Synthesis of 3E- And 6E-Monosulfated and 3E,6E-Disulfated Lewis X Pentasaccharides, Candidate Ligands for Human L-Selectin

ABSTRACT

Condensation of perbenzyl fucosyl bromide 4 with the known 2-acetamido derivative 1 and with the 2-phthalimido analog 3 gave, respectively, disaccharides 5 and 6 which, after reductive opening of the benzylidene group were glycosylated using peracetylated galactose trichloroacetimidate to give trisaccharides 10 and 11. After removal of the anomeric p-methoxybenzyl group and subsequent activation as the trichloroacetimidate, condensation onto the known lactose derivative 16 afforded protected pentasaccharides 18 and 17 in 24 and 70% yields, respectively. Compound 17 was transformed into 18 by a conventional method in 77% yield making the phthalimido route overall more attractive. The terminal galactose was then selectively deprotected and sulfated at the 3e, 6e and both 3e,6e positions to give the title compounds after complete deprotection.