N-p-Nitrobenzyloxycarbonyl galactosamine imidate as a glycosyl donor for the efficient synthesis of mucin core-2 analogue

An efficient synthesis of the mucin core-2 analogue 1a was accomplished using N-p-nitrobenzyloxycarbonyl(PNZ)-protected trichloroacetimidate 4 as a novel glycosyl donor. Figure 1. This C-2 position is blocked for commonly occurring α(1,2)- -fucosyltransferase. Scheme 2. Reagents and conditions: (i) 4 (1.5 equiv), TESOTf (0.24 equiv), CH2Cl2, 4 Å molecular sieves, rt, 15 min, 89%; (ii) Na2S2O4 (8 equiv), MeCN:EtOH:H2O (v/v/v 1:1:1), 10 min; (iii) Ac2O–MeOH; (iv) 75% acetic acid, 45 °C, 2 h, 90%; (v) 80% acetic acid, 40 °C, 2 h, 92%; (vi) 4 (1.2 equiv), TESOTf, CH2Cl2, −65 °C, 1 h, 78%; (vii) pyridine–Ac2O, DMAP; (viii) 4 (1.2 equiv), BF3•Et2O (0.5 equiv), CH2Cl2, −60 °C, 30 min, 82%.