Carbohydrate-protein Linkage Region Of Proteoglycans Research Articles

Tandem mass spectrometry for the characterisation of sulphated‐phosphorylated analogues of the carbohydrate–protein linkage region of proteoglycans

Carbohydrate-protein linkage region of proteoglycans is a key oligosaccharide structure because their sulphated and/or phosphorylated analogues control the biosynthesis of glucosaminoglycans or galactosaminoglycans. Therefore, synthesised sulphated and/or phosphorylated analogues were characterised by tandem mass spectrometry in the negative-ion mode. Results demonstrated that the product ion profile was characterised by glycosidic and cross-ring cleavages depending on the position and the type of the charged group (sulphate, phosphate or carboxylate). When the above compounds were sulphated and phosphorylated, the ion found at m/z 79 was the only one that demonstrated a phosphate group on the structure. The data also suggested that when a sodium cation was present in a sulphated and phosphorylated structure, the phosphate group in most cases was neutralised by the sodium cation, and therefore cleaved off the molecule, while the sulphate group was carrying the negative charge.

Regioselective deacetylation of peracetylated monosaccharide derivatives by polyethylene glycol-modified lipase for the oligosaccharide synthesis

Lipase modified with polyethylene glycol became soluble and active in organic solvents, and catalyzed regioselective deacetylation of peracetylated monosaccharide derivatives in 1,1,1-trichloroethane. The deacetylation occurred only at the positions of C-4 and C-6 of the glycopyranoside ring. Especially, peracetylated methyl β-D-xylopyranoside and peracetylated L-serine-β-D-xylopyranoside were hydrolyzed only at the position of C-4. Subsequently, one of the resulting products, that is L-serine-2,3-di-O-acetyl-β-D-xylopyranoside, was coupled with galactose residue to obtain L-serine-4-O-(β-D-galactopyranosyl)-β-D-xylopyranoside, a model compound of the carbohydrate-protein linkage region of proteoglycans.

Synthesis of sulfated and phosphorylated glycopeptides from the carbohydrate-protein linkage region of proteoglycans

The synthesis of the tetrasaccharide dipeptide β- d-Glc pA-(1 → 3)-β- d-Gal p4SO 3Na-(1 → 3)-β- d-Gal p-(1 → 4)-β- d-Xyl p-(1 → O)- l-Ser-Gly was achieved by coupling a suitably protected tetrasaccharide trichloroacetimidate, built up from the nonreducing end by the stepwise addition of monosaccharide units, to the protected dipeptide Z- l-Ser-Gly- OBn. Sulfation at O-4 of the second d-Gal unit and complete deprotection afforded the target molecule in high yield. Its phosphorylated analogue β- d-Glc pA-(1 → 3)-β- d-Gal p-(1 → 3)-β- d-Gal p-(1 → 4)-β- d-Xyl p2PO 3Na 2-(1 → O)- l-Ser-Gly was synthesized by coupling a protected trisaccharide trichloroacetimidate to the 2,3- O-isopropylidene derivative of Z-( d-Xyl-) l-Ser-Gly-OBn. Hydrolysis of the O-isopropylidene group, regioselective acetylation at O-3 of the O-Xyl unit, and phosphorylation at O-2 followed by complete deprotection gave the phosphoryltaed tetrasaccharide dipeptide in high yield. These structures are found in the carbohydrate-protein linkage region of several proteoglycans.

Synthesis of glycopeptides from the carbohydrate-protein linkage region of proteoglycans

2,3,4,6-Tetra- O-benzoyl-α- d-galactopyranosyl trichloroacetimidate was condensed with benzyl 2,3- O-isopropylidene-β- d-xylopyranoside to give the corresponding β-(1→4)-linked disaccharide derivative, which was transformed into 2,3-di- O-benzoyl-4- O-(2,3,4,6-tetra- O-benzoyl-β- d-galactopyranosyl)α- d-xylopyranosyl trichloroacetimidate. This glycosyl donor was condensed with a set of selectively C,N-protected l-seryl-glycine dipeptide units. Seletive deblocking at the C- or N-termini of the glycosylated or non-glycosylated dipeptide segments, and coupling using the mixed-anhydride procedure allowed the construction in high yield of partially or fully glycosylated oligopeptides from the carbohydrate-protein linkage region of proteoglycans.