Conformational flexibility of the methyltetrazolethiomethyl side chain of beta-lactam antibiotics. A computer graphics study

Analysis of X-ray crystallographic data for cephalosporins and 1- oxacephalosporins shows that, although the 1-methyl-1H- tetrazol -5- ylthiomethyl side chain at position 3 of a bicyclic beta-lactam nucleus has certain conformational preferences, it also has considerable flexibility. Both the C4 = C3-C3'-S and C3-C3'-S-C5" torsional angles are frequently observed in the vicinity of +/- 90 degrees. The distance between the tetrazole ring carbon C5" and the 4-carboxyl carbon ranges from 4.07 to 5.65 A. Mean bond lengths and bond angles for the 3 and 4 side chains are tabulated.