Synthesis of heparan sulfate tetrasaccharide as a substrate for human heparanase

Borane-Trimethylamine Complex: A Versatile Reagent in Organic Synthesis

Borane-trimethylamine complex (Me3N·BH3; BTM) is the most stable of the amine-borane complexes that are commercially available, and it is cost-effective. It is a valuable reagent in organic chemistry with applications in the reduction of carbonyl groups and carbon-nitrogen double bond reduction, with considerable examples in the reduction of oximes, hydrazones and azines. The transfer hydrogenation of aromatic N-heterocycles and the selective N-monomethylation of primary anilines are further examples of recent applications, whereas the reduction of nitrobenzenes to anilines and the reductive deprotection of N-tritylamines are useful tools in the organic synthesis. Moreover, BTM is the main reagent in the regioselective cleavage of cyclic acetals, a reaction of great importance for carbohydrate chemistry. Recent innovative applications of BTM, such as CO2 utilization as feedstock and radical chemistry by photocatalysis, have extended their usefulness in new reactions. The present review is focused on the applications of borane-trimethylamine complex as a reagent in organic synthesis and has not been covered in previous reviews regarding amine-borane complexes.

The Development of Assays for Heparanase Enzymatic Activity: Towards a Gold Standard

The enzyme heparanase, an endo-β-glucuronidase, degrades heparan sulfate (HS) chains on the cell surface and in the extracellular matrix. Heparanase regulates numerous biological processes that drive tumour growth, metastasis and angiogenesis. In addition to its key role in cancer progression, it has also been implicated in an ever-growing number of other diseases, particularly those associated with inflammation. The importance of heparanase in biology has led to numerous efforts over the years to develop assays to monitor its activity and to screen for new inhibitors as potential drug candidates. Despite these efforts and the commercialization of a few kits, most heparanase assays are still complex, labour intensive, costly or have limited application. Herein we review the various methods for assaying heparanase enzymatic activity, focusing on recent developments towards new assays that hold the promise of accelerating research into this important enzyme.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2011-2012

This review is the seventh update of the original article published in 1999 on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2012. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, and fragmentation are covered in the first part of the review and applications to various structural types constitute the remainder. The main groups of compound are oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2015 Wiley Periodicals, Inc. Mass Spec Rev 36:255-422, 2017.

Investigating Glycol-Split-Heparin-Derived Inhibitors of Heparanase: A Study of Synthetic Trisaccharides

Heparanase is the only known endoglycosidase able to cleave heparan sulfate. Roneparstat and necuparanib, heparanase inhibitors obtained from heparin and currently being tested in man as a potential drugs against cancer, contain in their structure glycol-split uronic acid moieties probably responsible for their strong inhibitory activity. We describe here the total chemical synthesis of the trisaccharide GlcNS6S-GlcA-1,6anGlcNS (1) and its glycol-split (gs) counterpart GlcNS6S-gsGlcA-1,6anGlcNS (2) from glucose. As expected, in a heparanase inhibition assay, compound 2 is one order of magnitude more potent than 1. Using molecular modeling techniques we have created a 3D model of 1 and 2 that has been validated by NOESY NMR experiments. The pure synthetic oligosaccharides have allowed the first in depth study of the conformation of a glycol-split glucuronic acid. Introducing a glycol-split unit in the structure of 1 increases the conformational flexibility and shortens the distance between the two glucosamine motives, thus promoting interaction with heparanase. However, comparing the relative activities of 2 and roneparstat, we can conclude that the glycol-split motive is not the only determinant of the strong inhibitory effect of roneparstat.

Heparanase: a rainbow pharmacological target associated to multiple pathologies including rare diseases

In recent years, heparanase has attracted considerable attention as a promising target for innovative pharmacological applications. Heparanase is a multifaceted protein endowed with enzymatic activity, as an endo-β-D-glucuronidase, and nonenzymatic functions. It is responsible for the cleavage of heparan sulfate side chains of proteoglycans, resulting in structural alterations of the extracellular matrix. Heparanase appears to be involved in major human diseases, from the most studied tumors to chronic inflammation, diabetic nephropathy, bone osteolysis, thrombosis and atherosclerosis, in addition to more recent investigation in various rare diseases. The present review provides an overview on heparanase, its biological role, inhibitors and possible clinical applications, covering the latest findings in these areas.

Development of new methods for determining the heparanase enzymatic activity

INTRODUCTION

Heparanase is a mammalian endo-β-glucuronidase. Notwithstanding its importance in various pathological and non-pathological events few straightforward methods for heparanase enzymatic activity has been stated. The aim of this study was to develop two heparanase activity assays to cover a whole range of applications. First, a fast and easy method based on commercial homogenous substrate, fondaparinux, was described. The other method is a quantitative assay based on biotinylated heparan sulfate that uses an easier technique to immobilize the substrate in a 96-well plate.

