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.

4-epi-Isofagomine derivatives as pharmacological chaperones for the treatment of lysosomal diseases linked to ß-galactosidase mutations: Improved synthesis and biological investigations.

(5aR)-5a-C-pentyl-4-epi-isofagomine 1 is a powerful inhibitor of lysosomal ß-galactosidase and a remarkable chaperone for mutations associated with GM1-gangliosidosis and Morquio disease type B. We report herein an improved synthesis of this compound and analogs (5a-C-methyl, pentyl, nonyl and phenylethyl derivatives), and a crystal structure of a synthetic intermediate that confirms its configuration resulting from the addition of a Grignard reagent. These compounds were evaluated as glycosidase inhibitors and their potential as chaperones for mutant lysosomal galactosidases determined. Based on these results and on docking studies, the 5-C-pentyl derivative 1 was selected as the optimal structure for further investigations: this compound induces the maturation of mutated ß-galactosidase in fibroblasts of a GM1-gangliosidosis patient and promote the decrease of keratan sulfate and oligosaccharide load in patient cells. Compound 1 is clearly capable of restoring ß-galactosidase activity and of promoting maturation of the protein, which should result in significant clinical benefit. These properties strongly support the development of compound 1 for the treatment of GM1-gangliosidosis and Morquio disease type B patients harboring ß-galactosidase mutations sensitive to pharmacological chaperoning.

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.

Synthesis and evaluation of N-alkylated analogues of aza-galacto-fagomine - potential pharmacological chaperones for Krabbe disease.

Seven novel alkylated or acylated analogues of hexahydropyridazine aza-galacto-fagomine (AGF) was prepared and studied as glycosidase inhibitors with the aim of increasing inhibitory potency and selectivity. The enzyme galactocerebrosidase, implicated in Krabbe disease, was found to be potently inhibited by n-butyl N2-alkylated AGF.

A fluorescence study of isofagomine protonation in ß-glucosidase.

N-(10-Chloro-9-anthracenemethyl)isofagomine 5 and N-(10-chloro-9-anthracenemethyl)-1-deoxynojirimycin 6 were prepared, and their inhibition of almond ß-glucosidase was measured. The isofagomine derivative 5 was found to be a potent inhibitor, while the 1-deoxynojirimycin derivative 6 displayed no inhibition at the concentrations investigated. Fluorescence spectroscopy of 5 with almond ß-glucosidase at different pH values showed that the inhibitor nitrogen is not protonated when bound to the enzyme. Analysis of pH inhibition data confirmed that 5 binds as the amine to the enzyme's unprotonated dicarboxylate form. This is a radically different binding mode than has been observed with isofagomine and other iminosugars in the literature.

γ-Aminoalcohol rearrangement applied to pentahydroxylated azepanes provides pyrrolidines epimeric to homoDMDP.

A series of pentahydroxylated pyrrolidines, displaying five contiguous stereogenic centres and epimeric to α-glucosidase inhibitor homoDMDP, have been synthesized. The key step involves a γ-aminoalcohol rearrangement applied to polyhydroxylated azepanes. These five-membered iminosugars demonstrate micromolar inhibition of glycosidases.

Combined inhibitor free-energy landscape and structural analysis reports on the mannosidase conformational coordinate.

Mannosidases catalyze the hydrolysis of a diverse range of polysaccharides and glycoconjugates, and the various sequence-based mannosidase families have evolved ingenious strategies to overcome the stereoelectronic challenges of mannoside chemistry. Using a combination of computational chemistry, inhibitor design and synthesis, and X-ray crystallography of inhibitor/enzyme complexes, it is demonstrated that mannoimidazole-type inhibitors are energetically poised to report faithfully on mannosidase transition-state conformation, and provide direct evidence for the conformational itinerary used by diverse mannosidases, including ß-mannanases from families GH26 and GH113. Isofagomine-type inhibitors are poor mimics of transition-state conformation, owing to the high energy barriers that must be crossed to attain mechanistically relevant conformations, however, these sugar-shaped heterocycles allow the acquisition of ternary complexes that span the active site, thus providing valuable insight into active-site residues involved in substrate recognition.

Ex vivo and in vivo effects of isofagomine on acid ß-glucosidase variants and substrate levels in Gaucher disease.

