sp 2 ‐Iminosugar O ‐, S ‐, and N ‐Glycosides as Conformational Mimics of α‐Linked Disaccharides; Implications for Glycosidase Inhibition

sp2-Iminosugar azobenzene O-glycosides: Light-sensitive glycosidase inhibitors with unprecedented tunability and switching factors

The conventional approach to developing light-sensitive glycosidase activity regulators, involving the combination of a glycomimetic moiety and a photoactive azobenzene module, results in conjugates with differences in glycosidase inhibitory activity between the interchangeable E and Z-isomers at the azo group that are generally below one-order of magnitude. In this study, we have exploited the chemical mimic character of sp2-iminosugars to access photoswitchable p- and o-azobenzene α-O-glycosides based on the gluco-configured representative ONJ. Notably, we achieved remarkably high switching factors for glycosidase inhibition, favoring either the E- or Z-isomer depending on the aglycone structure. Our data also indicate a correlation between the isomeric state of the azobenzene module and the selectivity towards α- and β-glucosidase isoenzymes. The most effective derivative reached over a 103-fold higher inhibitory potency towards human β-glucocerebrosidase in the Z as compared with the E isomeric form. This sharp contrast is compatible with ex-vivo activation and programmed self-deactivation at physiological temperatures, positioning it as a prime candidate for pharmacological chaperone therapy in Gaucher disease. Additionally, our results illustrate that chemical tailoring enables the engineering of photocommutators with the ability to toggle inhibition between α- and β-glucosidase enzymes in a reversible manner, thus expanding the versatility and potential therapeutic applications of this approach.

High-Mannose Oligosaccharide Hemimimetics that Recapitulate the Conformation and Binding Mode to Concanavalin A, DC-SIGN and Langerin

The "carbohydrate chemical mimicry" exhibited by sp2 -iminosugars has been utilized to develop practical syntheses for analogs of the branched high-mannose-type oligosaccharides (HMOs) Man3 and Man5 . In these compounds, the terminal nonreducing Man residues have been substituted with 5,6-oxomethylidenemannonojirimycin (OMJ) motifs. The resulting oligomannoside hemimimetic accurately reproduce the structure, configuration, and conformational behavior of the original mannooligosaccharides, as confirmed by NMR and computational techniques. Binding studies with mannose binding lectins, including concanavalin A, DC-SIGN, and langerin, by enzyme-linked lectin assay and surface plasmon resonance revealed significant variations in their ability to accommodate the OMJ unit in the mannose binding site. Intriguingly, OMJMan segments demonstrated "in line" heteromultivalent effects during binding to the three lectins. Similar to the mannobiose (Man2 ) branches in HMOs, the binding modes involving the external or internal monosaccharide unit at the carbohydrate binding-domain exist in equilibrium, facilitating sliding and recapture processes. This equilibrium, which influences the multivalent binding of HMOs, can be finely modulated upon incorporation of the OMJ sp2 -iminosugar caps. As a proof of concept, the affinity and selectivity towards DC-SIGN and langerin were adjustable by presenting the OMJMan epitope in platforms with diverse architectures and valencies.

New syntheses of thiosaccharides utilizing substitution reactions

Novel synthetic methods published since 2005 affording carbohydrates containing sulfur atom(s) are reviewed. The review is divided to subchapters based on the position of sulfur atom(s) in the sugar molecule. Only those methods that take advantage of substitution are discussed.

Serine-/Cysteine-Based sp2-Iminoglycolipids as Novel TLR4 Agonists: Evaluation of Their Adjuvancy and Immunotherapeutic Properties in a Murine Model of Asthma

Glycolipids with TLR4 agonistic properties can serve either as therapeutic agents or as vaccine adjuvants by stimulating the development of proinflammatory responses. Translating them to the clinical setting is hampered by synthetic difficulties, the lack of stability in biological media, and/or a suboptimal profile of balanced immune mediator secretion. Here, we show that replacement of the sugar fragment by an sp²-iminosugar moiety in a prototypic TLR4 agonist, CCL-34, yields iminoglycolipid analogues that retain or improve their biological activity in vitro and in vivo and can be accessed through scalable protocols with total stereoselectivity. Their adjuvant potential is manifested in their ability to induce the secretion of proinflammatory cytokines, prime the maturation of dendritic cells, and promote the proliferation of CD8⁺ T cells, pertaining to a Th1-biased profile. Additionally, their therapeutic potential for the treatment of asthma, a Th2-dominated inflammatory pathology, has been confirmed in an ovalbumin-induced airway hyperreactivity mouse model.

