General
Reagents (generally ≥ 99%) were used as purchased. Microwave assisted synthesis was carried out on a CEM focused microwave reactor (model Discover). Reactions were monitored by analytical thin-layer chromatography (TLC) using Merck silica gel 60 F 254 aluminum plates. Chromatograms were visualized either with UV-light, by staining with iodine or with a “cerium reagent” (prepared by dissolving 2 g of phosphomolybdic acid and 1 g of Ce(SO
4)
2 in 100 mL of 10% aqueous H
2SO
4) and subsequent heating. Flash chromatography [
12]: silica gel 60 (230-400 mesh) from Merck. Gas chromatography (GLC): HP-6890, with H
2 as a carrier gas, FID (flame ionisation detector). NMR: Bruker DPX 300, DRX 500 and AC 250 instruments. Chemical shifts (
δ) are given in ppm relative to the solvent reference. Unless noted otherwise DMSO-D
6 was the solvent used.
13C-NMR spectra were measured under proton decoupling and the number of bound protons (multiplicities) determined by DEPT. IR spectroscopy: Perkin Elmer FT-IR Paragon 1000 using the ATR-technique. MS: Finnigan MAT Incos 50 Galaxy System (DIP-MS) or a Finnigan MAT 900 spectrometer; HRMS were recorded on a Finnigan HSQ-30 (HR-EI-MS) or on a Finnigan MAT 900 (HR-ESI-MS). The method of ionization is given in parentheses. Melting points (m.p.) were measured on a Büchi B-545 apparatus and are uncorrected.
2-(6-Chloro-purin-9-ylmethoxy)-ethanol (
5) [
8]: In a first flask, NaH (55%, 311 mg, 7.12 mmol) was added to a stirred solution of 6-chloropurine (1.00 g, 6.47 mmol) in DMF (5 mL) at RT and stirring was continued for 2 h. In a second flask, a solution of 1,3-dioxolane (542 µL, 7.76 mmol) in cyclohexene (2 mL) was cooled to -78 °C and TMSI (1.02 mL, 7.12 mmol) was added slowly. After 30 min, the first flask was cooled to -50 °C (Note: a precipitate was observed at ca. -60 °C) and the contents of the second flask was added. After 2 hours the mixture was allowed to warm to RT and 10% aqueous solutions of KF (10 mL) and NaHCO
3 (10 mL) were added. After 1 h, the mixture was diluted with H
2O (50 mL) and extracted with EtOAc (5 x 50 mL). The combined organic phases were washed with brine (50 mL), dried (MgSO
4) and the solvent was removed under reduced pressure. After flash chromatography (EtOAc/MeOH 10:1) the product
5 was obtained as a light yellow solid (798 mg, 54%). (Note: Scale up of the reaction proved to be difficult. In each case a variety of byproducts were obtained, including regioisomers during the amination reactions. The product could still be purified by flash chromatography, but the yields were generally lower). M.p. 147 °C (lit. [8c]: 149-150 °C); TLC: R
f= 0.24 (EtOAc/MeOH 10:1);
1H-NMR (250 MHz, CDCl
3): δ = 8.77 (s, 1H, H-2), 8.27 (s, 1H, H-8), 5.75 (s, 2H, NCH
2O), 3.77-3.66 (m, 4H, HOCH
2CH
2O), 1.94 (bs, 1H, OH);
13C-NMR (63 MHz, CDCl
3): δ = 152.0 and 149.1 (C4 and C6), 151.9 (C2), 147.6 (C8), 130,7 (C5), 73.1 (N
CH
2O), 71.1 (HOCH
2CH
2O), 59.8 (HO
CH
2CH
2O); IR (ATR, cm
-1): 3378 (m), 1593 (m), 1560 (s), 1335 (m), 1208 (m), 1116 (s), 1073 (m), 940 (m), 753 (m), 635 (m); MS (EI, 70 eV): m/z (%) = 229 (13) [M(
35Cl) + 1
+], 198 (23), 183 (36), 168 (80), 154 (64), 119 (47), 104 (22); HRMS (EI, 70 eV) calcd. for [M(
35Cl) – CH
2O]
+ C
7H
735ClN
4O: 198.0308, found: 198.030.
