Photochemistry of the Thiazole Component of Vitamin B1

Photolysis of the pyrimidine component of vitamin B1 by ultraviolet radiation has been reported in a recent paper by the present writers (1). It was shown that inactivation resulted not only from the breakdown of the pyrimidine ring structure but also from the loss or alteration of those side groups or radicals known to be essential for the biological functioning of the vitamin. Nevertheless, only 1 quantum out of more than 50 was found to be effective in bringing about inactivation. With the thiazole component an analogous quantitative analysis can be made according to the same method, for it has been shown (2, 3) that the fungus, Phycomyces blakesleeanus, can develop quite as efficiently when administered equimolecular quantities of the two components of vitamin B1 as when given the thiamine itself, and hence an assay for either component can be carried out when the concentration of the other is known. In the case of the “thiazole” molecule, it is clear from the work of both Robbins and Kavanagh (4) and Bonner and Erickson (3) that inactivation may mean either some change in the hydrogen of the 2 posit,ion or in the 5hydroxyethyl group rather than a breakdown of the ring itself, as each of the two groups mentioned has been shown to be essential for growth. Since decomposition of the ring structure is reflected in the loss of selective absorption, these two types of photochemical inactivation may be distinguished experimentally.