Selective glycosylation of steroidal saponins by Arthrobacter nitroguajacolicus

• A strain of Arthrobacter nitroguajacolicus was found to fructosylate furostan saponins.
• One or two β-fructosyls were added at the C6-OH of 26-O-β-d-glucopyranosyl of furostan saponins with 2,6-linkage.
• The ten glycosylated products are new compounds.
• Sucrose was used as a non-activated sugar donor.

In this study seven strains of the genus Arthrobacter were screened by biotransformation to discover glycosylating patterns on steroid saponins. A strain of Arthrobacter nitroguajacolicus (CPCC 203516) was found to have the ability of fructosylation. Crude enzyme of the strain was extracted for the further study of conversion characteristics and patterns. Sucrose was used as a non-activated sugar donor, and fifteen steroidal saponins were involved. Nine furostan saponins of the substrates were converted, and ten products were isolated and identified. Based on the HR-ESI-MS, 1D, and 2D NMR spectral data, one fructosyl was added to furostan saponins at C6-OH of 26-O-β-d-glucopyranosyl by A. nitroguajacolicus for all nine products. One product was distinguished by an additional fructosyl at the position of C6-OH on the first added fructosyl. Spirostan saponins of the substrates could not be converted. Steroidal saponins embracing a fructosyl are quite rare according to other reports based on similar studies. This study successfully converted furostan saponins into new compounds.

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