A Short Synthetic Route to β-C-Glycosides of N-Acetylglucosamine

Stéphanie Rat; Stéphanie Norsikian

doi:10.1055/s-2006-939061

LETTER

A Short Synthetic Route to β-C-Glycosides of N-Acetylglucosamine

Stéphanie Rat, Stéphanie Norsikian*
Laboratoire de Chimie Organique Multifonctionnelle, UMR CNRS-UPS 8614 ‘Glycochimie Moléculaire’, Bât. 420, Université Paris Sud, 91405 Orsay Cedex, France
Fax: +33(1)69154715; e-Mail: stephnorsikian@icmo.u-psud.fr;

Abstract

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Abstract

A short and efficient process is described for the synthesis of protected and unprotected 1-formyl-C-glycosides of N-acetylglucosamine.

Key words

carbohydrates - glycosides - aldehydes - oxidations - enols

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References

References and Notes

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1b BeMiller JN. Yadav MP. Kalabokis VN. Myers RW. Carbohydr. Res. 1990, 200: 111

1c Schmidt RR. Dietrich H. Angew. Chem., Int. Ed. Engl. 1991, 30: 1328

1d Nicotra F. Top. Curr. Chem. 1997, 187: 55

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1f Marcaurelle LA. Bertozzi CR. Chem. Eur. J. 1999, 5: 1384

2a Jimenez-Barbero J. Espinosa JF. Asensio JL. Canada FJ. Poveda A. Adv. Carbohydr. Chem. Biochem. 2001, 56: 235

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3a Bertozzi CR. Cook DG. Kobertz WR. Gonzales-Scarano F. Bednarski MD. J. Am. Chem. Soc. 1992, 114: 10639

3b Xin Y.-C. Zhang Y.-M. Mallet J.-M. Glaudemans CPJ. Sinaӱ P. Eur. J. Org. Chem. 1999, 471

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3e Mikkelsen LM. Hernáiz MJ. Martín-Pastor M. Skrydstrup T. Jimenez-Barbero J. J. Am. Chem. Soc. 2002, 124: 14940

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5c Beau JM. Vauzeilles B. Skrydstrup T. In Glycoscience III Fraser-Reid B. Tatsuta K. Thiem J. Springer; Berlin: 2001. p.2679

6a Bertozzi CR. Bednarski MD. Tetrahedron Lett. 1992, 22: 3109

6b Dondoni A. Scherrmann M.-C. J. Org. Chem. 1994, 59: 604

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6d Gaurat O. Xie J. Valéry J.-M. J. Carbohydr. Chem. 2003, 22: 645

6e McGarvey GJ. Schmidtmann FW. Benedum TE. Kizer DE. Tetrahedron Lett. 2003, 44: 3775