Synthesis of sp2-Iminosugar Selenoglycolipids as Multitarget Drug Candidates with Antiproliferative, Leishmanicidal and Anti-Inflammatory Properties

sp²-Iminosugar glycolipids (sp²-IGLs) represent a consolidated family of glycoconjugate mimetics encompassing a monosaccharide-like glycone moiety with a pseudoamide-type nitrogen replacing the endocyclic oxygen atom of carbohydrates and an axially-oriented lipid chain anchored at the pseudoanomeric position. The combination of these structural features makes them promising candidates for the treatment of a variety of conditions, spanning from cancer and inflammatory disorders to parasite infections. The exacerbated anomeric effect associated to the putative sp²-hybridized N-atom imparts chemical and enzymatic stability to sp²-IGLs and warrants total α-anomeric stereoselectivity in the key glycoconjugation step. A variety of O-, N-, C- and S-pseudoglycosides, differing in glycone configurational patterns and lipid nature, have been previously prepared and evaluated. Here we expand the chemical space of sp²-IGLs by reporting the synthesis of α-d-gluco-configured analogs with a bicyclic (5N,6O-oxomethylidene)nojirimycin (ONJ) core incorporating selenium at the glycosidic position. Structure-activity relationship studies in three different scenarios, namely cancer, Leishmaniasis and inflammation, convey that the therapeutic potential of the sp²-IGLs is highly dependent, not only on the length of the lipid chain (linear aliphatic C₁₂ vs. C₈), but also on the nature of the glycosidic atom (nitrogen vs. sulfur vs. selenium). The ensemble of results highlights the α-dodecylseleno-ONJ-glycoside as a promising multitarget drug candidate.

Structure-based Design of Anti-cancer Vaccines: The Significance of Antigen Presentation to Boost the Immune Response

Immunotherapy, alone or in combination with other therapies, is widely used against cancer. Glycoprotein Mucin 1 (MUC1), which is overexpressed and aberrantly glycosylated in tumor cells, is one of the most promising candidates to engineer new cancer vaccines. In this context, the development of stable antigens that can elicit a robust immune response is mandatory. Here, we describe the design and in vivo biological evaluation of three vaccine candidates based on MUC1 glycopeptides that comprise unnatural elements in their structure. By placing the Tn antigen (GalNAcα-O-Ser/Thr) at the center of the design, the chemical modifications include changes to the peptide backbone, glycosidic linkage, and at the carbohydrate level. Significantly, the three vaccines elicit robust immune responses in mice and produce antibodies that can be recognized by several human cancer cells. In all cases, a link was stablished between the conformational changes induced by the new elements in the antigen presentation and the immune response induced in mice. According to our data, the development of effective MUC1-based vaccines should use surrogates that mimic the conformational space of aberrantly glycosylated MUC1 glycopeptides found in tumors.

Seven-Step Synthesis of All-Nitrogenated Sugar Derivatives Using Sequential Overman Rearrangements

All-nitrogenated sugars (ANSs), in which all hydroxy groups in a carbohydrate are replaced with amino groups, are anticipated to be privileged structures with useful biological activities. However, ANS synthesis has been challenging due to the difficulty in the installation of multi-amino groups. We report herein the development of a concise synthetic route to peracetylated ANSs in seven steps from commercially available monosaccharides. The key to success is the use of the sequential Overman rearrangement, which enables formal simultaneous substitution of four or five hydroxy groups in monosaccharides with amino groups. A variety of ANSs are available through the same reaction sequence starting from different initial monosaccharides by chirality transfer of secondary alcohols. Transformations of the resulting peracetylated ANSs such as glycosylation and deacetylation are also demonstrated. Biological studies reveal that ANS-modified cholesterol show cytotoxicity against human cancer cell lines, whereas each ANS and cholesterol have no cytotoxicity.

