S-Benzoxazolyl (SBox) Glycosides in Oligosaccharide Synthesis: Novel Glycosylation Approach to the Synthesis of β-d-Glucosides, β-d-Galactosides, and α-d-Mannosides

Abstract

Per-acetylated and per-benzoylated S-benzoxazolyl (SBox) glycosides have been synthesized and applied to highly efficient 1,2-trans glycosylation. Complete stereoselectivities and remarkably high yields were achieved for the synthesis of β-d-glucosides, β-d-galactosides, and α-d-mannosides. It was also de­monstrated that benzoylated ‘disarmed’ SBox glycosides could be selectively activated in the presence of both armed and disarmed ethyl thioglycosides. Convergent synthesis of the tetra­saccharide β-d-Glc-(1-6)-β-d-Gal-(1-6)-β-d-GlcNAc-(1-6)-α-d-GlcOMe was achieved in three sequential selective glycosylation steps.

Key words

carbohydrates - stereoselective synthesis - glycosyl­ation - chemoselectivity

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23

Selected analytical data for 22: ¹H NMR: 6.87-8.01 (m, 59 H), 5.80 (dd, 1 H, J = 9.5 Hz), 5.72-5.76 (m, 2 H), 5.66 (dd, 1 H, J = 7.8 Hz , 10.4 Hz), 5.6 (dd, 1 H, J = 8.4 Hz), 5.46 (dd, 1 H, J = 7.9 Hz, 9.7 Hz), 5.40 (dd, 1 H, J = 3.5 Hz, 10.4 Hz), 5.30 (d, 1 H, J = 8.4 Hz), 5.01 (d, 1 H, J = 7.8 Hz), 4.67 (dd, 2 H, J = 10.9 Hz), 4.66 (d, 1 H, J = 7.9 Hz), 4.56 (dd, 2 H, J = 12.2 Hz), 4.52 (dd, 1 H, J = 3.2 Hz), 4.26-4.36 (m, 3 H), 3.87-4.24 (m, 7 H), 3.62-3.77 (m, 4 H), 3.42-3.48 (m, 2 H), 3.34 (dd, 1 H, J = 3.1 Hz), 3.28 (dd, 1 H, J = 3.4 Hz, 9.6 Hz), 3.13 (m, 1 H), 3.06 (s, 3 H) ppm; ¹³C NMR: 166.94, 166.34, 166.30, 165.76, 165.59, 165.41, 165.30, 165.30, 127.70-138.98 (72 signals), 101.97, 101.38, 98.24, 98.12, 81.99, 79.99, 75.80, 75.25, 74.88, 74.28, 73.57, 73.19, 72.51, 71.94, 71.80, 70.58, 70.06, 69.62, 69.62, 69.42, 69.25, 69.04, 68.26, 68.07, 62.93, 55.30, 54.59, 29.92 ppm; HR-FAB MS [M + Na]⁺ calcd for C₁₁₀H₉₇NNaO₃₀ 1934.5993, found 1934.6022.