ABSTRACT
M asam i O kabe Process Research, Chemical Synthesis Department, Hoffmann-La Roche Inc., Nutley, New Jersey 07110-1199
Key words: vitamin D, photolysis
Vitamin D2 (1, ergocalciferol) and vitamin D3 (2, cholecalciferol), derived from ergosterol and cholesterol, respectively, are secosteroids, a family of compounds with broken steroid skeletons. Since ergosterol is a plant sterol and not produced in animals, the so-called ‘natural form of vitamin D ’ is 2 whose structure was elucidated by Windaus more than six decades ago.1 However, vitamin D3 (2) is also in reality not a ‘vitamin’ since this compound is produced in the skin :2 7dehydrocholesterol (3) derived from cholesterol undergoes a conrotatory opening of the diene ring upon exposure to sunlight (cleaving the C9-C10 single bond) to give previtamin D3 (4), followed by thermal conversion of 4 to give 2 (Figure 1).
