Methyl (2S,1S)- and (2S,1S)-2-(2-amino-2-oxo-1-phenylethylamino)-3-methylbutanoate (2 S ,1 S )-2a and (2 S ,1 R )-2a From diastereomeric mixture of (2 S ,1 S )-1a and (2 S ,1 R )-1a (3.98 g, 12.43 mmol) and BF3·2CH3COOH (37 mL); FC (gradient: PE/AcOEt 2:1–0:1): yield 2.31 g (70 %): 1.95 g (59 %) of (2 S ,1 S )-2a, 0.19 g (6 %) of (2 S ,1 R )-2a and 0.17 g (5 %) of diastereomeric mixture. (2 S ,1 S )-2a: find more colorless oil; [α]D = −133.5 (c click here 0.977, CHCl3); IR (KBr): 702, 759, 1152, 1205, 1456, 1682, 1732, 2874, 2960, 3196, 3332, 3445; TLC (AcOEt): R f = 0.54; 1H NMR (CDCl3, 500 MHz): δ 0.89 (d, 3 J = 7.0, 3H, CH 3), 0.93 (d, 3 J = 7.0, 3H, \( \rm CH_3^’ \)), 1.96 (m, 3 J = 7.0, 1H, CH), 2.22 (bs, 1H, NH), 2.87 (bs, 1H, H-2), 3.72 (s, 3H, OCH 3), 4.19 (s, 1H, H-1), 5.80 (bs, 1H, CONH), 6.23 (bs, 1H, CONH′), 7.30–7.40 (m, 5H, H–Ar); 13C NMR (CDCl3, 125 MHz): δ 18.4 (CH3), 19.3 (\( C\textH_3^’ \)), 31.4 (CH), 52.6 (OCH3), 64.2 (C-2), 65.6 (C-1), 128.1 (C-2′, C-6′), 128.5 (C-4′), 128.9 (C-3′, C-5′), 138.1 (C-1′), 174.3 (CONH), 174.8 (COOCH3); HRMS PFT�� cost (ESI) calcd for C14H20N2O3Na: 287.1372 (M+Na)+ found 287.1396. (2 S ,1 R )-2a: white powder; mp 107–109 °C;

[α]D = −5.2 (c 0.975, CHCl3); IR (KBr): 698, 758, 1150, 1202, 1456, 1685, 1733, 2874, 2960, 3196, 3331, 3443; TLC (AcOEt): R f = 0.58; 1H NMR (CDCl3, 500 MHz): δ 0.96 (d, 3 J = 7.0, 3H, CH 3), 1.03 (d, 3 J = 7.0, 3H, \( \rm CH_3^’ \)), 2.02 (m, 3 J = 7.0, 1H, CH), 2.18 (bs, 1H, NH), 3.17 (bs, 1H, H-2), 3.72 (s, 3H, OCH 3), 4.06 (s, 1H, H-1), 5.93 (bs, 1H, CONH), 7.22 (bs, 1H, CONH′), 7.28–7.44 (m, 5H, H–Ar); 13C NMR (CDCl3, 125 MHz): δ 18.2 (CH3), 19.6 (\( C\textH_3^’ \)), 31.6 (CH), 51.8 (OCH3), 66.2 (C-1), 66.7 (C-2), 127.3 (C-2′, C-6′), 128.4 (C-4′), 128.9 (C-3′, C-5′), 138.8

(C-1′), 174.8 (CONH), 174.9 (COOCH3); HRMS (ESI) calcd for C14H20N2O3Na: 287.1372 (M+Na)+ found 287.1359. Methyl (2S,1R)- and (2S,1S)-2-(2-amino-2-oxo-1-phenylethylamino)-4-methylpentanoate (2 S ,1 S )-2b and (2 S ,1 R )-2b From diastereomeric mixture of (2 S ,1 S )-1b and (2 S ,1 R )-1b (3.11 g, 9.31 mmol) and BF3·2CH3COOH (28 mL); FC (gradient: PE/AcOEt 2:1–0:1): yield 1.43 g (55 %): 1.03 g (40 %) of (2 S ,1 S )-2b, DOK2 0.08 g (3 %) of (2 S ,1 R )-2b and 0.32 g (12 %) of diastereomeric mixture.