Isofagomine (IFG) is an acid ß-glucosidase (GCase) active site inhibitor that acts as a pharmacological chaperone. The effect of IFG on GCase function was investigated in GCase mutant fibroblasts and mouse models. IFG inhibits GCase with K(i) ∼30 nM for wild-type and mutant enzymes (N370S and V394L). Fibroblasts treated with IFG at µM concentrations showed enhancement of WT and mutant GCase activities and protein levels. Administration of IFG (30 mg/kg/day) to the mice homozygous for GCase mutations (V394L, D409H, or D409V) led to increased GCase activity in visceral tissues and brain extracts. IFG effects on GCase stability and substrate levels were evaluated in a mouse model (hG/4L/PS-NA) that has doxycycline-controlled human WT GCase (hGCase) expression driven by a liver-specific promoter and is also homozygous for the IFG-responsive V394L GCase. Both human and mouse GCase activity and protein levels were increased in IFG-treated mice. The liver-secreted hGCase in serum was stabilized, and its effect on the lung and spleen involvement was enhanced by IFG treatment. In 8-week IFG-treated mice, the accumulated glucosylceramide and glucosylsphingosine were reduced by 75 and 33%, respectively. Decreases of storage cells were correlated with >50% reductions in substrate levels. These results indicate that IFG stabilizes GCase in tissues and serum and can reduce visceral substrates in vivo.

Bicyclic derivatives of L-idonojirimycin as pharmacological chaperones for neuronopathic forms of Gaucher disease.

New human ß-glucocerebrosidase (GCase) ligands with rigid 1,6-anhydro-ß-L-idonojirimycin cores have been designed with the aid of molecular modeling. Efficient pharmacological chaperones for the L444P (trafficking-incompetent) mutant GCase enzyme associated with type 2 and 3 Gaucher disease (GD) were identified.

Transgenic mice expressing human glucocerebrosidase variants: utility for the study of Gaucher disease.

Gaucher disease is an autosomal recessively inherited storage disorder caused by deficiency of the lysosomal hydrolase, acid ß-glucosidase. The disease manifestations seen in Gaucher patients are highly heterogeneous as is the responsiveness to therapy. The elucidation of the precise factors responsible for this heterogeneity has been challenging as the development of clinically relevant animal models of Gaucher disease has been problematic. Although numerous murine models for Gaucher disease have been described each has limitations in their specific utility. We describe here, transgenic murine models of Gaucher disease that will be particularly useful for the study of pharmacological chaperones. We have produced stable transgenic mouse strains that individually express wild type, N370S and L444P containing human acid ß-glucosidase and show that each of these transgenic lines rescues the lethal phenotype characteristic of acid ß-glucosidase null mice. Both the N370S and L444P transgenic models show early and progressive elevations of tissue sphingolipids with L444P mice developing progressive splenic Gaucher cell infiltration. We demonstrate the potential utility of these new transgenic models for the study of Gaucher disease pathogenesis. In addition, since these mice produce only human enzyme, they are particularly relevant for the study of pharmacological chaperones that are specifically targeted to human acid ß-glucosidase and the common mutations underlying Gaucher disease.

Divergent synthesis of 4-epi-fagomine, 3,4-dihydroxypipecolic acid, and a dihydroxyindolizidine and their ß-galactosidase inhibitory and immunomodulatory activities.

A divergent asymmetric synthesis of the titled iminosugars has been formulated starting from a chiral homoallyl alcohol as the versatile intermediate. The homoallyl alcohol was prepared by a highly diastereoselective Barbier reaction on a d-glucose-derived aldehyde. The protection of its hydroxyl function followed by reductive ozonolysis of the olefin and a subsequent one-pot three-step protocol involving a Staudinger reaction, reductive amination, and benzyloxy carbonyl protection yielded an important bicyclic furanopiperidine derivative. This was converted to the target compounds by following standard reactions. Among the synthesized compounds, 4-epi-fagomine (2b) was the best ß-galactosidase inhibitor, and it also prevented LPS-mediated activation of Raw 264.7 macrophage cells. Its congener, 3,4-dihydroxypipecolic acid (4b) also showed similar trends in its cytokine- and enzyme-inhibitory properties at a low concentration (10 µM) but was proinflammatory at higher concentrations. The bicyclic compound dihydroxyindolizidine (21) reduced the proinflammatory cytokine (IL-1ß and TNF-α) levels in the LPS-activated Raw 264.7 cells without showing any enzyme-inhibition activity.

Characterization of the N370S mutant of glucocerebrosidase by hydrogen/deuterium exchange mass spectrometry.

