Autoxidation of Siphonochilone in Processed Rhizomes and Stored Powders of <i>Siphonochilus aethiopicus</i> (Schweinf.) B.L. Burtt

Abstract

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/dichloromethane (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.