1,4-Dihydro-2,6-dimethyl-4-(3-isothiocyanatophenyl)-3,5-pyrazinedicarboxylic acid, dimethyl ester (144 mg, 0.40 mmol) was added into sodium cyanamide (28 mg, 0.44 mmol) in 3 mL of EtOH and the mixture was stirred for 20 minutes. EtOH was then removed in vacuo and the resultant foam-like material was mixed with 4-phenyl-piperidine-1-propanamine (105 mg, 0.48 mmol) in 5 mL of THF. The mixture was cooled down to 0° C. and HgCl2 (109 mg) was added. The reaction was completed in 15 min. After filtration and extraction, the organic layer was concentrated and purified by chromatography (silica gel, eluted with 10% (v/v) methanol in methylene chloride) to yield the title compound as isolated as a yellow foam (175 mg, 75%); 1H-NMR (CDCl3) δ 7.05-7.35 (m, 6H), 6.75 (br, 1H), 6.65 (d, 1H, J=7.5 Hz), 6.58 (d, 1H, J=8.3 Hz), 6.53 (br, 1H), 5.98 (br, 1H), 3.72 (s, 6H), 3.38 (m, 2H), 2.97 (m, 2H), 2.30-2.55 (m, 3H), 2.39 (s, 6H), 2.03 (m, 2H), 1.65-1.80 (m, 4H), 1.40-1.60 (m, 2H); 13C-NMR (CDCl3) δ 166.2, 152.6, 149.4, 129.9, 128.5, 126.9, 126.3, 118.3, 116.3, 112.5, 110.4, 108.7, 54.1, 51.8, 42.4, 41.0, 32.7, 29.8, 25.6, and 17.9.