An asparagine-to-serine substitution at residue 370 (N370S) in glucocerebrosidase (GCase) is the most prevalent mutation leading to Gaucher's disease, the most common lysosomal storage disorder. Two types of hydrogen/deuterium exchange experiment coupled with proteolysis and liquid chromatography-mass spectrometry (HDX-MS) were used to investigate the dynamic properties and unfolding stability of wt, R495H, and N370S GCases in the presence and absence of ligands. R495H GCase is used for enzyme replacement therapy and is considered to be a wt surrogate, whereas N370S is the most prevalent mutation leading to Gaucher's disease. Time-course HDX experiments of the GCases were performed under near-physiological conditions to detect the protein's local unfolding motions at a submolecular level. In guanidine-titration experiments, HDX reactions were performed with various concentrations of a chemical denaturant to provide the global stability of the proteins. The two types of experiment showed that all three purified GCases, wt, R495H, and N370S, have virtually identical local unfolding motions and global stabilities in solution. Combined with previous X-ray crystallographic studies, which showed indistinguishable backbone conformations for N370S and R495H GCase mutants and very similar melting temperatures for the wt, R495H, and N370S mutants, all three GCases are likely to have virtually identical structural and dynamic properties in solution. The guanidine-titration experiments revealed that the pharmacological chaperone, isofagomine (IFG), interacts more weakly with the N370S mutant than with the R495H GCase; this is consistent with the higher IC(50) value of IFG against N370S than against R495H. The time-course experiments showed that IFG restricts the local unfolding motions of N370S in the same way as those of R495H when the ligand saturates the proteins.

Ultrasensitive in situ visualization of active glucocerebrosidase molecules.

Deficiency of glucocerebrosidase (GBA) underlies Gaucher disease, a common lysosomal storage disorder. Carriership for Gaucher disease has recently been identified as major risk for parkinsonism. Presently, no method exists to visualize active GBA molecules in situ. We here report the design, synthesis and application of two fluorescent activity-based probes allowing highly specific labeling of active GBA molecules in vitro and in cultured cells and mice in vivo. Detection of in vitro labeled recombinant GBA on slab gels after electrophoresis is in the low attomolar range. Using cell or tissue lysates, we obtained exclusive labeling of GBA molecules. We present evidence from fluorescence-activated cell sorting analysis, fluorescence microscopy and pulse-chase experiments of highly efficient labeling of GBA molecules in intact cells as well as tissues of mice. In addition, we illustrate the use of the fluorescent probes to study inhibitors and tentative chaperones in living cells.

D-Fagomine lowers postprandial blood glucose and modulates bacterial adhesion.

D-Fagomine is an iminosugar originally isolated from seeds of buckwheat (Fagopyrum sculentum Moench), present in the human diet and now available as a pure crystalline product. We tested D-fagomine for activities connected to a reduction in the risk of developing insulin resistance, becoming overweight and suffering from an excess of potentially pathogenic bacteria. The activities were: intestinal sucrase inhibition in vitro (rat mucosa and everted intestine sleeves), modulation of postprandial blood glucose in rats, bacterial agglutination and bacterial adhesion to pig intestinal mucosa. When ingested together with sucrose or starch, D-fagomine lowered blood glucose in a dose-dependent manner without stimulating insulin secretion. D-Fagomine reduced the area under the curve (0-120 min) by 20 % (P < 0·01) and shifted the time to maximum blood glucose concentration (Tmax) by 15 min at doses of 1-2 mg/kg body weight when administered together with 1 g sucrose/kg body weight. Moreover, D-fagomine (0·14 mm) agglutinated 60 % of Enterobacteriaceae (Escherichia coli, Salmonella enterica serovar Typhimurium) populations (P < 0·01), while it did not show this effect on Bifidobacterium spp. or Lactobacillus spp. At the same concentration, d-fagomine significantly (P < 0·001) inhibited the adhesion of Enterobacteriaceae (95-99 % cells in the supernatant) and promoted the adhesion of Lactobacillus acidophilus (56 % cells in the supernatant) to intestinal mucosa. D-Fagomine did not show any effect on bacterial cell viability. Based on all this evidence, D-fagomine may be used as a dietary ingredient or functional food component to reduce the health risks associated with an excessive intake of fast-digestible carbohydrates, or an excess of potentially pathogenic bacteria.

Design, synthesis and in vitro antibacterial activity of 7-(4-alkoxyimino-3-aminomethylpiperidin-1-yl)fluoroquinolone derivatives.

We report herein the design and synthesis of novel 7-(4-alkoxyimino-3-aminomethylpiperidin-1-yl) fluoroquinolone derivatives. The antibacterial activity of the newly synthesized compounds was evaluated and compared with gemifloxacin, levofloxacin and ciprofloxacin. Results reveal that compounds 10, 16, and 17 have good activity against all of the tested gram-positive organisms including drug-resistance strains (MICs: 0.125-4 µg/mL). In addition, compounds 16 and 17 (MICs: 4 µg/mL) were 2- to 8-fold more potent than the reference drugs against Pseudomonas aeruginosa.

