Effective enzymatic caffeoylation of natural glucopyranosides

• Methyl β-d-glucopyranoside, salidroside and arbutin were enzymatically caffeoylated.
• Lipozyme TL IM catalyzed regioselective caffeoylation of the glucosyl acceptors.
• Robustaside B was synthetized enzymatically for the first time.

Reaction system was developed for enzymatic caffeoylation of model saccharidic acceptor methyl β-d-glucopyranoside to obtain exclusively methyl 6-O-caffeoyl-β-d-glucopyranoside. Reaction with starting concentration of acceptor 0.2 M provided 73% yield of purified product within 17 days. Reactions with low acceptor concentrations (0.04 and 0.08 M) run to the completion within 7 days. Such highly effective and regioselective reaction was promoted by Lipozyme TL IM in tert-butanol, using vinyl caffeate as acylation donor. The optimized reaction conditions were used in preparative caffeoylation of natural substances—arbutin and salidroside, giving 75% of 6-O-caffeoylated arbutin (robustaside B) and 74% of 6-O-caffeoylated salidroside as the only products after 12 and 16 days, respectively.

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