The dual role of fucosidases: tool or target

Regular intake of fucosylated oligosaccharides has been associated with several benefits for human health, particularly for new-borns. Since these biologically active molecules can be found naturally in human milk, research efforts have been focused on the alternative synthetic routes leading to their production. In particular, utilization of fucosidases to perform stereoselective transglycosylation reactions has been widely investigated. Other reasons that bring these enzymes to the spotlight are their role in viral infections and cancer proliferation. Since their involvement in the pathogenesis of these diseases have been widely described, fucosidases have become a target in newly developed therapies. Finally, activity disorders of biologically important fucosidases can lead to health problems such as fucosidosis. What is common for both mechanisms is the interaction between the enzyme and substrates in and around the active site. Therefore, this review will analyse different substrate structures that have been tested in terms of their interaction with fucosidases active sites, either in synthesis or inhibition reactions. The published results will be compared from this perspective.

Multivalent Pyrrolidine Iminosugars: Synthesis and Biological Relevance

Recently, the strategy of multivalency has been widely employed to design glycosidase inhibitors, as glycomimetic clusters often induce marked enzyme inhibition relative to monovalent analogs. Polyhydroxylated pyrrolidines, one of the most studied classes of iminosugars, are an attractive moiety due to their potent and specific inhibition of glycosidases and glycosyltransferases, which are associated with many crucial biological processes. The development of multivalent pyrrolidine derivatives as glycosidase inhibitors has resulted in several promising compounds that stand out. Herein, we comprehensively summarized the different synthetic approaches to the preparation of multivalent pyrrolidine clusters, from total synthesis of divalent iminosugars to complex architectures bearing twelve pyrrolidine motifs. Enzyme inhibitory properties and multivalent effects of these synthesized iminosugars were further discussed, especially for some less studied therapeutically relevant enzymes. We envision that this comprehensive review will help extend the applications of multivalent pyrrolidine iminosugars in future studies.

Demystifying Lysosomal α-l-Fucosidase in Liver Cancer-Bearing Mice by Specific Two-Photon Fluorescence Imaging

Liver cancer is one of the most frequently diagnosed cancers and has high mortality. However, the early treatment and prognosis can greatly prolong the survival time of patients, which depends on its early detection. α-l-Fucosidase (AFU), as a vital lysosomal hydrolase, is considered to be an ideal biomarker for early stage liver cancer. So, in vivo monitoring of AFU is essential for the early and accurate diagnosis of liver cancer. Hence, we designed the first two-photon turn-on fluorescent reporter, termed HcyCl-F, which localized to lysosomes for fast imaging of AFU. The 2-chloro-4-phenyl-α-l-fucoside bond of HcyCl-F could be effectively hydrolyzed by AFU and released the hydroxyl on the benzene ring, eventually obtaining a strong conjugated compound (HcyCl-OH) with shiny fluorescence. We demonstrated that HcyCl-F was able to rapidly and accurately respond to AFU. Using a two-photon fluorescence microscope, we successfully visualized the fluctuation of AFU in lysosomes. More importantly, a fascinatingly strong fluorescence signal was observed in the tumor tissue of liver cancer-bearing mice. Of note, we confirmed that HcyCl-F could clearly detect liver tumors in stage I. Altogether, our work provides a simple and convenient method for deciphering the critical pathological function of AFU in depth and facilitates the nondestructive and effective diagnosis of liver cancer in the early stage.

Synthesis and Glycosidase Inhibition Properties of Calix[8]arene-Based Iminosugar Click Clusters

A set of 6- to 24-valent clusters was constructed with terminal deoxynojirimycin (DNJ) inhibitory heads through C6 or C9 linkers by way of Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reactions between mono- or trivalent azido-armed iminosugars and calix[8]arene scaffolds differing in their valency and their rigidity but not in their size. The power of multivalency to upgrade the inhibition potency of the weak DNJ inhibitor (monovalent DNJ K_i being at 322 and 188 µM for C6 or C9 linkers, respectively) was evaluated on the model glycosidase Jack Bean α-mannosidase (JBα-man). Although for the clusters with the shorter C6 linker the rigidity of the scaffold was essential, these parameters had no influence for clusters with C9 chains: all of them showed rather good relative affinity enhancements per inhibitory epitopes between 70 and 160 highlighting the sound combination of the calix[8]arene core and the long alkyl arms. Preliminary docking studies were performed to get insights into the preferred binding modes.

