J. Frau et al., THEORETICAL CALCULATIONS OF BETA-LACTAM ANTIBIOTICS .4. AM1, MNDO, AND MINDO 3 CALCULATIONS OF HYDROLYSIS OF BICYCLIC SYSTEM OF PENICILLINS/, Theoretica Chimica Acta, 86(3), 1993, pp. 229-239
We carried out a comprehensive theoretical study on the alkaline hydro
lysis of the bicyclic system of penicillins (a four-member ring fused
to a thiazolidine ring) on the basis of a B(AC2) mechanism. We assayed
the MINDO/3, MNDO, and, AM1 semi-empirical calculation methods in ord
er to determine their suitability for studying beta-lactam rings. Both
the geometric and the energetic results obtained for the different in
termediate states were compared with literature values - chiefly those
determined by ab initio methods - with which they proved to be very c
onsistent. The conformation of the carboxyl group at position 3 was fo
und to be rather significant to the determination of the energy of the
different reaction maxima and minima.