Synthesis and glycosidase inhibitory activity of noeurostegine-a new and potent inhibitor of beta-glucoside hydrolases

Selectively Deoxyfluorinated N-Acetyllactosamine Analogues as 19 F NMR Probes to Study Carbohydrate-Galectin Interactions

Galectins are widely expressed galactose-binding lectins implied, for example, in immune regulation, metastatic spreading, and pathogen recognition. N-Acetyllactosamine (Galβ1-4GlcNAc, LacNAc) and its oligomeric or glycosylated forms are natural ligands of galectins. To probe substrate specificity and binding mode of galectins, we synthesized a complete series of six mono-deoxyfluorinated analogues of LacNAc, in which each hydroxyl has been selectively replaced by fluorine while the anomeric position has been protected as methyl β-glycoside. Initial evaluation of their binding to human galectin-1 and -3 by ELISA and ¹⁹ F NMR T₂ -filter revealed that deoxyfluorination at C3, C4' and C6' completely abolished binding to galectin-1 but very weak binding to galectin-3 was still detectable. Moreover, deoxyfluorination of C2' caused an approximately 8-fold increase in the binding affinity towards galectin-1, whereas binding to galectin-3 was essentially not affected. Lipophilicity measurement revealed that deoxyfluorination at the Gal moiety affects log P very differently compared to deoxyfluorination at the GlcNAc moiety.

The Bicyclic Form of galacto-Noeurostegine Is a Potent Inhibitor of β-Galactocerebrosidase

Competitive inhibitors of galactocerebrosidase (GALC) could be candidates for pharmacological chaperone therapy of patients with Krabbe disease. The known and selective nortropane-type iminosugar galacto-noeurostegine has been found to competitively inhibit GALC with K _i = 7 μM at pH 4.6, which is 330-fold more potent than the analogous deoxynoeurostegine. It was shown through X-ray protein crystallography that galacto-noeurostegine binds to the active site of GALC in its bicyclic form.

Stereospecific synthesis of methyl 2-amino-2,4-dideoxy-6S-deuterio-α-D-xylo-hexopyranoside and methyl 2-amino-2,4-dideoxy-6S-deuterio-4-propyl-α-d-glucopyranoside: Side chain conformation of the novel aminoglycoside antibiotic propylamycin

The stereospecific syntheses of methyl 2-amino-2,4-dideoxy-4-C-propyl-α-d-glucopyranoside and of methyl 2-amino-2,4-dideoxy-α-D-xylo-hexopyranoside and of their 6S-deuterioisotopomers are described as models for ring I of the aminoglycoside antibiotics propylamycin and 4'-deoxyparomomycin, respectively. Analysis of the ¹H NMR spectra of these compounds and of methyl 2-amino-2-deoxy-α-d-glucopyranoside, a model for paromomycin itself, reveals that neither deoxygenation at the 4-position, nor substitution of the C-O bond at the 4-postion by a C-C bond significantly changes the distribution of the side chain population between the three possible staggered conformations. From this it is concluded that the beneficial effect on antiribosomal and antibacterial activity of the propyl group in propylamycin does not derive from a change in side chain conformation. Rather, enhanced basicity of the ring oxygen and increased hydrophobicity and/or solvation effects are implicated.

The Chemical Synthesis and Applications of Tropane Alkaloids

Tropanes are an important class of alkaloid natural products that are found in plants all over the world. These compounds can exhibit significant biological activity and are among the oldest known medicines. In the early 19th century, tropanes were isolated, characterized, and synthesized by notable chemical researchers. Their significant biological activities have inspired tremendous research efforts toward their synthesis and the elucidation of their pharmacological activity both in academia and in industry. In this chapter, which addresses the developments in this field since 1994, the focus is on the synthesis of these compounds, and several examples of sophisticated synthetic protocols involving both asymmetric and catalytic approaches are described. In addition, the structures of more than 100 new alkaloids are included as well as the applications and pharmacological properties of some tropane alkaloids.

Divergent synthesis of new α-glucosidase inhibitors obtained through a vinyl Grignard-mediated carbocyclisation

Four new α-glucosidase inhibitors have been synthesised through 5–8 synthetic steps from a common synthetic intermediate obtained through a recently developed carbocyclisation.

