Diaminocyclopentane - l-Lysine Adducts: Potent and selective inhibitors of human O-GlcNAcase.

A new class of compounds, namely highly substituted diaminocyclopentane-l-lysine adducts, have been discovered as potent inhibitors of O-GlcNAcase, an enzyme crucial for protein de-O-glycosylation. These inhibitors exhibit exceptional selectivity and reversibility and are the first example of human O-GlcNAcase inhibitors that are structurally related to the transition state of the rate-limiting step with the "aglycon" still in bond-length proximity. The ease of their preparation, remarkable biological activities, stability, and non-toxicity make them promising candidates for the development of anti-tau-phosphorylation agents holding significant potential for the treatment of Alzheimer's disease.

Ligand-Directed Chemistry on Glycoside Hydrolases - A Proof of Concept Study.

Selective covalent labelling of enzymes using small molecule probes has advanced the scopes of protein profiling. The covalent bond formation to a specific target is the key step of activity-based protein profiling (ABPP), a method which has become an indispensable tool for measuring enzyme activity in complex matrices. With respect to carbohydrate processing enzymes, strategies for ABPP so far involve labelling the active site of the enzyme, which results in permanent loss of activity. Here, we report in a proof of concept study the use of ligand-directed chemistry (LDC) for labelling glycoside hydrolases near - but not in - the active site. During the labelling process, the competitive inhibitor is cleaved from the probe, departs the active site and the enzyme maintains its catalytic activity. To this end, we designed a building block synthetic concept for small molecule probes containing iminosugar-based reversible inhibitors for labelling of two model ß-glucosidases. The results indicate that the LDC approach can be adaptable for covalent proximity labelling of glycoside hydrolases.

Highly functionalized diaminocyclopentanes: A new route to potent and selective inhibitors of human O-GlcNAcase.

A new class of compounds inhibiting de-O-glycosylation of proteins has been identified. Highly substituted diaminocyclopentanes are impressively selective reversible non-transition state O-ß-N-acetyl-d-glucosaminidase (O-GlcNAcase) inhibitors. The ease of preparative access and remarkable biological activities provide highly viable leads for the development of anti-tau-phosphorylation agents with a view to eventually ameliorating Alzheimer's disease.

Pharmacological Chaperones for ß-Galactosidase Related to GM1 -Gangliosidosis and Morquio B: Recent Advances.

A short survey on selected ß-galactosidase inhibitors as potential pharmacological chaperones for GM1 -gangliosidosis and Morquio B associated mutants of human lysosomal ß-galactosidase is provided highlighting recent developments in this particular area of lysosomal storage disorders and orphan diseases.

N-Alkylated Iminosugar Based Ligands: Synthesis and Inhibition of Human Lysosomal ß-Glucocerebrosidase.

The scope of a series of N-alkylated iminosugar based inhibitors in the d-gluco as well as d-xylo configuration towards their interaction with human lysosomal ß-glucocerebrosidase has been evaluated. A versatile synthetic toolbox has been developed for the synthesis of N-alkylated iminosugar scaffolds conjugated to a variety of terminal groups via a benzoic acid ester linker. The terminal groups such as nitrile, azide, alkyne, nonafluoro-tert-butyl and amino substituents enable follow-up chemistry as well as visualisation experiments. All compounds showed promising inhibitory properties as well as selectivities for ß-glucosidases, some exhibiting activities in the low nanomolar range for ß-glucocerebrosidase.

Mechanistic Insights into the Chaperoning of Human Lysosomal-Galactosidase Activity: Highly Functionalized Aminocyclopentanes and C-5a-Substituted Derivatives of 4-epi-Isofagomine.

Glycosidase inhibitors have shown great potential as pharmacological chaperones for lysosomal storage diseases. In light of this, a series of new cyclopentanoid ß-galactosidase inhibitors were prepared and their inhibitory and pharmacological chaperoning activities determined and compared with those of lipophilic analogs of the potent ß-d-galactosidase inhibitor 4-epi-isofagomine. Structure-activity relationships were investigated by X-ray crystallography as well as by alterations in the cyclopentane moiety such as deoxygenation and replacement by fluorine of a "strategic" hydroxyl group. New compounds have revealed highly promising activities with a range of ß-galactosidase-compromised human cell lines and may serve as leads towards new pharmacological chaperones for GM1-gangliosidosis and Morquio B disease.

