Effect of wavelength on the photochemical reaction of ergocalciferol (vitamin D2) irradiated by monochromatic ultraviolet light

Abstract

The effect of wavelength on the photochemical reaction of ergocalciferol (vitamin D2) was investigated. An ergocalciferol solution in ethanol was irradiated by monochromatic UV light of various wavelengths with a fixed quantum (8.0×108erg/cm2), trimethylsilylated and then applied to a capillary column GLC as described previously (10) in order to estimate the reaction products. The results showed that UV light in a range of 295-312nm was most effective in the photochemical transformation of ergocalciferol into suprasterol2 I and II. The formation of compounds I, I2, II1 and II2, which had been found as novel reaction products by BARKER et al. (8), was not exactly confirmed because the former two were thermally isomerized into gyro- and isopyro-D2 via ergocalciferol while the latter two were isomerized into 5,6-tans-D2 at the temperature for GLC analysis. However, since the peaks caused by gyro and isopyro-D2 were observed to be rather large in the gas chromatograms of long-term irradiated solutions, although no information on the existence of ergocalciferol was obtained from the UV spectra and TLC of the solutions, significant amounts of the compounds h and 12 might be formed by irradiation of ergocalciferol. On the other hand, the peak due to 5,6-taans-D2 was observed to be very small in the gas chromatograms of irradiated solutions with different wavelengths although no information on the existence of 5,6-taans-D2was also obtained from the results of TLC. Therefore, the photochemical transformation of ergocalciferol into compounds II1 and II2 might occur to only a small extent regardless of irradiated wavelengths. © 1977, Center for Academic Publications Japan. All rights reserved.