Abstract
Softness values E(n)(double dagger) of estrogen derivatives and softness values E(m)(double dagger) 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 Delta E(nm)(double dagger) between E(n)(double dagger) and E(m)(double dagger) 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, Delta E(nm)(double dagger) values provide good relationship with biological activity.