Synthesis of ginsenoside Rg3, a minor constituent of Ginseng radix.

Glycosylation of 12beta-acetoxy-dammar-24-en-3beta,20(S)-diol (4), with hepta-O-acetyl-alpha-sophorosyl bromide (5) under catalysis by Ag2CO3 or Ag2O afforded a chromatographically unseparated mixture of the alpha- and beta-linked octaacetates 6 and 7 in an approximately 2.5:1 ratio. After deprotection and chromatographic purification, the free alpha- (8) and beta-glycosides (9) were obtained. Sophoroside 9 was identical in all respects with ginsenoside Rg3, the minor component of Ginseng Radix rubra. All compounds were fully characterized by 1H and 13C NMR spectroscopy.