1,1′-(Azodicarbonyl)dipiperidine (0.12 g, 0.48 mmol) was added to the solution of methyl 2-[(5-hydroxyindolyl)methyl]pentanoate (0.03 g, 0.12 mmol), as prepared in the preceding step, 2-(3-hydroxypropyl)aminopyridine (0.026 g, 0.17 mmol), as prepared in step b of Example 1, and tri-n-butylphosphine (0.09 g, 0.46 mmol) in tetrahydrofuran (6.0 mL). After stirring at ambient temperature overnight (16 h), the reaction was concentrated and the residue was purified by flash chromatography on silica gel (10%-50% ethyl acetate in hexane) to give the title compound as a yellow oil (0.016 g, 36%). 1H-NMR (400 MHz, CDCl3) δ 8.08 (m, 1H), 7.20 (d, J=8.9 Hz, 1H), 7.07 (d, J=2.4 Hz, 1H), 7.02 (d, J=3.3 Hz, 1H), 6.88 (dd, J=8.9, 2.4 Hz, 1H), 6.53 (m, 1H), 6.40 (m, 2H), 4.32 (br s, 1H), 4.42 (m, 1H), 4.25 (m, 3H), 3.52 (m, 5H), 2.91 (m, 1H), 2.20 (m, 2H), 1.72 (m, 2H), 1.43 (m, 3H), 0.95 (t, J=7.2 Hz, 3H).
