Quantitative relationships between steroid structure and binding to putative progesterone receptors.

Relationships between chemical structure of androst-4-en-3-one derivatives and their affinity for putative progesterone receptors are described. The binding affinity for 55 derivatives can be expressed by the equation log relative binding affinity (rabbit receptor) = 1.79 + 0.18 (+/-0.11) pia + 1.45 (+/-0.21) pib + 0.010 (+/-0.002) (surface area in hydrophobic pockets) - 0.012 (+/-0.003) (surface area out of hydrophobic pockets) - 0.99 (+/-0.21) MK - 0.33 (+/-0.08) (conformational changes). For this equation, r=0.88. The equation successfully predicts the affinities of other compounds in the literature. The importance of the surface area terms is discussed.