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

Abstract

Pepluanol B is a new Euphorbia diterpene with an unprecedented tetracyclic backbone. However, its biogenetic relationship with known Euphorbia 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 Euphorbia 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.

Rapid Access to Tigliane, Ingenane, and Rhamnofolane Diterpenes from a Lathyrane Precursor via Biomimetic Skeleton Transformation Strategy

“…C-17 position attacked by the methoxy group affords the intermediate 6 having a Δ 5 endocyclic double bond via a S N 2′ substitution, then 14-OH and 15-OH elimination gives the more stable conjugated cycloheptatrienones 7 and 8 . Notably, She’s group reported a direct conversion via a retro-aldol/aldol cascade conversion from pepluanol B into a tigliane-type compound which also has a cycloheptatrienone motif in B ring . They proposed a lathyrane-type intermediate might be generated during this process, but it regrettably was not be detected.…”