A short de novo synthesis of nucleoside analogs

Nucleoside analogs are commonly used in the treatment of cancer and viral infections. Their syntheses benefit from decades of research but are often protracted, unamenable to diversification, and reliant on a limited pool of chiral carbohydrate starting materials. We present a process for rapidly constructing nucleoside analogs from simple achiral materials. Using only proline catalysis, heteroaryl-substituted acetaldehydes are fluorinated and then directly engaged in enantioselective aldol reactions in a one-pot reaction. A subsequent intramolecular fluoride displacement reaction provides a functionalized nucleoside analog. The versatility of this process is highlighted in multigram syntheses of d- or l-nucleoside analogs, locked nucleic acids, iminonucleosides, and C2'- and C4'-modified nucleoside analogs. This de novo synthesis creates opportunities for the preparation of diversity libraries and will support efforts in both drug discovery and development.

Amplified Detection of Breast Cancer Autoantibodies Using MUC1-Based Tn Antigen Mimics

In many human carcinomas, mucin-1 (MUC1) is overexpressed and aberrantly glycosylated, resulting in the exposure of previously hidden antigens. This generates new patient antibody profiles that can be used in cancer diagnosis. In the present study, we focused on the MUC1-associated Tn antigen (α-O-GalNAc-Ser/Thr) and substituted the GalNAc monosaccharide by a glycomimic to identify MUC1-based glycopeptides with increased antigenicity. Two different glycopeptide libraries presenting the natural Tn antigen or the sp²-iminosugar analogue were synthesized and evaluated with anti-MUC1 monoclonal antibodies in a microarray platform. The most promising candidates were tested with healthy and breast cancer sera aiming for potential autoantibody-based biomarkers. The suitability of sp²-iminosugar glycopeptides to detect anti-MUC1 antibodies was demonstrated, and serological experiments showed stage I breast cancer autoantibodies binding with a specific unnatural glycopeptide with almost no healthy serum interaction. These results will promote further studies on their capabilities as early cancer biomarkers.

Synthesis, conformational analysis and in vivo assays of an anti-cancer vaccine that features an unnatural antigen based on an sp2-iminosugar fragment

The Tn antigen (GalNAc-α-1-O-Thr/Ser) is a well-known tumor-associated carbohydrate determinant. The use of glycopeptides that incorporate this structure has become a significant and promising niche of research owing to their potential use as anticancer vaccines. Herein, the conformational preferences of a glycopeptide with an unnatural Tn antigen, characterized by a threonine decorated with an sp²-iminosugar-type α-GalNAc mimic, have been studied both in solution, by combining NMR spectroscopy and molecular dynamics simulations, and in the solid state bound to an anti-mucin-1 (MUC1) antibody, by X-ray crystallography. The Tn surrogate can mimic the main conformer sampled by the natural antigen in solution and exhibits high affinity towards anti-MUC1 antibodies. Encouraged by these data, a cancer vaccine candidate based on this unnatural glycopeptide and conjugated to the carrier protein Keyhole Limpet Hemocyanin (KLH) has been prepared and tested in mice. Significantly, the experiments in vivo have proved that this vaccine elicits higher levels of specific anti-MUC1 IgG antibodies than the analog that bears the natural Tn antigen and that the elicited antibodies recognize human breast cancer cells with high selectivity. Altogether, we compile evidence to confirm that the presentation of the antigen, both in solution and in the bound state, plays a critical role in the efficacy of the designed cancer vaccines. Moreover, the outcomes derived from this vaccine prove that there is room for exploring further adjustments at the carbohydrate level that could contribute to designing more efficient cancer vaccines.

An anti-cancer vaccine based on an unnatural antigen with an sp²-iminosugar fragment.

