C. Colombo, A. Bernardi
FULL PAPER
Nα-Benzyloxycarbonyl-Nγ-(2,3,4,6-tetra-O-acetyl-α-
pyranosyl)-L-asparagine Methyl Ester (13): 2,3,4,6-Tetra-O-acetyl-
D
-gluco-
yield. [α]2D0 = +66.9 (c = 0.9, CH2Cl2). 1H NMR (400 MHz, CDCl3,
25 °C): δ = 7.80 (d, J = 7.8 Hz, 1 H, Glc-NH-Asn), 7.75 (d, J =
7.6 Hz, 2 H, 4-H-, 5-H-Fmoc), 7.58 (d, J = 7.2 Hz, 2 H, 1-H-, 8-
H-Fmoc), 7.39 (t, J = 7.2 Hz, 2 H, 3-H-, 6-H-Fmoc), 7.29 (t, J =
7.6 Hz, 2 H, 2-H-, 7-H-Fmoc), 6.57 (d, J = 7.2 Hz, 1 H, NH-
Fmoc), 5.83 (dd, J1,NH = 7.8, J1,2 = 5.6 Hz, 1 H, 1-H), 5.46 (t, J3,2
= J3,4 = 9.8 Hz, 1 H, 3-H), 5.15–5.05 (m, 2 H, 2-H, 4-H), 4.64 (br.
s, 1 H, α-H-Asn), 4.48–4.33 (m, 2 H, CH2-Fmoc), 4.30–4.18 (m, 2
H, 9-H-Fmoc, 6-H), 4.15–4.03 (m, 2 H, 6Ј-H, α-H-Gly), 4.00–3.87
(m, 2 H, 5-H, α-H-Gly), 3.72 (s, 3 H, COOCH3), 2.99–2.90 (m, 1
H, β-H-Asn), 2.74–2.66 (m, 1 H, β-H-Asn), 2.05 (s, 3 H, CH3CO),
2.02 (s, 3 H, CH3CO), 1.98 (s, 3 H, CH3CO), 1.96 (s, 3 H,
CH3CO) ppm. 13C NMR (100 MHz, CDCl3, 25 °C): δ = 171.5–
169.4 (CO), 143.8, 143.7 (CquatFmoc), 141.4 (CquatFmoc), 127.9 (C-
2-, C-7-Fmoc), 127.2 (C-3-, C-6-Fmoc), 125.2 (C-1-, C-8-Fmoc),
120.2 (C-4-, C-5-Fmoc), 74.5 (C-1), 68.8 (C-3), 68.3 (C-2), 68.2 (C-
4, C-5), 67.6 (CH2-Fmoc), 60.5 (C-6), 52.6 (COOCH3), 51.6 (α-C-
Asn), 47.2 (C-9-Fmoc), 41.4 (CH2-Gly), 37.8 (β-CH2-Asn), 20.7,
2 0 . 6 ( 4 ϫ OA c ) p p m . F T- I C R M S ( E S I ) : c a l c d . f o r
[C36H41O15N3Na]+ 778.24299; found 778.24140.
β-d-glucosyl azide (3;[5a] 250 mg, 0.670 mmol, 1 equiv.) and Ph3P
(193 mg, 0.737 mmol, 1.1 equiv.) were dissolved in nitroethane
(5 mL) in the presence of ground 3 Å molecular sieves (ca. 900 mg).
The resulting solution was heated at reflux for 15 h under N2 and
then cooled to room temperature before adding Cbz-Asp(SPy)-
OMe (12;[15] 325 mg, 0.871 mmol, 1.3 equiv.) and CuCl2·2H2O
(148 mg, 0.871 mmol, 1.3 equiv.). The mixture was stirred at 30 °C
for 6 h. After completion (TLC, 1:1 hexane/EtOAc) the reaction
mixture was diluted with CH2Cl2 and filtered through a pad of
Celite. The solvent was evaporated and the crude was dissolved in
EtOAc and washed with a saturated ammonium chloride solution.
