Crystal and molecular structures of three modifications of the androgen dehydroepiandrosterone (DHEA)

The crystal and molecular structures of three forms of the androgen DHEA (dehydroepiandrosterone) have been determined by single crystal X-ray diffraction. They are: Form I, a polymorph crystallizing in space group P2₁ withZ=4; Form S1, a hydrate with composition DHEA. (1/4)H₂O, space group C2,Z=8; and Form S4, a methanol half-solvate, DHEA. (1/2)CH₃OH, space group C222₁,Z=8. The A, B, and C steroid ring conformations adopted in the five crystallographically independent DHEA molecules are invariably: chair, 8, 9-half-chair, and chair, respectively, while the D ring conformation ranges from a 14-envelope to a 13, 14-half-chair. In Forms I and S1, intermolecular hydrogen bonding is of the head-to-tail type with water molecules participating as donors in Form S1. In Form S4, DHEA molecules pack in head-to-head fashion, their hydroxyl groups being linked by hydrogen bonding to the solvent hydroxyl group. The hydroxyl H atoms of both DHEA and the included methanol are disordered, giving rise to an unusual linearly-propagating flip-flop hydrogen bonding scheme.