QSAR analysis of some 5-amino-2-mercapto-1,3,4-thiadiazole based inhibitors of matrix metalloproteinases and bacterial collagenase.

A quantitative structure-activity relationship (QSAR) study has been performed on 5-amino-2-mercapto-1,3,4-thiadiazole based inhibitors of matrix metalloproteinases (MMPs) and a bacterial collagenase known as Clostridium histolyticum collagenase (ChC) to understand the structural features influencing the affinity of these inhibitors towards the enzyme. The compounds in the selected series were characterized by topological and fragmental descriptors calculated using QuaSAR module of molecular operating environment (MOE). An indicator variable was also assigned to account for the presence of amide function in vicinity of sulfonamide group in the parent structure. Correlations between different inhibitory activities and calculated predictor variables were established through stepwise multiple regression employing the method of least squares. The results of the study indicates that MMP inhibitory activity of 5-amino-2-mercapto-1,3,4-thiadiazoles can be successfully explained in terms of topology of the molecule. The obtained correlations also suggest that increase in the number of fluorine atoms in the aromatic ring will augment inhibitory activity of these molecules against all the MMPs probably by virtue of hydrogen bond interaction with some complementary groups in the active site of the enzymes. One prime requirement for better inhibition of MMPs (except for MMP-1) and ChC identified from the present study is the presence of amide function in vicinity of sulfonamide group in the parent structure as suggested by the presence of indicator variable in almost all correlations. While MMP-1 and ChC inhibitory activity of the compounds studied is shown to be dependent on Kier's first order carbon valence molecular connectivity index indicating that increase in branching and presence of heteroatoms in the molecule will improve the MMP-1 and ChC inhibitory potency of 5-amino-2-mercapto-1,3,4-thiadiazoles, correlations derived for other enzymes (MMP-2, MMP-8, MMP-9) are quite similar. In addition to the number of fluorine atoms and presence of indicator variable, MMP-2, MMP-8 and MMP-9 inhibitory activity of 5-amino-2-mercapto-1,3,4-thiadiazoles is found to be dependent on Kier's alpha modified index of third order in such a way that infer, terminally branched functions will increase the affinity of these molecules to the MMPs.