Preparation of\nRare Dehydrated Protopanaxadiol Ginsenosides\nfrom <i>Panax notoginseng</i> Leaves by Confined Microwave-Driven\nTransformation

Rare dehydrated ginsenosides barely exist in natural\nginseng plants.\nHerein, the confined microwave technique was utilized to transform\nthe main ginsenosides of <i>Panax notoginseng</i> leaves\n(PNL) into dehydrated ginsenosides. The main microwave-treated products\nof dried PNL are dehydrated ginsenoside Rk1, Rg5, notoginsenoside\nSFt3, and SFt4. Comparatively, the main microwave-treated products\nof water preimmersed PNL are dehydrated ginsenoside Rk2, Rh3, notoginsenoside\nSFt3, and SFt4. The impacts of solvent, solid–liquid ratio,\nmicrowave temperature and duration on the yield of dehydrated ginsenosides\nwere explored. Based on theoretical calculation, primary ginsenosides\nin water preimmersed PNL are more prone to deglycosylation at the\nC-20 site and dehydration elimination reactions at the side chain\nduring microwave treatment. Moreover, reference compounds were used\nto verify ginsenoside transformation pathway, and the dehydrated ginsenosides\nwere individually purified and identified. In short, this study elucidates\nnovel approach for preparing rare Δ20(21)- and Δ20(22)-dehydrated\nprotopanoxadiol ginsenosides.