N-Methylmorpholine (2.2 mL, 19.7 mmol) was added dropwise at room temperature to 7-amino-1-heptanol hydrochloride salt (3.3 g, 19.7 mmol), in 50 mL of dry DMF under argon with stirring. After stirring for 5 minutes the following were added: N-t-butoxycarbonyl-L-tryptophan, (5 g, 16.45 mmol), 1-hydroxybenzotriazole, (2.52 g, 16.45 mmol) and EDCI hydrochloride (4.73 g, 24.7 mmol). The mixture was stirred for 2 hours and then the DMF removed under reduced pressure. The residue was taken up in cold 2.5% HCl (100 mL) and ethyl acetate (3×100 mL) and transferred to a separatory funnel. The organic phase was isolated and washed consecutively with cold 2.5% HCl (100 mL) and then brine (100 mL). The ethyl acetate phase was dried (MgSO4), filtered and concentrated to obtain N-t-butoxycarbonyl-L-tryptophan-(7-hydroxyheptyl)amide; IR (neat): 3300, 2921, 1685, 1645, 1490, 1356, 1157 cm-1 ; 1H NMR (80 MHz, CDCl3): δ 0.98-1.62 (m, 10H, --(CH2)5 --), 1.45 (s, 9H, t-butyl), 2.86-3.32 (m, 4H,CH--CH2, HN--CH2), 3.68 (t, 2H, J=5.6 Hz, --CH2OH), 4.22-4.55 (m, 1H, CH), 5.12-5.32 (broad d, 1H, NH--CH), 5.65-5.9 (broad t, 1H, NH--CH2), 6.98-7.92 (m, 5H, ArH), 8.63 (broad 8, indole NH).
