Compounds of the general formula:
wherein R1 is heterocyclic group other than pryridyl and which is unsubstituted or substituted with lower alkyl or lower alkoxycarbonyl, R2 is hydrogen, halogen, or nitro, and R3 is carboxy group or its functional derivative, with the proviso that when R' is an unsubstituted furyl, or furyl mono-or polysubstituted with alkyl and R2 is hydrogen, then R3 is functional derivative of carboxy and, where applicable, pharmaceutically acceptable salts thereof are hyaluronidase inhibitors and useful as anti-allergic agent.