Sesquiterpenoids. Part XI. X-ray determination of the structure of vernolepin p-bromobenzenesulphonate

Abstract

Crystal-structure analysis of vernolepin p-bromobenzenesulphonate has elucidated the molecular structure of vernolepin, C₁₅H₁₆O₅, a novel elemanolide dilactone isolated from Vernonia hymenolepis. The derivative crystallizes in the monoclinic space group P2₁ with a= 9·80, b= 10·10, c= 11·04 Å, β= 90° 12′, and Z= 2. The atomic co-ordinates were determined by Fourier and least-squares methods. The cyclohexane ring of the sesquiter-penoid adopts a chair conformation, and the δ-lactone ring provides an example of a distorted boat-like form. The conformation of the secondary alcohol sulphonate group (CH·OSO₂-) is characterized by C–O–S–C and H–C–O–S torsion angles of 95 and –35°.