Indium(III) Iodide-Catalyzed Stereoselective Synthesis of β-Glucopyranosides by Using a Glucosyl Fluoride Donor with 2-O-Benzoyl-3,4,6-Tri-O-Benzyl Protection

Abstract

We have developed a novel protocol for glucosylation by adopting a glucosyl fluoride donor with 2-O-benzoyl-3,4,6-tri-O-benzyl protection. The protocol is useful for the ready assembly of β-linked functional glycoconjugates, and the reaction accommodates a broad range of substrates. Conveniently, water-tolerant and commercially available InI₃ is used as a catalyst, and no other additional reagent is required. The method involves an interesting process for glucosyl fluoride activation and, in particular, permits the stereoselective construction of partially benzylated glucopyranosides carrying a selectively removable 2-O-benzoyl group, which hold great potential as glycosyl receptors for building further 1,2-glycosidic linkages.

Key words

indium triiodide - glucopyranosides - glucosyl fluoride - ­stereoselectivity - benzoylation

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• 13 (2-Trimethylsilyl)ethyl 2-O-Benzoyl-3,4,6-tri-O-Benzyl-β-d-glucopyranoside; Typical Procedure 2-(Trimethylsilyl)ethanol (0.12 mmol) was added to a solution of glucopyranosyl fluoride G (56 mg, 0.1 mmol) in anhyd CH₂Cl₂ (2 mL) containing InI₃ (5 mg, 0.01mmol), and the mixture was stirred for 2 h at r.t. When the reaction was complete (TLC), the mixture was concentrated under reduced pressure and the resulting residue was purified by flash chromatograph [silica gel, PE–EtOAc (4:1)] to give a colorless oil; yield: 52 mg (98%). ¹H NMR (400 MHz, CDCl₃): δ = 8.02 (d, J = 7.2 Hz, 2 H), 7.56 (t, J = 7.2 Hz, 1 H), 7.43 (t, J = 7.6 Hz, 2 H), 7.38–7.26 (m, 8 H), 7.21–7.18 (m, 2 H), 7.12 (s, 5 H), 5.30–5.23 (m, 1 H), 4.82 (d, J = 10.8 Hz, 1 H), 4.73 (d, J = 11.2 Hz, 1 H), 4.66 (d, J = 2.4 Hz, 1 H), 4.63 (d, J = 3.6 Hz, 1 H), 4.59 (d, J = 2.8 Hz, 1 H), 4.58–4.51 (m, 2 H), 3.99 (dd, J = 10.0, 5.6 Hz, 1 H), 3.85–3.70 (m, 4 H), 3.59–3.48 (m, 2 H), 0.85 (td, J = 14.0, 12.0, 6.4 Hz, 2 H), –0.09 (s, 9 H). ¹³C NMR (100 MHz, CDCl₃): δ = 165.1, 138.1, 137.9, 137.8, 132.9, 130.2, 129.8, 128.4, 128.4, 128.3, 128.2, 128.0, 128.0, 127.8, 127.7, 127.6, 100.6, 82.9, 78.1, 75.2, 75.0, 73.9, 73.5, 68.9, 67.1, 18.0, –1.5. HRMS (ESI): m/z [M + H]⁺ calcd for C₃₉H₄₇O₇Si: 655.3091; found: 655.3092.