4020
C. R. Gade et al. / Bioorg. Med. Chem. 24 (2016) 4016–4022
Compounds 2–4 were synthesized by following literature
(3H, s) 3.72, (1H, m) 3.77–3.91, (1H, m) 4.09–4.15, (1H, m) 4.40–
report.36
4.47, (1H, m) 4.96–7.97, (1H, m, br) 5.23–5.28, (1H, s) 7.88. 13C
NMR (100 MHz, CDCl3): 28.31, 34.87, 35.81, 49.94, 50.49, 51.98,
52.52, 57.41, 57.70, 81.28, 125.50, 140.29, 151.65, 153.36, 153.81,
159.10, 159.16, 172.38. HRMS, (ESI-TOF): calcd for [C16H21N6O4Cl
(M+H)] m/z 397.1386, found m/z 397.1341.
4.1. (2S,4S)-4-N3benzoyl thymidyl Boc prolyl methyl ester (5a)
NBoc l-hydroxyl proline ester (0.5 g, 2.04 mmol) was dissolved
in anhydrous tetrahydrofuran (10 ml) and stirred under nitrogen
atmosphere for 10 min, N3benzoyl thymine (0.47 g, 2.04 mmol)
and triphenyl phosphine (0.642 g, 2.448 mmol) were added and
the resulting suspension stirred at 0 °C for 10 min under nitrogen
atmosphere. Diisopropyl azo dicarboxylate (0.485 ml, 2.44 mmol)
was added drop wise at 0 °C and the reaction was warmed to stir
at room temperature over night. The solvents were evaporated
and the crude reaction mixture purified by column chromatogra-
phy using methanol and dichloromethane on silica gel to obtain
466 mg of title compound as white foam in 50% yield. 1H NMR
(CDCl3, 400 MHz) d (ppm) (9H, s) 1.44, (3H, s) 1.96, (1H, m, br)
2.14, (1H, m, br) 2.76, (1H, m) 3.55–.367, (3H, s) 3.78, (1H, t
J = 8 Hz) 3.95, (1H, m, br) 4.33–4.39, (1H, m.br) 5.21, (1H, s) 7.37,
(2H, m) 7.46–7.50, (1H, t, J = 8 Hz) 7.64, (1H, d, J = 8 Hz. 13C NMR
(CDCl3, 100 MHz); d (ppm) 12.76, 28.31, 35.69, 49.38, 52.63,
57.98, 70.13, 81.39, 111.72, 129.27, 130.56, 131.59, 132.50,
135.20, 136.15, 150.06, 162.54, 168.93, 173.20. HRMS (ESI-TOF):
calcd for [C23H27N3O7Na, M+Na] m/z 480.1741 found m/z 480.1743.
4.6. (2S,4S)-N-Boc-4-thyminyl prolinol (6a)
Anhydrous THF (10 ml) was added to LiBH4 (0.038 g, 1.7 mmol)
and cooled to 0 °C and stirred under nitrogen atmosphere for
15 min followed by addition of compound 5a (0.2 g, 0.437 mmol dis-
solved in tetrahydrofuran) at 0 °C under nitrogen atmosphere, the
reaction was warmed to room temperature, and then stirred over
night at room temperature. After completion the reaction was
quenched with ammonium chloride solution and the reaction mix-
ture concentrated to dryness and the residue dissolved in water,
extracted with ethylacetate. Ethylacetate layer washed with water
and brine solution, dried with anhydrous sodium sulfate and con-
centrated followed by purification on silica gel using dichloro-
methane and methanol afforded 123 mg of alcohol 6a as white
solid in 87% yield. 1H NMR (CDCl3, 400 MHz): d (ppm) (s, 9H) 1.47,
(s, 3H) 1.94, (m, 1H) 1.98–2.0, (m, 1H) 2.39–2.46, (m, 1H) 3.23–
3.28, (m, 1H) 3.65–3.69, (m, 1H) 3.89–3.92, (m, 2H) 3.99–4.01, (s,
br 1H) 4.30, (m, 1H) 5.02–5.11, (s, 1H) 7.13, (s, 1H) 8.73. 13C NMR
(CDCl3, 100 MHz); d (ppm) 12.94, 28.22, 32.03, 31.67, 49.75, 51.40,
58.32, 66.63, 81.21, 112.03, 135.49, 151.06, 163.74. HRMS, (ESI-
TOF): calcd for [C15H23N3O5Na (M+Na)] m/z 348.1530 found m/z
348.1535.
4.2. General procedure for nucleosidation
Mesyl compound (1.0 g, 3.07 mmol), one of the protected nucle-
obases (N6benzoyl adenine or N4acetyl cytosine or 2-amino 6-
chloropurine (1.0 equiv)), anhydrous potassium carbonate
(0.636 g, 4.6 mmol) and
a
catalytic amount of 18-crown-6
4.7. Adeninealcohol (6b)
(0.162 g, 0.614 mmol, 0.2 equiv, 0.5 equiv in case of 2-amino 6-
chloro purine) were stirred at 75 °C for 12 h in 20 ml of anhydrous
DMF under nitrogen atmosphere. After completion of reaction
indicated by TLC, DMF removed in rota vapor under reduced pres-
sure and purified on silica gel using dichloromethane and
methanol.
