indole-3-carboxylic acid,
thionyl chloride,
tris(2-aminoethyl)amine(TREN),
triethylamine,
tetrahydrofuran

Indole-3-carboxylic acid (0.56 g, 3.4 mmol) was dissolved in SOCl₂ (6 mL) and stirred at 0°C for 1.5 h. The solution was concentrated in vacuo and to the resulting oil was added TREN (0.62 g, 4.2 mmol) and TEA (0.46 g, 4.6 mmol) in THF (25 mL). After stirring at 0°C for 30 min, the solution was filtered under vacuum to yield 5 as a beige solid which was recrystallized in MeOH.

Yield 0.28 g (43.0%); mp > 250°C. ¹H NMR (250 MHz, DMSO-d⁶) 7.98 (s, 3H, H₂), 7.44 (m, 3H, H₁), 7.17 (m, 3H, H₄), 7.15 (d, 3H, H₇), 7.14 (m, 3H, H₅ or H₆), 7.12 (m, 3H, H₆ or H₅), 3.40 (m, 12H, H_a and H_b); MS (M+1)⁺ = 576 for C₃₃H₃₃N₇O₃.

Sears, R. Bryan; Carpenter, Russell A.; Whitlock, Christine R. “A General Synthesis of Tris-Indole Derivatives as Potential Iron Chelators.” Molecules, A Journal of Synthetic Chemistry and Natural Product Chemistry, 2005, 10, 488-491.