Analogs of 1,25-Dihydroxyvitamin D₃ and 25-Hydroxyvitamin D₃

Abstract

Following the discovery of 25-OH-D₃ interest has been generated in analogs of vitamin D possessing the 25-hydroxyl function. In a sense the dihydrotachysterols, the 5,6-trans-25-OH-D₃, and the isotachysterols discussed above can be considered as analogs of either 25-OH-D₃ or l,25-(OH)₂D₃. Because of the rotation of ring A about the 5,6 double bond, these compounds assume the role of analogs of l,25-(OH)₂D₃ especially since they cannot be 1-hydroxylated by the 1-hydroxylase of the kidney. It is sufficient to reaffirm that these compounds, although effective in the absence of kidneys, are very poor analogs of l,25-(OH)₂D₃, being less than 1/1,000 as active as

l,25-(OH)₂D₃. The dihydrotachysterols are of some interest because they represent a commercially available substitute for l,25-(OH)₂D₃ in the treatment of renal osteodystrophy, hypoparathyroidism, and other diseases where there is defective absorption and utilization of calcium.