17-Oxo-5 alpha-androst-6-en-3 beta-yl acetate.

In the title compound, C(21)H(30)O(3), a potential inhibitor of aromatase, all rings are fused trans. Rings A and C have chair conformations which are slightly flattened, whereas the conformation of ring B is close to a half-chair. Ring D has a 14 alpha-envelope conformation. The steroid nucleus has a small twist, as shown by the C19-C10...C13-C18 (steroid numbering) torsion angle of -6.9 (3) degrees. Ab initio calculations of the equilibrium geometry of the molecule reproduce this small twist, which appears to be due to the conformation of ring B rather than to packing effects.