Efficient enzymatic preparation of esculentoside B following condition optimization by response surface methodology

• Efficient preparation of esculentoside B was achieved by biotransformation.
• β-d-glucosidase from snailase was used to perform such biotransformation.
• Response surface methodology was used to optimize the reaction conditions.
• Kinetic studies determined the catalytic efficiency in this preparation process.

Esculentoside B (EsB, also named phytolaccagenin 3-O-β-d-xylopyranoside), a pentacyclic triterpene isolated from herbal medicine Radix phytolaccae, has been found to possess multiple pharmacological activities. Nonetheless, the low content in nature and the difficulties in the total synthesis of EsB strongly limit its extensive investigations and further development as a drug candidate. This study aims to provide a practical method for highly efficient preparation of EsB using esculentoside A (EsA, phytolaccagenin 3-O-β-d-glucopyranosyl (1 → 4)-β-d-xylopyranoside) as the starting material. β-d-glucosidase from snailase was used to catalyze the formation of EsB, and the product was then purified and fully characterized by both HRMS and NMR. To prepare EsB in a more cost-effective way, response surface methodology (RSM) was used to explore the potential effects of the reaction conditions (such as reaction temperature, pH, enzyme load, and reaction time) on the conversion rates of EsA. The highest EsB yield of 0.66 mg/ml was obtained experimentally under optimized conditions as follows: temperature 48.28 °C, pH 6.4, enzyme load 4.43%, and reaction time 2.73 h. This result agreed well with the predicted yield of 0.68 mg/ml by RSM. The enzymatic kinetics of this biotransformation was characterized at the optimum pH and temperature. The S50 value was evaluated as 167.4 μM, while the Vmax value was 345.6 nmol/min/mg. In summary, this study provided a mild and practical method for the highly efficient preparation of EsB from EsA, which held great promise for large scale production of EsB.

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