AB-INITIO STUDY OF BETA-LACTAM COMPOUNDS - ACIDIC HYDROLYSIS

A complete study on the acidic hydrolysis of the azetidin-2-one ring, an essential component of beta-lactam compounds, has been carried out by means of ab initio calculations by using a 6-31G* type basis set. The former reaction has been studied by means of an A-1 type unimolecu lar mechanism, characterized by an N-protonation followed by an openin g of the ring and further addition of water to the carbonyl group. The system involving the azetidin-2-one ring, the H3O+ ion and a water mo lecule has been considered, where three transition states have been id entified, being the barriers corresponding to the addition of H+ to th e nitrogen and the addition of water to the carbonyl group being pract ically negligible (first and third reaction steps, respectively). The energy barrier for the opening of the ring (second reaction step) was 14.23 kcal mol(-1). (C) 1998 Elsevier Science B.V.