Scheme 1. Reagents and conditions: (a) 4-methyl thiophenol, DCM, DIEPA, rt, 12 h; (b) TfOH, NIS, DCM, –50 °C, 2 h, 40% for compound 4 and 37% for compound 6; (c) (i) NaOMe, MeOH, rt, 1 h; (ii) Pd(OH)2/C/H2, EtOH, rt, 12 h; (iii) 0.05 N NaOH in H2O, rt, 2 h, 94% for (4,7di-OMe)Sα2,6Gal and 88% for (4,7di-OMe)Sα2,3Gal over the three steps.
