Studies on vitamin D and related compounds V: Corroboration of the scheme proposed for the photochemical conversion of the provitamins D, in particular with regard to the place of the previtamins D

Abstract

Abstract In continuation of the irradiation experiments with mixtures of labelled provitamin D and inactive lumisterol and tachysterol, which led to the rejection of the traditional reaction scheme and the introduction of a new scheme for the photochemical conversion of provitamin D 1 ) 2 ), mixtures of C 14 ‐labelled ergosterol and inactive previtamin D 2 were irradiated and the resulting products analysed. Moreover, complementary spectrophotometric investigations into the photochemical conversion of previtamin D 2 were carried out. The results confirmed the non‐validity of the schemes which assign to one of the irradiation products of provitamin D the part of an essential intermediate for the formation of the other products. Particularly, the investigations confirmed that previtamin D 2 does not function as an essential intermediate with respect to the formation of tachysterol 2 from ergo‐sterol 4 ) 5 ). The possibility is mentioned that the unstable intermediate which holds a central position in the proposed scheme in its simplest form 1 ), might be a triplet state.