Potent GH20 N-Acetyl-ß-d-hexosaminidase Inhibitors: N-Substituted 3-acetamido-4-amino-5-hydroxymethyl-cyclopentanediols.

From 1,2;3,4-di-O-isopropylidene-d-galactopyranose, a preliminary series of highly functionalized amino(hydroxymethyl)cyclopentanes was easily available. These amine-containing basic carbasugars featuring the d-galacto configuration are potent inhibitors of the GH20 ß-d-hexosaminidases probed and may bear potential as regulators of N-acetyl-d-hexosaminidase activities in vivo.

A new type of pharmacological chaperone for GM1-gangliosidosis related human lysosomal ß-galactosidase: N-Substituted 5-amino-1-hydroxymethyl-cyclopentanetriols.

N-Functionalized amino(hydroxymethyl)cyclopentanetriols are potent inhibitors of ß-d-galactosidases and, for the first time, could be shown to act as pharmacological chaperones for GM1-gangliosidosis-associated lysosomal acid ß-galactosidase thus representing a new structural type of pharmacological chaperones for this lysosomal storage disease.

Synthesis of C-5a-chain extended derivatives of 4-epi-isofagomine: Powerful ß-galactosidase inhibitors and low concentration activators of GM1-gangliosidosis-related human lysosomal ß-galactosidase.

From an easily available partially protected formal derivative of 1-deoxymannojirimycin, by hydroxymethyl chain-branching and further elaboration, lipophilic analogs of the powerful ß-d-galactosidase inhibitor 4-epi-isofagomine have become available. New compounds exhibit improved inhibitory activities comparable to benchmark compound NOEV (N-octyl-epi-valienamine) and may serve as leads towards improved and more selective pharmacological chaperones for GM1-gangliosidosis.

Structural and mechanistic insight into N-glycan processing by endo-α-mannosidase.

N-linked glycans play key roles in protein folding, stability, and function. Biosynthetic modification of N-linked glycans, within the endoplasmic reticulum, features sequential trimming and readornment steps. One unusual enzyme, endo-α-mannosidase, cleaves mannoside linkages internally within an N-linked glycan chain, short circuiting the classical N-glycan biosynthetic pathway. Here, using two bacterial orthologs, we present the first structural and mechanistic dissection of endo-α-mannosidase. Structures solved at resolutions 1.7-2.1 Å reveal a (ß/α)(8) barrel fold in which the catalytic center is present in a long substrate-binding groove, consistent with cleavage within the N-glycan chain. Enzymatic cleavage of authentic Glc(1/3)Man(9)GlcNAc(2) yields Glc(1/3)-Man. Using the bespoke substrate α-Glc-1,3-α-Man fluoride, the enzyme was shown to act with retention of anomeric configuration. Complexes with the established endo-α-mannosidase inhibitor α-Glc-1,3-deoxymannonojirimycin and a newly developed inhibitor, α-Glc-1,3-isofagomine, and with the reducing-end product α-1,2-mannobiose structurally define the -2 to +2 subsites of the enzyme. These structural and mechanistic data provide a foundation upon which to develop new enzyme inhibitors targeting the hijacking of N-glycan synthesis in viral disease and cancer.

Fluorous iminoalditols act as effective pharmacological chaperones against gene products from GLB1 alleles causing GM1-gangliosidosis and Morquio B disease.

