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DOI: 10.1055/s-2006-939061
A Short Synthetic Route to β-C-Glycosides of N-Acetylglucosamine
Publikationsverlauf
Publikationsdatum:
24. April 2006 (online)
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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 and Notes
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.
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.
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).
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.
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).
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.
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).
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.