A Method for Rapid Microsynthesis of Radioactive Cholesterol Esters.

WITH THE growing interest in the metabolism of cholesterol esters, procedures have been developed which frequently make desirable the use of chemically pure compounds. Some of the radioactive cholesterol esters are either commercially unavailable or expensive when made to order. The high cost of the starting materials (cholesterol-4-CI4, pure fatty acids) makes it desirable to have a good yield of the end products. A rapid and efficient chemical synthesis of various labeled cholesterol esters is presented. As early as 1930 Page and Rudy (1) prepared certain cholesterol esters ; however, their synthetic method required large amounts of starting materials and the yield was not reported. An efficient preparation of acyl chlorides was accomplished by Wood et al. (2). Fatty acids and oxalyl chloride were refluxed for several hours. Further refluxing of acyl chlorides with cholesterol produced the desired esters. Mahadevan and Lundberg (3) prepared cholesterol esters of polyunsaturated fatty acids by the ester interchange method, in which cholesteryl acetate and the methyl ester of fatty acids are reacted in the presence of sodium ethoxide as catalyst. Purification was achieved by the combined use of repeated crystallizations and column chromatography. Recently Deykin and Goodman (4) reported a method of preparation of small quantities of radioactive cholesterol esters. However, these authors did not prepare cholesteryl linolenate or cholesteryl arachidonat e. The acyl chlorides of palmitic, stearic, oleic, linoleic, linolenic, and arachidonic acids were prepared as follows. The fatty acid (1 mmole) was placed in a small Florence flask with a side arm and oxalyl chloride then added in approximately 3-fold M excess. The flask was immediately closed with a ground glass stopper and the air was evacuated by a water aspirator (30 mm Hg) connected to the Cholesterol Ester Prepared