7 Zeitouni J. Norsikian S. Lubineau A. Tetrahedron Lett. 2004, 45: 7761

8 Bragnier N. Scherrmann M.-C. Synthesis 2005, 814

9

Preparation of 1-(2′- N -Acetylacetamido)-2′-deoxy-3′,4′,6′-tri- O -acetyl-β- d-glucopyranosyl)propane-2-one ( 2).
To a solution of 1 (1.16 g, 3 mmol) in isopropenyl acetate (35 mL) was added p-TSA (0.27 g, 1.4 mmol, 0.47 equiv). After stirring for 5 h at 65 °C, the reaction mixture was cooled to r.t. before addition of Et₃N (8 mL). After evaporation of the solvents under reduced pressure, the crude residue was purified by flash chromatography (SiO₂, PE-EtOAc, = 6:4 + 0.1% Et₃N) to afford 2 (1.26 g, 99%) as a white solid. Mp 127 °C; [α]_D ²⁰ +12.4 (c 1, CHCl₃). IR (KBr): 2937, 2890, 1743, 1716, 1697, 1365, 1241, 1065 cm^-1. ¹H NMR (360 MHz, CDCl₃): δ = 5.78 (dd, 1 H, J = 9, 10 Hz, H-3′), 5.03 (dd, 1 H, J = 9, 10 Hz, H-4′), 4.91 (ddd, 1 H, J = 4, 7, 11 Hz, H-1′), 4.23 (dd, 1 H, J = 5, 12 Hz, H-6′a), 4.06 (dd, 1 H, J = 2, 12 Hz, H-6′b), 3.89 (t, 1 H, J = 10 Hz, H-2′), 3.77 (ddd, 1 H, J = 2, 5, 10 Hz, H-5′), 2.62 (dd, 1 H, J = 4, 15 Hz, H-1a), 2.47 (dd, 1 H, J = 7, 15 Hz, H-1b), 2.42 (s, 3 H, COCH ₃), 2.32 (s, 3 H, COCH ₃), 2.17 (s, 3 H, COCH ₃), 2.07 (s, 3 H, COCH ₃), 2.02 (s, 3 H, COCH ₃), 1.99 (s, 3 H, COCH ₃). ¹³C NMR (90 MHz, CDCl₃): δ = 205.2 (C-3), 174.2 (COCH₃), 174.1 (COCH₃), 170.5 (COCH₃), 169.6 (COCH₃), 169.5 (COCH₃), 75.9 (C-5′), 73.2 (C-1′), 71.2 (C-3′), 69.6 (C-4′), 62.1 (C-6′), 60.9 (C-2′), 44.1 (C-1), 31.1 (C-3), 27.5 (COCH₃), 25.1 (COCH₃), 20.6 (COCH₃), 20.5 (COCH₃), 20.4 (COCH₃). MS (ES): m/z (%) = 452 (100) [M + Na]⁺. Anal. Calcd for C₁₉H₂₇O₁₀N: C, 53.14; H, 6.34; O, 37.26; N, 3.26. Found: C, 52.97; H, 6.27; O, 37.34; N, 3.12.

10 Prepared according to: Adam W. Bialas J. Hadjiarapoglou L. Chem. Ber. 1991, 124: 2377

11

Preparation of 2-(2′- N -Acetylacetamido)-2′-deoxy-3′,4′,6′-tri- O -acetyl-β- d-glucopyranosyl)-1,3-bis(phenylmethyl)imidazolidine ( 4).
To a solution of 2 (0.429 g, 1 mmol) in a mixture of MeCN (1.9 mL) and cyclohexane (1.6 mL) was added successively pyridine (0.4 mL, 5 mmol, 5 equiv), TMSCl (0.64 mL,
5 mmol, 5 equiv) and NaI (0.74 g, 5 mmol, 5 equiv). After stirring overnight at 70 °C, the reaction mixture was cooled to r.t. and was poured into sat. aq NaHCO₃ (20 mL). The aqueous phase was extracted with EtOAc (3 × 20 mL) and the combined organic layers were washed with brine (2 × 20 mL). The organic phase was then dried (Na₂SO₄), filtered and concentrated to afford crude enoxysilane, which was used without further purification. To this crude residue was added a solution of dimethyldioxirane (30 mL, 0.1 M in acetone, 3 equiv). The solution was stirred for 2 h at r.t. and concentrated. The residue was then diluted in a mixture of THF (3 mL) and H₂O (1.5 mL) and sodium metaperiodate (0.64 g, 3 mmol, 3 equiv) was added. After stirring for 3 h at r.t., a sat. aq NaHCO₃ was added until pH = 7. After addition of brine (10 mL), the aqueous phase was extracted with EtOAc (3 × 10 mL). The combined organic phases were washed with brine (2 × 10 mL), dried (Na₂SO₄), filtered and concentrated. Toluene (10 mL), N,N-dibenzylethylene-diamine (0.25 mL, 1.05 mmol, 1.05 equiv) and glacial AcOH (2 drops) were then added to the crude aldehyde. The solution was immediately concentrated under reduced pressure and toluene was added and evaporated twice (2 × 10 mL). The pure aminal 5 (0.405 g, 65% from 2) was obtained after flash chromatography on silica gel (PE-EtOAc = 8:2 + 0.5% Et₃N). [α]_D ²⁰ +19.8 (c 1, CHCl₃). IR (NaCl): 2940, 2883, 2807, 1749, 1700, 1367, 1227, 1060, 704 cm^-1. ¹H NMR (360 MHz, CDCl₃): δ = 7.35-7.20 (m, 5 H, Ph), 6.01 (dd, 1 H, J = 9, 10 Hz, H-3′), 5.13 (dd, 1 H, J = 9, 10 Hz, H-4′), 4.91 (d, 1 H, J = 9 Hz, H-1′), 4.41 (dd, 1 H, J = 9, 10 Hz, H-2′), 4.25-4.15 (m, 3 H, H-6′a, H-6′b, CH ₂Ph), 3.92 (d, 1 H, J = 13 Hz, CH ₂Ph), 3.80 (td, 1 H, J = 4, 10 Hz, H-5′), 3.54 (s, 1 H, H-1), 3.52 (d, 1 H, J = 13 Hz, CH ₂Ph), 3.29 (d, 1 H, J = 13 Hz, CH ₂Ph), 2.75-2.65 (m, 2 H, CH ₂N), 2.63-2.55 (m, 2 H, CH ₂N), 2.30 (s, 3 H, CH ₃), 2.20 (s, 3 H, CH ₃), 2.04 (s, 3 H, CH ₃), 2.00 (s, 6 H, 2 × CH ₃). ¹³C NMR (90 MHz, CDCl₃): δ = 174.9 (COCH₃), 174.7 (COCH₃), 170.6 (COCH₃), 169.9 (COCH₃), 169.6 (COCH₃), 138.6 (Cq Ph), 137.8 (Cq Ph), 129.3 (CH Ph), 129.2 (CH Ph), 128.3 (CH Ph), 128.0 (CH Ph), 127.2 (CH Ph), 127.2 (CH Ph), 127.1 (CH Ph), 86.7 (C-1), 75.9 (C-5′), 75.7 (C-1′), 72.3 (C-3′), 69.8 (C-4′), 62.1 (C-6′), 60.0 (CH ₂Ph), 59.2 (CH ₂Ph), 57.9 (C-2′), 50.4 (CH ₂N), 50.0 (CH ₂N), 28.2 (COCH₃), 24.6, 28.2 (COCH₃), 20.7, 28.2 (COCH₃), 20.6 (COCH₃), 20.4 (COCH₃). MS (ES): m/z (%) = 646 (100) [M + Na]⁺. Anal. Calcd for C₃₃H₄₁O₉N₃: C, 63.55; H, 6.63; O, 37.26; N, 6.74. Found: C, 63.93; H, 6.81; N, 6.53.

