Isolation of Lanosterol From “Isocholesterol”

Lanosterol (A8J4-lanostadien-38-01) has recently been shown to be an intermediary product in the biological transformation of squalene to cholesterol (1,2).For the continuation of this work, pure lanosterol in relatively large quantities was required, and it therefore became necessary to develop a practical method for securing this hitherto very scarce material.The Cao sterol fraction of yeast contains lanosterol (kryptosterol) as the sole component (3), but ordinarily in concentrations too small for preparative purposes.The mixture of wool fat sterols known as Yisocholesterol" consisting of lanosterol, dihydrolanosterol, and, in smaller amounts, of the conjugated dienes agnosterol and dihydroagnosterol offers an abundant source of C3,, sterols which, however, has proved difficult to resolve by crystallization or chromatography (4).Recently, the isolation of lanosterol from "isocholesterol" by way of the 24-bromo derivative has been reported (5).It was noted in this laboratory that treatment of lanosterol in ether with a concentrated solution of bromine in acetic acid as described by Do&e and Garratt (6) produces 24, 25-dibromo-As-lanosten-3/3-ol which precipitates quantitatively from solution.Likewise, on bromination of "isocholesterol" under the same conditions the sparingly soluble lanosterol dibromide separated rather cleanly from the mixture.For purification, the product is acetylated with acetic anhydride and acetyl chloride and crystallized.Following debromination and saponification, pure lanosterol is obtained in a yield of approximately 35 to 40 per cent of the estimated lanosterol content of "isocholesterol."The physical properties of the free sterol, of the acetate, and of the a-ketone were identical with those reported in the literature for A8*24-1anostadien-3P-ol and its derivatives.The product contained less than 1 per cent conjugated dienes (agnosterol and dihydroagnosterol) on the basis of ultraviolet measurements.Dihydrolanosterol acetate (3/?-acetoxy-A*-lanostene) may be isolated by acetylation and chromatography of the mother liquors obtained from the "isocholesterol" bromination.Since agnosterol acetate can be separated from "isocholesterol" acetate by fractional crystallization (3, 2), and since dihydroagnos-