Glycosylation of 3β,6α,12β-trihydroxy-20R,25-epoxydammarane (panaxatriol) and its and 3, were synthesized for the first time.Key words: dammarane triterpenoids, panaxatriol, glycosylation, Panax ginseng C. A. Meyer, panaxatriol 3-O-β-Dglucopyranoside, panaxatriol 6-O-β-D-glucopryanoside, panaxatriol 12-O-β-D-glucopyranoside.Glycosides of dammarane triterpenoids are components of ginseng (Panax ginseng C. A. Meyer) extract and have for many years drawn attention due to the breadth and variety of their physiological activity [1][2][3][4][5][6][7][8]. Although the biological properties of ginseng extract have been studied and active components have been found, the mechanism of action of these compounds is still unknown and the structure-activity relationships have not been established. Observed differences in the properties of ginseng glycosides are often linked to the structuer of their aglycons. For example, the mechanisms of cytotoxicity for B16 melanoma cells differ greatly for ginsenosides Rh2 and Rh1, which have a single glucose on C-3 and C-6 but different aglycons [9, 10].One of the approaches to studying the structure-activity relationship is to synthesize compounds that are identical to the natural ones and those related to them for subsequent study of their properties using biological tests. Dammarane glycosides from P. ginseng are divided into two groups depending on the aglycon structure. These are glycosides of 20S-protopanaxadiol and those of 20S-protopanaxatriol, which differs from the former by having an additional hydroxyl on C-6. We prepared semisynthetic glycosides of 20S-protopanaxadiol and their analogs by chemical transformation of betulafolientriol, a component of the extract of birch (Betula) leaves [11][12][13][14]. Then, they were tested biologically [15][16][17][18][19][20]. Unfortunately, compounds that could be used as starting materials for synthesizing 20S-protopanaxatriol glycosides were not found among the many dammarane triterpenoids isolated from Betula leaves [21]. The most suitable and relatively available compound for evaluating the reactivity of the C-6 hydroxyl of dammarane triterpenoids for glycosylation compared to the C-3 and C-12 hydroxyls was 3β,6α,12β-trihydroxy-20R,25-epoxydammarane (panaxatriol, 1), one of the acid-hydrolysis products of the total glycoside fraction from P. ginseng root [22]. O Br OAc AcO AcO AcOCH 2 5 1: R 1 = R 2 = R 3 = H; 2: R 1 = R 2 = Ac, R 3 = H; 3: R 1 = Ac, R 2 = R 3 = H; 4: R 1 = R 3 = H, R 2 = Ac 6: R 1 = GlcAc 4 , R 2 = R 3 = H; 7: R 1 = R 2 = H, R 3 = GlcAc 4 ; 8: R 1 = R 2 = Ac, R 3 = GlcAc 4 9: R 1 = Ac, R 2 = GlcAc 4 , R 3 = H; 10: R 1 = Ac, R 2 = H, R 3 = GlcAc 4 ; 11: R 1 = GlcAc 4 , R 2 = Ac, R 3 = H 12: R 1 = H, R 2 = Ac, R 3 = GlcAc 4 ; 13: R 1 = Glc, R 2 = R 3 = H; 14: R 1 = R 2 = H, R 3 = Glc 15: R 1 = R 2 = Ac, R 3 = Glc; 16: R 1 = Ac, R 2 = Glc, R 3 = H; 17: R 1 = Ac, R 2 = H, R 3 = Glc 18: R 1 = Glc, R 2 = Ac, R 3 = H; 19: R 1 = H, R 2 = Ac, R 3 = Glc; 20: R 1 = R 3 = H, R 2 = Glc