Synthesis of oligosaccharide fragments of the rhamnogalacturonan of Nerium indicum Original Research Article

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.