Syntheses of two kinds of disaccharide subunits of antitumor antibiotic bleomycins

Gram-scale syntheses of two kinds of bleomycin disaccharides are described. L-gulose subunit 12 was accomplished with a novel and short route in six steps and 37% overall yield from 4, which could be easily prepared from the commercially available inexpensive material D-sorbitol, while 6-deoxy-L-gulose subunit was synthesized in 11 steps in 8% yield from D-glucolactone. The disaccharides were then prepared in a previously reported glycosidation coupling of the 3-O-carbamoyl-mannosyl donor with the L-gulopyranoside acceptors. Both disaccharides were finally obtained in gram-scale and the total synthesis of disaccharide 2 was achieved the first time.