Determination of astragalosides in the roots of Astragalus spp. using liquid chromatography tandem atmospheric pressure chemical ionization mass spectrometry

A high-performance liquid chromatography tandem atmospheric pressure chemical ionization mass spectrometry method (HPLC-APCI-MS) has been developed for the characterization of astragalosides in the extracts of the roots of Astragalus spp. The [M - H](-) ions of astragalosides could be clearly observed in selected ion monitoring mode and APCI-MS-MS was used to further identify the structures of the astragalosides. Twelve astragalosides in the extracts of Radix Astragali obtained from Shandong in China were separated and identified. Using this method, astragalosides could be clearly identified and the profiles of these astragalosides could also be used to distinguish Astragalus spp. from different habitat regions.     

The biotransformation of astragalosides by a novel acetyl esterase from Absidia corymbifera AS2

Absidia corymbifera AS2 has been previously screened for effective biotransformation of astragalosides since it is able to catalyze the hydrolysis of acetyl ester moieties. In this study, an acetyl esterase from A. corymbifera AS2 was purified and its catalytic pathways were investigated. The purified enzyme was monomeric, with a molecular mass of 36 kDa, and with optimal activity observed at pH 8.0 and 35 °C. It was stable within pH 7.0–9.5 and at temperatures lower than 45 °C. The K_m and V_max values for p-nitrophenyl acetate was estimated to be 3.76 and 17.64 mmol (min mg)⁻¹, respectively. We found that this enzyme can hydrolyze the acetyl groups at positions O-2 or O-3 of xylopyranosyl residue at the C-3 position of AS-I, isoAS-I, AS-II and isoAS-II, and convert these all to ASI. The pathways of deacetylation catalyzed by this enzyme were also clarified for the first time: AS-II→ASI, isoAS-II→AS-II→ASI, AS-I→(AS-II, isoAS-II)→ASI and isoAS-I→AS-II→ASI. In summary, an acetyl esterase from A. corymbifera AS2 was extracted, which showed unique enzymatic characteristics and enabled clarification of the biotransformation pathways of astragalosides. This enzyme has potential industrial applications, especially for utilizing abundant astragaloside precursors for the production of rare ASI.     

A novel biotransformation of astragalosides to astragaloside IV with the deacetylation of fungal endophyte Penicillium canescens

Under the deacetylation of fungal endophyte Penicillium canescens, which was isolated from pigeon pea, a novel and highly efficient biotransformation method of astragalosides to astragaloside IV in Radix Astragali was investigated. After single factor tests of the biotransformation procedure, the optimum biotransformation conditions were confirmed as the liquid solid ratio 20:1, the biotransformation temperature 30 °C, time 36 h and pH 7, respectively. Final content of astragaloside IV in Radix Astragali reached 7.66 ± 0.44 mg/g, which was 5.51-fold to that of untreated one and contents of astragaloside I and astragaloside II significantly decreased. The immobilized Ca-alginate gel beads with P. canescens could be reused at least for 13 runs. This is the first report that fungal endophyte was applied for the biotransformation of astragalosides to astragaloside IV in Radix Astragali and this novel high-efficiency biotransformation method will be an alternative to enhance the content of astragaloside IV in Radix Astragali in commercial process.