Role of side chain moiety in the hydrolysis of penicillins by beta-lactamase.

Various beta-lactam compounds and structurally related moieties were examined as substrates of beta-lactamase from Bacillus cereus 5/B NCTC 9946. The enzyme was specific for penicillins and none of the cephalosporins were hydrolysed. Electronic environment of allylic carboxy group in dihydrothiazine ring restricts the acceptance of cephalosporins as substrates. The efficiency of hydrolysis of penicillins is dependent on dense resonating electronic environment of phenyl ring present in the side chain, flexibility of the side chain and the distance between the phenyl ring and carbonyl group in the side chain.