Unlike replacement therapy by infusion of exogenous recombinant lysosomal enzymes, pharmacological chaperones aim at a gain of function of endogenous gene products. Deficits resulting from missense mutations may become treatable by small, competitive inhibitors binding to the catalytical site and thus correcting the erroneous conformation of mutant enzymes. This may prevent their premature degradation and normalize intracellular trafficking as well as biological half-life. A major limitation currently arises from the huge number of individual missense mutations and the lack of knowledge on the structural requirements for specific interaction with mutant protein domains. Our previous work on mutations of the ß-galactosidase (ß-gal) gene, causing GM1 gangliosidosis (GM1) and Morquio B disease (MBD), respectively, characterized clinical phenotypes as well as biosynthesis, intracellular transport and subcellular localization of mutants. We recently identified an effective chaperone, DL-HexDGJ (Methyl 6-{[N(2)-(dansyl)-N(6)-(1,5-dideoxy-D-galactitol-1,5-diyl)- L-lysyl]amino} hexanoate), among a series of N-modified 1-deoxygalactonojirimycin derivatives carrying a dansyl group in its N-acyl moiety. Using novel and flexible synthetic routes, we now report on the effects of two oligofluoroalkyl-derivatives of 1-deoxygalactonojirimycin, Ph(TFM)(2)OHex-DGJ (N-(α,α-di-trifluoromethyl) benzyloxyhexyl-1,5-dideoxy-1,5-imino-D: -galactitol) and (TFM)(3)OHex-DGJ (N-(Nonafluoro-tert-butyloxy)hexyl-1,5-dideoxy-1,5-imino-D: -galactitol) on the ß-gal activity of GM1 and MBD fibroblasts. Both compounds are competitive inhibitors and increase the residual enzyme activities up to tenfold over base line activity in GM1 fibroblasts with chaperone-sensitive mutations. Western blots showed that this was due to a normalization of protein transport and intralysosomal maturation. The fact that the novel compounds were effective at very low concentrations (0.5-10 µM) in the cell culture medium as well as their novel chemical character suggest future testing in animal models. This may contribute to new aspects for efficient and personalized small molecule treatment of lysosomal storage diseases.

The Amadori rearrangement as glycoconjugation method: Synthesis of non-natural C-glycosyl type glycoconjugates.

The Amadori rearrangement was investigated as a potential method for the conjugation of carbohydrate moieties to suitable amino components. Starting from selected aldoheptoses, which are readily available by means of the Kiliani-Fischer C-elongation reaction of the corresponding aldohexoses, glycoconjugates presenting D-gluco, D-manno and D-galacto as well as GlcNAc motifs have been synthesised. Following this strategy, non-natural C-glycosyl type glycoconjugates, which can be utilised as building blocks for the composition of larger molecular constructions, are available by a very short synthetic approach.

Diaminocyclopentane-derived O-GlcNAcase inhibitors for combating tau hyperphosphorylation in Alzheimer's disease.

We developed potent and selective aminocyclopentane-derived inhibitors of human O-N-acetyl-ß-D-glucosaminidase (OGA) implicated in Alzheimer's disease. For example compound 13 was a nanomolar OGA inhibitor with 92 000-fold selectivity over human HexB. It was non-toxic and increased protein O-GlcNAcylation in the culture of murine neural cells, showing new alternatives in the treatment of tauopathies.

A fluorescent probe for GM1 gangliosidosis related ß-galactosidase: N-(dansylamino)hexylaminocarbonylpentyl-1,5-dideoxy-1,5-imino-D-galactitol.

N-(Dansylamino)hexylaminocarbonylpentyl-1,5-dideoxy-1,5-imino-D-galactitol, a strong competitive inhibitor of ß-galactosidase, enhances residual ß-galactosidase activities in fibroblasts and serves as lead en route to diagnostic compounds for tracking the fate of mutant ß-gal as well as aberrant GM1 gangliosides by live cell imaging.

New α-galactosidase-inhibiting aminohydroxycyclopentanes.

A set of cyclopentanoid α-galactosidase ligands was prepared from a partially protected ω-eno-aldose via a reliable (2 + 3)-cycloaddition protocol with slightly modified conditions. The obtained N-benzylisoxazolidine ring was selectively opened and the configuration of the hydroxymethylgroup was inverted. Consecutive deprotection provided an aminocyclopentane, which was N-alkylated to furnish a set of potential α-galactosidase inhibitors. Their glycosidase inhibitory activities were screened with a panel of standard glycosidases of biological significance.

Fluorous iminoalditols: a new family of glycosidase inhibitors and pharmacological chaperones.

A collection of new reversible glycosidase inhibitors of the iminoalditol type featuring N-substituents containing perfluorinated regions has been prepared for evaluation of physicochemical, biochemical and diagnostic properties. The vast variety of feasible oligofluoro moieties allows for modular approaches to customised structures according to the intended applications, which are influenced by the fluorine content as well as the distance of the fluorous moiety from the ring nitrogen. The first examples, in particular in the D-galacto series, exhibited excellent inhibitory activities. A preliminary screen with two human cell lines showed that, at subinhibitory concentrations, they are powerful pharmacological chaperones enhancing the activities of the catalytically handicapped lysosomal D-galactosidase mutants associated with GM1 gangliosidosis and Morquio B disease.

