C. Schmuck and U. Machon
0.447 mmol). The solution was stirred at room temperature for 15 min.
The excess trifluoroacetic acid was removed in vacuo, and the obtained
residue was dissolved in methanol (25 mL). A saturated solution of picric
acid in water (20 mL) was then added, and the mixture was stirred for
one day at room temperature. The picrate salt 2a crystallized and was fil-
tered, washed several times with methanol, and dried to provide a yellow
crystallized after one day and was filtered and washed several times with
hexane. The product was dried to provide 15 (32.4 g, 77%) as a white
1
solid: m.p. 628C; H NMR (400 MHz, [D6]DMSO, 258C, TMS): d = 1.80
(s, 3H), 2.06 (s, 3H), 2.38 (s, 3H), 6.92 (d, 1H), 7.62 (t, 1H), 7.86 (d,
1H), 10.36 (s, 1H), 11.90 ppm (brs, 1H); 13C NMR (100 MHz,
[D6]DMSO, 258C, TMS): d = 21.2, 23.7, 24.1, 110.4, 118.6, 138.6, 151.8,
156.6, 169.4, 172.3 ppm; IR (KBr): n˜ = 3242, 3067, 1903, 1705, 1580,
1
solid (180 mg, 87%): m.p. 2608C; H NMR (400 MHz, [D6]DMSO, 258C,
TMS): d = 1.22 (t, 3H), 3.45 (m, 2H), 8.30–8.39 (m, 3H), 8.50 (brs, 3H),
8.58 (s, 2H), 8.97 (brs, 1H), 11.39 ppm (brs, 1H); 13C NMR (100 MHz,
[D6]DMSO, 258C, TMS): d = 14.8, 34.0, 124.2, 125.2, 125.6, 126.5, 140.5,
141.8, 145.6, 149.2, 154.3, 160.8, 162.3, 164.1 ppm; IR (KBr): n˜ = 3421,
3330, 3089, 1731, 1656, 1530, 1326 cmÀ1; ESI-MS: m/z: 236.35 [M]+.
1455, 1309 cmÀ1
6-Acetylaminopyridine-2-carboxylic acid (16):
.
A
solution of NaOH
(1.90 g, 47.6 mmol) in water (15 mL) was added to a solution of 6-ace-
tylamino-2-methylpyridinium acetate (15; 10.0 g, 47.6 mmol) in water
(70 mL). The obtained suspension was heated to 708C, and potassium
permanganate (45.1 g, 94.9 mmol) was added in small increments over a
period of 30 min. The reaction mixture was heated at reflux for 30 min
and filtered, the residue was washed several times with boiling water
(20 mL), the washings and the filtrate were combined, and the volume
was decreased to 40 mL in vacuo. The yellow solution was acidified to
pH ꢀ4 with concentrated hydrochloric acid. The white solid was filtered
and dried to provide the desired product 16 (2.74 g, 32%) as a white
solid: m.p. 2178C; 1H NMR (400 MHz, [D6]DMSO, 258C, TMS): d =
2.09 (s, 3H), 7.71 (d, 1H), 7.92 (t, 1H), 8.26 (d, 1H), 10.79 ppm (s, 1H);
13C NMR (100 MHz, [D6]DMSO, 258C, TMS): d = 23.9, 116.9, 120.1,
139.4, 146.9, 152.1, 165.9, 169.8 ppm; IR (KBr): n˜ = 3413, 3251, 2925,
Methyl
6-[((S)-1-carbamoyl-2-methylpropyl)carbamoyl]pyridine-2-car-
boxylate (11): A solution of 6-(methoxycarbonyl)pyridine-2-carboxylic
acid (6; 322 mg, 1.78 mmol), N,N-dimethylpyridin-4-ylamine (435 mg,
3.56 mmol), H-Val-NH2 hydrochloride (272 mg, 1.78 mmol), and DCC
(367 mg, 1.78 mmol) in dichloromethane (20 mL) was stirred at room
temperature for three days. The solvent was then removed in vacuo and
the crude product was purified by flash column chromatography on silica
gel (ethyl acetate/cyclohexane/ methanol 4:4:1) to give 11 (383 mg, 77%)
as a white solid: m.p. 1508C; 1H NMR (400 MHz, [D6]DMSO, 258C,
TMS): d = 0.91 (dd, 6H), 2.10 (m, 1H), 3.94 (s, 3H), 4.43 (dd, 1H), 7.24
(brs, 1H), 7.70 (brs, 1H), 8.18–8.26 (m, 3H), 8.39 ppm (d, 1H); 13C
NMR (100 MHz, [D6]DMSO, 258C, TMS): d = 17.7, 19.3, 31.4, 52.8,
57.1, 125.2, 127.4, 139.6, 146.4, 149.5, 162.4, 164.4, 172.2 ppm; IR (KBr):
n˜ = 3384, 2956, 1731, 1665, 1530, 1328 cmÀ1; EI-MS: m/z : 279.1 [M]+.
