Side‐chain autoxidation of stigmasterol and analysis of a mixture of phytosterol oxidation products by chromatographic and spectroscopic methods

Although the structure of phytosterols is closely related to cholesterol, there is a gap in knowledge concerning the formation and occurrence of oxidation products from phytosterols. The main objective of this study was to isolate and characterize some side‐chain oxidation products formed after autoxidation of stigmasterol. Another objective was to highlight the difficulties in the analysis of phytosterol and a mixture of their oxidation products by GC. Pure stigmasterol was oxidized at 120°C for 72 h in an air‐ventilated oven. Preparative TLC separated the oxidation products, and the products were characterized with GC‐MS and NMR. In addition to the common ring‐structure oxidation compounds, three semipolar oxidation products—24‐ethylcholest‐5,22‐dien‐3β,25‐diol, 24‐ethylcholest‐5,22‐dien‐3β,24‐diol, and 24‐ethyl‐5,22‐choladien‐3β‐ol‐24‐one—were characterized for the first time by TLC, GC‐MS, and NMR. Moreover, the results of the analysis of a large number of oxidation products from sitosterol, campesterol, and stigmasterol by capillary column GC indicated that further efforts and optimization are required in this area.