6 (C-1′), 170.9 (CONH), 175.0 (learn more COOCH3). Methyl (2S,1S)- and (2S,1R)-2-(2-(tert-butylamino)-2-oxo-1-phenylethylamino)-4-methylpentanoate (2 S ,1 S )-1b and (2 S ,1 R )-1b From l-leucine (2.64 g, 20.16 mmol), benzaldehyde (16.80 mmol, 1.71 mL) and tert-butyl isocyanide (2.00 mL, 16.80 mmol); FC (gradient: PE/AcOEt 9:1–4:1): yield 3.58 g (64 %) of diastereomeric mixture (d r = 5.3/1, 1H NMR). Colorless oil; IR (KBr): 700, 733, 1155, 1200, 1227, 1454, 1516, 1680, 1738, 2870, 2959, 3331; TLC (PE/AcOEt 3:1): R f = 0.35 (major isomer) and 0.38 (minor isomer); 1H NMR (from diastereomeric mixture, CDCl3, 500 MHz): PHA-848125 datasheet (2 S ,1 S )-1b

(major isomer): δ 0.77 (d, 3 J = 6.5, 3H, CH 3), 0.87 (d, 3 J = 6.5, 3H, \( \rm CH_3^’ \)), 1.31 (s, 9H, C(CH 3)3), 1.58 (m, 2H, CH 2), 1.71 (m, 3 J = 6.5, 1H, CH), 2.26 (bs, 1H, NH), 3.11 PLX3397 (pt, 3 J = 7.5, 1H, H-2), 3.70 (s, 3H, OCH 3), 4.11 (s, 1H, H-1), 6.49 (bs, 1H,

CONH), 7.28–7.37 (m, 5H, H–Ar); (2 S ,1 R )-1b (minor isomer): δ 0.96 (d, 3 J = 6.5, 3H, CH 3), 0.99 (d, 3 J = 6.5, 3H, \( \rm CH_3^’ \)), 1.38 (s, 9H, C(CH 3)3), 1.86 (m, 3 J = 6.5, 1H, CH), 3.32 (dd, 3 J 1 = 9.0, 3 J 2 = 5.0, 1H, H-2), 3.72 (s, 3H, OCH 3), 3.95 (s, 1H, H-1), the remaining signals overlap with the signals of (2 S ,1 S )-1b; 13C NMR (from diastereomeric mixture, CDCl3, 125 MHz): (2 S ,1 S )-1b (major isomer): δ 22.0 (CH3), 22.8 (\( C\textH_3^’ \)), 24.8 (CH), 28.6 (C(CH3)3), 42.5 (CH2), 50.9 (C(CH3)3), 51.2 (OCH3), 57.5 (C-2), Loperamide 66.4 (C-1), 127.8 (C-2′, C-6′), 128.2 (C-4′), 128.9 (C-3′, C-5′), 139.0 (C-1′), 170.8 (CONH), 175.4 (COOCH3); (2 S ,1 R )-1b (minor isomer): δ 22.2 (CH3), 23.2 (\( C\textH_3^’ \)), 24.9 (CH), 28.7 (C(CH3)3), 43.4 (CH2), 50.7 (C(CH3)3), 52.0 (OCH3), 59.0 (C-2), 66.9 (C-1), 127.2 (C-2′, C-6′), 128.1 (C-4′), 128.8 (C-3′, C-5′), 139.9 (C-1′), 170.9 (CONH), 175.9 (COOCH3); HRMS (ESI) calcd for C18H28N2O3Na: 357.2154 (M+Na)+ found 357.2171. Methyl (2S,1S,3S)- and (2S,1R,3S)-2-(2-(tert-butylamino)-2-oxo-1-phenylethylamino)-3-methylpentanoate (2 S ,1 S ,3 S )-1c and (2 S ,1 R ,3 S )-1c From l-isoleucine (2.64 g, 20.16 mmol), benzaldehyde (16.80 mmol, 1.71 mL) and tert-butyl isocyanide (2.00 mL, 16.80 mmol);

FC (gradient: PE/AcOEt 9:1–4:1): yield 3.97 g (71 %) of chromatographically inseparable diastereomeric mixture (d r = 9.0/1, 1H NMR).