What is "lumisterol"

n. Constituent of vitamin D1.

Lumisterol is a compound that is part of the vitamin D family of steroid compounds. It is the (9β,10α) stereoisomer of ergosterol and was produced as a photochemical by-product in the preparation of vitamin D, which was a mixture of vitamin D and lumisterol. Vitamin D can be formed from lumisterol by an electrocyclic ring opening and subsequent [[Sigmatropic reaction#.5B1.2C7.5D_Shifts|sigmatropic [1,7] hydride shift]].