Glycoconjugate J (1987) 4:119-127 Ganglioside Lactones: 1H-NMR Determination of the Inner Ester Position of GDlb-Ganglioside Lactone Naturally Occurring in Human Brain or Produced by Chemical Synthesis DOMENICO ACQUOTTI 1, GIOVANNI FRONZA 2, LAURA RIBONI 1, SANDRO SONNINO 1. and GUIDO TETTAMANTI 1 1Study Center for the Functional Biochemistry of Brain Lipids, Department of Biological Chemistry, The Medical School, University of Milan, Via Saldini 50, 20133Milano, Italy ZCNRStudy Center for Natural Organic Substances, Department of Chemistry, Polytechnic of Milan, Milano, Italy ReceivedJanuary16/March13, 198Z Key words: ganglioside lactones, NMR The complete definition of the chemical structure of GDlb-ganglioside (GDlb) lactone isolated from human brain has been given by means of spectrometric and spec- troscopic analyses. GDlb lactone contains a single ester linkage involving the external sialic acid carboxyl group and the C-9 hydroxyl group of the internal sialic acid unit. A synthetic lactone of GDlb prepared treating GDlb with glacial acetic acid characterized in the same way showed an identical chemical structure. Gangliosides are sialic acid-containing glycosphinglipids that reside in the outer leaflet of the plasma membranes of vertebrate cells [1]. They are assumed to play a role in a variety of surface events such as specific recognition of external [igands and biotransduction of membrane mediated information [2]. The sialic acid residue(s) of gangliosides may play a fundamental role in these events. The sialic acid carboxyl groups are dissociated at physiological pH I3]. The presence of the negative charge enhances the hydrophilic character and introduces additional -Abbreviations: Ganglioside nomenclature is according to Svennerhofm [16]and the IUPAC-IUB Recommen- dations 117 I. GMI,GM~-ganglioside, ll3NeuAc-GgOse4Cer, Gal~1-3GalNAc~1-41NeuAcc~2-3]Gal~l.4Glc~1-1'Cer; GDIb, ,GD1b-ganglioside, ll3(NeuAc)2GgOse4Cer,Gal131-3GalNAc~1-4[NeuAco~2.8NeuAc~2_31Gal/31_4Glc~1_1, C_ er; GDIb lactone, GDI6-L, Gal~1-3GalNAci31-4[NeuAc(1-9)c~2-8NeuAccz2-3]Gal/31-4Glc~1-1'Cer; Cer, ceramide; FAB-MS,fast atom bombardment-mass spectrometry; ~H-NMR, proton nuclear magnetic resonance; ID- NMR, one dimensional NMR; 2D-COSY,two dimensional correlated spectroscopy; DMSO-d6,deuterated dimethylsuffoxide. *Au thor for correspondence. 119