General
1H-NMR spectra were recorded on a General Electric QE-300 (300 MHz) instrument. The spectral data are reported in the following format: chemical shift (all relative to Me4Si as an internal reference standard unless otherwise indicated), multiplicity (s = singlet, d = doublet, dd = doublet of doublets, t = triplet, q = quartet, m = multiplet, b = broad ), integration, coupling constants, exchangeability after D2O addition, and assignment of resonances. Elemental Microanalyses were performed by Atlantic Microlab, Inc., Norcross, Georgia. The mass spectra were recorded at the Mass Spectral Facility, Department of Biochemistry, Michigan State University. Thin layer chromatography was performed on Merck Kieselgel 60 GF254 plates (0.2 mm thickness). Melting points were determined on a Thomas-Hoover capillary melting point apparatus, and are uncorrected.
Methyl 1-[(2’-O-methyl-3’,5’-O-(1,1,3,3-tetraisopropyldisiloxan-1,3-diyl))-ß-D-erythropentofurano-syl]–4,5-imidazoledicarboxylate (5). A mixture of methyl 1-[(3',5'-
O-(1,1,3,3,-tetraisopropyl-disiloxan-1,3-diyl))-
ß-D-ribofuranosyl]-4,5- imidazoledicarboxylate (
3) [
8] (560 mg, 1 mmol), Ag
2O (1.85 g, 8 mmol) and MeI (10 mL) was refluxed for 5 h. The mixture was diluted with Et
2O, and was filtered over Celite.
TM The filtrate was concentrated
in vacuo and the residue was purified by silica gel column chromatography, eluting with chloroform, to give
5 as a colorless oily product in quantitative yield, R
f 0.35 (hexane/ethyl acetate, 3:1);
1H-NMR (CDCl
3) 8.20 (s, 1H, imidazole), 6.02(s, 1H, 1'-H), 4.42 (dd, 1H,
J=4.2 and 9.6 Hz, 3'-H), 4.28 (d, 1H,
Jgem=13.8 Hz, 5'-H), 4.16 (dd, 1H,
J=9.6 and 2.4 Hz, 4'-H), 4.00 (dd, 1H,
Jgem=13.8 Hz,
J5',4'=2.4 Hz, 5'-H), 3.94 (s, 3H, COOCH
3), 3.93 (s, 3H, COOCH
3), 3.78 (d, 1H,
J=4.2 Hz, 2'-H), 3.69 (s, 3H, OCH
3), 1.05 (m, 28H, isopropyl groups);
13C-NMR (CDCl
3, 75.48 MHz) 12.53 (CHSi), 12.90 (CHSi), 12.96 (CHSi), 13.46 (CHSi), 16.87 (CCH
3), 17.01 (CCH
3), 17.01 (CCH
3), 17.15 (CCH
3), 17.30 (CCH
3), 17.30 (CCH
3), 17.38 (CCH
3), 17.49 (CCH
3), 52.45 (COOCH
3), 52.62 (COOCH
3), 59.46 (OCH
3), 59.96 (C-5'), 68.66 (C-3'), 81.59 (C-4'), 84.99 (C-2'), 90.76 (C-1'), 122.84 (C-4 or 5), 137.55 (C-2), 138.57 (C-5 or 4), 160.23 (C=O), 163.06 (C=O).
Anal. Calcd. for C
25H
44N
2O
9Si
2 (MW 572.80): C, 52.42; H, 7.74; N, 4.89. Found: C, 52.46; H, 7.85; N, 4.63.
Methyl 1-(2'-O-methyl-ß-D-erythropentofuranosyl)-4,5-imidazoledicarboxylate (6). A 1M solution of tetra-n-butylammonium fluoride in THF (2 mL, 2 mmol) was added to an ice-cooled solution of methyl 1-[(2'-O-methyl-3',5'-O-(1,1,3,3,-tetraisopropyldisiloxan-1,3-diyl))-ß-D-erythropentofuranosyl]-4,5-imidazoledicarboxylate (5) (573 mg, 1 mmol) in 10 mL of dry THF. The reaction mixture was stirred for 45 min at 0 oC. The solvent was evaporated in vacuo and the pure product was obtained as a foam after silica gel column chromatography, eluting with a mixture of chloroform-methanol (20:1), 85 % yield, Rf 0.29 (chloroform/methanol, 10:1); 1H-NMR (CDCl3) 8.67 (s, 1H, imidazole), 6.17 (d, 1H, J=2.1Hz, 1'-H), 5.03 (brs, 1H, 3'-OH, exchangeable with D2O), 4.47 (t, 1H, 5'-OH, exchangeable with D2O), 4.12 (m, 2H, 2',3'-H), 3.93 (s, 3H, COOCH3), 3.91 (s, 3H, COOCH3), 3.91 (m, 2H, 4',5'-H), 3.60 (s, 3H, OCH3), 3.32 (m, 1H, 5'-H); 13C-NMR (CDCl3, 75.48 MHz) 52.31 (COOCH3), 52.74 (COOCH3), 59.10 (OCH3), 60.03 (C-5'), 68.15 (C-3'), 84.85 (C-4'), 85.58 (C-2'), 88.83 (C-1'), 123.96 (C-4 or 5), 136.43 (C-5 or 4), 138.37 (C-2), 160.52 (C=O), 162.26 (C=O). Anal. Calcd. for C13H18N2O8 (MW 330.29): C, 47.27; H, 5.49; N, 8.48. Found: C, 47.54; H, 5.64; N, 8.28.
1-(2'-O-Methyl-ß-D-erythropentofuranosyl)-1H-imidazo[4,5-d]pyridazine-4,7(5H,6H)-dione (1). A solution of methyl 1-(2'-O-methyl-β-D-erythropentofuranosyl)-4,5-imidazoledicarboxylate (6) (165 mg, 0.5 mmol) and 99% hydrazine was refluxed for 6 hours. The excess hydrazine was removed by distillation in vacuo and the residue was coevaporated several times with water. The residue was dissolved in water and acidified with 2N HCl to pH 3. The solution was evaporated to dryness in vacuo. The residue was purified by preparative TLC on silica gel to afford a colorless solid 97 mg (65%). mp. >250 °C; Rf, 0.35 (chloroform/methanol/30% ammonium hydroxide, 2:2:1); 1H NMR (DMSO-d6): δ 8.73 (s,1H, imidazole), 6.50 (d, 1H, J=4.5 Hz, 1’-H), 4.27 (t, 1H, J= 4.8 Hz, 3’-H), 4.08 (t, 1H, J=4.5 Hz, 2’-H), 3.93 (m, 1H, 4’-H), 3.70 (dd, 1H, J=12.6 and 2.4 Hz, 5’-H), 3.58 (dd, 1H, J=12.6 and 3.0 Hz, 5’-H), 3.35 (s, 3H, OCH3). ms: (FAB) m/z 299 (MH+). HRMS Calcd. for C11H15N4O6: m/z 299.0992. Found (FAB): m/z 299.0990.