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Synthesis of gentianine N-oxide by enzymatic hydrolysis of swertiamarin in the presence of hydroxylamine and reaction pathway to gentianine and gentianol

Fujii, Mikio, Kuramochi, Taiki, Nakakuki, Yuhi, Hatazawa, Rina, Konno, Kiju, Munakata, Tatsuo, Hirai, Yasuaki
Tetrahedron letters 2019 v.60 no.10 pp. 721-725
Swertia, antihypertensive effect, chemical structure, enzymatic hydrolysis, glycemic effect, hydrolysis, hydroxylamine, metabolites, organic compounds
Gentianine is a metabolite of gentiopicroside and swertiamarin. Several biological activities have been reported for gentianine, such as antiinflammatory and antidiabetic activity, and hypotensive effect. Gentiopicroside is found in 0.9–9.8% content in Gentian root or Gentian scabra root, and Swertiamarin is contained in Swertia herb in 2–10%. These natural products can be potential starting materials for the synthesis of gentianine. This study describes the β-glucosidase-catalyzed hydrolysis of gentiopicroside and swertiamarin in the presence of hydroxylamine to afford gentianine N-oxide, which can be a synthetic precursor of gentianine derivatives. Enzymatic hydrolysis of swertiamarin selectively afforded gentianine N-oxide in 81% yield, whereas gentiopicroside afforded gentianine N-oxide and gentianol N-oxide. Plausible reaction pathways leading to gentianine, gentianol, and their N-oxides were also investigated.