Compound 3 was synthesized from Compound 2 as follows. To a solution of Compound 2 (1.193 g, 5.492 mmol) and FmocN(Me)NHMe (2.147 g, 7.604 mmol, 1.38 equiv) in 1,2-dichloroethane (anhydrous, 25 mL) was added sodium triacetoxyborohydride (1.273 g, 6.006 mmol, 1.09 equiv). The resulting yellow suspension was stirred for 2 h and then quenched with sodium bicarbonate (saturated aqueous solution, 10 mL), followed by addition of hydrogen chloride (1 M aqueous solution) to pH 4. The organic layer was separated, and the aqueous layer was extracted with dichloromethane (5×10 mL). The pooled organic extracts were dried over sodium sulfate, filtered, and concentrated to an orange oil. Purification by C18 silica gel chromatography (20-90% acetonitrile in water) yielded 3 as a waxy pink solid (1.656 g, 3.425 mmol, 62%). 1H NMR (400 MHz, CDCl3) δ 7.76 (d, J=7.4 Hz, 2H), 7.70-7.47 (br m, 3H), 7.42-7.16 (br m, 6H), 7.12-7.05 (m, 1H), 6.37 (s, 0.6H), 6.05 (s, 0.4H), 4.75-4.30 (br m, 4H), 4.23 (m, 1H), 4.10 (br s, 1H), 3.55 (br d, 1H), 3.11-2.69 (m, 5H), 2.57 (br s, 2H), 2.09 (br s, 1H). 13C NMR (101 MHz, CDCl3) δ 174.90, 155.65, 143.81, 141.42, 136.98, 134.64, 127.75, 127.48, 127.12, 124.92, 122.00, 120.73, 120.01, 119.75, 109.19, 103.74, 67.33, 66.80, 51.39, 47.30, 39.58, 39.32, 35.23, 32.10. HRMS (ESI) calcd for C29H30N3O4 [M+H]+: 484.2236. found: 484.2222.
