Abstract: Penicillanic acid derivatives of the formula ##STR1## wherein E is selected from the group consisting of hydrogen, a salt forming cation, and an ester forming residue which is known to improve the absorption characteristics of penicillanic compounds after oral administration to humans or animals, and Y is a group of the formula ##STR2## wherein Z.sub.1 and Z.sub.2 are individually selected from the group consisting of lower alkoxy, optionally substituted phenoxy, optionally substituted benzyl and benzyloxy group, optionally substituted lower alkyl, optionally substituted phenyl, hydroxy and -OM wherein M represents a salt forming cation, and hydrates of the said salts having antibacterial properties and their preparation and novel intermediates.

Abstract: Novel therapeutically useful and disinfecting penicillanic and cephalosporanic acid derivatives of the formula: ##SPC1##Wherein W represents a penicillanic or cephalosporanic acid residue or derivatives thereof and wherein Y represents a carbonamido group N-substituted by a phosphorous or sulfur containing residue or Y represents a phosphorous or sulfur containing substituent, and pharmaceutical and disinfecting compositions containing them and their use and process for the preparation of the said compounds.