Description | 25-Hydroxytachysterol3 is a hydroxylated derivative of tachysterol3. 25-hydroxytachysterol is converted to 25-hydroxyprevitamin D3, which is then converted to the hydroxyvitamin D3 through a thermally induced rearrangement. It is now established that, during exposure to sunlight, the cutaneous reservoir of 7-dehydrocholesterol converts to previtamin D3. Once this thermally labile previtamin is formed, it undergoes a temperature-dependent isomerization to vitamin D3 over a period of 3 days. The plasma vitamin-D binding protein preferentially translocates vitamin D3 from the skin into the circulation. During prolonged exposure to the sun, the accumulation of previtamin D3 is limited to about 10 to 15% of the original 7-dehydrocholesterol content because the previtamin photoisomerizes to 2 biologically inert photoproducts, lumisterol3 and tachysterol3. (PMID 12617640). 25-Hydroxytachysterol3 is characterized by antirachitic activity and by its ability to elevate serum calcium concentration in conditions of hypoparathyroidism. 25-Hydroxytachysterol3 can be used in the preparation of 25-hydroxydihydrotachysterol 3 (25-OH-DHT3) is considered an effective adjunct in the treatment of hypoparathyroidism, particularly where rapid action in elevating serum calcium concentration is being sought. (25-OH-DHT3) exhibits substantially greater antirachitic activity than DHT 3 |