A potential fortuitous binding of inhibitors of an inverting family GH9 ß-glycosidase derived from isofagomine.

Using structural insight, the binding mode of isofagomine-derived inhibitors with family GH9 glycosidases is achieved via the study of Alicyclobacillus acidocaldarius (AaCel9A) endoglucanase. In contrast to what was observed in the first report using these compounds with inverting glycosidases from family GH6, these inhibitors do not adopt a distorted conformation in the active site.

Docking and SAR studies of D- and L-isofagomine isomers as human ß-glucocerebrosidase inhibitors.

We report the structure-activity relationship of a series of D-, and L-isofagomine and fagomine isomers as glycosidase inhibitors. Our study revealed that a positive charge at the anomeric position of d-isofagomines enhanced the potency toward ß-glycosidases, while the epimerization at the C3 OH group drastically reduced their inhibitory potency by over three orders of magnitude. Furthermore, d-3,4-di-epi-isofagomine abolished their inhibition activities against all enzymes. L-Isofagomine was also a fairly potent inhibitor of human ß-glucocerebrosidase, with an IC50 value of 8.7 µM. A molecular docking study revealed that the positions and orientations of the piperidine ring of D-3-epi-isofagomine in the binding site was similar to that of D-isofagomine, while D-3-epi-isofagomine missed the hydrogen bond interactions between Asp127 and the 3-OH group and between Trp179 and the 3-OH group. Furthermore, the top 10 docking models ranked by IFDscore suggested that D-3,4-di-epi-isofagomine can not bind to ß-glucocerebrosidase at a stable interaction mode. These results provide an insight into the structural requirements of isofagomine isomers for developing a new type of pharmacological chaperone for Gaucher disease.

[Synthesis of L-Iminofuranoses and Their Biological Evaluations].

Iminosugars are one of the compounds that mimic the structure of monosaccharides. Such sugar mimics have the ability to effectively and specifically inhibit various glycosidases and glycosyltransferases. After studying iminopyranose, miglitol, which has α-glucosidase inhibitory activity, was approved and used in the clinical treatment of diabetes. This study focused on l-iminofuranose derivatives to develop new anti-diabetic drug. As a result, it was found that l-iminofuranose having an alkyl group at C1 position show potent α-glucosidase inhibitory activity. Further structural-activity relationship studies were conducted, and interesting findings were obtained. This paper describes the details of those research developments.

Entropy-driven binding of gut bacterial ß-glucuronidase inhibitors ameliorates irinotecan-induced toxicity.

Irinotecan inhibits cell proliferation and thus is used for the primary treatment of colorectal cancer. Metabolism of irinotecan involves incorporation of ß-glucuronic acid to facilitate excretion. During transit of the glucuronidated product through the gastrointestinal tract, an induced upregulation of gut microbial ß-glucuronidase (GUS) activity may cause severe diarrhea and thus force many patients to stop treatment. We herein report the development of uronic isofagomine (UIFG) derivatives that act as general, potent inhibitors of bacterial GUSs, especially those of Escherichia coli and Clostridium perfringens. The best inhibitor, C6-nonyl UIFG, is 23,300-fold more selective for E. coli GUS than for human GUS (Ki = 0.0045 and 105 µM, respectively). Structural evidence indicated that the loss of coordinated water molecules, with the consequent increase in entropy, contributes to the high affinity and selectivity for bacterial GUSs. The inhibitors also effectively reduced irinotecan-induced diarrhea in mice without damaging intestinal epithelial cells.

Cytotoxicity and enzymatic activity inhibition in cell lines treated with novel iminosugar derivatives.

Iminosugars are monosaccharide analogues that have been demonstrated to be specific inhibitors for glycosidases and are currently used therapeutically in several human disorders. N-alkylated derivatives of D-fagomine and (2R,3S,4R,5S)-2-(hydroxymethyl)-5-methylpyrrolidine-3,4-diol with aliphatic chains were tested in eight human cancer cell lines to analyze their cytotoxicity and the inhibitory effect in the activities of specific glycosidases. Results indicate that these compounds were more cytotoxic as the length of the alkyl chain increases. N-dodecyl-D-fagomine inhibited specifically the alpha-D-glucosidase activity in cell lysates, whereas no effect was detected in other glycosidases. The N-dodecyl derivative of (2R,3S,4R,5S)-2-(Hydroxymethyl)-5-methylpyrrolidine-3,4-diol induced specific inhibition against alpha-L-fucosidase in cell lysates. Our results indicated that the length of the alkyl chain linked to the iminosugars determine their cytotoxicity as well as the inhibitory effect on the enzymatic activities of specific glycosidases, in human cancer cell lines.