0.5 g of N6benzoyl adenine methyl ester was reduced to Ade-
nine alcohol by following procedure as described for the synthesis
of compound 6a. 0.284 g of 5b obtained as white powder in 75%
yield. 1H NMR (400 MHz, CDCl3) (9H, s) 1.43, (1H, m) 2.30–2.41,
(1H, m, br) 2.65, (2H, m) 3.63–3.72, (1H, m, br) 3.89, (3H, m)
4.1–4.18, (1H, t J = 8 Hz) 5.0, (2H, s, br) 6.55, (1H, s) 7.93, (1H, s)
8.26. 13C NMR (100 MHz, CDCl3): 28.47, 33.56, 51.34, 52.22,
58.91, 66.30, 81.02, 114.34, 119.77, 124.05, 138.76, 139.34,
149.85, 152.88, 155.92, HRMS, ESI-TOF calcd for [C15H22N6O3 (M
+H)] m/z 335.1826, found m/z 335.1873.
4.3. Adenine methyl ester (5b)
0.932 g of white solid obtained in 65% yield. 1H NMR 400
MHzCDCl3: (9H, s) 1.46, (1H, m, br) 2.55, (1H, m) 2.97–2.99, (3H,
s) 3.71, (1H, m) 3.94–4.07, (1H, m) 4.18–4.22, (1H, m) 4.45–4.52,
(1H, m) 5.26, (2H, t J = 8 Hz) 7.53, (1H, m) 7.60–7.63, (1H, d,
J = 8 Hz) 8.03, (1H, s) 8.21, (1H, s) 8.79, (1H, s, br) 9.05. 13C NMR
100 MHz CDCl3: 28.23, 35.09, 36.16, 50.12, 50.92, 52.12, 52.45,
57.61, 81.26, 123.18, 128.01, 128.79, 132.76, 133.65, 141.18,
149.76, 152.00, 152.53, 153.31, 164.97, 172.34. HRMS (ESI-TOF):
calcd for [C23H26N6O5 (M+H)] m/z 467.2037, found m/z 467.2044.
4.8. Cytosine alcohol (6c)
0.5 g of N4acetyl cytosine methyl ester was reduced to cytosine
alcohol by following procedure as described for the synthesis of
compound 6a. 0.326 g of 5c obtained as white powder in 80% yield.
1H NMR (400 MHz, CDCl3): (9H, s) 1.43, (2H, m) 1.95–2.04, (1H, s)
2.35–2.36, (1H, s) 3.53–3.56, (2H, s) 3.63–3.72, (1H, s) 3.89–3.94,
(1H, s) 4.06–4.12, (1H, s, br) 5.36, (2H, s, br) 5.49, (1H, d J = 4 Hz)
6.08–6.09, (1H, d J = 4 Hz) 7.92–7.93. 13C NMR (100 MHz, CDCl3):
28.5, 34.37, 53.33, 59.54, 60.50, 67.50, 74.46, 80.70, 100.09,
156.82, 157.04, 164.17, 165.15, 17.31, 175.20. HRMS, (ESI-TOF)
calcd for [C14H24N4O4 (M+H)] m/z 311.1714 found m/z 311.1726.
4.4. Cytosine methylester (5c)
0.700 g of cytosine ester obtained as white solid in 60% yield. 1H
NMR (400 MHz, CDCl3): (9H, s) 1.38 ma, 1.42 mi, (3H, s) 2.18, (1H,
m) 2.34–2.37, (2H, m), 2.56–2.61, (3H, s) 3.65 mi, 3.67 ma, (1H, m)
4.35–4.38 ma, 4.57–4.60 mi, (1H, m) 5.35–5.41, (1H, m) 7.74–7.76,
(1H, m) 8.29–8.32, (1H, s, br) 8.89 ma, 8.95 mi. 13C NMR (100 MHz,
CDCl3): 24.71, 28.29, 28.42, 35.45, 36.18, 51.77, 52.25, 52.39, 57.54,
57.82, 74.10, 75.33, 80.36, 80.42, 104.2, 114.10, 153.87, 154.38,
159.40, 160.30, 163.51, 170.08, 172.60. HRMS: calcd for
[C17H24N4O6 (M+H)] m/z 381.1769 found m/z 381.1743.
4.9. (2S,4S)2-Amino 6-chloro purine alcohol (6d)
0.5 g of 2-amino 6-chloro purine ester was reduced to 2-amino
6-chloro purine alcohol by following procedure as described for the
synthesis of compound 6a. 0.326 g of compound 6d obtained in
70% yield as a white foam. 1H NMR (400 MHz, CDCl3 (9H, s) 1.45,
(1H, m) 2.02–2.07, (1H, m) 2.30–2.37, (1H, m) 2.60–2.65, (1H, m)
3.62–3.66, (1H, m) 3.71–3.75, (1H, m) 3.85–3.87, (2H, m) 4.08–
4.10, (1H, m) 4.82–4.90, (2H, s, br) 5.39, (1H, s) 7.87 13C NMR
100 MHz CDCl3: 28.47, 31.99, 33.25, 50.77, 52.22, 59.04, 62.71,
4.5. (2S,4S) 2-Amino 6-chloro purine ester (5d)
0.609 g of obtained as white solid in 50% yield. 1H NMR
(400 MHz, CDCl3): (9H, s) 1.43, (1H, m, br) 2.48, (1H, m, br) 2.86,