Force field parametrization for 6-aminopenicillanic acid

A complete set of AMBER force field parameters for 6-aminopenicillanic acid, crucial moiety of beta-lactam antibiotics, has been developed. Equilibrium geometry was derived from RHF/6-31G* calculations, stretching constants were computed from quantum mechanical hessian, partial atomic charges were assigned according to restrained electrostatic potential fit methodology. Torsional parameters were also derived from quantum mechanical calculations. It was shown that unusual chemical structure of 6-aminopenicillanic acid with two merged four- and five-member rings has found its reflection in the set of molecular mechanical parameters: a number of bonds and angles appeared to be much more rigid than those described by classic AMBER field. The quality of derived set parameters was attested by computing molecular geometry, spectroscopic and thermodynamic proper-ties. (C) 2003 Elsevier B.V. All rights reserved.