An Investigation of the Triterpene alpha-Amyrin and of 6-Chloro-3-Benzoyloxy-Cholest-4-Ene

Part I - alpha-Amyrin. Investigations were carried out on the naturally occurring triterpene alpha-amyrin, C30H50O, with a view to elucidating its structure. Oxidation of the hydrocarbon 1-alpha-amyradiene, C30H48, by various reagents, failed to give homogeneous products or reproducible results though potassium permanganates gave material analysing as C30H48O. Both hydrogen peroxide and ozone have been shown to react with alpha-amyrin esters to give oxides which may be isomerised to saturated ketones. The compound described in the literature as alpha-amyranonyl benzoate is, in fact, alpha-amyrin benzoate oxide. Both the oxides and ketones may be partially dehydrogenated by bromine to give iso-alpha-amyrenonyl esters. Reduction of alpha-amyrone by three different methods gave the same hydrocarbon alpha-amyrene, C30H50, in every case. This was oxidised to alpha-amyrene oxide which could be isomerised to the saturated ketone iso-alpha-amyranone (also obtained by Kishner-Wolff reduction of alpha-amyrane dione) or reduced to the alcohol iso-alpha-amyranol. Attempts to chlorinate this alcohol so that the halogens-ted derivative might be reduced to the saturated hydrocarbon alpha-amyrane, resulted in every case in dehydration, and alpha-amyrene was formed. In hydrogen peroxide oxidations of alpha-amyrin esters high melting by-products are formed together with the oxide, but investigation of these failed to elucidate their nature. It was hoped to prepare various a-diketones and ketols so that these could be treated with periodic acid, Ring opening might occur giving acid products. alpha-amyradionol, alpha-amyradionyl acetate and alpha-amyradondiol monobenzoate were all prepared. The first of these was made by an improvement of a published method, and the last (an alpha-ketol) by replacement of bromine by hydroxyl in bromo-alpha-amyranonyl benzoate. These, on treatment with periodic acid, gave neutral products which were apparently isomeric with the starting material, but without the original ketol, or dione, grouping. Reduction of alpha-amyrin benzoate oxide gave the compound described in the literature, but the action of various reducing agents on alpha-amyranonyl benzoate gave non-homogenous products. New methods of investigation of the problem were examined, and the amyrin nucleus was found to be stable to alkali at high temperature, but completely broken down by aluminium trichloride. Many other compounds were prepared, among them a sulphite of alpha-amyrin, and an examination of molecular rotation differences between some of the compounds and their esters showed that changes in the neighbourhood of the double bond appear to exert a vicinal action on the hydroxyl group. Part II. 6-Chloro-3-Benzoyloxy-Cholest-4-ene. This compound, formulated as above by Spring and Swain (J. (1939),1356) as 4-chloro-3-benzoyloxy-cholest-5-ene by Petrow, Rosenheim and Starling (J. (1943),135) and as 3-chloro-4-benzoyloxy-cholest-5-ene by Berg and Wallis, (J. Biol. Chem. (194b)162(3),683) was investigated. A synthesis of 3-chloro-4-hydroxy-cholest-5-ene was carried out by the action of selenium dioxide on cholesteryl chloride, and a new synthesis of 6-chloro-3-acetoxy-cholest-5-ene achieved by the action of phosphorus pentachloride on 6-keto-cholestanyl acetate. Degradative experiments on Spring and Swain's compound by way of its oxide failed to give the required products because of ready loss of halogen, but some new light has been thrown on the problem. A comparison of the optical rotations of the compound under investigation (as acetate) and 3-chloro-4-acetoxy-cholest-5-ene leads to the belief that Petrow, Rosenheim and Starling's formulation may be correct