Stereoselective Synthesis of Iminosugar 2-Deoxy(thio)glycosides from Bicyclic Iminoglycal Carbamates Promoted by Cerium(IV) Ammonium Nitrate and Cooperative Brønsted Acid-Type Organocatalysis

The first examples of iminosugar-type 2-deoxy(thio)glycoside mimetics are reported. The key step is the activation of a bicyclic iminoglycal carbamate to generate a highly reactive acyliminium cation. Cerium(IV) ammonium nitrate efficiently promoted the formation of 2-deoxy S-glycosides in the presence of thiols, probably by in situ generation of catalytic HNO₃, with complete α-stereoselectivity. Cooperative phosphoric acid/Schreiner's thiourea organocatalysis proved better suited for generating 2-deoxy O-glycosides, significantly broadening the scope of the approach.

Carbohydrate supramolecular chemistry: beyond the multivalent effect

(Hetero)multivalency acts as a multichannel switch that shapes the supramolecular properties of carbohydrates in an intrinsically multifactorial biological context.

Metal-free synthesis of imino-disaccharides and calix-iminosugars by photoinduced radical thiol–ene coupling (TEC)

Deprotected iminosugar alkenes were subjected to thiol–ene coupling with deprotected sugar thiols to afford new imino-disaccharides. Two thiol–ene couplings converted these alkenes into iminosugar thiols and then multivalent iminosugars.

Synthesis of polyfluoroalkyl sp2-iminosugar glycolipids and evaluation of their immunomodulatory properties towards anti-tumor, anti-leishmanial and anti-inflammatory therapies

Immunomodulatory glycolipids, among which α-galactosylceramide (KRN7000) is an iconic example, have shown strong therapeutic potential in a variety of conditions ranging from cancer and infection to autoimmune or neurodegenerative diseases. A main difficulty for those channels is that they often provoke a cytokine storm comprising both pro- and anti-inflammatory mediators that antagonize each other and negatively affect the immune response. The synthesis of analogues with narrower cytokine secretion-inducing capabilities is hampered by the intrinsic difficulty at controlling the stereochemical outcome in glycosidation reactions, particularly if targeting the α-anomer, which seriously hampers drug optimization strategies. Here we show that replacing the monosaccharide glycone by a sp²-iminosugar glycomimetic moiety allows accessing N-linked sp²-iminosugar glycolipids (sp²-IGLs) with total α-stereocontrol in a single step with no need of protecting groups or glycosidation promotors. The lipid tail has been then readily tailored by incorporating polyfluoroalkyl segments of varied lengths in view of favouring binding to the lipid binding site of the master p38 mitogen activated protein kinase (p38 MAPK), thereby polarizing the immune response in a cell-context dependent manner. The compounds have been evaluated for their antiproliferative, anti-leishmanial and anti-inflammatory activities in different cell assays. The size of the fluorous segment was found to be critical for the biological activity, probably by regulating the aggregation and membrane-crossing properties, whereas the hydroxylation profile (gluco or galacto-like) was less relevant. Biochemical and computational data further support a mechanism of action implying binding to the allosteric lipid binding site of p38 MAPK and subsequent activation of the noncanonical autophosphorylation route. The ensemble of results provide a proof of concept of the potential of sp²-IGLs as immunoregulators.

Thiol-ene "Click" Synthesis and Pharmacological Evaluation of C-Glycoside sp2-Iminosugar Glycolipids

