K. Yoshikawa et al. / Bioorg. Med. Chem. 17 (2009) 8206–8220
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washed with brine (1.50 L) and dried over Na2SO4. Concentration
of the solution in vacuo afforded (1S,3R,4S)-4-{[(benzyloxy)car-
bonyl]amino}-3-[(tert-butoxycarbonyl)amino]cyclohexanecarbox-
ylic acid (323 g) as a colorless solid. This compound was used in
the next step without further purification. 1H NMR (CDCl3) d:
1.30–1.48 (1H, br), 1.43 (9H, s), 1.50–1.68 (1H, br), 1.70–1.88
(2H, br), 1.90–2.12 (2H, br), 2.35–2.57 (1H, br), 3.64–3.77 (1H,
br), 4.00–4.14 (1H, br), 4.60–4.75 (0.5H, br), 5.02–5.14 (2.5H, m),
5.20–5.35 (0.5H, m), 6.30–6.50 (0.5H, br), 7.29–7.37 (5H, m). MS
(ESI) m/z: 393 (M+H)+.
(203 mg, 0.438 mmol, 92%) as a pale yellow powder. 1H NMR
(CDCl3) d: 1.43 (9H, br s), 1.47–2.15 (6H, m), 2.62–2.75 (1H, m),
2.95 (3H, s), 3.06 (3H, s), 4.12–4.22 (1H, m), 4.23–4.30 (1H, br),
4.81–4.90 (1H, m), 6.83 (1H, dd, J = 7.3, 2.0 Hz), 7.50–7.58 (2H,
m), 8.06 (1H, dd, J = 7.3, 0.7 Hz), 8.10 (1H, d, J = 0.7 Hz). MS (ESI)
m/z: 464 (M+H)+.
5.1.6. tert-Butyl (1R,2S,5S)-2-{[(5-chloro-1H-benzimidazol-2-yl)-
carbonyl]amino}-5-[(dimethylamino)carbonyl]cyclohexylcarba-
mate (6e)
To a solution of (1S,3R,4S)-4-{[(benzyloxy)carbonyl]amino}-3-
[(tert-butoxycarbonyl)amino]cyclohexanecarboxylic acid (322 g)
in CH2Cl2 (3.00 L) were added dimethylamine hydrochloride
(119 g, 1.45 mol), 1-ethyl-3-(3-dimethylaminopropyl)carbodiim-
ide hydrochloride (EDCꢀHCl) (209 g, 1.09 mol), 1-hydroxybenzotri-
azole (HOBt) (148 g, 1.10 mol), and Et3N (101 mL, 724 mmol). After
stirring for four days at room temperature, 10% citric acid aqueous
solution (6.00 L) and CH2Cl2 (3.00 L) were added. After the precip-
itate was removed by filtration, the organic layer was separated
and washed successively with saturated NaHCO3 aqueous solution
(1.50 L), a mixture of 10% citric acid aqueous solution (5.00 L) and
brine (6.00 L), saturated NaHCO3 aqueous solution (1.50 L), and
then brine (1.50 L). The organic layer was dried over Na2SO4 and
concentrated in vacuo. The residue was dissolved in EtOAc
(1.00 L), and hexane (1.50 L) was added to this solution. The resul-
tant precipitate was collected by filtration to give the title
compound (230 g, 548 mmol, 76%) as a colorless solid. mp: 129–
132 °C. 1H NMR (CDCl3) d: 1.23–1.41 (2H, m), 1.44 (9H, s), 1.68–
2.05 (4H, m), 2.56–2.66 (1H, m), 2.90 (3H, s), 3.03 (3H, s), 3.67–
3.77 (1H, br), 4.09–4.17 (1H, m), 4.60–4.75 (1H, br), 5.03–5.25
(3H, m), 7.29–7.37 (5H, m). MS (ESI) m/z: 420 (M+H)+. HRMS
(ESI) m/z: Calcd for C22H34N3O5: 420.24985. Found: 420.25018
(M+H)+.
To a solution of 3 (235 mg, 0.558 mmol) in THF (5 mL) was
added 10% Pd/C (50 mg) and the mixture was stirred overnight at
room temperature under hydrogen atmosphere (ambient pres-
sure). The catalyst was removed by filtration and the filtrate was
concentrated in vacuo. The residue was dissolved in DMF (5 mL)
and to this solution were added 5e19 (165 mg, 0.844 mmol), HOBt
(100 mg, 0.740 mmol), and EDCꢀHCl (171 mg, 0.892 mmol). After
stirring for four days, the mixture was concentrated in vacuo. To
the residue were added CH2Cl2 and saturated NaHCO3 aqueous
solution. The organic layer was separated, dried over Na2SO4, and
concentrated in vacuo. The residue was chromatographed
(MeOH/CH2Cl2 = 1:10) to give the title compound (250 mg, 0.539
mmol, 97%) as a colorless solid. 1H NMR (DMSO-d6) d: 1.01–2.00
(6H, m), 1.34 (9H, s), 2.79 (3H, s), 2.80–2.95 (1H, m), 2.98 (3H, s),
3.89–4.06 (2H, m), 7.08 (1H, d, J = 6.6 Hz), 7.31 (1H, d, J = 8.5 Hz),
7.62 (2H, br s), 8.47 (1H, d, J = 8.5 Hz), 13.46 (1H, br s). IR (KBr)
cmꢁ1: 3660, 3163, 2971, 1709, 1668, 1622, 1552, 1423, 1242,
1159, 1066, 1057. MS (ESI) m/z: 464 (M+H)+.
