PMC:7571312 / 91592-92783 JSONTXT

{"target":"https://pubannotation.org/docs/sourcedb/PMC/sourceid/7571312","sourcedb":"PMC","sourceid":"7571312","source_url":"https://www.ncbi.nlm.nih.gov/pmc/7571312","text":"Methyl N-(tert-Butoxycarbonyl)-5-methyl-l-norleucinate\nTo a solution of methyl N-[(9H-fluoren-9-ylmethoxy)carbonyl]-5-methyl-l-norleucinate (2.18 g, 5.72 mmol) in DMF (50 mL) was added KF (2.33 g, 40.04 mmol) followed by triethylamine (1.70 mL, 12.24 mmol) and di-tert-butyl dicarbonate (7.39 mmol), and the mixture was stirred at an ambient temperature. After 4 h, TLC analysis indicated incomplete reaction and the reaction mixture was treated with a second portion of KF (2.7 g, 46.55 mmol) and BOC2O (800 mg, 3.67 mmol). After 16 h, the mixture was diluted with diethyl ether (300 mL), washed with satd. NaHCO3 (2 × 50 mL), 1 M hydrochloric acid (2 × 50 mL), NaHCO3 (50 mL), and brine (50 mL), dried over MgSO4, filtered, and the solvents were evaporated in vacuo to yield the crude product, which was purified by Biotage flash chromatography eluting with dichloromethane/hexane to afford the title compound as a clear oil, 980 mg, 66%. 1H NMR (400 MHz, CDCl3) δ 4.96 (d, J = 6.8 Hz, 1H), 4.21–4.32 (m, 1H), 3.72 (s, 3H), 1.72–1.85 (m, 1H), 1.46–1.66 (m, 2H), 1.43 (s, 9H), 1.11–1.29 (m, 2H), 0.88 (d, J = 4 Hz, 3H), 0.86 (d, J = 4 Hz, 3H); MS (API-ES+) for C13H25NO4m/z 282.2 (M + 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