The organic phase was dried with Na2SO4 and the solvent removed
under reduced pressure. The crude was purified by flash
chromatography (1:1 hexane/EtOAc) to afford 13 (143 mg) in 35%
yield. [α]2D0 = +45.6 (c = 0.15, MeOH). 1H NMR (400 MHz, CDCl3,
25 °C): δ = 7.36–7.30 (m, 5 H, HAr-Bn), 6.88 (br. s, 1 H, Glc-NH-
Asn), 5.96 (d, J = 7.6 Hz, 1 H, NH-Cbz), 5.83 (t, 1 H, 1-H), 5.35
(t, J3,4 = J3,2 = 9.6 Hz, 1 H, 3-H), 5.18–5.10 (m, 3 H, 2-H, CH2-
Cbz), 5.06 (t, J4,3 = J4,5 = 9.6 Hz, 1 H, 4-H), 4.64 (br. s, 1 H, α-H-
Asn), 4.27 (dd, Jgem = 12.0, J6,5 = 4.0 Hz, 1 H, 6-H), 4.04 (dd, Jgem
= 12.0, J6Ј,5 = 1.8 Hz, 1 H, 6Ј-H), 3.90 (m, 1 H, 5-H), 3.75 (s, 3 H,
COOCH3), 3.02–2.78 (m, 2 H, CH2-Asn), 2.06 (s, 3 H, CH3CO),
2.03 (s, 3 H, CH3CO), 2.02 (s, 3 H, CH3CO), 1.98 (s, 3 H,
CH3CO) ppm. 13C NMR (100 MHz, CDCl3, 25 °C): δ = 171.4–
169.3 (CO), 136.2 (CquatCbz), 128.7, 128.4, 128.3 (CH-Cbz), 74.5
(C-1), 70.3 (C-3), 68.6 (C-2, C-4), 68.5 (C-5), 67.5 (CH2-Cbz), 61.9
(C-6), 53.1 (COOCH3), 51.0 (α-C-Asn), 38.6 (β-CH2-Asn), 20.9,
20.8, 20.6 (4ϫ OAc) ppm. MS (ESI): m/z = 633.3 [M + Na]+.
(S)-1-(2,3,4,6-Tetra-O-acetyl-α-D-glucopyranosyl)-3-(N-fluorenyl-
methoxycarbonyl)-2,5-dioxopyrrolidine (11): This compound was
isolated as a byproduct in some of the coupling reactions leading
to 10, as described in Table 1 (flash chromatography, 40:60 hexane/
EtOAc, Rf = 0.37). [α]2D0 = +41.2 (c = 0.45, CH2Cl2). 1H NMR
(400 MHz, CD3OD, 25 °C): δ = 7.79 (d, J = 7.2 Hz, 2 H, 4-H-
Fmoc, 5-H-Fmoc), 7.66 (t, J = 7.2 Hz, 2 H, 1-H-Fmoc, 8-H-
Fmoc), 7.40 (t, J = 7.2 Hz, 2 H, 3-H-Fmoc, 6-H-Fmoc), 7.32 (t, J
= 7.2 Hz, 2-H-Fmoc, 7-H-Fmoc), 6.28 (t, J = 9.2 Hz, 1 H, 3-H),
6.05 (d, J1,2 = 7.8 Hz, 1 H, 1-H), 5.29 (t, J2,1 = 7.8 Hz, 1 H, 2-H),
5.13 (t, J = 9.2 Hz, 1 H, 4-H), 4.44–4.28 (m, 3 H, α-H-Asn, 9-H-
Fmoc, CH-Fmoc), 4.29–4.17 (m, 3 H, 6-H, 5-H, CH-Fmoc), 4.08–
4.02 (m, 1 H, 6Ј-H), 3.18–3.00 (dd, Jgem = 15.6, Jα,β = 9.2 Hz, 1 H,
β-H-Asn), 2.84–2.73 (dd, Jgem = 15.6, Jα,β = 6.4 Hz, 1 H, β-H-Asn),
2.02 (s, 3 H, CH3CO), 2.01 (s, 3 H, CH3CO), 2.00 (s, 3 H, CH3CO),
1.99 (s, 3 H, CH3CO) ppm. 13C NMR (100 MHz, CDCl3, 25 °C):
δ = 175.7–169.9 (CO), 143.7, 143.5 (CquatFmoc), 141.6, 141.5
(CquatFmoc), 128.1, 128.0 (C-2-, C-7-Fmoc), 127.4 (C-3-, C-6-
Fmoc), 125.1 (C-1-, C-8-Fmoc), 120.3 (C-4-, C-5-Fmoc), 74.9 (C-
1), 72.9 (C-5), 72.3 (C-3), 68.5 (C-4, C-5), 67.5 (CH2-Fmoc), 61.9
(C-6), 50.7 (α-C-Asn), 47.3 (C-9-Fmoc), 35.3 (β-CH2-Asn), 21.9,
20.9, 20.7 (4ϫ OAc) ppm. MS (ESI): m/z = 689.4 [M + Na]+.
Nγ-(2,3,4,6-Tetra-O-acetyl-α-
D-glucopyranosyl)-L-asparagine-O-
methyl Ester Hydrocloride (14b): Compound 13 (35 mg,
0.057 mmol) and acetyl chloride (0.057 mmol, 4 μL) were dissolved
in MeOH/H2O (5:1, 6 mL). Pd/C (10%) was added and the mixture
was stirred under hydrogen for 2 h, filtered through a pad of Celite
and washed with methanol. The solvent was evaporated to afford
14b (29 mg) in quantitative yield. [α]2D0 = +96.6 (c = 1.2, MeOH).
