Synthesis of oleanolic acid glycoconjugates

Four glycoconjugates (D-glucose, D-galactose, D-lactose and D-glucuronic acid) of oleanolic acid were synthesized through a facile approach. Firstly, D-glucose, D-galactose and D-lactose were converted into benzoyl group protected glycosyl trichloroacetimidates (10a similar to 10c) as donors. D-glucuronic acid was converted into methyl (tri-O-acetyl-alpha-D-glucopyranosyl bromide) -uronate (10d) as donor. Secondly, oleanolic acid was converted into methyl N-(3-hydroxylolean-12-en-28-oyl)-6-aminohexanoate (6). Then the coupling of the sugar moieties (10a similar to 10c) to 3-OH of 6 was promoted by trimethylsilyl trifluoromethanesulfonate (TMSOTf). AgOTf was used as the promoter in the glycosylation of 10d with 6. Finally, deprotection of the corresponding glycocongjugates afforded the target products 132 similar to 13d. The structures of all products were characterized by IR, H-1 NMR, C-13 NMR, DEPT, tow-dimensional shift-correlated spectra (COSY, HMQC) and HRMS.