Reaction Steps
Treatment with Fmoc-Cl followed by coupling to benzyl alcohol using 1-ethyl-3-[3-(dimethylamino)propyl]-carbodiimide [by] hydrochloride (EDCL) provided 2-(9H-Fluoren-9-ylmethoxycarbonylamino)-pentanedioic acid 5-allyl ester 1-benzyl ester 6 in 82% yield. To a solution of 1.5 g (36.6 mmol) of 5 in 5 mL of CH2Cl2 was added 0.42 mL (40.3 mmol) of benzyl alcohol, 0.912 g (47.6 mmol) of EDCI, and 45 mg (3.66 mmol) of dimethylaminopyridine (DMAP). The reaction mixture was stirred at 22° C. for 6 h, diluted with 20 mL of CH2Cl2, and extracted with H2O (1×15 mL), 0.1M HCl (2×15 mL), and brine (2×10 mL). The organic layer was dried (Na2SO4), concentrated in vacuo, and chromatographed on SiO2 (Hexanes/EtOAc, 5:1) to give 1.83 g (82%) of 6 as a white solid: Mp 66.2-67.1° C. (EtOAc/Hexanes); [α]D +1.40° (c 1.64, CHCl3, 21° C.); IR (neat) 3314, 1726, 1682, 1527, 1443, 1414, 1383, 1254, 1173, 1099, 1082, 980, 754, 735 cm-1 ; 1H NMR δ 7.75 (d, 2 H, J=7.4 Hz), 7.59 (d, 2 H, J=7.1 Hz), 7.41-7.27 (m, 9 H), 5.95-5.85 (m, 1 H), 5.44 (d, 1 H, J=8.2 Hz), 5.34-5.19 (m, 4 H), 4.56 (d, 2 H, J=5.6 Hz), 4.5-4.4 (m, 3 H), 4.21 (t, 1 H, J=7.0 Hz), 2.5-2.0 (m, 4 H); 13C NMR δ 172.2, 171.6, 155.8, 143.7, 143.5, 141.1, 135.0, 131.8, 128.5, 128.3, 128.1, 127.6, 126.9, 124.9, 119.8, 118.3, 67.2, 66.9, 66.2, 53.3, 47.0, 28.0, 27.3; MS (FAB, MNBA/MeOH) m/z (relative intensity) 500 ([M+H]+, 40), 465 (8), 448 (14), 433 (12), 413 (8), 386 (38), 371 (24), 349 (9), 324 (16), 309 (26), 293 (11), 265 (10), 247 (24), 231 (56), 215 (39), 202 (26), 191 (24), 179 (67), 165 (48), 154 (67), 143 (31), 133 (71), 117 (100).
