C. Cadena-Amaro, S. Pochet / Tetrahedron 61 (2005) 5081–5087
5085
5.5 mL/min and a linear gradient of CH3CN (A) in 10 mM
triethylammonium acetate buffer (B) at pH 7.5 over 20 min.
Purity of all tested compounds was checked by analytical
HPLC on a Perkin Elmer system with a reverse phase
column (C18) using a flow rate of 1 mL/min and a linear
gradient of A in B at pH 7.5 over 20 min and using a diode
array detector. Solvents were spectroscopic or HPLC grade
and reagents used without purification.
added acetic anhydride (2.26 mL, 24 mmol). After stirring
for 3 h under argon, methanol (2 mL) was added. The
reaction mixture was evaporated, the resulting residue
adsorbed on silica gel and loaded onto a column (0–20%
MeOH in CH2Cl2) to give 5 as a powder (1.65 g, 84%). Rf
1
(iPrOH/NH4OH/H2O: 70:10:20): 0.56. H NMR (DMSO-
d6) d: 2.05 (s, 3H, CH3), 2.06 (s, 3H, CH3), 2.25 (m, 1H,
H2000), 2.60 (m, 1H, H20), 4.09 (m, 1H, H40), 4.12 (m, 1H,
H50), 4.21 (m, 1H, H500), 5.19 (m, 1H, H30), 5.85 (dd, 1H,
H1 , JZ6.0, 8.7 Hz), 7.23 (s, 1H, H5), 10.51 (bs, 1H, NH).
13C NMR (DMSO-d6) d: 21.40 (CH3), 21.64 (CH3), 35.86
(C20), 64.63 (C50), 75.20 (C30), 81.76 (C40), 82.81 (C10),
115.64 (C4), 117.45 (C5), 153.14 (C2), 161.18 (4-COOH),
170.85 (COOCH3), 170.98 (COOCH3). MS (ESI-TOF) m/z
329.1 (MCH)C, 351.1 (MCNa)C, 367.0 (MCK)C.
4.2. Synthesis of 1-(2-deoxy-b-D-ribofuranosyl)-2-oxo-
2,3-dihydro-1H-imidazole-4-carboxamide (3)
4.2.1. 1-(2-Deoxy-b-D-ribofuranosyl)-2-oxo-2,3-dihydro-
1H-imidazole-4-carboxylic acid (4b). Method A. A
solution of 5-bromo-20-deoxyuridine (3.34 g, 10.89 mmol)
in 0.1 N NaOH (385 mL) was refluxed for 6 h while the pH
was maintained at 13 by addition of 1 N NaOH (2!0.5 mL,
after 2 and 4 h, respectively). The cooled reaction was
neutralized by addition of 0.1 N HCl, concentrated and the
resulting solution was passed through a column of cationic
resin (Dowex HC). The product was eluated with water and
the eluate was concentrated under vacuo. The crude product
was purified by silica gel column chromatography (0–20%
MeOH in CH2Cl2, then 0–10% CH3COOH in 80:20
CH2Cl2/MeOH); first fractions were collected to give 4b
as a pale yellow powder (1.46 g, 55%). Rf (iPrOH/NH4OH/
4.2.3. 1-(3,5-O-diacetyl-2-deoxy-b-D-ribofuranosyl)-2-
oxo-2,3-dihydro-1H-imidazole-4-carboxamide (6). To
compound 5 (1.57 g, 4.78 mmol) in anhydrous acetonitrile
(50 mL) were added at 4 8C pentafluorophenol (1.32 g,
7.18 mmol) and DCC (1.48 g, 7.17 mmol). After stirring for
45 min at room temperature, the insolubles were filtered off
and rinsed with acetonitrile. The filtrates were evaporated,
taken up in acetonitrile (50 mL) and treated at 4 8C with
33% aqueous ammonia (8 mL). After 20 min, the solution
was evaporated at low bath temperature and the resulting
residue purified by silica gel column chromatography
(0–15% MeOH in CH2Cl2) to give 6 as a white foam
1
H2O: 70:10:20): 0.34. H NMR (DMSO-d6) d: 1.88 (ddd,
1H, H20, JZ2.5, 6.0, 13.0 Hz), 2.12 (m, 1H, H200), 3.31–
3.40 (m, 2H, H50 and H500), 3.60 (m, 1H, H40), 4.12 (m, 1H,
H30), 5.72 (dd, 1H, H10, JZ6.0, 8.3 Hz), 6.97 (s, 1H, H5),
1
(1.22 g, 78%). Rf (CH2Cl2/MeOH 90:10): 0.28. H NMR
(DMSO-d6) d: 2.12 (s, 3H, CH3), 2.13 (s, 3H, CH3), 2.38
(oct, 1H, H200, JZ2.70, 6.1, 14.1 Hz), 2.51 (m, 1H, H20),
4.13–4.20 (m, 2H, H4 and H500), 4.26 (m, 1H, H500), 5.28
(m, 1H, H30), 5.90 (dd, 1H, H1 , JZ6.2, 8.1 Hz), 7.19 (bs,
1H, NH2), 7.39 (d, 1H, H5, JZ1.9 Hz), 7.43 (bs, 1H, NH2),
10.58 (bs, 1H, NH). 13C NMR (DMSO-d6) d: 21.43 (CH3),
21.62 (CH3), 36.23 (C20), 64.63 (C50), 79.92 (C30), 81.54
(C40), 82.63 (C10), 113.04 (C5), 118.59 (C4), 152.93 (C2),
160.93 (CONH2), 170.87 (COOCH3), 171.05 (COOCH3).
