Molecules 2011, 16
561
and the mixture was the poured into an ice-cold solution of 5% NaHCO3 (50 mL). The product was
extracted with diethyl ether (3 50 mL), washed with saturated aqueous NaCl
×
(3 × 50 mL) and dried over Na2SO4. The solvent was evaporated and the crude product, 5-cyano-2-
ethoxy-2-methyl-N-(2-phenyl)-ethyl-1,3-dioxane-5-carboxamide (9), was subjected to silica gel
chromatography, eluting with a mixture of DCM and MeOH (90:10, v/v). The product (9) was
1
obtained as oil (1.5 g, 76%). H-NMR (400 MHz, DMSO) δ = 8.55, 8.44, 8.26, 7.98 (t each, 1H,
J = 5.5 Hz, NH), 7.28 (m, 2H, Ph), 7.21 (m, 3H, Ph), 4.32, 4.02, 3.57, 3.45 (q each, 2H, J = 7 Hz,
CH2CH3), 5.82, 5.81, 5.54, 5.53, 4.28, 4.23, 4.07, 3.99 (d each, 4H, J = 5.5 Hz and J = 11.5 Hz,
CH2O), 3.79-3.66 and 3.41-3.29 (m, 2H, J = 6 Hz, CH2N), 2.77, 2.74, 2.56 (t each, 2H, J = 7.5 Hz,
CH2Ph), 2.03, 1.99, 1.42 1.36 (s each, 3H, CH3), 1.33, 1.17, 1.15, 1.06 (t each, 3H, J = 7.0 Hz,
CH2CH3). ESI+-MS: m/z[M + Na]+ obsd.341.3, calcd. 341.1.
5-cyano-2-ethoxy-2-methyl-N-(2-phenyl)-ethyl-1,3-dioxane-5-carboxamide (9) (1.3 g, 4.08 mmol) was
dissolved in 80% aqueous acetic acid (50 mL) and left for 1 h at room temperature. The solution was
evaporated to dryness and the residue was coevaporated three times with water. The product was
purified by silica gel colum chromatogaphy eluting with a mixture of DCM and MeOH (95:5, v/v). The
1
product (10) was obtained as solid foam (1.2 g, 90%). H-NMR (400 MHz, CDCl3): δ = 8.28 (t, 1H,
J = 5.6 Hz, NH), 7.30 (m, 2H, Ph), 7.21 (m, 3H, Ph), 5.81 (t, 1H, J = 5.6 Hz, OH), 4.34 (s, 2H,
CH2OAc), 3.74 (t, 2H, J = 5.2 Hz, CH2OH), 3.31 (2H, CH2N), 2.74 (t, 2H, J = 7.6 Hz, CH2Ph), 2.03
(s, 3H, C(O)CH3). 13C-NMR (101 MHz, CDCl3): δ = 170.05 (C=O Ac), 164.73 (C(O)NH), 137.93
(Ph), 128.82 (Ph), 128.75 (Ph), 126.92 (Ph), 117.60 (CN), 63.41(CH2OAc), 62.96 (CH2OH),
51.01(C2), 41.55 (CH2NH), 35.27 (CH2Ph), 20.54 (CH3) ppm. ESI+-MS: m/z [M + Na]+ obsd.
313.1146, calcd. 313.1159.
Thymidine 5´-bis[3-acetyloxy-2-cyano-2-(2-phenylethylcarbamoyl)propyl]phosphate (1). 3’-O-
Levulinoylthymidine (11) was coevaporated three times from dry pyridine and dried on P2O5
overnight. To a solution of dried 11 (0.15 g, 0.45 mmol) in dry DCM (1.2 mL), anhydrous
triethylamine (0.32 mL, 2.27 mmol) and bis(diethylamino)chlorophosphine (135 µL, 0.64 mmol) was
added, and the reaction mixture was stirred for 2 h under nitrogen. The product 12 was filtered through
a short silica gel column eluting with a mixture of anhydrous ethyl acetate and triethylamine in hexane
(60:0.5:39.5, v/v/v). The solvent was removed under reduced pressure and the residue was
coevaporated three times from dry MeCN to remove the traces of triethylamine.The residue (0.16 g)
was dissolved in dry MeCN (0.5 mL) and compound 10 (0.44 g, 1.53 mmol) in dry MeCN (0.5 mL)
and tetrazole (2.72 mmol; 6.10 mL of 0.45 mol L-1 solution in MeCN) were added under nitrogen. The
reaction mixture was stirred for 4 h at room temperature. The phosphite ester 13 formed was oxidized
with I2 (0.1 mol L-1) in a mixture of THF, H2O and lutidine (4:2:1, v/v/v; 7 mL) by stirring overnight at
room temperature. The crude product, 3´-O-levulinoylthymidine 5´-bis[3-acetyloxy-2-cyano-2-(2-
phenylethylcarbamoyl)propyl]phosphate (13) was isolated by DCM/aq. NaHSO3 work up, and purified
on a silica gel column eluted with ethylacetate, followed by a stepwise gradient from a mixture of
DCM and MeOH (98:2, v/v) up to 30% MeOH. The purification was repeated using ethyl acetate and a
mixture of DCM and MeOH (90:10, v/v) as an eluent. The product (13) obtained as solid foam was
contaminated by some unidentified impurities. The product was characterizied by HPLC-MS eluting