Diosgenone: a second P2₁ polymorph

Diosgenone [(20S,22R,25R)-spirost-4-en-3-one, C₂₇H₄₀O₃] has been proposed as a new therapeutic alternative for the treatment of malaria. The first X-ray structure report for diosgenone was by Piro et al. [(2002). Z. Naturforsch. Teil C, 57, 947–950] in the space group P2₁ (Z′ = 2). We now report a new polymorph in the same space group, with two mol­ecules in the asymmetric unit. Both mol­ecules have similar conformations, characterized by a skewed envelope A ring, which contains the C=C bond conjugated with the ketone functionality at C3. The dimorphism results from a modification of the relative orientation of the mol­ecules in the asymmetric unit: two independent mol­ecules were arranged anti­parallel in the Piro report, while they are parallel in the present determination.

(25R)-6α-Hy­droxy-5α-spiro­stan-3β-yl tosyl­ate

The title steroid, C₃₄H₅₀O₆S, is an inter­mediate on the synthetic route between diosgenin and brassinosteroids, which possess the A ring modified with the 2α,3α-diol functionality. The polycyclic spiro­stan system has the expected conformation, with six-membered rings adopting chair forms and the five-membered rings envelope forms (flap atoms are the methine C atom in the C/D-ring junction and the spiro C atom connecting rings E and F). The 3β-tosyl­ate group is oriented in such a way that S=O bonds are engaged in inter­molecular hydrogen bonds with O—H and C—H donors. Chains of mol­ecules are formed along [100] via O—H...O hydrogen bonds, and secondary weak C—H...O inter­actions connect two neighbouring chains in the [001] direction.