A PROCESS FOR THE PREPARATION OF A PENICILLIN COMPOUND OF A SALT THEREOF THE FORMULA I

2-(HOOC-),3,3-DI(CH3-),6-((4-A-1,2,5-THIADIAZOL-3-YL)-Y-

C(-B)(-X)-CO-NH-)PENAM

WHEREIN A IS HYDROGEN, ALKYL HAVING 1 TO 4 CARBON ATOMS, ARALKYL SELECTED FROM THE GROUP WHICH CONSISTS OF BENZYL AND PHENYLETHYL UNSUBSTITUTED OR SUBSTITUTED WITH CHLORO, METHOXY OR ETHOXY, OR ARYL SELECTED FROM THE GROUP WICH CONSISTS OF PHENYL AND NAPHTHYL UNSUBSTITUED OR SUBSTITUTED WITH CHLORINE, METHOXY OR ETHOXY; B IS HYDROGEN OR ALKYL HAVING 1 TO 4 CARBON ATOMS, Y IS OXYGEN OR SULFUR, X IS HYDROGEN OR ALKYL HAVING 1 TO 4 CARBON ATOMS, WHICH COMPRISES REACTING 6-AMINOPENICILLANIC ACID OR A TRIALKYLXYLYL ESTER THEREOF WITH A CARBOXYLIC ACID OF THE FORMULA II

3-(HOOC-C(-B)(-X)-Y-),4-A-1,2,5-THIADIAZOLE

OR A REACTIVE DERIVATIVE THEREOF SELECTED THE GROUP WHICH CONSISTS OF THE AZIDES, ACID CHLORIDES, ACID BROMIDES AND HYDRIDES OF SAID CARBOXYLIC ACID.