12

Preparation of 2-( N -Acetylacetamido)-2-deoxy-1-formyl-3,4,6-tri- O -acetyl-β- d-glucopyranoside ( 5).
To a solution of the aminal 5 (75 mg, 0.12 mmol) in a mixture of THF (2 mL) and H₂O (2 mL) was added Dowex-50 (H⁺) resin (150 mg). After stirring for 1 h at r.t., the reaction mixture was filtered, concentrated and coevaporated with toluene (3 × 10 mL). The aldehyde 4 (48 mg) was obtained quantitatively. ¹H NMR (360 MHz, CDCl₃): δ = 9.67 (s, 1 H, CHO), 5.88 (t, 1 H, J = 10 Hz, H-3), 5.08 (t, 1 H, J = 10 Hz, H-4), 5.03 (d, 1 H, J = 10 Hz, H-1), 4.33 (dd, 1 H, J = 5, 12 Hz, H-6a), 4.18 (dd, 1 H, J = 2, 12 Hz, H-6b), 4.04 (t, 1 H, J = 10 Hz, H-2), 3.90 (ddd, 1 H, J = 2, 5, 10 Hz, H-5), 2.41 (s, 6 H, COCH ₃), 2.11 (s, 3 H, COCH ₃), 2.04 (s, 3 H, COCH ₃), 2.00 (s, 3 H, COCH ₃). ¹³C NMR (90 MHz, CDCl₃): δ = 197.8 (C-7), 170.6 (COCH₃), 169.8 (COCH₃), 169.7 (COCH₃), 77.0 (C-1), 76.1 (C-5), 71.1 (C-3), 68.9 (C-4), 62.0 (C-6), 57.3 (C-2), 20.7 (COCH₃), 20.6 (COCH₃), 20.4 (COCH₃).

