| Popis: |
A partial synthesis of cincholic acid from oleanolic acid has been completed. Photolysis of the nitrite ester of 12α-hydroxyoleanolic acid acetate lactone gave inter alia the expected 27-oxime which, with nitrous acid, afforded the 27-nitrimine. Since this nitrimine was resistant to normal hydrolytic conditions new methods for the conversion of nitrimine to aldehyde were developed. The 27-aldehydo-12α-hydroxyoleanolic acid acetate lactone thus obtained unexpectedly existed in the open (unmasked) form. Conversion to the diacetate and oxidation gave, after methylation, the 27-carboxylic acid methyl ester. A novel reduction procedure applied to this compound then afforded cincholic acid isolated, after methylation, as its dimethyl ester. The rather limited scope of this reductive elimination procedure has been explored in other compounds of appropriate structure. |
