Dichloromethane → N-(1-Carbobenzyloxy-5-phthalimidopentyl)-alpha-azaalanyl-(L)-proline-t-butyl ester

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Reaction Steps

A solution of carbazide 2 (0.665 g; 2.74 mmol) and benzyl 6-phthalimido-2-oxohexanoate (1.00 g; 2.74 mmol) in THF (5 ml) containing glacial acetic acid (3 drops) was heated at reflux for 3 hours. TLC (silica gel, CH2Cl2 --CH3OH,20:1) showed a single product spot, Rf=0.5. The crude product was treated as for 14 (Example 10) with sodium cyanoborohydride (172 mg; 2.74 mmol), giving pure carbazide 24 (1.18 g; 2.00 mmol; 73%) after flash chromatography on silica gel (hexanes-EtAc, 1:1). TLC (silica gel; hexanes-EtOAc, 1:1) showed a mixture (1:1) of diastereomers, Rf=0.25, 0.30. MS m/e 592 (M+). Analysis: Calculated for C32H40N4O7 : C, 64.85; H, 6.80; N, 9.45. Found: C, 64.24; H, 6.98; N, 8.95. NMR (CDCl3): δ 1.40 (9H,s); 1.5-2.0 (8H,m); 2.88, 2.90 (3H,2 x S); 3.2-3.7 (6H,m); 4.2-4.4 (1H,m); 4.8-5.1 (1H,m); 5.12, 5.15 (2H,2 x S); 7.27 (5H,s); 7.6-7.9 (4H,m). IR (CHCl3): 2980, 1770, 1730, 1720, 1640 cm-1.

Provenance & Evidence