Reaction Steps
A solution of the regioisomeric C-[1-(4-methoxy-benzyl)-1H-[1,2,3]triazol-4-yl]-methylamine and C-[3-(4-methoxy-benzyl)-3H-[1,2,3]triazol-4-yl]-methylamine (1003 and 1004, 20.0 g, 91.74 mmol) in 1,2-dichloroethane (DCE, 280 mL) was treated with 4-formylphenylboronic acid 1005 (commercially available, 12.39 g, 82.57 mmol, 0.9 equiv) at room temperature, and the resulting reaction mixture was stirred at room temperature for 10 min. Sodium triacetoxyborohydride (NaB(OAc)3H, 29.2 g, 137.6 mmol, 1.5 equiv) was then added to the reaction mixture in three portions over the period of 1.5 h at room temperature, and the resulting reaction mixture was stirred at room temperature for an additional 3.5 h. When TLC and HPLC/MS showed that the reductive amination reaction was complete, the reaction mixture was concentrated in vacuo. The residue, which contained a regioisomeric mixture of 4-({[1-(4-methoxy-benzyl)-1H-[1,2,3]triazol-4-ylmethyl]-amino}-methyl)-phenylboronic acid and 4-({[3-(4-methoxy-benzyl)-3H-[1,2,3]triazol-4-ylmethyl]-amino}-methyl)-phenylboronic acid as the reductive amination products (1006 and 1007), was then treated with tetrahydrofuran (THF, 100 mL) and water (H2O, 100 mL). The resulting solution was subsequently treated with solid potassium carbonate (K2CO3, 37.98 g, 275.2 mmol, 3.0 equiv) and di-tert-butyl dicarbonate (BOC2O, 20.02 g, 91.74 mmol, 1.0 equiv) at room temperature and the reaction mixture was stirred at room temperature for 2 h. When TLC and HPLC/MS showed that the N—BOC protection reaction was complete, the reaction mixture was treated with ethyl acetate (EtOAc, 150 mL) and water (H2O, 100 mL). The two layers were separated, and the aqueous layer was extracted with ethyl acetate (50 mL). The combined organic extracts were washed with H2O (50 mL), 1.5 N aqueous HCl solution (2×100 mL), H2O (100 mL), and saturated aqueous NaCl solution (100 mL), dried over MgSO4, and concentrated in vacuo. The crude, regioisomeric 4-({tert-butoxycarbonyl-[1-(4-methoxy-benzyl)-1H-[1,2,3]triazol-4-ylmethyl]-amino}-methyl)-phenylboronic acid and 4-({tert-butoxycarbonyl-[3-(4-methoxy-benzyl)-3H-[1,2,3]triazol-4-ylmethyl]-amino}-methyl)-phenylboronic acid (1008 and 1009, 35.98 g, 37.32 g, 96.4%) was obtained as a pale-yellow oil, which solidified upon standing at room temperature in vacuo. This crude material was directly used in the subsequent reaction without further purification. For 1008 and 1009: 1H NMR (300 MHz, DMSO-d6) δ 1.32 and 1.37 (two br. s, 9H, COOC(CH3)3), 3.70, 3.73 and 3.74 (three s, 3H, Ar—OCH3), 4.07-4.39 (m, 4H), 5.49 and 5.52 (two s, 2H), 6.70-8.04 (m, 9H, Ar—H and triazole-CH); C23H29BN4O5, LCMS (EI) m/e 453 (M++H) and 475 (M++Na).
