Crystal structure of 17-oxo-5α-androstano [3,4-C] 1′2′5′-oxadiazole (HS1000)

The title compound (C19H26N2O2) is one of a series of novel heteroatom steroidal derivatives recently prepared for testing their antifertility profiles and progesterone binding affinity. It is one of a pair of epimers differing in configuration at position 5. The X-ray analysis has uniquivocally resolved this ambiguity. The compound crystallizes in space group P212121, a = 9.257(3), b = 9.419(3), c = 19.089(5)A, and Z = 4 and the structure was solved by direct methods. In the steroid skeleton Ring A does not exhibit the chair conformation commonly found in the steroid nucleus, being considerably strained, presumably as a consequence of the fused planar oxadiazole ring E. Rings B and C, however, are chairs and ring D is in an intermediate envelope/half-chair conformation. All rings of the steroid skeleton are trans connected.