Synthesis of 20 S -Protopanaxatriol β-D-Glucopyranosides

Condensation of 20S-protopanaxatriol (3β,6α,12β,20S-tetrahydroxydammar-24-ene) ( 1 ) with 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide ( 2 ) in the presence of Ag 2 O in CH 2 Cl 2 gave a mixture of acetylated 3-, 12-, 20-, 3,12-di-, and 3,20-di-O-β-D-glucopyranosides 3 – 7 that was dominated by 3-O-β-Dglucopyranoside tetraacetate 3 (47%). Subsequent deacetylation by sodium methoxide produced free β-D-glucopyranosides 8 – 12 , three of which were identical to chikusetsusaponin-L 10 , ginsenoside-F 1 , and ginsenoside-Ia, which were isolated earlier from leaves of Panax japonicus and P. ginseng. 3-Mono- and 3,12-di-O-β-D-glucopyranosides 8 and 11 were prepared for the first time.