Green synthesis of zero-valent iron nanoparticles using <i>Flos Sophorae Immaturus</i> extract for the transformation of ginsenoside Rb1 to 25-OH derivatives

In this study, zero-valent iron nanoparticles (nZVI) were green synthesized through a one-pot thermal method using Flos Sophorae Immaturus (FSI) extract, and subsequently used for the heterogeneous transformation of ginsenoside Rb1 to prepare 25-OH ginsenoside derivatives. Detailed characterization of the synthesized FSI-nZVI revealed aggregated spherical nanoparticles with a size distribution ranging from 30 to 60 nm and multiple functional groups encapsulated on the surface. HPLC-MS analysis indicated that polyphenolic compounds such as rutin in the extract were involved in the green synthesis of FSI-nZVI and were responsible for these functional groups. In the transformation of ginsenoside Rb1 catalyzed by FSI-nZVI, the intermediate 20(S/R)-Rg3 and the final product 20(S/R)−25-OH-Rg3 were obtained via deglycosylation at the C20 position and hydration at the C24(25) double bond of Rb1. The transformation pathways were established as Rb1→20(S/R)-Rg3→20(S/R)−25-OH-Rg3 based on time-course experiments. Under optimized conditions, FSI-nZVI achieved a complete transformation of Rb1 to 25-OH-Rg3 epimers with 100% selectivity within 2 h, demonstrating superior transformation efficiency and selectivity compared to five commercial solid acid catalysts. This study provides a promising method for the green synthesis of efficient catalyst nZVI using biomass, and also facilitates the preparation of 25-OH rare ginsenosides with high efficiency and selectivity.