NEW MATERIAL: Compd. (their salts) of formula I [wherein A is a 1-12C alkylene, a 1-12C alkylidene, phenylene, etc.; R is formula II (wherein R2 is H, a group of formula III, etc.), formula IV, etc.; R3 is H or a 1-3C alkyl; R1 is H, a 1-4C alkyl, benzyl, tetrabutylammonium, etc.].

EXAMPLE: Benzyl-1,1-dioxopenicillanoyloxymethyl succinate.

USE: Antibacterial agents.

PROCESS: For example, a monobenzyl dicarboxylate of formula V (wherein M is Na, K, etc.), is reacted with such a compd. as iodomethyl-penicillanate-1,1- dioxide of the formula, BCO2CH2X (wherein B is a group of formula IV; X is a halogen) in an org. solvent and then, after precipitate is removed, the solvent is distilled out and it is refined by means of a silica gel chromatography to obtain a compd. of formula I.