Rearrangement of the Tetra- and Tricyclic Skeletons of Pepluanol B to Access the Core Structures of Tigliane- and Myrsinane-Type <i>Euphorbia</i> Diterpenes

Abstract

Pepluanol B is a new <i>Euphorbia</i> diterpene with an unprecedented tetracyclic backbone. However, its biogenetic relationship with known <i>Euphorbia</i> diterpenes is unclear. We report herein that its β-hydroxyl ketone motif could undergo a base-promoted retro-aldol/aldol process in two pathways and afford the skeletons of tigliane- and myrsinane-type <i>Euphorbia</i> diterpenes through the formation of the C8-C14 and C7-C13 bonds, respectively. The retro-aldol/aldol cascade indicates that pepluanol B is possibly a biosynthetic precursor of lathyranes and other relevant dipterpenes.