General protocols for the amination of 5 (compare Table 1): Conditions A: In a sealed microwave tube
5 (57.2 mg, 0.25 mmol) was reacted with the amine (1.1 eq, 0.275 mmol) and
iPr
2NEt (1.1 eq, 0.275 mmol) in EtOH (3 mL) as solvent. The reaction mixture was stirred for 10 min under microwave irradiation (120 °C, 150 W). The solvent was removed under reduced pressure and the crude mixture was directly subjected to flash chromatography (EtOAc/MeOH 10:1).
Conditions B: In a Schlenk flask,
5 (57.2 mg, 0.25 mmol) was reacted with the amine (1.1 eq, 0.275 mmol) and
iPr
2NEt (1.1 eq, 0.275 mmol) in BuOH (3 mL) as solvent. The reaction mixture was stirred for 16 h at 75 °C. The solvent was removed under reduced pressure and the crude mixture was directly subjected to flash chromatography (EtOAc/MeOH 10:1).
Conditions C: In a Schlenk flask,
5 (57.2 mg, 0.25 mmol) was reacted with the amine (5 eq, 1.25 mmol) in EtOH (3 mL) as solvent. The reaction mixture was stirred for 16 h at 75 °C. The solvent was removed under reduced pressure and the crude mixture was directly subjected to flash chromatography (EtOAc/MeOH 10:1).
2-(6’-Cyclohexylamino-purin-9’-ylmethoxy)-ethanol (
12): The acyclic nucleoside analog
12 was prepared according to the general protocols for the amination of
5 using conditions A, B or C (for yields see
Table 1). M.p. 102 °C; TLC: R
f = 0.21 (EtOAc/MeOH 10:1);
1H-NMR (250 MHz): δ = 8.26 and 8.22 (2s, 2H, H-2’ and H-8’), 7.53 (d, J = 8.4 Hz, 1H, N
H), 5.56 (s, 2H, NCH
2O), 4.67 (t, J = 5.2 Hz, 1H, OH), 3.53-3.45 (m, 4H, HOC
H2C
H2O) 1.90-1.10 (m, 11H, CyHex);
13C-NMR (63 MHz): δ = 152.8 (C2’), 153.7 and 149.0 (C4’ and C6’), 140.7 (C8’), 118.5 (C5’), 72.1 (N
CH
2O), 70.7 (HOCH
2CH
2O), 59.8 (HO
CH
2CH
2O), 48.6 (NCH), 32.3, 25.1, 24.9 (CyH); IR (ATR, cm
-1): 3323 (m), 2927 (m), 1615 (s), 1478 (m), 1343 (m), 1293 (m), 1217 (m), 1114 (m), 754 (m); MS (EI, 70 eV): m/z (%) = 291 (8) [M
+], 216 (19), 209 (50), 174 (24), 160 (26), 148 (26), 135 (100)55 (17); HRMS (EI, 70 EV) calcd. for [M
+] C
14H
21N
5O
2: 291.1695, found: 291.169.
