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5.4 A solution of 3-nitro-tyrosine (1 g, 4.4 mmol, 1 eq) was dissolved in acetone:H20 (1 : 1 , 10 mL) and treated with NaHC03 (554 mg, 1.5 eq) and Boc20 (946 iL, 1 eq) and allowed to stir overnight. The reaction was acidified with 5% citric acid (pH - 3) and extracted 3x with EtOAc then the combined organic fractions were washed with brine, dried over sodium sulfate and concentrated. The crude (1.37 g, 4.2 mmol, 1 eq) was taken up in a 5:2 mixture of DCM MeOH (56 mL), treated with BTMA-IC12 (1.6 g, 1.1 eq) and NaHC03 (2.47 g, 7 eq) and allowed to stir overnight. The solid NaHCCb was then filtered, the filtrate was concentrated and acidified with 5 % citric acid (pH - 3). The aqueous layer was extracted 3x with EtOAc and the combined organic layers were dried over sodium sulfate and concentrated. The crude material (1.89 g, 4.19 mmol, 1 eq) was dissolved in acetone, and treated with K2CO3 (2.9 g, 5 eq) and Mel (1.3 mL, 5 eq) and heated to reflux over two days. The reaction mixture was then allowed to cool to room temperature, the reaction was quenched with a small amount of water and the volatiles were evaporated. 5% citric acid (pH - 3) and EtOAc were added then separated and the aqueous layer was extracted 2x with EtOAc. The combined organic layers were washed with brine, dried over sodium sulfate and concentrated. The crude material was purified via column chromatography (0-0.5% MeOH in DCM) to yield compound 5.4 (1.67 g, 82% yield over 3 steps). H NMR (CDC13, 500 MHz) delta (ppm) 7.80 (d, J = 1.5 Hz, 1H), 7.56 (d, J = 1.5 Hz, 1 H), 5.12 (d, J = 6.5 Hz, 1 H), 4.54-4.53 (m, 1H), 3.94 (s, 3H), 3.76 (s, 3H), 3.18 (dd, J = 5.0 Hz, J = 14.0 Hz, 1H) 2.98 (dd, J = 6.5 Hz, J = 14.0 Hz, 1H) 1.41 (s, 9H) 13C NMR (CDC13, 500 MHz) delta (ppm) 171.5, 155.0, 152.1 , 144.9, 143.8, 135.1, 126.4, 94.3, 80.5, 62.8, 54.2, 52.8, 37.0, 28.4. MS (ESI) m/z 503.0 (M + Na+). Compound 5.4 (127 mg, 0.27mmol, 1 eq) was then dissolved in DCM (2.5 mL) and treated with TFA (0.5 mL). When TLC analysis indicated the complete consumption of starting material the volatiles were blown off and the residue was diried under vacuum. The residue was then taken up in EtOAc and saturated NaHC03, the aqueous layer was extracted 3x with EtOAc, the combined organic layers were dried over sodium sulfate and concentrated. The resulting compound 5.6 (101 mg) was used without further purification. |