MS (ESI-TOF) m/z 350.1 (MCNa)C, 366.1 (MCK)C.
13
10.20 (bs,01H, NH). C NMR (DMSO-d6) d: 39.74 (C20),
62.81 (C5 ), 71.81 (C30), 82.54 (C10), 87.82 (C40), 114.15
(C5), 119.28 (C4), 153.15 (C2), 162.63 (COOH). HRMS
(MALDI-TOF) m/z calcd for C9H12N2O6CNa 267.0593,
found 267.0719.
Method B. A solution of 5-bromo-20-deoxyuridine (5.0 g,
16.28 mmol) in 0.16 N NaHCO3 (4.53 g in 0.33 mL) was
refluxed for 25 h while the pH was maintained at 8.0 by
addition of CO2. The CO2 arrival was suppressed and the pH
raised rapidly to 10. After refluxing for 16 h, the cooled
reaction was neutralized by addition of cationic resin
(Dowex HC), concentrated and the resulting solution was
passed through a column of resin Dowex HC. The product
was eluated with water and the eluate was concentrated
under vacuo. Purification by silica gel column chromato-
graphy afford compound 4 as a pale yellow powder (3.42 g,
86%) as a mixture of anomers b/a (95:5). 1H NMR (D2O) d:
2.17 (dt, 0.05H, H200a, JZ3.7, 14.7 Hz), 2.27 (ddd, 00.95H,
H200b, JZ3.6, 6.4, 14.0 Hz), 2.41 (ddd, 0.95H, H2 b, JZ
6.4, 7.4, 14.0 Hz), 2.69 (ddd, 0.000 5H, H20a, JZ7.4, 14.7 Hz),
3.59–3.70 (m, 2H, H50 and H5 ab), 3.92 (m, 0.95H, H40b),
4.16 (m, 0.005H, H40a), 4,36 (m,00.05H, H30a), 4.42 (m, 1H,
0.95H, H3 b), 5.94 (m, 1H, H1 ab), 7.04 (s, 0.95H, H5b),
4.2.4. 1-(2-Deoxy-b-D-ribofuranosyl)-2-oxo-2,3-dihydro-
1H-imidazole-4-carboxamide (3). To compound 6 (1.22 g,
3.74 mmol) in MeOH (85 mL) was added 33% aqueous
ammonia (85 mL). After stirring for 20 min at room
temperature, solvents were removed and the residue purified
by silica gel column chromatography (0–25% MeOH in
CH2Cl2). Compound 3 was obtained as a white powder
(0.90 g, 95%). Rf (CH2Cl2/MeOH 90:10): 0.38. Mp 160–
162 8C. Rt (0–20% A in B): 9.21 min. 1H NMR (DMSO-d6)
d: 2.06 (ddd, 1H, H200, JZ3.1, 6.2, 13.2 Hz), 2.15 (ddd, 1H,
H20, JZ5.8,0 7.9, 13.2 Hz), 3.47 (m, 2H, H50 and H500), 3.72
(m, 1H, H4 ), 4.24 (m, 1H, H30), 4.85 (t, 1H, 50OH, JZ
5.6 Hz), 5.21 (d, 1H, 30OH, JZ4.3 Hz), 5.83 (dd, 1H, H10,
JZ6.2, 7.8 Hz), 7.20 (bs, 1H, NH2), 7.31 (s, 1H, H5), 7.35
(bs, 1H, NH2), 10.43 (bs, 1H, NH). 13C NMR (DMSO-d6) d:
39.22 (C20), 62.45 (C50), 71.17 (C30), 81.87 (C10), 87.31
(C40), 112.89 (C5), 117.66 (C4), 152.50 (C2), 160.52
(CONH2). MS (ESI-TOF) m/z 244.2 (MCH)C, 266.1 (MC
Na), 282.1 MCK)C. HRMS (ESI-TOF) m/z calcd for
C9H13N3O5CNa 266.0753, found 266.0738. Anal. calcd for
C9H13N3O5C3/4H2O: C, 42.11; H, 5.31; N, 16.37, found C,
42.46; H, 5.34; N, 16.24. UV (H2O/pH 6.2) lmax 263 nm (3
13
7.25 (s, 0.05H, H5a). C NMR (D2O) d: 38.49 (C20b),
39.02 (C200a), 61.71 (C500a), 62.07 (C500b), 71.12 (C300a),
71.47 (C30b), 82.96 (C1 b), 83.57 (C1 a), 86.76 (C4 b),
87.40 (C4 a), 113.90 (C5b), 115.07 (C5a), 120.50 (C4),
153.51 (C2), 166.47 (COOH).
4.2.2. 1-(3,5-O-diacetyl-2-deoxy-b-D-ribofuranosyl)-2-
oxo-2,3-dihydro-1H-imidazole-4-carboxylic acid (5). To
compound 4 (1.46 g, 6.0 mmol) in dry pyridine (60 mL) was