Vitamin D<sub>5</sub> (sitocalciferol) is a form of vitamin D.
Analogs of calcitriol, a form of vitamin D<sub>3</sub>, have been proposed for use as antitumor agents. Studies on vitamin D<sub>3</sub> have shown inhibition of cell proliferation in prostate cancer, but high doses of vitamin D<sub>3</sub> result in hypercalcemia. The effects of vitamin D<sub>5</sub> on prostate cancer have also been studied, and unlike vitamin D<sub>3</sub>, vitamin D<sub>5</sub> does not cause hypercalcemia while inhibiting tumor cell proliferation. The most researched analogue of vitamin D<sub>5</sub> as an antitumor agent is 1ñ-hydroxyvitamin D<sub>5.</sub>
1ñ-Hydroxyvitamin D<sub>5</sub> is a chemical derivative of vitamin D<sub>5</sub>. The motive to study 1ñ-hydroxyvitamin D<sub>5</sub> as a potential pharmaceutical drug stemmed from the tendency of calcitriol, a natural metabolite produced in the kidney, to cause toxic hypercalcemia in patients when dosed at concentrations needed to interrupt prostate cancer cells' cycle and stimulate apoptosis. And while supplementation with dexamethasone decreases hypercalcemia, bypassing it with an equally effective tumor suppressant would reduce patient cost and stress. Thus, the therapeutic effects of 1ñ-Hydroxyvitamin D<sub>5</sub> as a potential antitumor agent without the side effects of calcitriol became a topic of study.
1ñ-Hydroxyvitamin D<sub>5</sub> was first synthesized in 1997 by researchers in the Department of Chemistry at the University of Chicago, under Robert M. Moriarty and Dragos Albinescu. By 2005, the group had revised its synthesis method for a more streamlined, higher yield-producing route. It involved the photochemical conversion of precursor 7-dehydrositosteryl acetate to contain a conjugated triene system, a hallmark of this analog, followed by hydroxylation, photoisomerization, and deprotection steps. Their overall yield was 48%.