The structure and absolute configuration of (–)-2β,9α-dihydroxyverrucosane isolated from the liverwort Mylia verrucosa : X-ray analysis of the mono-p-bromobenzoate

Abstract

The structure of dihydroxyverrucosane (I), a novel diterpene-diol isolated from the liverwort Mylia verrucosa has been determined from single-crystal X-ray analysis of the mono-p-bromobenzoate (II) by the heavy-atom method. The crystals were monoclinic, a= 6.670(1), b= 19.269(1), c= 10.379(1)Å, β= 112.6(4)°, space group P2₁, Z= 2. Block-diagonal least-squares refinement based on 1 929 independent reflections converged to R 0.078. The absolute configuration was established by the anomalous dispersion effect. The molecule contains a 3,6,6,5-tetracyclic ring system in which ring B is considerably distorted by fusion with the cyclopropane ring A. Ring C adopts a chair conformation and ring D is a conformation somewhere between a half-chair and β-envelope.