NEW THIOXANTHENE AND SERENOXANTHENE DERIVATIVE

摘要

Compounds of the formula IMAGE (I) wherein R1-R4 is hydrogen or chlorine, R5 is -COOMe or -SO3Me, Me is an alkali metal cation and X is oxygen, sulfur or selenium, photosensitizers for the conversion of tachysterol into previtamin D are described. The tachysterol content in mixtures of previtamin D and tachysterol can be greatly reduced by visible light irradiation in the presence of such photosensitizers.