METHODS

1): The heparanase recombinant enzyme and fondaparinux were incubated overnight. After incubation, a fluorescent redox marker, resazurin, was added. The reduction of resazurin depends on the amount of glucuronic acid released by heparanase digestion. Fluorescence measurements were done using excitation and emission wavelengths of 560 nm and 590 nm, respectively.

METHODS

2): The 96-well plate was incubated with protamine sulfate. Subsequently, biotinylated heparan sulfate was immobilized. The enzymatic assay was performed using chimeric recombinant heparanase at different concentrations. In sequence, the immobilized biotinylated heparan sulfate that was not digested by recombinant heparanase was bound to streptavidin conjugated with europium. Fluorescence was measured using a time-resolved fluorometer.

CONCLUSION

Both methods have high sensitivity and can be used to detect heparanase activity. Fondaparinux assay is a quick and easy method for screening of heparanase inhibitors using recombinant enzyme or bacterial crude extract. Biotinylated heparan sulfate assay can be used for quantitative analysis in biological samples and protamine sulfate showed been capable to immobilized heparan sulfate.

Side reactions with 2,2,2-trichloroethoxysulfates during the synthesis of glycans

Protected sulfate groups may be used as an alternative tool to provide sulfate esters at hydroxyl and amino groups, particularly on complex glycans. We examined 2,2,2-trichloroethoxysulfation at the mono-, di-, and trihydroxyl groups of saccharide moieties to show regioselective sulfation. We found some side reactions including inter- and intramolecular nucleophilic reactions with 2,2,2-trichloroethoxysulfates.

Heparan sulfate containing unsubstituted glucosamine residues: biosynthesis and heparanase-inhibitory activity

Degradation of heparan sulfate (HS) in the extracellular matrix by heparanase is linked to the processes of tumor invasion and metastasis. Thus, a heparanase inhibitor can be a potential anticancer drug. Because HS with unsubstituted glucosamine residues accumulates in heparanase-expressing breast cancer cells, we assumed that these HS structures are resistant to heparanase and can therefore be utilized as a heparanase inhibitor. As expected, chemically synthetic HS-tetrasaccharides containing unsubstituted glucosamine residues, GlcAβ1-4GlcNH3 (+)(6-O-sulfate)α1-4GlcAβ1-4GlcNH3 (+)(6-O-sulfate), inhibited heparanase activity and suppressed invasion of breast cancer cells in vitro. Bifunctional NDST-1 (N-deacetylase/N-sulfotransferase-1) catalyzes the modification of N-acetylglucosamine residues within HS chains, and the balance of N-deacetylase and N-sulfotransferase activities of NDST-1 is thought to be a determinant of the generation of unsubstituted glucosamine. We also report here that EXTL3 (exostosin-like 3) controls N-sulfotransferase activity of NDST-1 by forming a complex with NDST-1 and contributes to generation of unsubstituted glucosamine residues.

Efficient synthesis of a library of heparin tri- and tetrasaccharides relevant to the substrate of heparanase

A robust glycosylation protocol was fixed to construct the GlcN–(1α→4)-GlcA/IdoA linkagesen routeto heparin oligosaccharides.

Convergent stereoselective synthesis of multiple sulfated GlcNα(1,4)GlcAβ(1,4) dodecasaccharides

In this paper, we describe an effective method for the elongation of a GlcNα(1,4)GlcAβ(1,4) sequence using a GlcNTrocα(1,4)GlcA disaccharide unit and the synthesis of the N- and/or O-sulfated GlcNα(1,4)GlcAβ(1,4) oligosaccharides. N-Troc protection of GlcNα(1,4)GlcA units was effective for the synthesis of the GlcNα(1,4)GlcAβ(1,4) oligosaccharides in comparison with the azido substituent. The GlcNα(1,4)GlcAβ(1,4) dodecasaccharide was successfully prepared by the direct β-selective glycosidation of glucuronate in the GlcNα(1,4)GlcAβ(1,4)GlcNα(1,4)GlcAβ(1,4) tetrasaccharide. In addition, the synthesis of the N- and/or O-sulfated GlcNα(1,4)GlcAβ(1,4) oligosaccharides was accomplished by fluorous-assisted deprotection and sulfation. The fluorous-assisted synthetic technology applied to the highly polar sulfated oligosaccharide permits it to be more easily separated from the highly polar reagents, such as SO(3)·NEt(3).