Stereospecific synthesis of methyl 2-amino-2-deoxy-(6S)-deuterio-α,β-d-glucopyranoside and methyl 2,6-diamino-2,6-dideoxy-(6R)-deuterio-α,β-d-glucopyranoside: Side chain conformations of the 2-amino-2-deoxy and 2,6-diamino-2,6-dideoxyglucopyranosides

The stereospecifically labeled 6-monodeuterio methyl 2,6-diamino-2,6-dideoxy-α- and β- d-glucopyranosides were synthesized with a view to determining their side chain conformations. NMR studies in D₂O at pH 5 and pH 11 reveal both anomers to adopt very predominantly the gt conformation consistent with the gauche conformation of 2-aminoethanol and its acetate salt. In contrast, as also revealed with the help of stereospecifically-labelled monodeuterio isotopomers, the methyl 2-amino-2-deoxy-α- and β- d-glucopyranosides are an approximately 1:1 mixture of gg and gt conformers as is found in glucopyranose itself.

Glycomimetic-based pharmacological chaperones for lysosomal storage disorders: lessons from Gaucher, GM1-gangliosidosis and Fabry diseases

Lysosomal storage disorders (LSDs) are often caused by mutations that destabilize native folding and impair the trafficking of enzymes, leading to premature endoplasmic reticulum (ER)-associated degradation, deficiencies of specific hydrolytic functions and aberrant storage of metabolites in the lysosomes. Enzyme replacement therapy (ERT) and substrate reduction therapy (SRT) are available for a few of these conditions, but most remain orphan. A main difficulty is that virtually all LSDs involve neurological decline and neither proteins nor the current SRT drugs can cross the blood-brain barrier. Twenty years ago a new therapeutic paradigm better suited for neuropathic LSDs was launched, namely pharmacological chaperone (PC) therapy. PCs are small molecules capable of binding to the mutant protein at the ER, inducing proper folding, restoring trafficking and increasing enzyme activity and substrate processing in the lysosome. In many LSDs the mutated protein is a glycosidase and the accumulated substrate is an oligo- or polysaccharide or a glycoconjugate, e.g. a glycosphingolipid. Although it might appear counterintuitive, substrate analogues (glycomimetics) behaving as competitive glycosidase inhibitors are good candidates to perform PC tasks. The advancements in the knowledge of the molecular basis of LSDs, including enzyme structures, binding modes, trafficking pathways and substrate processing mechanisms, have been put forward to optimize PC selectivity and efficacy. Moreover, the chemical versatility of glycomimetics and the variety of structures at hand allow simultaneous optimization of chaperone and pharmacokinetic properties. In this Feature Article we review the advancements made in this field in the last few years and the future outlook through the lessons taught by three archetypical LSDs: Gaucher disease, GM1-gangliosidosis and Fabry disease.

Concise synthesis of calystegines B2 and B3via intramolecular Nozaki-Hiyama-Kishi reaction

The key step in the concise syntheses of calystegine B2 and its C-2 epimer calystegine B3 was the construction of cycloheptanone 8via an intramolecular Nozaki-Hiyama-Kishi (NHK) reaction of 9, an aldehyde containing a Z-vinyl iodide. Vinyl iodide 9 was obtained by the Stork olefination of aldehyde 10, derived from carbohydrate starting materials. Calystegines B2 (3) and B3 (4) were synthesized from d-xylose and l-arabinose derivatives respectively in 11 steps in excellent overall yields (27% and 19%).

Synthesis and evaluation of galacto-noeurostegine and its 2-deoxy analogue as glycosidase inhibitors

An epimer of the known glycosidase inhibitor noeurostegine, galacto-noeurostegine, was synthesised in 21 steps from levoglucosan and found to be a potent, competitive and highly selective galactosidase inhibitor of Aspergillus oryzae β-galactosidase.

Stable analogues of nojirimycin – synthesis and biological evaluation of nojiristegine and manno-nojiristegine

Two novel iminosugars called nojiristegines, being structural hybrids between nor-tropane alkaloid calystegine and nojirimycins, have been synthesised and the hemiaminal functionality found to be stable.

Synthesis of N-alkylated noeurostegines and evaluation of their potential as treatment for Gaucher's disease

The potent and selective inhibitor of β-glucosidases, noeurostegine, was evaluated as an inhibitor of glucocerebrosidase (GCase) to give an IC(50) value of 0.4 μM, being 250- and 150-fold better than N-butyl and N-nonyl noeurostegine, respectively. The parent noeurostegine and its N-butyl and N-nonyl alkylated congeners were also tested as pharmacological chaperones against a N370S GCase mutant. Of these, only noeurostegine, was found to increase enzyme activity, which in potency was comparable to that previously reported for isofagomine.