A theoretical study of the molecular structure of a series of synthetic and natural brassinosteroids in relation to their biological activity

Abstract

In the approximation of molecular mechanics and PM3 quantum chemical methods, a conformational analysis of the side chain of five representatives of steroid phytohormones is performed: synthetic (22S,23S)-(epi- and homobrassinolides) and natural (two stereoisomers of (22R,23R)-24-epibrassinolide and (22R,23R)-28-homobrassinolide). It is shown that the 22R,23R-diol structure in the steroid side chain enhances its flexibility as compared to the 22S,23S-configuration. This leads to a high possibility of the occurrence of two conformers of natural brassinosteroids in the solution. In one of these conformers, hydroxyl can form an intermolecular hydrogen bond instead of forming an intramolecular hydrogen bond within the diol system of the side chain, which is important for hormone-receptor interactions.