To a stirred solution of N-(t-butyloxycarbonyl)-N-(2-pyridinylmethyl)-N′-(5,6,7,8-tetrahydro-8-quinolinyl)-1,4-benzenedimethanamine (0.295 g, 0.643 mmol) in anhydrous methanol (6.5 mL), at room temperature, was added thiazole-2-carboxaldehyde (0.33 mL, 3.76 mmol) followed by NaBH3CN (0.131 g, 2.09 mmol) and the resultant solution was stirred at room temperature. After 2 days, an additional amount of NaBH3CN (0.134 g, 2.10 mmol) was added and the solution was stirred at room temperature for an additional 4 days. The solvent was removed under reduced pressure and CH2Cl2 (20 mL) and water (10 mL) were added to the residue. The phases were separated and the aqueous phase was extracted with CH2Cl2 (3×10 mL). The combined organic phases were dried (Na2SO4) and concentrated. Purification of the crude material by radial chromatography on silica gel (2 mm plate, 40:1 CH2Cl2-MeOH containing 1% NH4OH) afforded 0.164 g of the protected amine as a yellow oil.
