5429-56-1

19436-52-3

The general procedure for the synthesis of N-acetyl-D-alanine from 2-acetamidoacrylic acid is as follows: the substrate (Eq. 3), enantiomeric excess (ee), and absolute stereoconfigurations of the chiral products (Eq. 2) prepared by asymmetric hydrogenation using a chiral catalyst precursor are listed in Table 3. The catalyst precursor was (S)-(+)-(2-{[(di-tert-butyl)-[phosphinylidene]-methyl]-methyl-phosphinyl}-2-methyl-propyl)-(1,5-cyclooctadiene)rhodium(I) tetrafluoroborate (Eq. 23). For each entry in Table 3, the catalyst precursor (0.01 mmol) was dissolved in degassed methanol (1 mL) in a Griffin-Worden pressure vessel equipped with the accessories required for connection to a hydrogen cylinder. The substrate (1 mmol) was first dissolved in methanol (4 mL) and then delivered via syringe into the catalyst-methanol solution. The vessel was sealed and pressurized to 50 psi H2. The time to completion of the reaction was determined by monitoring the cessation of H2 gas absorption. Table 3: Enantioselectivity of chiral compounds prepared by asymmetric hydrogenation of prechiral substrates (Formula 2) (Formula 3) Example R1 R2 R3 R4 X ee Configuration.5 AcNH H H CO2H >99% R 6 AcNH Ph H H CO2H >99% R 7 AcNH H H CO2Me >99% R 8 AcNH Ph H H CO2Me >99% R 9 AcNH - C5H10- CO2Me 99% R For each reaction shown in Table 3, the enantiomeric excess was determined by chiral gas chromatography (GC) or chiral high performance liquid chromatography (HPLC). Table 4 provides details of the ee determination methods. To determine the ee of N-acetylalanine (Example 5) and N-acetylphenylalanine (Example 6), each compound was treated with trimethylsilyl diazomethane, which was converted to its corresponding methyl ester, and analyzed as described in Example 7 or Example 8, respectively. Absolute stereochemical configurations were determined by comparing the sign of the spinodal and literature values: (S)-N-acetylalanine methyl ester [α]20D = -91.7° (c 2, H2O), JP Wolf III C. Neimann, Biochemistry 2: 493 (1963); (S)-N-acetylphenylalanine methyl ester [α]20D = + 16.4° (c 2, MeOH), B.D. Vineyard et al, J. Am. Chem. Soc. 99: 5946 (1997); (S)-N-acetylcyclohexylglycine methyl ester [α]20D = -4.6° (c = 0.13, EtOH), M.J. Burk et al, J. Am. Chem. Soc. 117: 9375 (1995). Table 4: Conditions for Enantiomeric Excess Determination Example Method Column Mobile Phase Flow Rate Column Temperature Concentration Retention Time-R Retention Time-S5 Capillary GC Chrompack Chiral-Daicel - - 120°C - 10.5 min 11.0 min 6 HPLC Chiralcel OJ 10% IPA/hexane 1 mL/min 30°C 2 mg/mL 11.6 min 17.7 min9 Capillary GC Chirasil-L-Val - - 145°C - 11.3 min 12.0 min