Autoxidation of Siphonochilone in Processed Rhizomes and Stored Powders of Siphonochilus aethiopicus (Schweinf.) BL Burtt

Abstract

A furano sesquiterpenoid, known as siphonochilone (1), is commonly reported as the major compound in the roots and the rhizomes of Siphonochilus aethiopicus together with related oxidized sesquiterpenoids (2-5). As part of investigating the UPLC QTOF MS ES + chemical profiles of n-hexane/dichloro-methane (1:1) extracts from crushed fresh rhizomes, dried and powdered rhizomes and the dried powders held under storage at room temperature, we have recently realized that decomposition of 1 occurs during the processing of the rhizomes and the storage of the powders. This decomposition which involves autoxidation of the furan moiety leads to formation of the artefact sesquiterpenoid lactone (3) and potentially (4), which numerous papers misreport as naturally present in the plant. MP2/6-31 + G(d,p), B3LYP/6-31+ G(d,p) and B3LYP/6-311 + G (2d,p) calculations were performed on siphonochilone (1) and the sesquiterpenoid lactone artifacts (3) and (4) and results rationalized the observed autoxidation.