2-(6’-Phenylamino-purin-9’-ylmethoxy)-ethanol (
13): The acyclic nucleoside analog
13 was prepared according to the general protocols for the amination of
5 using conditions A, B or C (for yields see
Table 1). M.p. 169 °C; TLC: R
f = 0.27 (EtOAc/MeOH 10:1);
1H-NMR (250 MHz): δ = 9.90 (s, 1H, N
H), 8.46 and 8.44 (2s, 2H, H-2’ and H-8’), 7.95 (d, J = 7.8 Hz, 2H, H
ar), 7.33 (t, J = 7.7 Hz, 2H, H
ar), 7.04 (t, J = 7.3 Hz, 1H, H
ar), 5.64 (s, 2H, NCH
2O), 4.69 (t, J = 5.3 Hz, 1H, OH), 3.58-3.46 (m, 4H, HOC
H2C
H2O);
13C-NMR (63 MHz): δ = 152.3 (C2’), 152.0 and 149.8 (C4’ and C6’), 142.0 (C8’), 139.5 (s, C
ar), 128.3, 122.5, 120.7 (d, C
ar), 119.5 (C5’), 72.3 (N
CH
2O), 70.8 (HOCH
2CH
2O), 59.8 (HO
CH
2CH
2O); IR (ATR, cm
-1): 3322 (m), 1621 (s), 1580 (s), 1496 (m), 1477 (m), 1115 (m), 753 (m); MS (EI, 70 eV): m/z (%) = 285 (21) [M
+], 240 (8), 224 (30), 211 (41), 210 (100), 77 (23); HRMS (EI, 70 eV) calcd. for [M
+] C
14H
15N
5O
2: 285.1226, found: 285.122.
2-(6’-Benzylamino-purin-9’-ylmethoxy)-ethanol (
14) [
10]: The acyclic nucleoside analog
14 was prepared according to the general protocols for the amination of
5 using conditions A, B or C (for yields see
Table 1). M.p. 111 °C (lit. [
10]: 113-114 °C); TLC: R
f = 0.22 (EtOAc/MeOH 10:1);
1H- NMR (250 MHz): δ = 8.38 (s, 1H, N
H), 8.30 and 8.24 (2s, 2H, H-2’ and H-8’), 7.36-7.18 (m, 5H, H
ar), 5.58 (s, 2H, NCH
2O), 4.72 (s, 2H, NCH
2C
ar), 4.67 (t, J = 5.2 Hz, 1H, OH), 3.54-3.46 (m, 4H, HOC
H2C
H2O);
13C-NMR (63 MHz): δ = 154.3 and 152.7 (C4’ and C6’), 154.3 (C2’), 141.0 (C8’), 139.9 (s, C
ar), 128.1, 127.0, 126.5 (d, C
ar), 118.8 (C5’), 72.2 (N
CH
2O), 70.7 (HOCH
2CH
2O), 59.8 (HO
CH
2CH
2O), 42.8 (N
CH
2C
ar); IR (ATR, cm
-1): 3283 (m), 2926 (m), 1616 (s), 1482 (m), 1343 (m), 1217 (m), 1114 (m), 1073 (m), 761 (m), 645 (m); MS (EI, 70 eV): m/z (%) = 299 (39) [M
+], 254 (8), 238 (16), 225 (66), 224 (91), 120 (26), 106 (95), 91 (100), 79 (16), 65 (25); HRMS (EI, 70 eV) calcd. for [M
+] C
15H
17N
5O
2: 299.1382, found: 299.138.