13 Burk MJ. Allen JG. J. Org. Chem. 1997, 62: 7054

14

Preparation of 2-(2′- N -Acetyl)-2′-deoxy-3′,4′,6′-tri- O -acetyl-β- d-glucopyranosyl)-1,3-bis(phenyl-methyl)imidazolidine ( 6).
To a solution of the aminal 5 (0.156 g, 0.25 mmol) in CH₂Cl₂ (3.1 mL) was added hydrazine monohydrate (85 µL, 1.75 mmol, 7 equiv). After stirring for 24 h at r.t., brine (10 mL) was added and the aqueous phase was extracted with CH₂Cl₂ (3 × 10 mL). The combined organic phases were dried (Na₂SO₄), filtered and concentrated. The pure aminal 6 (0.128 g, 88%) was obtained after flash chromatography on silica gel (PE-EtOAc = 4:6 to 3:7 + 0.1% Et₃N). [α]_D ²⁰ +0.6 (c 1, CHCl₃). IR (NaCl): 3329, 2935, 1745, 1653, 1531, 1371, 1240, 1056, 1034, 739, 701 cm^-1. ¹H NMR (360 MHz, CDCl₃): δ = 7.35-7.10 (m, 10 H, Ph), 5.79 (d, 1 H, J = 7 Hz, NH), 5.22 (t, 1 H, J = 10 Hz, H-3), 5.07 (t, 1 H, J = 10 Hz, H-4), 4.30-4.05 (m, 4 H, H-2, H-6, H-6′ and CH ₂Ph), 3.96 (d, 1 H, J = 13 Hz, CH ₂Ph), 3.65-3.50 (m, 4 H, H-5, H-7 and 2 × CH ₂Ph), 2.95-2.85 (m, 2 H, CH ₂N), 2.60-2.50 (m, 2 H, CH ₂N), 2.03 (s, 3 H, COCH ₃), 2.01 (s, 3 H, COCH ₃), 1.99 (s, 3 H, COCH ₃), 1.75 (s, 3 H, COCH ₃). ¹³C NMR (90 MHz, CDCl₃): δ = 170.9 (COCH₃), 170.5 (COCH₃), 169.9 (COCH₃), 169.3 (COCH₃), 139.0 (Cq Ph), 138.8 (Cq Ph), 128.7 (CH Ph), 128.4 (CH Ph), 128.2 (CH Ph), 127.2 (CH Ph), 126.8 (CH Ph), 84.9 (C-7), 78.0 (C-1), 75.9 (C-5), 75.0 (C-3), 68.6 (C-4), 62.2 (C-6), 60.1 (CH₂Ph), 58.5 (CH₂Ph), 51.7 (C-2), 51.0 (CH₂N), 50.6 (CH₂N), 23.3 (COCH₃), 20.7 (COCH₃), 20.5 (COCH₃). MS (ES): m/z (%) = 582 (100) [M + H]⁺, 604 (50) [M + Na]⁺. Anal. Calcd for C₃₁H₃₉O₈N₃: C, 64.01; H, 6.76; O, 22.01; N, 7.22. Found: C, 63.84; H, 7.06; O, 22.09; N, 6.88.

15

Preparation of 2-( N -Acetyl)-2-deoxy-1-formyl-3′,4′,6′-tri- O -acetyl-β- d-glucopyranoside ( 7).
To a solution of the aminal 6 (75 mg, 0.13 mmol) in a mixture of THF (2 mL) and H₂O (2 mL) is added Dowex-50 (H⁺) resin (150 mg). After stirring for 1 h at r.t., the reaction mixture was filtered, concentrated and coevaporated with toluene (3 × 10 mL). The aldehyde 7 (46 mg) was obtained quantitatively. ¹H NMR (360 MHz, CDCl₃): δ = 9.52 (d, 1 H, J = 3 Hz, H-7), 5.79 (d, 1 H, J = 9 Hz, NH), 5.20-5.10 (m, 2 H, H-4 and H-3), 4.35-4.20 (m, 2 H, H-6 and H-2), 4.17 (dd, 1 H, J = 2, 12 Hz, H-6′), 3.75-3.65 (m, 1 H, H-5), 3.67 (dd, 1 H, J = 3, 10 Hz, H-1), 2.14 (s, 3 H, COCH ₃), 2.06 (s, 3 H, COCH ₃), 2.04 (s, 3 H, COCH ₃), 1.93 (s, 3 H, COCH ₃). ¹³C NMR (90 MHz, CDCl₃): δ = 195.8 (C-7), 171.6 (COCH₃), 170.7 (COCH₃), 170.6 (COCH₃), 169.2 (COCH₃), 82.0 (C-1), 75.9 (C-5), 73.1 (C-3 or C-4), 67.8 (C-3 or C-4), 61.8 (C-6), 50.3 (C-2), 23.0 (COCH₃), 20.8 (COCH₃), 20.7 (COCH₃), 20.6 (COCH₃).

