Molecules, Vol. 21, Pages 1139: Structural Modifications of Deoxycholic Acid to Obtain Three Known Brassinosteroid Analogues and Full NMR Spectroscopic Characterization (Molecules)

An improved synthesis route for obtaining known brassinosteroid analogues, i.e., methyl 2?,3?-dihydroxy-6-oxo-5?-cholan-24-oate (11), methyl 3?-hydroxy-6-oxo-7-oxa-5?-cholan-24-oate (15) and methyl 3?-hydroxy-6-oxa-7-oxo-5?-cholan-24-oate (16), from hyodeoxycholic acid (4) maintaining the native side chain is described. In the alternative procedure, the di-oxidized product 6, obtained in the oxidation of methyl hyodeoxycholate 5, was converted almost quantitatively into the target monoketone 7 by stereoselective reduction with NaBH4, increasing the overall yield of this synthetic route to 96.8%. The complete 1H- and 13C-NMR assignments for all compounds synthesized in this work have been made by 1D and 2D heteronuclear correlation gs-HSQC and gs-HMBC techniques. Thus, it was possible to update the spectroscopic information of 1H-NMR and to accomplish a complete assignment of all 13C-NMR signals for analogues 5-16, which were previously reported only in partial form.