Multivalent Effect in Glycosidase Inhibition: The End of the Beginning

Glycosidases are ubiquitous enzymes involved in a diversity of key biological processes such as energy uptake or cell wall degradation. The design of specific glycosidase inhibitors has been therefore the subject of intense research efforts in academia and pharmaceutical industry. However, until recently, the study of the impact of multivalency on glycosidase inhibition was almost completely neglected. The following account will review our ten year journey on the design of multivalent glycomimetics within our research group, from the discovery of the first strong multivalent effect in glycosidase inhibition to the high-resolution crystal structures of Jack bean α-mannosidase in complex with the multimeric inhibitor displaying the largest binding enhancements reported so far.

Harnessing pyrrolidine iminosugars into dimeric structures for the rapid discovery of divalent glycosidase inhibitors

The synthesis of three libraries (1a-l, 1a'-l' and 2a-l) of dimeric iminosugars through CuAAC reaction between three different alkynyl pyrrolidines and a set of diazides was carried out. The resulting crude dimers were screened in situ against two α-fucosidases (libraries 1a-l and 1a'-l') and one β-galactosidase (2a-l). This method is pioneer in the search of divalent glycosidase inhibitors. It has allowed the rapid identification of dimer 1i as the best inhibitor of α-fucosidases from bovine kidney (K_i = 0.15 nM) and Homo sapiens (K_i = 60 nM), and dimer 2e as the best inhibitor of β-galactosidase from bovine liver (K_i = 5.8 μM). In order to evaluate a possible divalent effect in the inhibition, the synthesis and biological analysis of the reference monomers were also performed. Divalent effect was only detected in the inhibition of bovine liver β-galactosidase by dimer 2e.

Exploring the divalent effect in fucosidase inhibition with stereoisomeric pyrrolidine dimers

Multi-valent inhibitors offer promise for the enhancement of therapeutic compounds across a range of chemical and biological processes. Here, a significant increase in enzyme-inhibition potencies was observed with a dimeric iminosugar-templated fucosidase inhibitor (IC50 = 0.108 μM) when compared to its monovalent equivalent (IC50 = 2.0 μM). Such a gain in binding is often attributed to a "multivalent effect" rising from alternative recapture of the scaffolded binding epitopes. The use of control molecules such as the meso analogue (IC50 = 0.365 μM) or the enantiomer (IC50 = 569 μM), as well as structural analysis of the fucosidase-inhibitor complex, allowed a detailed analysis of the possible mechanism of action, at the molecular level. Here, the enhanced binding affinity of the dimer over the monomer can be attributed to additional interactions in non-catalytic sites as also revealed in the 3-D structure of a bacterial fucosidase inhibitor complex.

Nanotechnology in Glycomics: Applications in Diagnostics, Therapy, Imaging, and Separation Processes

This review comprehensively covers the most recent achievements (from 2013) in the successful integration of nanomaterials in the field of glycomics. The first part of the paper addresses the beneficial properties of nanomaterials for the construction of biosensors, bioanalytical devices, and protocols for the detection of various analytes, including viruses and whole cells, together with their key characteristics. The second part of the review focuses on the application of nanomaterials integrated with glycans for various biomedical applications, that is, vaccines against viral and bacterial infections and cancer cells, as therapeutic agents, for in vivo imaging and nuclear magnetic resonance imaging, and for selective drug delivery. The final part of the review describes various ways in which glycan enrichment can be effectively done using nanomaterials, molecularly imprinted polymers with polymer thickness controlled at the nanoscale, with a subsequent analysis of glycans by mass spectrometry. A short section describing an active glycoprofiling by microengines (microrockets) is covered as well.

