Acta Cryst. (2000). B56, 512-525 [ doi:10.1107/S0108768199015542 ]
Abstract: The crystal structures of six synthetic 2-oxa-steroids (A-ring lactone steroids) have been determined by single-crystal X-ray diffraction. The conformation and hydrogen bonding in these oxa-steroids is compared with packing motifs in the natural steroids and the anabolic agent, Anavar®. O-H
O hydrogen bonding with lactone carbonyl O is the preferred arrangement in molecules with a C-OH group. The donor H atoms of A, B and D rings participate in C-HO interactions with lactone carbonyl O and D-ring hydroxyl/ketone O acceptor atoms. The conformation of the lactone ring in these analogues is different from the natural androgens because replacement of the C2-methylene group by an O atom changes the geometry of the A ring. Two structurally related lactone steroids provide the first example of O-HO/C-HO interaction mimicry and furthermore the two components form a binary solid solution. The O-HO and C-HO hydrogen bonds in 2-oxa-steroid crystal structures are analysed and the observed preferences discussed in terms of geometric and chemical factors.
Keywords: 2-Oxa-steroids; Conformation; Packing; Isostructurality; Lactones; Hydrogen bonding.
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