1H NMR (400 MHz, CD3OD, 25 °C): δ = 5.85 (d, J1,2 = 5.6 Hz, 1
H, 1-H), 5.60 (t, J3,2 = J3,4 = 9.6 Hz, 1 H, 3-H), 5.09–5.02 (m, 2
H, 2-H, 4-H), 4.37 (br. s, 1 H, α-H-Asn), 4.28 (dd, Jgem = 12.0, J6,5
= 4.0 Hz, 1 H, 6-H), 4.04 (dd, Jgem = 12.0, J6Ј,5 = 1.8 Hz, 1 H, 6Ј-
H), 3.94–3.90 (m, 1 H, 5-H), 3.85 (s, 3 H, COOCH3), 3.10–2.97
(m, 2 H, β-CH2-Asn), 2.12 (s, 3 H, CH3CO), 2.07 (s, 3 H, CH3CO),
2.03 (s, 3 H, CH3CO), 2.01 (s, 3 H, CH3CO) ppm. 13C NMR
(100 MHz, CD3OD, 25 °C): δ = 172.4–170.0 (CO), 75.3 (C-1), 71.7
(C-3), 70.5 (C-2), 70.1 (C-4), 69.9 (C-5), 63.3 (C-6), 54.1 (CO-
OCH3), 50.7 (α-C-Asn), 35.5 (β-CH2-Asn), 20.8, 20.7, 20.6 (4ϫ
OAc) ppm. MS (ESI): m/z = 499.3 [M + Na]+.
N-tert-Butoxycarbonyl-
-glucopyranosyl)- -asparagine Methyl Ester (16): Compound 14b
L
-phenylalanyl-Nγ-(2,3,4,6-tetra-O-acetyl-α-
D
L
(18 mg, 0.035 mmol, 1 equiv.), Boc-Phe-OH (15; 33 mg,
0.123 mmol, 3.5 equiv.) and HATU (47 mg, 0.123 mmol, 3.5 equiv.)
were dissolved in dry DMF (400 μL) under nitrogen at 0 °C. DI-
PEA (28 μL, 0.158 mmol, 4.5 equiv.) was added and the reaction
mixture was stirred at 0 °C for 2 h and then at room temperature
for 4 h (TLC, 85:15 chloroform/methanol and 30:70 hexane/
EtOAc). The solvent was evaporated, the residue was dissolved in
EtOAc and the organic phase was washed with 1 m HCl and satu-
rated NaHCO3 and then dried with sodium sulfate. The solvent
was evaporated and the crude was purified by flash chromatog-
Nα-Fluorenylmethoxycarbonyl-Nγ-(2,3,4,6-tetra-O-acetyl-α-
pyranosyl)- -asparagylglycine Methyl Ester (10): Compound 1
D-gluco-
L
(25 mg, 0.036 mmol, 1 equiv.) and PyBROP (37 mg, 0.080 mmol,
2.2 equiv.) were dissolved in dry CH2Cl2 (400 μL) under nitrogen
at 0 °C. DIPEA (20 μL, 0.117 mmol, 3.2 equiv.) was added. After
10 min, glycine methyl ester hydrochloride (14 mg, 0.109 mmol,
3 equiv.) and DIPEA (19 μL, 0.109 mmol, 3 equiv.) were added and raphy (40:60 hexane/EtOAc) to afford 16 (23 mg) in 87% yield.
the reaction mixture was stirred at 0 °C for 2 h and then at room
temperature for 3 h. After completion (TLC, 85:15 chloroform/
[α]2D0 = +51.9 (c = 1.35, MeOH). 1H NMR (400 MHz, CDCl3,
25 °C): δ = 7.90 (d, JNH,1 = 8.6 Hz, 1 H, Glc-NH-Asn), 7.31–7.22
methanol and 30:70 hexane/EtOAc) the solvent was evaporated, (m, 5 H, CHAr), 6.77 (d, J = 7.2 Hz, 1 H, Asn-NH-Phe), 5.88 (dd,
the residue was dissolved in EtOAc and the organic phase was
washed with 1 m HCl and saturated NaHCO3 and then dried with
sodium sulfate. The solvent was evaporated under reduced pressure
to yield 33 mg of the crude product, which was purified by flash
chromatography (40:60 hexane/EtOAc) to afford 10 (19 mg) in 69%
J1,NH = 8.6, J1,2 = 5.6 Hz, 1 H, 1-H), 5.58 (t, J3,2 = J3,4 = 9.6 Hz,
1 H, 3-H), 5.28–5.17 (m, 2 H, NHBoc, 2-H), 5.13 (t, J4,3 = J4,5
9.6 Hz, 1 H, 4-H), 4.98 (br. s, 1 H, α-H-Asn), 4.39–4.25 (m, 2 H,
6-H, α-H-Phe), 4.10–3.98 (m, 2 H, 6Ј-H, 5-H), 3.73 (s, 3 H, CO-
OCH3), 3.14–2.83 (m, 2 H, β-H-Phe), 2.84–2.70 (m, 2 H, β-H-Asn),
=
3916
www.eurjoc.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 3911–3919