Reaction Steps
The crude carboxylic acid (45 mg, 0.11 mmol) was dried by evaporation of a toluene solution and then dissolved in DMF (0.40 mL). Molecular sieves (4 Å, 0.16 g) and N-methylmorpholine (0.027 mL, 25 mg, 0.25 mmol) were added. After 10 min., benzotfiazol-1-yloxytris(dimethylamino)phosphonium hexafiuorophosphate (60 mg, 0.14 mmol) was added and the solution was stirred for 40 min. before the addition of L-leucine anilide (28 mg, 0.14 mmol). After 1.5 h at room temperature, the solution was diluted with 20 mL of EtOAc and washed with 2 N aq. HCl (10 mL), saturated aq. NaHCO3 (10 mL), and saturated aq. NaCl (10 mL). The organic layer was dried (Na2SO4), decanted, and evaporated. Purification by flash column chromatography on silica gel (4.7 g) eluting with 100 mL of 3% EtOAc/dichloromethane gave 55 mg (83% yield) of the title compound as a colorless film. NMR (400 MHz, CDCl3) indicated a 1:1 mixture of diastereomers: δ8.50 (s, 1 H), 7.47 (d, 2H, J=7 Hz), 7.38-7.29 (m, 5H), 7.25 (t, 2H, J=7 Hz), 7.06 (t, 1H, J=7 Hz), 7.04 (d, 1H, J=8 Hz), 7.02 (d, 1H, J=8 Hz), 6.96 (d, 1H, J=8 Hz), 6.93 (d, 1H, J=8 Hz), 6.21 (d, 0.5H, J=8 Hz), 6.16 (d, 0.5H, J=8 Hz), 5.11 (s, 2H), 4.66 (bq, 1H, J=7 Hz), 2.95 (quintet, 0.5 H, J=8 Hz), 2.92 (quintet, 0.5H, J=8 Hz), 2.60-2.37 (m, 5H), 2.16-2.06 (m, 1H), 2.00-1.54 (m, 11H), 0.99 (d, 3H, J=6 Hz), 0.97 (d, 1.5H, J=6 Hz), 0.96 (d, 1.5 H, J=6 Hz), 0.93 (t, 1.5H, J=7 Hz), 0.92 (t, 1.5H, J=7 Hz).
