Studies on vitamin D (calciferol) and its analogues. 10. Side-chain analogues of 25-hydroxyvitamin D3

A homologous series of side-chain analogues of 25-hydroxyvitamin D3 (25-hydroxycholecalciferol) in which the length of the side chain is modified while maintaining its characteristic tertiary hydroxyl moiety has been synthesized. The following five analogues have been prepared and characterized: pentanor-25-OH-D3 (2a), trinor-25-OH-D3 (2b), dinor-25-OH-D3 (2c), nor-25-OH-D3 (2d), and homo-25-OH-D3 T2e). Biological assays in vivo of intestinal calcium absorption and bone calcium mobilization in the chick of the five analogues revealed that the homo analogue 2e exhibited a significant biological response relative to the -D (vitamin D3) control. Compared to the natural vitamin D3, 2e is as active in its ability to mobilize bone calcium and is about half as effective in stimulating intestinal calcium transport. The remaining analogues (2a-d) exhibited no significant activity in either assay, although the nor analogue 2d was previously observed to exhibit antimetabolite activity.