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abstractenterotoxigenic escherichia coli ( etec ) like the o139 strain are mostly responsible for traveler 's diarrhea and causes diseases in pigs , cattle , and poultry . 
 a convenient synthetic strategy was developed for the synthesis of the heptasaccharide repeating unit of the cell wall lipopolysaccharide of the e.  coli o139 strain . 
 the pmethoxybenzyl ( pmb ) group was used as a temporary protecting group which was removed in situ under the glycosylation conditions by changing the reaction temperature during the synthesis of the target compound . 
 all glycosylation steps gave high yields with good stereoselectivity . 
 a ( 2,2,6,6tetramethylpiperidin1yl)oxyl ( tempo)mediated selective oxidation of the primary hydroxyl group was carried out using a biphasic reaction condition at the late stage of the synthesis . 
 such synthetic oligosaccharides could later be effectively conjugated with proteins to prepare glycoconjugate derivatives as vaccine candidates .