Molecular mechanics (MM3) calculations on phosphonamidate compounds

Phosphonamidate compounds are regarded as transition-state analogs for amid e hydrolysis reactions and can be used as potent haptens to elicit catalyti c antibodies. The MM3 force field has been extended to cover these compound s, based on the structures, conformational energies, and vibrational analys es from MP2/6-31G* or B3LYP/6-31G* calculations. It was necessary to includ e a "trans-lone pair effect" in the MM3 force field so that the conformatio nal dependence of the N-P and P-C bond lengths could be reproduced. This ef fect is similar to the Bohlman effect and the anomeric effect. The MM3-calc ulated molecular structures agree well with the quantum mechanics results, and the conformational equilibria and vibrational spectra are in fair agree ment. (C) 2000 Elsevier Science B.V. All rights reserved.