16

Preparation of 2-(2′- N -Acetyl)-2′-deoxy-3′,4′,6′-tri- O -benzyl-β- d-glucopyranosyl)-1,3-bis(phenyl-methyl)imidazolidine ( 8).
To a solution of the aminal 5 (0.137 g, 0.22 mmol) in MeOH (2.2 mL) was added MeONa (2 mg). After stirring for 2 h at r.t., the solvents were coevaporated under reduced pressure with toluene (2 × 5 mL). DMF (4.4 mL), NaH (60% dispersion in mineral oil, 34 mg, 0.86 mmol) and benzyl bromide (82 µL, 0.68 mmol) were then added. After stirring for 2 h at r.t., MeOH (1 mL) and H₂O (10 mL) were added and the aqueous phase was extracted with EtOAc (4 × 10 mL). The combined organic phases were then dried (Na₂SO₄), filtered and concentrated. Flash chromatography (SiO₂, PE-EtOAc +1% Et₃N = 7:3 to 5:5) of the crude residue afforded the pure aminal 8 (0.120 mg, 75% from 4) as a white solid. Mp 116 °C. [α]_D ²⁰ +16.7 (c 0.6, CHCl₃). IR (ATR-FTIR, diamond prism): 3278, 3028, 2909, 2854, 1643, 1598, 1552, 1102, 1088, 1070, 745, 694 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 7.45-7.15 (m, 25 H, Ph), 5.36 (d, 1 H, J = 5 Hz, NH), 4.83 (d, 2 H, J = 12 Hz, 2 × CH ₂Ph), 4.70 (d, 1 H, J = 11 Hz, CH ₂Ph), 4.59 (d, 2 H, J = 11 Hz, 2 × CH ₂Ph), 4.54 (d, 1 H, J = 12 Hz, CH ₂Ph), 4.22 (d, 1 H, J = 14 Hz, CH ₂Ph), 4.08 (t, 1 H, J = 9 Hz, H-3′), 3.95 (d, 2 H, J = 13 Hz, 2 × CH ₂Ph), 3.89-3.82 (m, 2 H, H-1′, H-2′), 3.74 (dd, 1 H, J = 2, 11 Hz, H-6′a), 3.69 (dd, 1 H, J = 4, 11 Hz, H-6′b), 3.62-3.51 (m, 5 H, H-4′, H-5′, H-1, 2 × CH ₂Ph), 3.10-3.02 (m, 1 H, CH ₂N), 3.00-2.90 (m, 1 H, CH ₂N), 2.65-2.55 (m, 2 H, 2 × CH ₂N), 1.68 (s, 3 H, COCH ₃). ¹³C NMR (90 MHz, CDCl₃): δ = 170.3 (COCH₃), 139.7 (Cq Ph), 139.3 (Cq Ph), 138.9 (Cq Ph), 138.5 (Cq Ph), 129.1 (CH Ph), 128.7 (CH Ph), 128.3 (CH Ph), 128.0 (CH Ph), 127.8 (CH Ph), 127.5 (CH Ph), 127.4 (CH Ph), 127.1 (CH Ph), 126.8 (CH Ph), 85.1 (C-1), 83. 5 (C-3′), 79.5 (C-5′), 79.0 (C-4′), 77.2 (C-1′), 75.0 (CH₂Ph), 74.6 (CH₂Ph), 73.3 (CH₂Ph), 69.7 (C-6′), 60.4 (CH₂Ph), 58.6 (CH₂Ph), 54.2 (C-2′), 51.7 (CH₂N), 50.8 (CH₂N), 23.8 (COCH₃). MS (ESI): m/z (%) = 726.2 (100) [M + H]⁺, 748.2 (35) [M + Na]⁺. HRMS (ESI high resolution): m/z calcd for C₄₆H₅₂O₅N₃: 726.3901; found: 726.3914. Anal. Calcd for C₄₆H₅₁O₅N₃: C, 76.11; H, 7.08; O, 11.02; N, 5.79. Found: C, 76.02; H, 6.83; N, 5.76.

