Getting discriminant functions of antibacterial activity from physicochemical and topological parameters

Linear discriminant analysis has been demonstrated to be a very useful tool in the selection and design of new drugs. Up to now we have used it throug h the search of a topological pattern of activity. In this work our goal is to calculate a complete set of physicochemical parameters using semiempiri cal (quantum chemical) calculations as well as topological indices (TIs) an d try to find out any discriminant function for antibacterial activity thro ugh the combined use of both types of descriptors. The physicochemical para meters, such as heat of formation, HOMO, LUMO, dipole moment, polarizabilit y, hyperpolarizability, PM3 generated IR vibrational frequencies, etc., wer e calculated using PM3 Hamiltonian implemented within the MOPAC97 package. Among the ns, connectivity as well as topological charge indices stands as the most representatives. The obtained results suggest that one of the maxi ma and minima vibrational frequencies play an important role in the antibac terial activity. These frequencies are associated with the torsional molecu lar vibration (N3) and the stretching vibration (N5) of X-H groups (X = C, N, O). Furthermore, the differences between the maxima and minima values sh owed an even better discriminant ability than the values themselves. The ad ditional use of the topological indices provided a clear improvement in the discriminant function and also provided a straightforward way to predict t he values of such frequencies, so that the results can be applied to a larg e set of compounds searching for new candidates as antibacterials.