Optimization of synthesis process and photocatalytic mechanism of tachysterol under ultraviolet irradiation

Tachysterol is an intermediate product in the synthesis of vitamin D₂ from ergosterol and vitamin D₃ from 7-dehydrocholesterol under ultraviolet irradiation. Recent studies have shown that tachysterol is also a crucial intermediate in the synthesis of the natural anti-tumor product Chaxine C. Although there have been numerous studies on the synthesis of vitamin D₂ and other photoisomers from ergosterol, research on the synthesis of tachysterol is relatively limited. In addition, the yield of tachysterol is not high (57.0%), and the mechanism is unclear. In this study, a method was developed for the qualitative and quantitative analysis of tachysterol. Meanwhile, an efficient synthesis process for tachysterol was reported. The qualitative and quantitative analysis of ergosterol isomers, including tachysterol, a precursor of vitamin D₂, and photosterol, was conducted using high-performance liquid chromatography, and the quantitative method for tachysterol was confirmed using quantitative nuclear magnetic resonance. There were strong linear relationships between tachysterol content and the testing parameters, with the correlation coefficients of 0.9997 and 0.9971, respectively. The synthesis process of tachysterol from ergosterol through our self-designed photoreactors was optimized, and the effects of reaction temperature, reaction time, photoprotectants, reaction substrate concentration, and the power of ultraviolet lamps were investigated. The yield of the reaction was 85.7%, which is 28.7% higher than the previously reported results. The mechanism and by-products of the reaction were further studied using ultraviolet spectrophotometry and gas chromatography mass spectrometry. This study explored the potential for the large-scale preparation of tachysterol, particularly for the total synthesis of the anti-tumor natural product Chaxine C. It also offered insights into the synthesis of structural similar compounds and the analysis of photocatalytic reaction products.