Scheme 2. Synthesis of C-4-, C-7-, and C-8-Modified Sialic Acid Inhibitors; (i) (1) NaIO4, MeOH; (2) NaBH4, MeOH; (3) Ac2O, Py, 37% (14); 66% (18); (ii) (1) Selectfluor, DMF, H2O; (2) Ac2O, Py, 21% (16); 23% (17); 33% (20); 14% (21); 54% (23); (iii) (1) Tf2O, 2-FPy, DCM, then 1,2-Propanediol; (2) Ethyl Chloroformate, DIPEA, DCM, 68% (15); 39% (19); 28% (24); and (iv) PMe3, THF, then Propargyl Chloroformate, 24% (25).
