Efficient synthesis of differently protected methyl (ethyl 1-thio-β-D-glucopyranosid)uronates and their evaluation as glucuronic acid donors and acceptors

Methyl [ethyl 2-O-acetyl-3,4-0-(1,1,3,3-tetraisopropyl-1,3-disiloxane-1,3-diyl)-1-thio-beta-D-glucopyranosid]uronate (7), and its 2-O-benzoyl and -pivaloyl analogues, 13 and 14, have been synthesised from methyl 2,3,4 -tri-O-acetyl-alpha-D-glucopyranosyluronate bromide, via formation and rearrangement of a 1,2-thioorthoester, in a stereospecific and high-yielding manner. Dimethyl(methylthio)sulfonium trifluoromethanesulfonate (DMTST)-promoted glycosylations with these derivatives as donors gave high to excellent yields (59-95%) of exclusively beta-linked disaccharides in coupling with monosaccharide accepters. Removal of the tetraisopropyldisiloxyl acetal with tetrabutylammonium fluoride in tetrahydrofuran from one of the obtained disaccharides gave a 3',4'-diol, which was used as acceptor in a DMTST-promoted coupling with ethyl 2,3,4-tri-0-acetyl-2-deoxy-2-phthalimido1-thio-beta-D-glucopyranoside as donor to give trisaccharides, albeit with low regioselectivity (3-O-linked 38%, 4-O-linked 57%). (C) 1998 Elsevier Science Ltd. All rights reserved.