title: Lactones of disialyl lactose: characterisation by NMR and mass spectra.
abstract: The lactonisation of alpha-Neup5Ac-(2-->8)-alpha-Neup5Ac-(2-->3)-beta-D-Galp-(1-->4)-D-Glc (disialyl lactose) was investigated. (1)H and (13)C NMR chemical shifts of disialyl lactose and alpha-Neup5Ac-(2-->8, 1-->9)-alpha-Neup5Ac-(2-->3, 1-->2)-beta-D-Galp-(1-->4)-D-Glc (disialyl lactose-dilactone) were assigned based on 1D and 2D NMR results, including edited HSQC, HSQC-TOSCY and HMBC. The time course of lactonisation was followed by thin layer chromatography (TLC) and high-performance liquid chromatography (HPLC) with electrospray ionisation (ESI) mass spectrometry (MS) detection. The rate of lactonisation between alpha-(8)Neu5Ac and alpha-(3)Neu5Ac residues (lactonisation at the alpha-(2-->8) linkage) was faster than that of lactonisation between alpha-(3)Neu5Ac and Gal residues (lactonisation at the alpha-(2-->3) linkage). The mass spectra of disialyl lactose, its lactones, alpha-Neup5Ac-(2-->8)-alpha-Neup5Ac (alpha-(2-->8) disialic acid) and alpha-Neup5Ac-(2-->3)-beta-D-Galp-(1-->4)-D-Glc-lactone (3'-sialyllactose-lactone) showed that the alpha-(2-->8) linkage between Neu5Ac residues is difficult to cleave in the ESI-MS, compared with the alpha-(2-->3) linkage between Neu5Ac and Gal residues.
authors.affiliation: Department of Chemistry, The University of Auckland, Private Bag 92019, Auckland, New Zealand.
authors.forename: Geoffrey Ge
authors.initials: GG
authors.lastname: Pan
authors.forename: Laurence D
authors.initials: LD
authors.lastname: Melton
mesh_terms: D000818:Animals; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D003126:Colostrum / Q000737:chemistry; D005260:Female; D006863:Hydrogen-Ion Concentration; D007783:Lactones / Q000737:chemistry*; D007785:Lactose / Q000031:analogs & derivatives* / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D021241:Spectrometry, Mass, Electrospray Ionization; D014312:Trisaccharides / Q000737:chemistry*
chemical_list: D007783:Lactones; D014312:Trisaccharides; C509062:disialyllactose; D007785:Lactose