A comparison of the biological properties of of androst‐5‐en‐3β‐ol, a series of (20R)‐ n ‐alkylpregn‐5‐en‐3β‐ols and 21‐isopentylcholesterol with those of cholesterol

The Δ 5 ‐sterol, androst‐5‐en‐3β‐ol, which has no side chain at C‐17, did not permit molting of the insect Heliothis zea , growth of either the protozoan Tetrahymena pyriformis , or the yeast Saccharomyces cerevisiae adapted to anaerobic conditions, nor was the sterol esterified by a mammalian microsomal ACAT preparation. However, the sterol did form a liposome with egg lecithin and, when fed to mice, did inhibit hepatic cholesterol synthesis. 21‐Isopentylcholesterol also formed a liposome but neither supported the growth of the yeast nor was metabolized by the protozoan. When sterols, 20(R)‐ n ‐alkylpregn‐5‐en‐3β‐ols, with side chains of varying lengths were added to the medium of the protozoan, maximal esterification with fatty acids occurred with the 20(R)‐ n ‐pentyl derivative, and maximal inhibition of tetrahymanol formation occurred with the n ‐butyl, n ‐pentyl and n ‐hexyl derivatives. In all of the assays, cholesterol showed a positive response, either permitting molting or growth, being metabolized, inhibiting sterol or tetrahymanol synthesis, or forming a liposome.