Reaction Steps
NMM (155 mg, 169 μl, 1.54 mmol), HOBT (227 mg, 1.68 mmol), 4-acetyl-1,2,5-trimethylpyrrole-3-carboxylic acid (300 mg, 1.54 mmol) and EDC (295 mg, 1.54 mmol) were added sequentially to a stirred solution of O-(2,6-dichlorobenzyl)-L-tyrosine methyl ester hydrochloric (546 mg, 1.40 mmol) in dry DMF (15 ml). The reaction was stirred at room temperature under N2 for 18 h. The solvent was removed in vacuo and the residue partitioned between EtOAc (50 ml), and 10%aqueous Na2CO3 (40 ml). The phases were separated and the queous phase extracted with EtOac (2×25 ml). The combined organic extracts were washed consecutively with 5% aqueous hydrochloric acid (20 ml), 10% aqueous Na2SO3 (20 ml) and brine (10 ml), dried (Na2SO4) and evaporated in vacuo. The obtained orange foam (0.6 g) was chromatographed (silica; 50% EtOAc/Hexane→100% EtOAc) affording the title compound as a white foam (380 mg, 51%); 'Hnmr (d6DMSO) 8.53 (1H, d, J 8Hz, NH), 7.57-7.43 (3H, m's, aryl-H), 7.22 (2H, d, J 8.5Hz), aryl-H), 6.95 (2H, d, J 8.5 Hz, aryl-H), 5.18 (2H, br s, CH2-O), 4.67 (1H, m, α-tyr-H), 3.66 (3H, s, Me-O), 3.34 (3H, s, Me-N), 3.12 (1H, dd, J 4.1, 13.8Hz, CHABBAr), 2.90 (1H, dd, J 11.3 13.8Hz, CH2HBAr), 2.32 (3H, s, MeCO), 2.0 (3H, s, pyrrole-Me) and 1.94 (3H, s, pyrrole-Me). m/z (ES+60V) 531 (MH+, 100 ), 533 (MH+, 75) 553( MNz+, 15%).
