Riboflavin‐photosensitized singlet oxygen oxidation product of vitamin D2

The riboflavin‐photosensitized singlet oxygen oxidation of vitamin D2 in a model system of 12% water and 88% acetone was studied to understand the possible oxidation of fortified vitamin D in milk. Only the samples containing vitamin D2 and riboflavin under light storage showed two new peaks in the HPLC chromatogram, indicating that singlet oxygen oxidation of vitamin D2 had occurred. UV analysis indicated that a new compound was formed from the reaction of the triene of vitamin D2 with oxygen. The mass spectrum showed that one of the two compounds had a molecular ion at m/z=412, which was an increase of the mass of vitamin D2 by the mass of exactly one oxygen. The IR spectrum suggested the presence of a hydroxyl group and no carbonyl group in the product. The combned information from UV, MS, and FTIR spectra and the chemical mechanisms of singlet oxygen oxidation of vitamin D2 indicated that a 5,6‐epoxide of vitamin D2 was formed from vitamin D2 in the presence of riboflavin under light.