Semiempirical QSAR study and ligand receptor interaction of estrogens.

Softness values E(n)+/+ of estrogen derivatives and softness values E(m)+/+ of receptor lysine, histidine, tyrosine and cysteine have been evaluated by Klopman equation. The required parameters for the solution of Klopman equation have been calculated with the help of PM3 method. The difference deltaE(nm)+/+ between E(n)+/+ and E(m)+/+ has been derived for QSAR study. The estrogen derivatives have been divided into four different sets on the basis of their structural similarities, and their biological activity taken from literature in terms of relative binding affinity (RBA). The QSAR study shows that, deltaE(nm)+/+ values provide good relationship with biological activity.