A mixture of 1-benzyl-4-[N-propyl-N-(3-amino-2-pyridinyl)amino]piperidine (EXAMPLE 114, 0.35 g) in absolute ethanol (4.3 ml) under nitrogen is treated with acetaldehyde (120 μl) and sodium cyanoborohydride (84 mg) and the pH is adjusted to 5 with glacial acetic acid as measured on moistened pH test paper. The resulting mixture is stirred at 20°-25° for 48 hrs, during which additional acetaldehyde (180 μl) and sodium cyanoborohydride (70 mg) is added, and is then adjusted to pH 3 with hydrochloric acid (3M), neutralized with sodium hydroxide (5%), and concentrated under reduced pressure. The residue is chromatographed (silica gel, 70-230 mesh, 35 g; eluting with a gradient of methanol/methylene chloride (1/99-2/98)) to give the title compound, NMR (CDCl3) 7.72, 7.31, 7.27, 6.91, 6.79, 4.66, 3.51, 3.10, 2.92, 2.05, 1.74, 1.27 and 0.79δ.