The unique stereoelectronic properties of sp2-iminosugars enable their participation in glycosylation reactions, thereby behaving as true carbohydrate chemical mimics. Among sp2-iminosugar conjugates, the sp2-iminosugar glycolipids (sp2-IGLs) have shown a variety of interesting pharmacological properties ranging from glycosidase inhibition to antiproliferative, antiparasitic, and anti-inflammatory activities. Developing strategies compatible with molecular diversity-oriented strategies for structure-activity relationship studies was therefore highly wanted. Here we show that a reaction sequence consisting in stereoselective C-allylation followed by thiol-ene "click" coupling provides a very convenient access to α-C-glycoside sp2-IGLs. Both the glycone moiety and the aglycone tail can be modified by using sp2-iminosugar precursors with different configurational profiles (d-gluco or d-galacto in this work) and varied thiols, as well as by oxidation of the sulfide adducts (to the corresponding sulfones in this work). A series of derivatives was prepared in this manner and their glycosidase inhibitory, antiproliferative and antileishmanial activities were evaluated in different settings. The results confirm that the inhibition of glycosidases, particularly α-glucosidase, and the antitumor/leishmanicidal activities are unrelated. The data are also consistent with the two later activities arising from the ability of the sp2-IGLs to interfere in the immune system response in a cell line and cell context dependent manner.

Bioisosteres of Carbohydrate Functional Groups in Glycomimetic Design

The aberrant presentation of carbohydrates has been linked to a number of diseases, such as cancer metastasis and immune dysregulation. These altered glycan structures represent a target for novel therapies by modulating their associated interactions with neighboring cells and molecules. Although these interactions are highly specific, native carbohydrates are characterized by very low affinities and inherently poor pharmacokinetic properties. Glycomimetic compounds, which mimic the structure and function of native glycans, have been successful in producing molecules with improved pharmacokinetic (PK) and pharmacodynamic (PD) features. Several strategies have been developed for glycomimetic design such as ligand pre-organization or reducing polar surface area. A related approach to developing glycomimetics relies on the bioisosteric replacement of carbohydrate functional groups. These changes can offer improvements to both binding affinity (e.g., reduced desolvation costs, enhanced metal chelation) and pharmacokinetic parameters (e.g., improved oral bioavailability). Several examples of bioisosteric modifications to carbohydrates have been reported; this review aims to consolidate them and presents different possibilities for enhancing core interactions in glycomimetics.

Probing the Inhibitor versus Chaperone Properties of sp²-Iminosugars towards Human β-Glucocerebrosidase: A Picomolar Chaperone for Gaucher Disease

A series of sp²-iminosugar glycomimetics differing in the reducing or nonreducing character, the configurational pattern (d-gluco or l-ido), the architecture of the glycone skeleton, and the nature of the nonglycone substituent has been synthesized and assayed for their inhibition properties towards commercial glycosidases. On the basis of their affinity and selectivity towards GH1 β-glucosidases, reducing and nonreducing bicyclic derivatives having a hydroxylation profile of structural complementarity with d-glucose and incorporating an N′-octyl-isourea or -isothiourea segment were selected for further evaluation of their inhibitory/chaperoning potential against human glucocerebrosidase (GCase). The 1-deoxynojirimycin (DNJ)-related nonreducing conjugates behaved as stronger GCase inhibitors than the reducing counterparts and exhibited potent chaperoning capabilities in Gaucher fibroblasts hosting the neuronopathic G188S/G183W mutation, the isothiourea derivative being indeed one of the most efficient chaperone candidates reported up to date (70% activity enhancement at 20 pM). At their optimal concentration, the four selected compounds promoted mutant GCase activity enhancements over 3-fold; yet, the inhibitor/chaperoning balance became unfavorable at much lower concentration for nonreducing as compared to reducing derivatives.

The Impact of Heteromultivalency in Lectin Recognition and Glycosidase Inhibition: An Integrated Mechanistic Study

The vision of multivalency as a strategy limited to achieve affinity enhancements between a protein receptor and its putative sugar ligand (glycotope) has proven too simplistic. On the one hand, binding of a glycotope in a dense glycocalix-like construct to a lectin partner has been shown to be sensitive to the presence of a third sugar entity (heterocluster effect). On the other hand, several carbohydrate processing enzymes (glycosidases and glycosyltransferases) have been found to be also responsive to multivalent presentations of binding partners (multivalent enzyme inhibition), a phenomenon first discovered for iminosugar-type inhibitory species (inhitopes) and recently demonstrated for multivalent carbohydrate constructs. By assessing a series of homo- and heteroclusters combining α-d-glucopyranosyl-related glycotopes and inhitopes, it was shown that multivalency and heteromultivalency govern both kinds of events, allowing for activation, deactivation or enhancement of specific recognition phenomena towards a spectrum of lectin and glycosidase partners in a multimodal manner. This unified scenario originates from the ability of (hetero)multivalent architectures to trigger glycosidase binding modes that are reminiscent of those harnessed by lectins, which should be considered when profiling the biological activity of multivalent architectures.

