A mixture of 4-amino-2-(2,6-dioxo(3-piperidyl))isoindoline-1,3-dione (1.1 g, 4.0 mmol) and heptanal (3.4 mL, 24 mmol) and acetic acid (2 mL) in DMF (20 mL) was heated until all solid was dissolved. To the mixture was added sodium borohydride (605 mg, 16 mmol) and kept at room temperature for 18 h. To the mixture was added sodium borohydride (150 mg, 3.9 mmol) and kept at room temperature for 1 d. The mixture was extracted with ethyl acetate (200 mL) and water (100 mL). The organic layer was washed with water (100 mL), The solvent was removed in vacuo to give an oil. The oil was purified by column chromatography (Silca Gel, 33% EtOAc:CH2Cl2) to give 2-(2,6-Dioxo-piperidin-3-yl)-4-heptylamino-isoindole-1,3-dione as a yellow solid (610 mg, 41% yield): mp, 107–109° C.; 1H NMR (DMSO-d6) δ 0.82–0.87 (m, 3H, CH3), 1.24–1.29 (m, 8H, 4 CH2), 2.00–2.04 (m, 1H, CHH), 2.43–2.62 (m, 2H, CH2), 2.82–2.96 (m, 1H, CHH), 3.23–3.31 (m, 2H, CH2), 5.06 (dd, J=5.3, 12.4 Hz, 1H, NCH), 6.51 (t, J=5.9 Hz, 1H, NH), 7.01 (d, J=7.0 Hz, 1H, Ar), 7.07 (d, J=8.6 Hz, 1H, Ar), 7.57 (dd, J=7.4, 8.4 Hz, 1H, Ar), 11.10 (s, 1H, NH); 13C NMR (DMSO-d6) δ 13.91, 22.03, 22.17, 26.28, 28.42, 28.69, 30.98, 31.22, 34.84, 48.55, 109.03, 110.36, 117.13, 132.18, 136.24, 146.43, 167.29, 168.96, 170.05, 172.77; Anal Calcd for C20H25N3O4: C, 64.67; H, 6.78; N, 11.31. Found: C, 64.62; H, 6.76; N, 11.13.
