyl)amino] derivative of penicillanic acid, while the reaction of the same intermediates in DMF gave the mono‐substituted amino derivative of 6‐apa. The synthesized compounds were screened for their biological activities, and some of them were found to possess good to moderate antimicrobial activity. Moreover, some of the compounds displayed antiurease, anti‐β‐lactamase, and/or antilipase activities.