17

Preparation of 2-( N -Acetyl)-2-deoxy-1-formyl-3,4,6-tri- O -benzyl-β- d-glucopyranoside ( 9).
To a solution of the aminal 8 (30 mg, 0.04 mmol) in a mixture of THF (1 mL) and H₂O (1 mL) was added Dowex-50 (H⁺) resin (100 mg). After stirring for 1 h at r.t., the suspension was filtered, concentrated and coevaporated with toluene (3 × 10 mL). The aldehyde 9 (20 mg) was obtained quantitatively. ¹H NMR (400 MHz, CDCl₃): δ = 9.53 (d, 1 H, J = 2 Hz, H-7), 7.45-7.15 (m, 15 H, Ph), 5.24 (d, 1 H, J = 8 Hz, NH), 4.86 (d, 1 H, J = 12 Hz, CH ₂Ph), 4.82 (d, 1 H, J = 11 Hz, CH ₂Ph), 4.65 (d, 1 H, J = 12 Hz, CH ₂Ph), 4.63 (d, 1 H, J = 12 Hz, CH ₂Ph), 4.60 (d, 1 H, J = 11 Hz, CH ₂Ph), 4.57 (d, 1 H, J = 12 Hz, CH ₂Ph), 3.96 (q, 1 H, J = 8 Hz, H-2), 3.75 (d, 2 H, J = 3 Hz, 2 × H-6), 3.73-3.69 (m, 2 H, H-3 and H-4), 3.65 (dd, 1 H, J = 2, 10 Hz, H-1), 3.55 (dt, 1 H, J = 3, 9 Hz, H-5), 1.75 (s, 3 H, COCH ₃). ¹³C NMR (100 MHz, CDCl₃): δ = 197.4 (C-7), 170.5 (COCH₃), 138.0 (Cq Ph), 137.8 (Cq Ph), 137.7 (Cq Ph), 128.7 (CH Ph), 128.5 (CH Ph), 128.4 (CH Ph), 128.2 (CH Ph), 128.0 (CH Ph), 127.8 (CH Ph), 127.7 (CH Ph), 81.9 (C-1), 81.5 (C-3 or C-4), 78.9 (C-5), 78.2 (C-3 or C-4), 75.0 (CH₂Ph), 74.6 (CH₂Ph), 73.5 (CH₂Ph), 68.6 (C-6), 51.0 (C-2), 23.1 (COCH₃).