2607, 1726, 1644, 1538, 1452, 1306 cmÀ1
.
(6-Acetylaminopyridine-2-carbonyl)-tert-butoxycarbonylguanidine (17):
A solution of PyBOP (2.89 g, 5.55 mmol) and NMM (615 mg, 6.08 mmol)
in DMF (15 mL) was added to a solution of 6-acetylaminopyridine-2-car-
boxylic acid (16; 1.00 g, 5.55 mmol), Boc-protected guanidine (9, 884 mg,
5.55 mmol), and NMM (615 mg, 6.08 mmol) in DMF (15 mL). The reac-
tion mixture was stirred overnight at room temperature. After addition
of water (100 mL) and diethyl ether (50 mL) a white solid crystallized
and the suspension was stirred for 10 min at room temperature. The solid
was filtered, washed with diethyl ether, and dried to provide the desired
tert-Butoxycarbonyl-{6-[((S)-1-carbamoyl-2-methylpropyl)carbamoyl]pyr-
idine-2-carbonyl}guanidine (13): A solution of methyl 6-[((S)-1-carbamo-
yl-2-methylpropyl)carbamoyl]pyridine-2-carboxylate
(11;
900 mg,
3.22 mmol) and KOH (181 mg, 3.22 mmol) in methanol (30 mL) was
heated at 458C for 5 h. The solvent was removed under reduced pressure.
The obtained white solid, Boc-protected guanidine (9; 513 mg,
3.22 mmol), and NMM (410 mg, 4.05 mmol) were dissolved in DMF
(10 mL). To this solution was added
a
solution of PyBOP (1.67 g,
product 17 (1.32 g, 74%) as a
white solid: m.p. 1548C; 1H NMR
3.22 mmol) and NMM (410 mg, 4.05 mmol) in DMF (10 mL). The reac-
tion mixture was stirred at room temperature for one day. After addition
of water (100 mL), the solution was extracted with diethyl ether (3ꢃ
50 mL). The combined organic phases were dried over MgSO4, and the
solvent was removed in vacuo. The yellow crude product was purified by
flash column chromatography on silica gel (ethyl acetate/cyclohexane/
methanol 8:8:3) to give 13 (500 mg, 38%) as a white solid: m.p. 1658C;
1H NMR (400 MHz, [D6]DMSO, 258C, TMS): d = 0.96 (dd, 6H), 1.43 (s,
9H), 2.22 (m, 1H), 4.37 (dd, 1H), 7.15 (brs, 1H), 7.62 (brs, 1H), 8.23–
8.35 (m, 3H), 8.72 (brs, 1H) 8.87 ppm (brs, 1H); 13C NMR (100 MHz,
[D6]DMSO, 258C, TMS): d = 18.9, 19.4, 27.8, 30.5, 58.2, 78.5, 126.1,
139.8, 149.1, 157.6, 162.7, 172.3 ppm; IR (KBr): n˜ = 3385, 2972, 1670,
(400 MHz, [D6]DMSO, 258C, TMS): d = 1.42 (s, 9H), 2.13 (s, 3H), 7.84
(d, 1H), 8.04 (t, 1H), 8.35 (d, 1H), 8.85 (brs, 1H), 10.36 (brs, 1H),
10.91 ppm (brs, 1H); 13C NMR (100 MHz, [D6]DMSO, 258C, TMS): d =
23.9, 27.9, 78.1, 117.5, 117.9, 140.4, 151.2, 157.5, 169.7, 169.7 ppm; IR
(KBr): n˜
= 3467, 3386, 3130, 2983, 1703, 1672, 1555, 1407, 1313,
1149 cmÀ1; HR-MS (ESI) calcd for [M+Na]+: 344.1335; found 344.134.
