a) Synthesis of N-(tert-butoxycarbonyl)-2-(4-hydroxyphenyl)ethylamine
Tyramine hydrochloride (1.0 g, 5.76 mmol, 1 equiv.) was dissolved in a solvent mixture of dioxane and distilled water (25 mL/12 mL), followed by the addition of 10 mL of aqueous solution of NaOH (0.46 g, 11.5 mmol). After stirring for 10 min, di-tert-butyl dicarbonate (Boc2O) (1.26 g, 5.76 mmol, 1 equiv) was added. The reaction mixture was stirred overnight under argon protection and at room temperature. Upon completion of the reaction, dioxane was removed by evaporation and 40 mL of ethyl acetate (EtOAc) was added to the residual aqueous phase and the pH was adjusted to 7-8 with 1 M HCl solution.The organic and aqueous phases were separated, and the aqueous phase was extracted with EtOAc (2 x 15 mL). The organic phases were combined, dried with anhydrous Na2SO4, filtered and concentrated. The crude product was purified by column chromatography (Al2O3, CH2Cl2/Hex, 85:15) to afford N-(tert-butoxycarbonyl)-2-(4-hydroxyphenyl)ethylamine (0.98 g, 73% yield).
Melting point: 61-62°C.
IR (KBr, cm-1): 3378.9 (-OH); 1686.6 (C=O).
UV-Vis (CH2Cl2, λmax/nm): 277 (ε=1803).
1H-NMR (400 MHz, CDCl3): δ 1.441 (s, 9H, t-Bu); 2.703 (t, J=7.9 Hz, 2H, CH2CH2N); 3.329 (m, 2H, CH2CH2N); 4.602 (br s, 1H, NH or OH); 6.023 (br s, 1H, NH or OH); 6.774 (d, J=8.3 Hz, 2H, ArH); 7.013 (d, J=8.3 Hz, 2H, ArH).
13C-NMR (100 MHz, CDCl3): δ 28.84 (CMe3); 35.64 (CH2CH2N); 42.49 (CH2CH2N); 80.15 (CMe3); 115.97 (Cm); 130.18 (Ci); 130.50 (Cp); 155.38 (Cipso); 156.84 (C=O).
Elemental analysis (C13H19NO3, calculated values): C, 65.80%; H, 8.07%; N, 5.90%; measured values: C, 65.77%; H, 8.09%; N, 5.90%.
IE MS: m/z 181 [M-(Me)3CO-H+Na]+; 107 [M-(Me)3COC(O)NHCH2]+.
