Acyl Sulfonamide Catalysts for Glycosylation Reactions with Trichloroacetimidate Donors

Abstract

The acyl sulfonamide functional group has been found to serve as a catalytic moiety for the glycosylation of several alcohols when glycosyl donors based on trichloroacetimidates are employed.

Key words

glycosylation - hydrogen bond - trichloroacetimidate - organocatalysis

References

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• 6a

  See ref. [5a]

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7

Caution: picric acid is a potentially explosive compound when thoroughly dried (water content <10%). We did not observe any difficulties of this type during these experiments.

11

Compounds 3 and 4 were prepared by the reaction of l-proline methylester with either 4-chlorophenylsulfonyl isocyanate or p-toluenesulfonyl isocyanate according to the following procedure: To a solution of l-proline methylester hydrogen chloride (48.0 mg, 0.289 mmol) in CH₂Cl₂ (720 µL) stirring at 0 °C was added Et₃N (40.0 µL, 0.289 mmol). Isocyanate was then added dropwise and the reaction was allowed to warm to 25 °C. The reaction was allowed to stir for 30 min at 25 °C and was then diluted with 5 mL of CH₂Cl₂ and washed with 1 N HCl. The organic layer was dried over Na₂SO₄ and concentrated in vacuo. The resulting residue was chromatographed on silica gel with 0-5% MeOH/CH₂Cl₂ (>95% yield). Data for 3: ¹H NMR (400 MHz, CDCl₃): δ = 7.96 (d, J = 8.4 Hz, 2 H), 7.32 (d, J = 8.1 Hz, 2 H), 4.40 (dd, J = 8.4, 3.9 Hz, 1 H), 3.70 (s, 3 H), 3.56-3.34 (m, 2 H), 2.43 (s, 3 H), 2.20-1.81 (m, 4 H). ¹³C NMR (100 MHz, CDCl₃): δ = 172.2, 150.5, 144.4, 136.3, 129.4, 128.3, 59.1, 52.5, 46.5, 29.5, 24.5, 21.6. IR (film): 3245, 2948, 1747, 1676, 1456, 1379, 1325, 1171 cm^-1. TLC: R_f = 0.50 (10% MeOH/CH₂Cl₂). Exact mass calcd for [C₁₄H₁₈N₂O₅NaS] requires m/z 349.0834. Found: 349.0827 (ESI+). Data for compound 4: ¹H NMR (400 MHz, CDCl₃): δ = 8.03 (d, J = 8.9 Hz, 2 H), 7.50 (d, J = 8.8 Hz, 2 H), 4.41 (dd, J = 8.7, 3.8 Hz, 1 H), 3.82-3.63 (m, 1 H), 3.72 (s, 3 H), 3.54-3.34 (m, 1 H), 2.20-1.86 (m, 4 H). ¹³C NMR (100 MHz, CDCl₃): δ = 172.0, 150.4, 139.7, 137.4, 129.5, 128.8, 59.1, 52.3, 46.5, 29.4, 24.1. IR(film): 3245, 2954, 1747, 1670, 1456, 1379, 1183 cm^-1. TLC: R_f = 0.40 (10% MeOH/CH₂Cl₂). Exact mass calcd for [C₁₃H₁₅ N₂O₅Na₁S₁C_l1] requires m/z 369.0288. Found: 369.0282 (ESI+).

12

All compounds gave satisfactory analytical data.

13

The general experimental procedure is as follows: Trichloroacetimidate 1 (50.0 mg, 0.0730 mmol) was suspended in methylene chloride (300 µL). The glycosyl acceptor (0.0487 mmol) was then introduced, followed by the addition of activated 4 Å molecular sieves (50.0 mg). The solution was allowed to stir at 25 °C for 10 min upon which a stock solution of catalyst was added (50.0 µL, 0.00730 mmol). When the reaction was judged to be finished by TLC, the suspension was filtered through a layer of celite and concentrated in vacuo. The resulting residue was subjected to flash chromatography on silica gel, eluting with 5% EtOAc/hexanes. The products are isolated as a mixture of α/β anomers, which could be assigned by ¹H NMR spectroscopy.

15

(a) Characterization data for compound 6: α-anomer: ¹H NMR (400 MHz, CDCl₃): δ = 7.36-7.12 (m, 20 H), 4.99 (d, J = 11.0 Hz, 1 H), 4.84-4.75 (m, 4 H), 4.66-4.59 (m, 2 H), 4.47 (d, J = 12.1 Hz, 2 H), 3.99 (t, J = 9.3 Hz, 1 H), 3.79-3.72 (m, 2 H), 3.65-3.54 (m, 4 H), 3.44-3.39 (m, 1 H), 1.64-1.58 (m, 2 H), 1.23 (bs, 10 H), 0.88 (t, J = 6.8 Hz, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 138.8, 138.2, 138.1, 137.8, 128.2, 127.9, 127.8, 127.7, 127.5, 127.4, 96.8, 82.1, 80.1, 77.8, 75.7, 75,1, 73.5, 73.1, 70.1, 68.6, 68.3, 32.0, 29.5, 29.4, 26.3, 22.8, 14.3. IR(film): 3089, 3063, 3030, 2926, 2856 cm^-1. TLC: R_f = 0.39 (20% EtOAc/hexanes). Anal. Calcd for C₄₂H₅₂O₆: C, 77.27; H, 8.03. Found: C, 76.94; H, 8.05. β-Anomer ¹H NMR (400 MHz, CDCl₃): δ = 7.36-7.14 (m, 20 H), 4.95 (t, J = 11.0 Hz, 2 H), 4 .80 (t, J = 11.4 Hz, 2 H), 4.72 (d, J = 11.0 Hz, 1 H), 4.63-4.51 (m, 3 H), 4.39 (d, J = 7.7 Hz, 1 H), 3.99-3.94 (m, 1 H), 3.75 (dd, J = 10.8, 2.0 Hz, 1 H), 3.69-3.43 (m, 6 H), 1.68-1.62 (m, 2 H), 1.42-1.26 (m, 10 H), 0.87 (t, J = 7.0 Hz, 3 H). ¹³C NMR (100 MHz, CDCl₃) δ = 138.5, 138.3, 138.0, 137.9, 128.2, 128.0, 127.8, 127.7, 127.6, 127.5, 127.4, 123.6, 84.7, 82.8, 77.9, 75.7, 75.0, 74.8, 73.4, 70.1, 69.0, 31.9, 29.9, 29.5, 29.4, 26.3, 22.8, 14.2. IR (film): 3087, 3063, 3032, 2927, 2857 cm^-1. TLC: R_f = 0.50 (20% EtOAc/hexanes). Anal. Calcd for C₄₂H₅₂O₆: C, 77.27; H, 8.03. Found: C, 77.00; H, 8.00.