The synthesis of a series of modified mannotrisaccharides as probes of the enzymes involved in the early stages of mammalian complex N-glycan formation.
A series of mannotrisaccharides were synthesized by two distinct chemical pathways as probes of the enzymes involved in the early stages of mammalian complex N-glycan formation. Methyl (alpha-D-mannopyranosyl)-(1-->3)-[(alpha-D-mannopyranosyl)-(1-->6)]-beta-D-mannopyranoside (6) and methyl (2-deoxy-2-fluoro-alpha-D-mannopyranosyl)-(1-->3)-[(2-deoxy-2-fluoro-alpha-D-mannopyranosyl)-(1-->6)]-beta-D-mannopyranoside (8) were rapidly synthesized from unprotected methyl beta-D-mannopyranoside (12). Methyl (2-deoxy-2-fluoro-alpha-D-mannopyranosyl)-(1-->3)-[(alpha-D-mannopyranosyl)-(1-->6)]-beta-D-mannopyranoside (7) and methyl (alpha-D-mannopyranosyl)-(1-->3)-[(2-deoxy-2-fluoro-alpha-D-mannopyranosyl)-(1-->6)]-beta-D-mannopyranoside (9) were synthesized from the common orthogonally protected precursor methyl 2-O-acetyl-4,6-O-benzylidene-beta-D-mannopyranoside (15). The 2-deoxy-2-fluoro substitution common to trisaccharides 7-9 renders these analogues resistant to enzyme action in two distinct ways. Firstly the fluorine serves as a non-nucleophilic isostere for the acceptor hydroxyl in studies with glycosyl transferases GnT-I and GnT-II (7 and 9, respectively). Secondly it should render trisaccharide 8 stable to hydrolysis by the mannosidases Man-II and Man-III by inductive destabilization of their oxocarbenium ion-like transition states. These analogues should be useful for structural studies on these enzymes.
Tarling
Chris A
CA
Department of Chemistry, 2036 Main Mall, University of British Columbia, Vancouver, BC, Canada V6T 1Z1.
Withers
Stephen G
SG
D002236:Carbohydrate Conformation; D004791:Enzyme Inhibitors / Q000138:chemical synthesis; D004798:Enzymes / Q000737:chemistry*; D016695:Glycosyltransferases / Q000037:antagonists & inhibitors / Q000737:chemistry; D008358:Mannose; D008361:Mannosidases / Q000037:antagonists & inhibitors / Q000737:chemistry; D015335:Molecular Probes / Q000138:chemical synthesis* / Q000737:chemistry; D011134:Polysaccharides / Q000096:biosynthesis*; D014312:Trisaccharides / Q000138:chemical synthesis* / Q000737:chemistry
D004791:Enzyme Inhibitors; D004798:Enzymes; D015335:Molecular Probes; D011134:Polysaccharides; D014312:Trisaccharides; D016695:Glycosyltransferases; D008361:Mannosidases; D008358:Mannose