Sterol(s)
formed by
ultraviolet irradiation of any 5,7-diene-3b-sterol, which breaks the 9,10 bond,
but generally from
either or both of
ergosterol and
lumisterol to manufacture tachysterol2 (ertacalciol, (6E,22E)-9,10-secoergosta-5(10),6,8,22-tetraen-3b-ol) and from 7-dehydrocholesterol to manufacture tachysterol3 (tacalciol,(6E,3S)-9,10-secocholesta-5(10),6,8-trien-3b-ol). When reduced to the 5,7-diene (or 5,7,22-triene) form, dihydrotachysterol3 (10,19-dihydrocalciol) or dihydrotachysterol2 (10,19-dihydroercalciol),
antirachitic action appears. This property has been of
therapeutic interest,
but tachysterol is
being replaced by the true
vitamin D
hormone (calcitriol) and its derivatives.