A total of 14 ocotillol-type ginsenosides were conveniently synthesized employing glycosylation of ocotillol sapogenin derivatives with glucosyl ortho-alkynylbenzoate donors under the promotion of a gold(I) catalyst as the key step. Relying on a rational protecting group strategy and the unexpected regioselectivity of the glycosylation of the 3,25-diol sapogenins (2a/2b, 5a/5b) for the tertiary 25-OH, mono 3-O-glucosyl ocotillol-PPD, 6-O-glucosyl ocotillol-PPT, 25-O-glucosyl ocotillol-PPD/PPT and 3,25-di-O-glucosyl ocotillol-PPD/PPT ginsenosides were prepared in which the configuration at the C-24 is either R or S.

Highlights•Synthesis of well-defined Nerium indicum RG-I fragments for the first time.•New method for the introduction of α-linked galacturonic acid moieties reported.•Highly stereoselective formation of α-d-GalA-linkage with GalA N-PTFAI donors.Three trisaccharides, one pentasaccharide, and one heptasaccharide, namely α-d-GalA-(1→2)-α-l-Rha-(1→4)-β-d-GalA-OC3H7 (1), α-l-Rha-(1→4)-α-d-GalA-(1→4)-β-d-GalA-OC3H7 (2), α-d-GalA-(1→4)-α-d-GalA-(1→2)-α-l-Rha-OC3H7 (3), α-d-GalA-(1→2)-α-l-Rha-(1→4)-α-d-GalA-(1→2)-α-l-Rha-(1→4)-β-d-GalA-OC3H7 (4), and α-d-GalA-(1→2)-α-l-Rha-(1→4)-α-d-GalA-(1→2)-α-l-Rha-(1→4)-α-d-GalA-(1→2)-α-l-Rha-(1→4)-β-d-GalA-OC3H7 (5), which are relevant to the fragments of the rhamnogalacturonan of Nerium indicum, were concisely synthesized. The syntheses feature highly stereoselective formation of the α-d-GalA-linkage with GalA N-phenyltrifluoroacetimidates as donors.