Example 4: General procedure for the synthesis of D-phenylalanine methyl ester hydrochloride: anhydrous methanol (50 mL) was added to a 100 mL two-necked round-bottomed flask equipped with a reflux condenser and a dropping funnel, and the system was cooled to ice bath temperature. Acetyl chloride (3 mL) was slowly added dropwise through the dropping funnel.After 15 min, D-phenylalanine (3 g, 18.16 mmol) was added to the reaction system, followed by refluxing the reaction mixture at 70 °C overnight. Upon completion of the reaction, D-phenylalanine methyl ester hydrochloride was obtained by vacuum drying, and the product could be used for subsequent reactions without further purification.
Procedure for synthesizing methyl phthalimide (D-NDI or NDI 3B): 1,4,5,8-naphthalenetetracarboxylic acid dianhydride (200 mg, 0.74 mmol) and D-phenylalanine methyl ester hydrochloride (322 mg, 1.49 mmol) were suspended in DMF (20 mL) in a 100 mL round-bottom flask. Triethylamine (0.6 mL) was added to the suspension under inert atmosphere. The reaction mixture was refluxed at 75 °C for 24 hours. At the end of the reaction, the solvent was removed by vacuum evaporation and the residue was purified by column chromatography (eluent: 1% chloroform solution in methanol) to afford the target product in 71% yield.
Product characterization data: 1H NMR (400 MHz, CDCl3): δ8.63 (s, 4H), 7.1 (m, 10H), 6.02 (dd, 2H, J=4Hz, 4Hz), 3.77 (s, 6H), 3.73 (dd, 2H, J=8Hz, 4Hz), 3.50 (dd, 2H, J=12Hz, 4Hz). 13C NMR (400MHz, CDCl3): δ169.6, 162.4, 136.9, 131.3, 129.2, 128.5, 126.9, 126.8, 126.4, 54.9, 52.8, 34.9. mass spectra (EI): m/z=590.17 [M]+ (C34H26N2O8). Elemental analysis results: measured values: C, 69.10; H, 4.49; N, 4.78; calculated values: C, 69.15; H, 4.44; N, 4.74 (C34H26N2O8).