18

Preparation of (1 R )- and (1 S )-1-(2′- N -Acetyl)-2′-deoxy-3′,4′,6′-tri- O -acetyl-β- d-glucopyranosyl)-1-acetoxy-1-but-3-ene ( 11).
To a solution of the aminal 5 (0.32 mmol, 200 mg) in MeOH (3 mL) was added sodium methoxide (2 mg). After stirring for 1 h at r.t. MeOH was evaporated. THF (1.6 mL), H₂O (1.6 mL) and Dowex-50 (H⁺) resin (400 mg) were added. After stirring for 1 h at r.t., the suspension was filtered, concentrated and coevaporated with toluene (3 × 10 mL). The residue was dissolved in a 1:1 mixture of THF-H₂O (3.2 mL) and allyl bromide (0.64 mmol, 55 mL) and In (0.96 mmol, 110 mg) were added. After stirring for 12 h at r.t., the suspension was filtered over Celite^®. After washing with EtOH and evaporation of the solvents under reduced pressure, the residue was dissolved in a 2:1 mixture of pyridine and Ac₂O (1.5 mL). After stirring for 12 h at r.t., the reaction mixture was concentrated and coevaporated with toluene. Then, EtOAc (15 mL) was added and the mixture was washed with aq HCl (0.1 N, 5 mL) then with brine (10 mL). The organic phase was dried (Na₂SO₄) and concentrated. The crude residue was purified by flash chromatography (PE-EtOAc = 3:7 to 2:8) to afford 11 as a mixture of two diastereomers (87% from 5).
Diastereomer 1 (32 mg, white solid): mp 124 °C; [α]_D ²⁰
-44.3 (c 0.3, CHCl₃). IR (ATR-FTIR, diamond prism): 3258, 3075, 2863, 1752, 1734, 1635, 1560, 1453, 1358, 1314, 1101, 1054, 735, 695 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 5.85-5.60 (m, 2 H, H-3 and NH), 5.11 (dd, 1 H, J = 1, 17 Hz, H-4a), 5.09-5.05 (m, 2 H, H-4′, H-4b), 5.01 (t, 1 H, J = 10 Hz, H-3′), 4.88 (ddd, 1 H, J = 1, 4, 9 Hz, H-1), 4.23 (dd, 1 H, J = 4, 12 Hz, H-6′a), 4.19-4.09 (m, 2 H, H-2 and H-6′b), 3.57 (ddd, 1 H, J = 2, 4, 10 Hz, H-5′), 3.51 (dd, 1 H, J = 2, 11 Hz, H-1′), 2.60-2.45 (m, 2 H, 2 × H-2), 2.08 (s, 3 H, COCH ₃), 2.05 (s, 3 H, COCH ₃), 2.02 (s, 3 H, COCH ₃), 2.01 (s, 3 H, COCH ₃), 1.96 (s, 3 H, COCH ₃). ¹³C NMR (100 MHz, CDCl₃): δ = 171.3 (COCH₃), 171.0 (COCH₃), 170.6 (COCH₃), 170.2 (COCH₃), 169.2 (COCH₃), 133.9 (C-3), 117.8 (C-4), 79.8 (C-1′), 75.7 (C-5′), 74.4 (C-3′), 72.6 (C-1), 68.3 (C-4′), 62.2 (C-6′), 50.9 (C-2′), 31.9 (C-2), 23.1 (COCH₃), 21.0 (COCH₃), 20.7 (COCH₃), 20.6 (COCH₃), 20.5 (COCH₃). MS (ESI): m/z (%) = 466.2 (100) [M + Na]⁺. HRMS (ESI high resolution): m/z calcd for C₂₀H₂₉O₁₀NNa: 466.1684; found: 466.1695.
Diastereomer 2 (91 mg, white solid): mp 165 °C; [α]_D ²⁰ +16.2 (c 0.6, CHCl₃). IR (ATR-FTIR, diamond prism): 3273, 3087, 2858, 1778, 1743, 1645, 1563, 1453, 1358, 1314, 1101, 1065, 745, 690 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 5.76-5.64 (m, 1 H, H-3), 5.49 (d, 1 H, J = 10 Hz, NH), 5.18-5.01 (m, 4 H, H-3′, H-4′, 2 × H-4), 4.96 (td, 1 H, J = 2, 7 Hz, H-1), 4.23 (dd, 1 H, J = 6, 12 Hz, H-6′a), 4.19 (q, 1 H, J = 10 Hz, H-2′), 4.14 (dd, 1 H, J = 2, 12 Hz, H-6′), 3.59 (ddd, 1 H, J = 2, 6, 10 Hz, H-5′), 3.52 (dd, 1 H, J = 2, 10 Hz, H-1′), 2.46 (t, 2 H, J = 7 Hz, 2 × H-2), 2.09 (s, 3 H, COCH ₃), 2.07 (s, 3 H, COCH ₃), 2.01 (s, 3 H, COCH ₃), 2.00 (s, 3 H, COCH ₃), 1.88 (s, 3 H, COCH ₃). ¹³C NMR (100 MHz, CDCl₃): δ = 171.2 (COCH₃), 170.8 (COCH₃), 170.6 (COCH₃), 169.9 (COCH₃), 169.3 (COCH₃), 132.9 (C-3), 118.6 (C-4), 77.4 (C-1′), 76.3 (C-5′), 74.4 (C-3′), 69.2 (C-1), 68.9 (C-4′), 62.7 (C-6′), 49.9 (C-2′), 34.6 (C-2), 23.1 (COCH₃), 21.0 (COCH₃), 20.7 (COCH₃), 20.6 (COCH₃), 20.5 (COCH₃). MS (ESI): m/z = 466.2 (100) [M + Na]⁺. HRMS (ESI high resolution): m/z calcd for C₂₀H₂₉O₁₀NNa: 466.1684; found: 466.1695. Anal. Calcd for C₂₀H₂₈O₁₀N: C, 54.17; H, 6.59; O, 36.08; N, 3.16. Found: C, 53.72; H, 6.64; N, 3.06.