The synthesis and antibacterial activity of new ureidopenicillin derivatives having catechol moieties in the 6-acyl side chain are described. These compounds showed remarkably strong VOL. XXXIX NO. 2 THE JOURNAL OF ANTIBIOTICS 231

thiomethyl]-3-cephem-4-carboxylic acid (5) had the most potent activity in vitro against gramnegative bacteria, its activity being 8-to 32-fold and 4-fold greater than those of cefoperazone and ceftazidime, respectively, against two strains of P. aeruginosa. The structure-activity relationship is discussed.

The cephalosporins (III) mentioned in the title are prepared either by coupling the ureidocarboxylic acids (I) with 7‐aminocephalosporanic acid (II) or by reaction of the carbamic acid chlorides (VII) with the aminocephem (VIII).

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