5.1.7. N-{(1R,2S,5S)-2-{[(7-Chloroimidazo[1,2-a]pyridin-2-yl)car-
bonyl]amino}-5-[(dimethylamino)carbonyl]cyclohexyl}-5-meth-
yl-4,5,6,7-tetrahydrothiazolo[5,4-c]pyridine-2-carboxamide hyd-
rochloride (8a)
To a suspension of 6a (203 mg, 0.438 mmol) in CH2Cl2 (5 mL)
was added saturated HCl ethanolic solution (5 mL) and the mixture
was stirred for 2 h. The solvent was evaporated and to the residue
were added MeOH and Et2O. After concentration, Et2O was added
again and the resultant precipitate was collected by filtration to
5.1.4. tert-Butyl (1R,2S,5S)-2-amino-5-[(dimethylamino)carbonyl]-
cyclohexylcarbamate (4)
To a solution of 3 (189 g, 454 mmol) in MeOH (8.00 L) was
added 10% Pd/C (57.0 g) and the mixture was stirred for 3 h at
room temperature under hydrogen atmosphere (7 atm). The cata-
lyst was removed by filtration and the filtrate was concentrated
in vacuo. After codistillation of EtOH with toluene, hexane
(1.50 L) was added to the residue. The resultant precipitate was
collected by filtration to give the title compound (121 g, 424 mmol,
93%) as a colorless powder. 1H NMR (CDCl3) d: 1.20–1.77 (6H, m),
1.45 (9H, s), 2.20–2.35 (1H, br), 2.63–2.74 (1H, m), 2.92 (3H, s),
3.02 (3H, s), 3.02–3.11 (2H, m), 3.74–3.82 (1H, m), 4.88–5.00 (1H,
br). MS (ESI) m/z: 286 (M+H)+.
give
N-{(1S,2R,4S)-2-amino-4-[(dimethylamino)carbonyl]cyclo-
hexyl}-7-chloroimidazo[1,2-a]pyridine-2-carboxamide (193 mg)
as a colorless solid. 1H NMR (DMSO-d6) d: 1.41–1.56 (1H, m),
1.69–1.90 (3H, m), 1.92–2.08 (2H, m), 2.82 (3H, s), 3.07 (3H, s),
3.23–3.33 (1H, m), 3.74 (1H, br s), 4.05–4.15 (1H, m), 7.28 (1H,
dd, J = 7.3, 2.0 Hz), 7.86 (1H, d, J = 2.0 Hz), 8.30 (3H, br s), 8.64
(1H, d, J = 6.8 Hz), 8.68 (1H, s), 8.80 (1H, d, J = 7.3 Hz). MS (ESI)
m/z: 364 (M+H)+.
This solid was dissolved in DMF (5 mL) and lithium 5-methyl-
4,5,6,7-tetrahydrothiazolo[5,4-c]pyridine-2-carboxylate (7) (134 mg,
0.657 mmol), HOBt (88.8 mg, 0.657 mmol), and EDCꢀHCl (168 mg,
0.876 mmol) were added. After stirring for three days, the mixture
was concentrated in vacuo. To the residue were added CH2Cl2 and
saturated NaHCO3 aqueous solution. The organic layer was sepa-
rated, dried over Na2SO4, and concentrated in vacuo. The residue
was chromatographed (MeOH/CH2Cl2 = 1:9). The obtained com-
pound was dissolved in 1 N HCl ethanolic solution and concen-
trated in vacuo. To the residue was added Et2O and the resultant
precipitate was collected by filtration to give the title compound
(112 mg, 0.175 mmol, 40%) as a colorless powder. Mp 190–195 °C
(decomp.). 1H NMR (DMSO-d6) d: 1.45–1.60 (1H, m), 1.60–1.90
(3H, m), 1.95–2.25 (2H, m), 2.79 (3H, s), 2.92 (3H, s), 2.93 (3H, s),
3.05–3.40 (2H, m), 3.48 (1H, br s), 3.71 (1H, br s), 4.16 (1H, br s),
4.30–4.90 (4H, br), 7.11–7.22 (1H, m), 7.68–7.82 (1H, m), 8.45
(1H, s), 8.59–8.74 (2H, m), 8.75–8.95 (1H, m), 11.53 (0.5H, br s),
11.65 (0.5H, br s). MS (FAB) m/z: 544 (M+H)+. Anal. Calcd for
C25H30ClN7O3Sꢀ1.6HClꢀ2H2O: C, 47.03; H, 5.62; Cl, 14.44; N,
15.36; S, 5.02. Found: C, 46.83; H, 5.74; Cl, 14.51; N, 15.26; S, 5.29.
5.1.5. tert-Butyl (1R,2S,5S)-2-{[(7-chloroimidazo[1,2-a]pyridin-
2-yl)carbonyl]amino}-5-[(dimethylamino)carbonyl]cyclohexyl-
carbamate (6a)
(i) Hydrolysis step: To a solution of ethyl 7-chloroimidazo[1,2-
a]pyridine-2-carboxylate (5a) (118 mg, 0.525 mmol) in THF
(5 mL) were added LiOH (13.8 mg, 0.578 mmol) and water (2 mL)
at room temperature. The mixture was stirred for 3 h and the sol-
vent was evaporated to give lithium 7-chloroimidazo[1,2-a]pyri-
dine-2-carboxylate.
(ii) Condensationstep: The residue was dissolved in DMF (10 mL)
and to the mixture were added 4 (136 mg, 0.477 mmol), HOBt
(71.0 mg, 0.525 mmol), and EDCꢀHCl (192 mg, 1.00 mmol). After
stirring overnight, the mixture was concentrated in vacuo. The
residue was partitioned between CH2Cl2 and saturated NaHCO3
aqueous solution. The water layer was extracted with CH2Cl2.
The combined organic layer was dried over Na2SO4 and concen-
trated in vacuo. To the residue was added Et2O and the resultant
precipitate was collected by filtration to give the title compound