A new class of natural steroids, with ring D aromatic, from Nicandra physaloides(solanaceae). X-Ray analysis of Nic-10, and the structures of Nic-1 (‘nicandrenone’),-12, and -17

Abstract

X-Ray analysis of Nic-10 from Nicandra physaloides shows it to be the novel 6α,7α-epoxy-5-hydroxy-17(13 → 18)abeo-5α-pregna-2,13,15,17-tetraene-1,20-dione (1), in which ring D is aromatic and six-membered, apparently by inclusion of the C-13 methyl. The nature of the oxygenated A and B rings, however, show clearly its familial relationships with other Solanaceae steroids.

Structure work on three further aromatic (n.m.r.) steroids was carried out spectrally. Nic-1 (nicandrenone)(4) proved to have the ABCD system of Nic-10, but carried the full ergostane side-chain oxidatively elaborated into the same epoxidised cyclic hemiacetal ring E feature as previously encountered in Nic-3. Nic-12 (2) and Nic-17 (3) also have the same ABCD system as Nic-1 and Nic-10, but unlike the latter, which have C₉ and C₃ side-chains respectively, these both have a C₆ side-chain. The four ring-D-aromatic steroids can be arranged in a biosynthetic sequence involving plausible degradation steps. Possible mechanisms for the ring D expansion–aromatisation reaction are mentioned.