Carbohydrate-Processing Enzymes of the Lysosome: Diseases Caused by Misfolded Mutants and Sugar Mimetics as Correcting Pharmacological Chaperones

Lysosomal storage diseases are hereditary disorders caused by mutations on genes encoding for one of the more than fifty lysosomal enzymes involved in the highly ordered degradation cascades of glycans, glycoconjugates, and other complex biomolecules in the lysosome. Several of these metabolic disorders are associated with the absence or the lack of activity of carbohydrate-processing enzymes in this cell compartment. In a recently introduced therapy concept, for susceptible mutants, small substrate-related molecules (so-called pharmacological chaperones), such as reversible inhibitors of these enzymes, may serve as templates for the correct folding and transport of the respective protein mutant, thus improving its concentration and, consequently, its enzymatic activity in the lysosome. Carbohydrate-processing enzymes in the lysosome, related lysosomal diseases, and the scope and limitations of reported reversible inhibitors as pharmacological chaperones are discussed with a view to possibly extending and improving research efforts in this area of orphan diseases.

Understanding multivalent effects in glycosidase inhibition using C-glycoside click clusters as molecular probes

Multivalent C-glycosides based on C₆₀ or β-cyclodextrin cores were designed to probe the influence of inhitopes in glycosidase binding events.

Evidence for a multivalent effect in inhibition of sulfatases involved in lysosomal storage disorders (LSDs)

New targets sensitive to multivalency: synthesis of nonavalent pyrrolidine iminosugars.

Expanding the library of divalent fucosidase inhibitors with polyamino and triazole-benzyl bridged bispyrrolidines

A small library of divalent fucosidase inhibitors containing pyrrolidine motifs were prepared and evaluated as α-fucosidase inhibitors.

Exploring architectures displaying multimeric presentations of a trihydroxypiperidine iminosugar

The synthesis of new multivalent architectures based on a trihydroxypiperidine α-fucosidase inhibitor is reported herein. Tetravalent and nonavalent dendrimers were obtained by means of the click chemistry approach involving the copper azide-alkyne-catalyzed cycloaddition (CuAAC) between suitable scaffolds bearing terminal alkyne moieties and an azido-functionalized piperidine as the bioactive moiety. A preliminary biological investigation is also reported towards commercially available and human glycosidases.

Design, synthesis and photochemical properties of the first examples of iminosugar clusters based on fluorescent cores

The synthesis and photophysical properties of the first examples of iminosugar clusters based on a BODIPY or a pyrene core are reported. The tri- and tetravalent systems designed as molecular probes and synthesized by way of Cu(I)-catalysed azide-alkyne cycloadditions are fluorescent analogues of potent pharmacological chaperones/correctors recently reported in the field of Gaucher disease and cystic fibrosis, two rare genetic diseases caused by protein misfolding.

Gold nanoparticles are suitable cores for building tunable iminosugar multivalency

Inhibition in the low micromolar range towards amyloglucosidase.

Synthesis and biological properties of multivalent iminosugars

Clustering 1-deoxynojirimycin (DNJ), first isolated from white mulberry, and other iminosugars around various scaffolds gave strong glycosidase inhibitors.

Synthesis of the first examples of iminosugar clusters based on cyclopeptoid cores

Cyclic N-propargyl α-peptoids of various sizes were prepared by way of macrocyclizations of linear N-substituted oligoglycines. These compounds were used as molecular platforms to synthesize a series of iminosugar clusters with different valency and alkyl spacer lengths by means of Cu(I)-catalysed azide-alkyne cycloadditions. Evaluation of these compounds as α-mannosidase inhibitors led to significant multivalent effects and further demonstrated the decisive influence of scaffold rigidity on binding affinity enhancements.

Rapid discovery of potent α-fucosidase inhibitors by in situ screening of a library of (pyrrolidin-2-yl)triazoles

The fucosidase inhibitory activity of a library of (pyrrolidin-2-yl)triazoles generated by CuAAC can be in situ analyzed, avoiding tedious purification steps. A potent and selective inhibitor was identified.