Glycosyl N-Tosyl Benzimidate as a New Building Block for Chemical Glycosylation

Abstract

Seven novel glycosyl N-tosyl benzimidates were prepared by the reactions of the corresponding hemiacetals with imidoyl chloride in 55–88% yields, which were smoothly converted to glycosides, upon treatment with alcohols and catalytic TMSOTf, in 57–99% yields.

Key words

glycosylation - glycosyl N-tosyl benzimidate - glycosyl donor - oligosaccarides synthesis - saponins synthesis

• References

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• 10 A Typical Procedure for the Preparation of Glycosyl N-Tosyl Benzimidate To a solution of mannosyl hemiactal (500 mg, 0.84 mmol) in acetone (3 mL) was added K₂CO₃ (290 mg, 2.10 mmol, 2.50 equiv) and N-tosylbenzimidoyl chloride (296 mg, 1.0 mmol, 1.20 equiv) at ambient temperature. After stirring for 2 h the solid was filtered off, and the filtrate was concentrated under vacuum, and the residue was purified by silica gel chroma-tography (EtOAc–PE = 1:4) to give imidate 2a as a white solid (617 mg, 0.72 mmol, 86%). [α]_D ²⁰ = –30.1 (c 1.09 CHCl₃). ¹H NMR (600 MHz, CDCl₃): δ = 8.11 (d, J = 7.2 Hz, 2 H), 8.03 (m, 4 H), 7.93 (d, J = 7.14 Hz, 2 H), 7.82 (m, 4 H), 7.68 (t, J = 7.68 Hz, 1 H), 7.59 (m, 4 H), 7.50 (t, J = 7.14 Hz, 1 H), 7.43 (m, 5 H), 7.35 (t, J = 7.74 Hz, 2 H), 7.28 (d, J = 8.28 Hz, 2 H), 7.20 (d, J = 8.28 Hz, 2 H), 6.38 (d, J = 1.62 Hz, 1 H), 6.20 (t, J = 10.44 Hz, 1 H), 5.91 (m, 2 H), 4.73 (dd, J = 2.16, 12.06 Hz, 1 H), 4.59 (m, 1 H), 4.47 (dd, J = 4.38, 12.12 Hz, 1 H), 2.34 (s, 3 H). ¹³C NMR (150 MHz,CDCl₃): δ = 166.5, 166.1, 165.6, 165.4, 164.9, 143.5, 138.6, 133.9, 133.8, 133.5, 133.4, 133.3, 130.0, 129.9, 129.8, 129.5, 128.8, 128.7, 128.65, 128.6, 128.5, 127.0, 94.6, 71.8, 69.7, 68.9, 66.0, 62.5, 21.6. ESI-MS: m/z = 876.2 [M + Na]⁺. HRMS: m/z calcd for C₄₈H₃₉O₁₂NNaS [M + Na]⁺: 876.2091; found: 876.2085
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