2-[6’-(p-Morpholinyl-phenylamino)-purin-9’-ylmethoxy]-ethanol (
15): The acyclic nucleoside analog
15 was prepared according to the general protocols for the amination of
5 using conditions A, B or C (for yields see
Table 1). M.p. 186 °C; TLC: R
f = 0.16 (EtOAc/MeOH 10:1);
1H-NMR (250 MHz): δ = 9.69 (s, 1H, N
H), 8.41 and 8.36 (2s, 2H, H-2’ and H-8’), 7.74 (d, J = 9.0 Hz, 2H, H
ar), 6.92 (d, J = 9.0 Hz, 2H, H
ar), 5.62 (s, 2H, NCH
2O), 4.68 (t, J = 5.3 Hz, 1H, OH), 3.74 (t, J = 4.8 Hz, 4H, NCH
2C
H2O), 3.56-3.45 (m, 4H, HOC
H2C
H2O), 3.06 (t, J = 4.8 Hz, 4H, NC
H2CH
2O);
13C-NMR (63 MHz): δ = 152.4 (C2’), 152.1 and 149.5 (C4’ and C6’), 147.0 (s, C
ar), 141.6 (C8’), 131.6 (s, C
ar), 122.2 (d, C
ar), 119.2 (C5’), 115.2 (d, C
ar), 72.3 (N
CH
2O), 70.8 (HOCH
2CH
2O), 66.0 (NCH
2CH
2O), 59.8 (HO
CH
2CH
2O), 49.0 (N
CH
2CH
2O); IR (ATR, cm
-1): 3323 (m), 2922 (m), 1618 (s), 1583 (m), 1511 (s), 1477 (m), 1230 (m), 1117 (m), 926 (m), 758 (m); MS (EI, 70 eV): m/z (%) = 270 (100) [M
+], 309 (10), 296 (67), 238 (57), 209 (12), 155 (7), 125 (19), 77 (10); HRMS (EI, 70 eV) calcd. for [M
+] C
18H
22N
6O
3: 370.1753, found: 370.175.
2-{6’-[2-(1’’H-Indol-2’’-yl)-ethylamino]-purin-9’-ylmethoxy}-ethanol (
16): The acyclic nucleoside analog
16 was prepared according to the general protocols for the amination of
5 using conditions A, B or C (for yields see
Table 1). M.p. 147 °C; TLC: R
f = 0.17 (EtOAc/MeOH 10:1);
1H-NMR (250 MHz): δ = 10.80 (s, 1H, H-1’’), 8.31 and 8.28 (2s, 2H, H-2’ and H-8’), 7.87 (s, 1H, CH
2N
H), 7.65 (d, J = 7.5 Hz, 1H, H-7’’), 7.35 (d, J = 7.8 Hz, 1H, H-4’’), 7.21 (s, 1H, H-2’’), 7.10-6.96 (m, 2H, H-5’’ and H- 6’’), 5.58 (s, 2H, NCH
2O), 4.68 (bs, 1H, OH), 3.56-3.47 (m, 6H, HOC
H2C
H2O and NC
H2CH
2), 3.04 (t, J = 8.0 Hz, 2H, NCH
2C
H2);
13C-NMR (63 MHz): δ = 154.4 and 148.9 (C4’ and C6’), 152.8 (C2’), 140.9 (C8’), 136.2 (C3a’’), 127.2 (C7a’’), 122.5 (C2’’), 120.8 (C5’’), 118.8 (C5), 118.4 and 118.1 (C4’’ and C6’’), 111.8 (C3’’), 111.2 (C7’’), 72.2 (N
CH
2O), 70.7 (HOCH
2CH
2O), 59.8 (HO
CH
2CH
2O), 48.5 (N
CH
2CH
2C
ar), 25.1 (NCH
2CH
2C
ar); IR (ATR, cm
-1): 3284 (m), 2924 (m), 1619 (s), 1454 (m), 1337 (m), 1223 (m), 1112 (m), 1072 (m), 742 (m); MS (ESI): m/z (%) = 727 (9) [2M +Na
+], 449 (10), 375 (100) [M + Na
+], 353 (50) [M + H
+], 279 (12); HRMS (ESI) calcd. for [M + H
+] C
18H
21N
6O
2: 353.1725, found: 353.172.
