63% |
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Some N-methylmorpholine (15.0 mmol, 1.65 mL) was added to a solution of tBOC-L-Nva-OH (10.0 mmol, 2.17 g) in dry THF (60 mL). The solution was cooled to ?5° C. and some isobutyl chloroformate (15.0 mmol, 1.95 mL) was added dropwise. The mixture was agitated at ?5° C. for 1 hour. Some L-alanine benzyl ester p-toluenesulfonate salt (10.0 mmol, 3.52 g) in dry DCM (30 mL) which had been neutralised with diisopropylethylamine (15.0 mmol, 2.60 mL) at ?5° C., was added dropwise to the agitated mixture. The resulting solution was agitated under nitrogen at ?5° C. for 30 minutes, and then overnight at ambient temperature. The solution was filtered and concentrated under vacuum, then washed with 10percent weight/volume citric acid (2×25 mL), 10percent weight/volume potassium carbonate (25 mL) and water (25 mL). The organic layer was dried on MgSO4, filtered and concentrated under vacuum to give a yellow hygroscopic liquid, which was purified by column chromatography [40-60 petrol/ethyl acetate (7:3)] to give the product in the form of an off-white solid (2.40 g, 6,3 mmol, 63percent); m.p. 60-63° C.; numax/cm?1 3299 (NH), 1743 (C?O), 1655 (C?O), 1527 (NH bend), 1245 (C?O), 1162 (C?O); 1H NMR (300 MHz, CDCl3) deltaH 0.83 (3H, t, J=9.0 Hz, CH3-8), 1.25-1.36 (14H, [d, J=6.0 Hz, CH3-3], [m, CH2-7], [s, C(CH3)3]), 1.42-1.54 (1H, m, CHa/b-6), 1.64-1.73 (1H, m, CHa/b-6), 4.02 (1H, m, CH-5), 4.54 (1H, pentet, J=6.0 Hz, CH-2), 4.96 (1H, d, J=9.0 Hz, NHCO2), 5.07 (1H, d, J=12.0 Hz, OCHa/bAr), 5.12 (1H, d, J=12.0 Hz, OCHa/bAr), 6.56 (1H, d, J=6.0 Hz, NHCO), 7.27 (5H, m, 5×CHAr); 13C NMR (75 MHz, CDCl3) deltaC 12.7 (CH3-8), 17.3 (CH3-3), 17.8 (CH2-7), 27.3 (C(CH3)3), 33.7 (CH2-6), 47.1 (CH-2), 53.4 (CH-5), 66.1(OCH2Ar), 79.0 (C(CH3)3), 127.1-127.6 (5×CHAr), 134.3 (CHAr quat.), 154.6 (C?O-9), 170.8 (C?O-4), 171.5 (C?O-1); CHN [Found: C, 63.75; H, 8.37; N, 7.86. C20H30N2O5 requires C, 63,47; H, 7.99; N, 7.40percent]; HRMS (nanospray ionisation) calculated for (C20H31N2O5)+ 379.2227, found 379.2222 |