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.

Synthesis and antibacterial evaluation of new N- and S-glycosides analogues with dinitrophenyl-substituted heterocyclic bases

Four N- and S-glycosides 13-16 having nucleobases 7-12 binding to sugar molecules from one side and to 3,5-dinitrophenyl moieties from another side were synthesized from 3,5-dinitrobenzoic acid 2. The synthetic intermediates, hydrazide 5 and thiosemicarbazide 6 regarded as important key compounds for the synthesis of nucleobases 7-12, each was obtained by two approaches. Structures of synthesized compounds were determined spectroscopically. Antibacterial activities for synthetic intermediates and glycosides were assessed using the paper disk diffusion method against Gram-negative bacteria: Pseudomonas aeruginosa, Pseudomonas fluorescens, and Escherichia coli and Gram-positive bacteria: Bacillus cereus and Staphylococcus aureus. Some of the synthetic compounds showed variant activity against some of the microorganisms tested. Nucleobases 8-10 and 12 showed moderate to slight activity against microorganisms under test at relatively high concentration, while the N-glycosides 14 and 15 exhibited persistent effect even at lower concentrations. Commercially available antibiotics polymyxine and oxytetracycline were used as positive controls.

Influence of the configurational pattern of sp(2)-iminosugar pseudo N-, S-, O- and C-glycosides on their glycoside inhibitory and antitumor properties

The synthesis of a complete series of cyclic carbamate-type sp(2)-iminosugar N-, S-, O- and C-octyl pseudoglycosides related to nojirimycin, mannojirimycin and galactonojirimycin, all having the α-pseudoanomeric configuration, is reported. The gem-diamine-type N-pseudoglycosides can be accessed directly from the corresponding reducing sp(2)-imisosugar precursors by reaction with octylamine in methanol, whereas per-O-acetyl or 1-fluoro derivatives were used as pseudoglycosyl donors for the preparation of S-pseudoglycosides or O- and C-pseudoglycosides, respectively. Evaluation of their inhibitory properties against a panel of glycosidases evidenced selectivity profiles that strongly depend on the configurational pattern and the nature of the glycosidic linkage. On the contrary, the antiproliferative activity determined against a panel of tumor cell lines was largely independent of the relative orientation of the hydroxyl groups in the sp(2)-iminosugar moiety. Indeed, sp(2)-iminosugar representatives exhibiting significant growth inhibition potencies were identified in all three configurationally different types of compounds studied, namely α-d-gluco, α-d-manno and α-d-galacto glycoside analogs. Interestingly, none of the compounds affected viability and mortality of normal cells at the used concentrations. Altogether, the results strongly suggest that the anticancer activity of amphiphilic sp(2)-iminosugar glycosides might be unrelated, or not solely related, to their glycosidase inhibitory activity.

Amino-functionalized iminocyclitols: synthetic glycomimetics of medicinal interest

A review on the syntheses and biological activities of unnatural glycomimetics highlighting the effect of replacement of hydroxyl groups of natural iminosugars by amino functionalities is presented.

Conformationally-locked C-glycosides: tuning aglycone interactions for optimal chaperone behaviour in Gaucher fibroblasts

A series of conformationally locked C-glycosides based on the 3-aminopyrano[3,2-b]pyrrol-2(1H)-one (APP) scaffold has been synthesized.

