Reaction Steps
A solution of 5-nitroindole (38) (2.0 g, 12.334 mmol) in dry ethanol (20 mL) was treated with pyrrolidine (3.08 mL, 37.002 mmol) followed by N-Boc-4-piperidone (4.91 g, 24.668 mmol) at room temperature and the resulting solution was refluxed for 3 days. The reaction was brought to room temperature, the solvent was evaporated and the crude product was purified by column chromatography (ethyl acetate:hexanes, 1:3) to obtain compound 85 (4.2 g, quantitative) as a solid. mp 210-212° C.; 1H NMR (DMSO-d6) δ 1.36-1.43 (m, 11H), 3.57 (t, 2H, J=5.7 Hz), 4.08 (s, 2H), 6.20 (s, 1H), 7.56 (d, 1H, J=9.0 Hz), 7.71 (s, 1H), 8.02 (dd, 1H, J=2.1, 9.0 Hz), 8.71 (d, 1H, J=2.1, Hz), 11.93 (s, 1H); ESI-MS m/z (%): 366 (M.Na+, 100), 288 (52). tert-Butyl 4-(5-amino-1H-indol-3-yl)piperidine-1-carboxylate (86): A solution of compound 85 (0.5 g, 1.456 mmol) in 2 M NH3 in methanol (15 mL) was treated with Pd—C (0.05 g) and purged with hydrogen gas. The reaction was stirred under hydrogen atm. for overnight. The solution was filtered through a celite bed and washed with methanol: CH2Cl2 (1:1, 2 20 mL). The combined organic layer was evaporated to obtain compound 86 (0.46 g, quantitative) as a solid. mp 205-207° C.; 1H NMR (DMSO-d6) δ 1.41-1.53 (m, 11H), 1.87-1.91 (m, 2H), 2.73-2.85 (m, 3H), 4.03-4.07 (m, 2H), 4.43 (s, 2H), 6.45 (dd, 1H, J=1.8, 8.4 Hz), 6.69 (d, 1H, J=1.5 Hz), 6.90 (d, 1H, J=2.4 Hz), 7.01 (d, 1H, J=8.4 Hz), 10.28 (s, 1H); ESI-MS m/z (%): 338 (M.Na+, 23), 316 (MH+, 11), 216 (100). tert-Butyl 4-(5-(thiophene-2-carboximidamido)-1H-indol-3-yl)piperidine-1-carboxylate (87): A solution of compound 86 (0.45 g, 1.426 mmol) in dry ethanol (25 mL) was treated with thiophene-2-carboximidothioic acid methyl ester hydroiodide (0.81 g, 2.853 mmol) at room temperature and resulting solution was stirred for 24 h. The solvent was evaporated, crude was diluted with sat. NaHCO3 solution (25 mL) and CH2Cl2 (50 mL). The organic layer was separated and aqueous layer was extracted into CH2Cl2 (2 25 mL). The combined organic layer was washed with brine (20 mL) and dried (Na2SO4). The solvent was evaporated and the crude product was purified by column chromatography on silica gel (2 M NH3 in methanol: CH2Cl2, 3:97) to obtain compound 87 (0.6 g, quantitative) as a foam. 1H NMR (DMSO-d6) δ 1.40-1.56 (m, 11H), 1.90-1.94 (m, 2H), 2.86-2.94 (m, 3H), 4.02-4.06 (m, 2H), 6.26 (s, 1H), 6.64 (dd, 1H, J=1.2, 8.4 Hz), 6.99 (s, 1H), 7.05 (d, 1H, J=1.8 Hz), 7.09 (dd, 1H, J=3.6, 4.9 Hz), 7.27 (d, 1H, J=8.4 Hz), 7.59 (d, 1H, J=5.1 Hz), 7.71 (d, 1H, J=3.3 Hz), 10.63 (s, 1H); ESI-MS m/z (%): 425 (MH+, 100). Dihydrochloride salt of N-(3-(piperidin-4-yl)-1H-indol-5-yl)thiophene-2-carboximidamide (88): A solution of compound 87 (0.3 g, 0.706 mmol) was treated with 1 N HCl solution (20 mL) and refluxed for 2 h. The reaction was brought to room temperature, solid was filtered off and washed with water (5 mL). The water layer was evaporated and crude was recrystallised from ethanol/ether to obtain compound 88 (0.29 g, 72%) as a solid. Decomposed at 230° C. 1H NMR (DMSO-d6) δ 1.90-2.10 (m, 4H), 3.00-3.13 (m, 3H), 3.31-3.35 (m, 2H), 7.11 (d, 1H, J=8.7 Hz), 7.28 (d, 1H, J=1.8 Hz), 7.39 (t, 1H, J=4.5 Hz), 7.53 (d, 1H, J=8.7 Hz), 7.77 (s, 1H), 8.16-8.20 (m, 2H), 8.58 (s, 1H), 9.18 (brs, 2H), 9.68 (s, 1H), 11.29 (s, 1H), 11.49 (s, 1H); ESI-MS m/z (%): 325 (MH+, free base, 100), 242 (34), 163 (70); HRMS Calculated for C18H21N4S (MH+); Calculated: 325.1494; Found: 325.1481.
