Conformational Analysis of (+)‐Germacrene D‐4‐ol Using the Crystalline Sponge Method to Elucidate the Origin of its Instability

Abstract

AbstractUnsaturated cyclic terpenes often exhibit instability due to the proximation of C=C bonds in the cyclic skeleton, leading to nonenzymatic degradation. In this study, the crystalline sponge (CS) method was employed for the X‐ray conformational analysis of a minute amount of oily and cyclic terpene compound, (+)‐germacrene D‐4‐ol, which was produced by a terpene synthase OILTS under in vitro conditions. The CS method revealed a reactive conformation of the cyclic terpene with proximal double bonds. Under weakly acidic in vivo conditions, OILTS gave four pseudo‐natural products or artifacts. The CS method also elucidated the structures of these degraded compounds, proposing a degradation mechanism triggered by the transannular reactions.