Kinetic and HPLC-MS analyses revealed the catalysis behavior of total saponins from MOF-based solid acids

Diosgenin is an influential intermediate for the preparation of various steroidal drugs, and has the reputation of “mother of hormones” and “medicinal gold”. In this work, UiO-66-NH₂ is quaternary ammoniated by functional modification of 3,5-diamino-1,2,4-triazole and then ion-exchanged with different concentrations of CF₃SO₃H to produce ionic liquids grafted MOF-based solid acids, namely UNS-0.96 and UNS-1.28, where 0.96 and 1.28 represent the volume (mL) of CF₃SO₃H consumed. They were used to extract diosgenin from total saponins, suggesting that UNS-1.28 can achieve high diosgenin extraction with a shorter time (2.5 h) and a lower addition amount (0.15 g) and the optimum diosgenin yield of 22.5 % was obtained. The extraction efficiency is higher than that obtained by hydrolysis of 2 M H₂SO₄ and commercial ion exchange resins. Kinetic studies have shown that the catalytic of total saponins by UNS-1.28 is in perfect agreement with the pseudo-first-order kinetic model, and that the activation energy required for extraction is low, only 2.83 × 10⁴ J/mol. In addition, HPLC-MS was used to analyze the total saponins and products at different extraction times. The fragmentation peak types and relative abundances of the different extracted products are compared to reveal the cleavage pathways of the total saponins and the optimal period of diosgenin production, and to suggest the mechanism of action of the solid acid on the total saponins.