Structure-activity relationships of penem antibiotics: crystallographic structures and implications for their...

Twelve closely related crystal structures of the penem derivatives revealed a characteristic short contact of the oxygen atom in the C2 side-chains with the S1 atom. The side-chain conformations of the crystal structures showed a good correlation with the antimicrobial activity. In particular, the penems which show high antimicrobial activity have similar torsion angles for S1-C2-C1'-C2', suggesting that the disposition of the C2' atom would be important for binding to penicillin-interacting enzymes. Two conformations of the C6 hydroxyethyl group were observed in the crystal structures. Of those two, the conformation with a larger torsion angle (delta = 179.2 degrees) is deduced to be the enzyme-bound conformation in the Michaelis complex.