(6-Acetylaminopyridine-2-carbonyl)guanidinium picrate (3): Trifluoro-
acetic acid (10 mL) was added to the protected receptor 17 (150 mg,
0.467 mmol), and the reaction mixture was stirred at room temperature
for 15 min. The excess trifluoroacetic acid was removed in vacuo, and the
obtained residue was dissolved in methanol (40 mL). A saturated so-
lution of picric acid in water (50 mL) was then added and the mixture
was stirred for 1 h. The salt 3 crystallized and was filtered and dried to
provide a yellow solid (179 mg, 85%): m.p. 2458C; 1H NMR (400 MHz,
[D6]DMSO, 258C, TMS): d = 2.16 (s, 3H), 7.86 (dd, 1H), 8.09 (t, 1H),
8.29 (d, 1H), 8.40 (brs, 2H), 8.58 (s, 2H), 8.61 (brs, 2H), 10.38 (s, 1H),
11.21 ppm (brs, 1H); 13C NMR (100 MHz, [D6]DMSO, 258C, TMS): d =
23.9, 119.0, 119.3, 124.2, 125.2, 140.4, 141.8, 145.6, 151.1, 154.6, 160.8,
163.2, 165.0, 169.6 ppm; IR (KBr): n˜ = 3361, 3200, 1739, 1692, 1643,
1569, 1298 cmÀ1; ESI-MS: m/z: 222.26 [M]+.
1573, 1414, 1308, 1142 cmÀ1
835.3826; found 835.383.
;
HR-MS (ESI) calcd for [2ꢃM+Na]+:
6-[((S)-1-Carbamoyl-2-methylpropyl)carbamoyl]pyridine-2-carbonylgua-
nidinium picrate (2b): Trifluoroacetic acid (6 mL) was added to the pro-
tected receptor 13 (150 mg, 0.369 mmol). The reaction mixture was stir-
red at room temperature for 90 min, the excess trifluoroacetic acid was
removed in vacuo, and the obtained residue was dissolved in methanol
(2 mL). A saturated solution of picric acid in water (5 mL) was then
added and the mixture was stirred for one day. The salt 2b crystallized,
and was filtered, washed with mixture of water and methanol (1:1), and
dried to provide a yellow solid (150 mg, 76%): m.p. 1628C; 1H NMR
(400 MHz, [D6]DMSO, 258C, TMS): d = 0.97 (d, 6H), 2.18 (m, 1H),
4.31 (dd, 1H), 7.16 (brs, 1H), 7.67 (brs, 1H), 8.30–8.39 (m, 3H), 8.44
(brs, 4H), 8.58 (s, 2H), 8.65 (d, 1H), 11.73 ppm (brs, 1H); 13C NMR
(100 MHz, [D6]DMSO, 258C, TMS): d = 19.0, 19.4, 30.0, 58.8, 124.2,
125.2, 126.0, 127.0, 140.3, 141.9, 146.3, 149.1, 154.5, 154.6, 160.8, 162.8,
164.6, 168.8, 172.6 ppm; IR (KBr): n˜ = 3381, 3200, 2993, 1728, 1643,
1566, 1313 cmÀ1; ESI-MS: m/z: 307.30 [M]+.
Isophthalic acid monobenzyl ester (24): A solution of triethylamine
(2.45 g, 24.2 mmol) in methanol (25 mL) was added to a suspension of
isophthalic acid (23; 4.00 g, 24.1 mmol) in methanol (50 mL) and water
(5 mL). The reaction mixture was stirred at room temperature overnight.
The methanol was removed under reduced pressure and the residue was
dried in vacuo. The oily residue was dissolved in DMF (60 mL), benzyl
bromide (4.53 g, 26.5 mmol) was added dropwise, and the solution was
heated at 1008C for 2 h. After cooling to room temperature, the mixture
was poured into aqueous sodium hydrogen carbonate (5%, 120 mL) and
extracted with ethyl acetate (3ꢃ70 mL) to remove diester impurities. The
aqueous layer was acidified to pH 3–4 with concentrated hydrochloric
acid and was then extracted with ethyl acetate (3ꢃ70 mL). The collected
organic layers were dried over MgSO4 and evaporated to dryness. The
white solid was purified by flash column chromatography on silica gel
6-Acetylamino-2-methylpyridinium acetate (15): A mixture of 6-methyl-
pyridin-2-ylamine (14; 21.6 g, 200 mmol) and acetic anhydride (43.3 g,
424 mmol) in toluene (150 mL) was heated at 958C. The solvent and the
excess acetic anhydride was removed in vacuo. The product had slowly
1116
ꢂ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2005, 11, 1109 – 1118