“…(S)-tert-Butyl 2-((S)-1-(methoxycarbonyl)-2-phenylethylcarbamoyl)pyrrolidine-1-carboxylate (4a) Yellow oil, yield 73 %, [α] 20 D = −38.7 (c = 1.24, CHCl 3 ); 45 1 H NMR (CDCl 3 , 500 MHz) δ 1.42 (bs, 9H, C(CH 3 ) 3 ), 1.77-1.86 (m, 2H, pro-γ), 1.88-2.06 (m, 2H, pro-β), 2.90-3.03 (m, 1H, PhCH 2 ), 3.19 (dd, J = 14.0, 5.5 Hz, 1H, PhCH 2 ), 3.29-3.39 (m, 2H, pro-δ), 3.72 (s, 3H, OCH 3 ), 4.19-4.29 (m, 1H, pro-α), 4.85 (bs, 1H, Phe-CH), 7.09 (bd, J = 7.0 Hz, 2H, ArH), 7.22-7.25 (m, 3H, ArH) ppm; 13 C NMR (CD 3 OD, 125 MHz) δ 24.3 (pro-γ), 28.5 (3 × CH 3 ), 32.2 (pro-β), 38.1 (PhCH 2 ), 47.8 (pro-δ), 52.7 (Phe-CH), 55.1 (OCH 3 ), 61.6 (pro-α), 81.5 (OC(CH 3 ) 3 ), 127.9 (C aro H), 129.5 (C aro H), 130.1 (C aro H), 138.3 (C aro ), 173.3 (C=O), 175.1 (C=O), 175.8 (C=O) ppm; FTIR (ATR) ν 3277, 3079, 3028, 2976, 2877, 1738, 1689, 1660, 1552, 1445, 1389, 1365, 1210 cm -1 . (S)-tert-Butyl 2-(((S)-3-hydroxy-1-methoxy-1-oxopropane-2-yl)carbamoyl)-pyrrolidine-1-carboxylate (4c)Colorless oil, yield 94 %, [α] 20 D = +88.0 (c = 1.00, CH 3 OH);46 1 H NMR (CD 3 OD, 500 MHz) δ 1.45 and 1.48 (s, 9H, 3 × CH 3 , rotamers), 1.88-1.92 (m, 1H, pro-γ), 1.94-1.98 (m, 1H, pro-γ), 2.00-2.05 (m, 1H, pro-β), 2.12-2.29 (m, 1H, pro-β), 3.33 (brs, 1H, OH), 3.40-3.45 (m, 1H, pro-δ), 3.51-3.55 (m, 1H, pro-δ), 3.74 (s, 3H, OCH 3 ), 3.79-3.85 (m, 1H, CH 2 OH), 3.91-3.96 (m, 1H, CH 2 OH), 4.27-4.30 (m, 1H, pro-α), 4.53-4.55 (m, 1H, CHCH 2 OH) ppm; FTIR (ATR) ν 3293, 3082, 2975, 2881, 1743, 1662, 1533, 1470, 1454, 1205, 1160 cm -1 . (S)-2-((S)-tert-Butyl 2-carbamoylpyrrolidine-1-carboxyloyl)-3-phenyl-propanoic acid (5a)White solid, yield 96 %, mp 143−144 °C (mp 145-147 °C)45,47 ; [α] 20 D = −43.1 (c= 1.3, CHCl 3 ).…”