Two uronic acid-contg. trisaccharides, (4-deoxy-b-L-threo-hex-4-enopyranosyluronic acid)- and (4-O-methyl-a-D-gluropyranosyluronic acid)-(1,2)-b-D-xylopyranosyl-(1,4)-D-xylopyranose, found in enzyme hydrolyzates from pulp are synthesized. A common dixyloside 2'-OH acceptor, p-methoxyphenyl [3,4-O-(2',3'-dimethoxybutane-2',3'-diyl)-b-D-xylopyranosyl]-(1,4)-2,3-di-O-benzoyl-b-D-xylopyranoside, is constructed and coupled with two glucuronate thioglycoside donors differently substituted in the 4-position, O-Me and O-mesyl, resp., to give trisaccharides. DMTST as promoter in di-Et ether gives exclusively the a-linked products in high yield. Treatment of the 4''-O-mesyl trisaccharide with DBU then gives the a,b-unsatd. uronic acid deriv. The protection pattern introduced in the acceptor allows continued synthesis of larger oligosaccharides. Removal of the butanedione acetal produces 3',4'-acceptors, and the p-methoxyphenyl glycoside can be transformed into various glycosyl donors, e.g. thioglycosides and sugar halides. Complete deprotection gives the two target reducing trisaccharides. [on SciFinder (R)]