2-(6-chloro-purin-9-ylmethoxy)-ethyl acetate (
17) [
11]: Ac
2O (275 µL, 2.88 mmol) was added at RT to a stirred solution of
5 (300 mg, 1.31 mmol), Et
3N (235 µL, 1.57 mmol) and DMAP (20 mg, 0.16 mmol) in CH
2Cl
2 (8 mL). The resulting mixture was stirred for 1 h at RT and was then quenched by addition of sat. aq. NaHCO
3 (10 mL). The water phase was extracted with CH
2Cl
2 (3 x 10 mL) and the combined organic layers were washed with sat. aq. NaHCO
3 (2 x 10 mL) and brine (10 mL), dried (MgSO
4) and concentrated under reduced pressure. The residue was purified by flash chromatography (EtOAc) to give the product
17 as a white solid (270 mg, 76%). M.p. 96 °C (lit. [11b]: 96-97 °C); TLC: R
f = 0.44 (EtOAc);
1H-NMR (250 MHz): δ = 8.85 (s, 1H, H-2), 8.82 (s, 1H, H-8), 5.73 (s, 2H, NCH
2O), 4.08-4.05 and 3.77-3.74 (m, 4H, HOCH
2CH
2O), 1.90 (s, 3H, CH
3);
13C-NMR (63 MHz): δ = 170.0 (C=O), 152.0 and 149.1 (C4 and C6), 151.9 (C2), 147.6 (C8), 130.8 (C5), 72.8 (N
CH
2O), 67.2 (HOCH
2CH
2O), 62.6 (HO
CH
2CH
2O), 20.4 (CH
3); IR (ATR, cm
-1): 2950 (s), 1735 (s), 1592 (m), 1560 (s), 1335 (m), 1234 (s), 1141 (m), 1102 (m), 1049 (m), 938 (m), 752 (m), 636 (m); MS (EI, 70 eV): m/z (%) = 270 (5) [M]
+, 259 (19), 210 (9), 183 (31), 197 (92), 154 (12), 104 (13), 87 (100); HRMS (EI, 70 eV) calcd. for [M]
+ C
10H
11ClN
4O
3: 270.0520, found: 270.052.
6-Chloro-9-{2-[dimethyl-(1,1,2-trimethyl-propyl)-silanyloxy]-ethoxymethyl}-9H-purine (18): Chloro-purine 5 (300 mg, 1.31 mmol) was added to dry pyridine (2.5 mL) at RT and the mixture was stirred for 5 min. ThxMe2SiCl (409 µL, 1.97 mmol) was added and after stirring was continued for 16 h, the reaction was quenched by addition of sat. aq. NaHCO3 (10 mL). The resulting mixture was stirred at RT for 30 min, then the water phase was extracted with EtOAc (4 x 10 mL). The combined organic layers were washed with water (10 mL) and brine (10 mL), dried (MgSO4) and concentrated under reduced pressure. The residue was then purified by flash chromatography (c-Hex/EtOAc 2:1), giving 18 as a white solid (412 mg, 85%). M.p. 58 °C; TLC: Rf = 0.18 (c-Hex/EtOAc 2:1); 1H-NMR (250 MHz): δ = 8.84 and 8.82 (2s, 2H, H-2 and H-8), 5.72 (s, 2H, NCH2O), 3.62 (s, 4H, OCH2CH2O), 1.45 (septet, J = 6.8 Hz, 1H, Me2CH), 0.73 (d, J = 6.8 Hz, 6H, (CH3)2CH), 0.69 (s, 6H, C(CH3)2), -0.03 (s, 6H, (CH3)2Si); 13C-NMR (63 MHz): δ = 152.0 and 149.1 (C4 and C6), 151.8 (C2), 147.5 (C8), 130.8 (C5), 73.1 (NCH2O), 70.9 (HOCH2CH2O), 61.4 (HOCH2CH2O), 33.5 (Me2CH), 24.4 (Me2CSi), 20.0 ((CH3)2CH), 18.1 ((CH3)2CSi), -3.6 ((CH3)2Si); IR (ATR, cm-1): 2955 (m), 2866 (m), 1592 (m), 1560 (s), 1251 (m), 1208 (m), 1141 (m), 1096 (s), 937 (m), 830 (s), 777 (m); MS (EI, 70 eV): m/z (%) = 285 (8) [M – C6H13+], 169 (33), 167 (100), 117 (5), 104 (6), 73 (12); HRMS (ESI) calcd. for [M – C6H13+] C10H14ClN4O2Si: 285.0574, found: 285.057.