The metabolites of steroids which contain alkyl side chains are a very important classof biologically-active compounds. For example the activation of vitamin D and conversion of cholesterol to the steroid sex hormones both involve the hydroxylation of the alkyl side chain. A major problem in the study of these metabolites is the preparation of suthentic samples, analogs and labeled compounds. Few methods exist for control of stereochimistry in the alkyl side chain. The major goals of this proposal are to develop efficient and stereoselective methods for the attachment of side chains to readily available 17- and 20-keto steroids, to control carbon-carbon bond stereochemistry in the side chain and to stereospecifically provide functionally-substituted side chain analogs. These methods should provide ready access to stereochemically defined steroid metabolites and labeled compounds for biological testing and for pharmaceutical studies. The methods and materials developed as a result of this proposed will be made available to researchers studying the metabolism of cholesterol and other enzymatic reactions of steroid side chains.