Biophysical studies on molecular mechanism of abortificient action of prostaglandins—IV. Conformation energy calculations on PGA 1, PGB 1 and PGE 1

Abstract

This paper reports the conformation energy (CE) calculations on three forms of prostaglandins (PGs) PGA 1, PGB 1 and PGE 1 on the basis of the empirical potential energy functions, for the simultaneous rotations around C 7–C 8 (θ), C 12–C 13 (β) and C 14–C 15 (β) bonds [Fig. 1(a)]. The isoenergy contours plotted for θβ rotations for the different β values show the existence of two low energy regions for thg equal to about 90° and 240° in all the three cases. The absolute minimum was obtained for thg = 240° and almost coincided with the crystallographic conformation for PGE 1 and PGA 1. In the case of PGB 1 series of low energy conformations were obtained with the thg values equal to about 90° and 270°, but none of them coincided with the observed crystallographic conformation. The paper discusses the comparison of the different low energy conformations in these three molecules, their biological relevance and the cause of disagreement in the case of PGB 1 with the crystallographic data.