Complexes of sodium vanadate(V) with methyl alpha-D-mannopyranoside, methyl alpha- and beta-D-galactopyranoside, and selected O-methyl derivatives: a 51V and 13C NMR study.
The hydroxyl group stereochemistry of complexation of sodium vanadate(V) with Me alpha-Manp, Me alpha- and beta-Galp and selected O-methyl derivatives in D(2)O was determined by 51V, 1D and 2D 13C NMR spectroscopy at pD 7.8. The 51V approach served to show the extent of complexation and the minimum number of esters formed. That of Me alpha-Manp gave rise mainly to a 51V signal at delta -515, identical with that of its 4,6-di-O-methyl derivative, which had only a 2,3-cis-diol exposed. The 13C NMR spectra contained much weaker signals of the complexes, but both glycosides showed strong C-2 and C-3 alpha-shifts of +17.3 and +10.8 ppm, respectively. As expected, Me 2,3-Me(2)-alpha-Manp, which contains a 4,6-diol, did not complex. Me Galp anomers and their derivatives showed more diversity in the structure of its oxyvanadium derivatives. Me alpha-Galp, with its 3,4-cis-diol, complexed to give rise to 51V signals at delta -495 (9%), -508 (10%), and -534 (4%). These shifts and proportions were maintained with Me beta-Galp and Me 6Me-alpha-Galp. 51V NMR spectroscopy showed that Me 3Me-beta-Galp, with its possibly available 4,6-diol, did not complex. Similarly, Me alpha-Galp+vanadate gave a 13C DEPT spectrum that did not contain an inverted signal at delta >71.4, as would be expected of a C-6 resonance suffering a strong downfield alpha-shift. Me 2,6-Me(2)-alpha-Galp, with a 3,4-cis-diol group, gave rise to two 51V signals of complexes at delta -492 (9%) and -508 (9%), showing more than one structure of oxyvanadium derivatives.
Noleto
Guilhermina R
GR
Departamento de Bioqui;mica, Universidade Federal do Paraná, Caixa Postal 19046, Curitiba PR 81530-990, Brazil.
Tischer
Cesar A
CA
Gorin
Philip A J
PA
Iacomini
Marcello
M
Oliveira
Maria Benigna M
MB
D002236:Carbohydrate Conformation; D005690:Galactose / Q000031:analogs & derivatives*; D006031:Glycosylation; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008745:Methylation; D008766:Methylmannosides / Q000737:chemistry*; D015394:Molecular Structure; D014638:Vanadates / Q000737:chemistry*
D008766:Methylmannosides; D014638:Vanadates; D005690:Galactose