metabolic pathway of secondary metabolites penicillins and cephalosporins biosynthetic pathway PW:0000254 Those metabolic reactions involved in the biosynthesis of penicillin and cephalosporins. The former is the best known antibiotic which blocks the cross linking reaction in peptidoglycan synthesis, thus destroying the bacterial cell wall. The latter represents a broad class of antibiotics similar to penicillin, both chemically and in mode of action. pathway