General procedure for the synthesis of (R)-2-((tert-butylcarbonyl)amino)pentanoic acid from D-norvaline and di-tert-butyl dicarbonate: (R)-2-aminopentanoic acid (2.343 g) and Na2CO3 (2.120 g) were dissolved in water (60.00 mL) to form a mixture. A solution of THF (20 mL) in Boc2O (4.88 mL) was added slowly and dropwise to the mixture at room temperature. The reaction mixture was stirred overnight at room temperature. Upon completion of the reaction, the mixture was washed with ether (2 × 20 mL), followed by adjusting the pH of the aqueous phase with K2SO4 solution to 3. The aqueous phase was extracted with EtOAc (2 × 30 mL), the organic phases were combined, and the solvents were evaporated after drying to give (R)-2-((tert-butylcarbonyl)amino)pentanoic acid (4 g) as a viscous oil product. Mass spectrometry (ESI) analysis showed that the theoretical molecular weight of C10H19NO4 was 217; the measured value was 216 [M-H].