DLHex-DGJ, a novel derivative of 1-deoxygalactonojirimycin with pharmacological chaperone activity in human G(M1)-gangliosidosis fibroblasts.

G(M1)-gangliosidosis (GM1) and Morquio B disease (MBD) are rare lysosomal storage disorders caused by mutations in the gene GLB1. Its main gene product, human acid beta-galactosidase (beta-Gal) degrades two functionally important molecules, G(M1)-ganglioside and keratan sulfate in brain and connective tissues, respectively. While GM1 is a severe, phenotypically heterogenous neurodegenerative disorder, MBD is a systemic bone disease without effects on the central nervous system. A MBD-specific mutation, p.W273L, was shown to produce stable beta-Gal precursors, normally transported and processed to mature, intralysosomal beta-Gal. In accordance with the MBD phenotype, elevated residual activity against G(M1)-ganglioside, but strongly reduced affinity towards keratan sulfate was found. Most GM1 alleles, in contrast, were shown to affect precursor stability and intracellular transport. Specific alleles, p.R201C and p.R201H result in misfolded, unstable precursor proteins rapidly degraded by endoplasmic reticulum-associated protein degradation (ERAD). They may therefore be sensitive to stabilization by small molecules which bind at the active site and provide proper conformation. Thus the stabilized protein may escape from ERAD processes, and reach the lysosomes in an active state, as proposed for enzyme enhancement therapy (EET). This paper demonstrates that a novel iminosugar, DLHex-DGJ, has potent effects as competitive inhibitor of human acid beta-galactosidase in vitro, and describes its effects on activity, protein expression, maturation and intracellular transport in vivo in 13 fibroblasts lines with GLB1 mutations. Beside p.R201C and p.R201H, two further alleles, p.C230R and p.G438E, displayed significant sensitivity against DLHex-DGJ, with an increase of catalytic activity, and a normalization of transport and lysosomal processing of beta-Gal precursors.

Synthesis and biological evaluation of novel biotin-iminoalditol conjugates.

Biotin-iminosugar conjugates of different configuration such as D-gluco, D-galacto, L-ido as well as a furanoid representative in the D-manno configuration have been synthesised and exhibit powerful inhibition of beta-glucosidase from Agrobacterium sp. with K(i) values in the range of the respective parent compounds. Such molecular probes have potential for activity-based protein profiling taking advantage of the biotin-(strept)avidin interaction.

Fluorescent-tagged sp2-iminosugars with potent ß-glucosidase inhibitory activity.

New fluorescently-labelled sp(2)-iminosugars based on the 5N,6S-[N'-(4-aminobutyl)iminomethylidene]-6-thionojirimycin skeleton have been synthesized as photoprobes to monitor glycosidase binding. Dansyl, dapoxyl and coumarin fluorophores were appended to the terminal amino group at the N'-substituent by either sulfonamide or amide bridging reaction. All the conjugates behaved as strong (low micromolar to nanomolar) and selective inhibitors of ß-glucosidases (almonds and bovine liver) and naringinase, in agreement with the inhibition pattern previously encountered for related iso(thio)urea-type bicyclic sp(2)-iminosugars. The presence of the fluorescent probe allows real-time and continuous monitoring of ß-glucosidase inhibition by fluorescence resonance energy transfer (FRET), taking advantage of the intrinsic tryptophan-associated fluorescence of the protein.

Synthesis of lipophilic 1-deoxygalactonojirimycin derivatives as D-galactosidase inhibitors.

N-Alkylation at the ring nitrogen of the D-galactosidase inhibitor 1-deoxygalactonojirimycin with a functionalised C 6alkyl chain followed by modification with different aromatic substituents provided lipophilic 1-deoxygalactonojirimycin derivatives which exhibit inhibitory properties against ß-glycosidases from E. coli and Agrobacterium sp. as well as green coffee bean α-galactosidase. In preliminary studies, these compounds also showed potential as chemical chaperones for GM1-gangliosidosis related ß-galactosidase mutants.