Ion-pairing liquid chromatography with on-line electrospray ion trap mass spectrometry for the structural analysis of N-unsubstituted heparin/heparan sulfate.

The rare N-unsubstituted glucosamine (GlcNH3(+)) residues in heparan sulfate (HS) have important biological and pathophysiological roles. In this study, a high-resolution method for the separation and analysis of N-unsubstituted disaccharides of heparin/HS is described. Four N-unsubstituted disaccharides, together with eight N-substituted species, can be well-separated by ion-pair reverse-phase ultra-performance liquid chromatography. Each disaccharide can then be detected and its relative abundance quantified using electrospray ionization mass spectrometry in the negative mode. Because of its high sensitivity, without interference from proteins and other sample impurities, this method is particularly useful in the analysis of low content GlcNH3(+) residues in small amounts of biological materials, eg. sera, tissue and cell culture-derived samples. This would lead to a better understanding of the biological origin of GlcNH3(+) residues and their increasingly important function in human health and disease.

Preparation and characterization of heparin hexasaccharide library with N-unsubstituted glucosamine residues.

The rare N-unsubstituted glucosamine (GlcNH3(+)) residues in heparan sulfate (HS) have important biological and pathophysiological roles. Therefore, the ability to chemically generate a series of oligosaccharides, which have a similar structure to the naturally-occurring, GlcNH3(+)--containing oligosaccharides from HS, would greatly contribute to investigating their natural role in HS. In this study, a hexasaccharide library that possess GlcNH3(+) residues were prepared from the chemical modification of the fully sulfated dp6. Chemical reaction conditions were optimized to generate different pattern of GlcNH3(+)--containing oligosaccharides, then the structure of the library was detected by high-performance liquid chromatography-ion trap/time-of-flight mass spectrometry (LC/MS-ITTOF) analysis. EIC/MS and MS(2) analysis showed different fragmentation patterns of dp6s with different GlcNH3(+) residues. This provides a foundation for further identification and quantification of GlcNH3(+)--oligosaccharides by mass spectrum analysis.

A new sequencing approach for N-unsubstituted heparin/heparan sulfate oligosaccharides.

The rare N-unsubstituted glucosamine (GlcNH(3)(+)) residues in heparan sulfate (HS) have important biological and pathophysiological roles. Because of their low natural abundance, the use of chemically generated, structurally defined, N-unsubstituted heparin/HS oligosaccharides can greatly contribute to the investigation of their natural role in HS. However, the sequencing of mixtures of chemically generated oligosaccharides presents major challenges due to the difficulties in separating isomers and the available detection methods. In this study, we developed and validated a simple and sensitive method for the sequence analysis of N-unsubstituted heparin/HS oligosaccharides. This protocol involves pH 4 nitrous acid (HNO(2)) degradation, size-exclusion HPLC and ion-pair reversed-phase liquid chromatography-ion trap/time-of-flight mass spectrometry (IPRP-LC-ITTOF MS). We unexpectedly found that absorbance at 232 nm (normally used for specific detection of C4-C5 unsaturated oligosaccharides) was, in most cases, still sufficiently sensitive to also simultaneously detect saturated oligosaccharides during HPLC, thus simplifying the positional analysis of GlcNH(3)(+)) residues. The IPRP-LC-ITTOF MS system can supply further structural information leading to full sequence determination of the original oligosaccharide. This new methodology has been used to separate and sequence a variety of chemically generated, N-unsubstituted dp6 species containing between 1 and 3 GlcNH(3)(+)) residues per oligosaccharide in different positional combinations. This strategy offers possibilities for the sequencing of natural N-unsubstituted oligosaccharides from HS and should also be applicable, with minor modification, for sequencing at N-sulfated residues using alternative pH 1.5 HNO(2) scission.