Allylic Azide Rearrangement in Tandem with Huisgen Cycloaddition for Stereoselective Annulation: Synthesis of C-Glycosyl Iminosugars

Allylic azide rearrangement is used in tandem with intramolecular azide-alkene cycloaddition to give a triazoline that when subsequently decomposed in the presence of a nucleophile gives piperidines. The tandem reaction gives two stereocenters that are generated with high control. The formation of the piperidines required the presence of innate conformational constraint. The applicability of the annulation reaction is demonstrated by the synthesis of iminosugars. A proposal is included to account for the observed stereoselectivity, which is influenced by the precursor structure.

Efficient stereoselective synthesis of 2-acetamido-1,2-dideoxyallonojirimycin (DAJNAc) and sp(2)-iminosugar conjugates: Novel hexosaminidase inhibitors with discrimination capabilities between the mature and precursor forms of the enzyme

Due to their capacity to inhibit hexosaminidases, 2-acetamido-1,2-dideoxy-iminosugars have been widely studied as potential therapeutic agents for various diseases. An efficient stereoselective synthesis of 2-acetamido-1,2-dideoxyallonojirimycin (DAJNAc), the most potent inhibitor of human placenta β-N-acetylglucosaminidase (β-hexosaminidase) among the epimeric series, is here described. This novel procedure can be easily scaled up, providing enough material for structural modifications and further biological tests. Thus, two series of sp(2)-iminosugar conjugates derived from DAJNAc have been prepared, namely monocyclic DAJNAc-thioureas and bicyclic 2-iminothiazolidines, and their glycosidase inhibitory activity evaluated. The data evidence the utmost importance of developing diversity-oriented synthetic strategies allowing optimization of electrostatic and hydrophobic interactions to achieve high inhibitory potencies and selectivities among isoenzymes. Notably, strong differences in the inhibition potency of the compounds towards β-hexosaminidase from human placenta (mature) or cultured fibroblasts (precursor form) were encountered. The ensemble of data suggests that the ratio between them, and not the inhibition potency towards the placenta enzyme, is a good indication of the chaperoning potential of TaySachs disease-associated mutant hexosaminidase.

Antileishmanial activity of sp2-iminosugar derivatives

sp²-iminosugar S-linked pseudoglycosides selectively inhibit growth of the intracellular form of Leishmania donovani.

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.

Unprecedented inhibition of glycosidase-catalyzed substrate hydrolysis by nanodiamond-grafted O-glycosides

Carbohydrate-coated nanodiamond particles with lectin recognition capabilities are not only stable towards the hydrolytic action of glycosidases, but also are endowed with the ability to inhibit them.

Conformationally-locked N-glycosides: exploiting long-range non-glycone interactions in the design of pharmacological chaperones for Gaucher disease

Pyranoid-type glycomimetics having a cis-1,2-fused glucopyranose-2-alkylsulfanyl-1,3-oxazoline (Glc-PSO) structure exhibit an unprecedented specificity as inhibitors of mammalian β-glucosidase. Notably, their inhibitory potency against human β-glucocerebrosidase (GCase) was found to be strongly dependent on the nature of aglycone-type moieties attached at the sulfur atom. In the particular case of ω-substituted hexadecyl chains, an amazing influence of the terminal group was observed. A comparative study on a series of Glc-PSO derivatives suggests that hydrogen bond acceptor functionalities, e.g. fluoro or methyloxycarbonyl, significantly stabilize the Glc-PSO:GCase complex. The S-(16-fluorohexadecyl)-PSO glycomimetic turned out to be a more potent GCase competitive inhibitor than ambroxol, a non glycomimetic drug currently in pilot trials as a pharmacological chaperone for Gaucher disease. Moreover, the inhibition constant increased by one order of magnitude when shifting from neutral (pH 7) to acidic (pH 5) media, a favorable characteristic for a chaperone candidate. Indeed, the fluoro-PSO derivative also proved superior to ambroxol in mutant GCase activity enhancement assays in N370S/N370S Gaucher fibroblasts. The results presented here represent a proof of concept of the potential of exploiting long-range non-glycone interactions for the optimization of glycosidase inhibitors with chaperone activity.

Structural basis of pharmacological chaperoning for human β-galactosidase

GM1 gangliosidosis and Morquio B disease are autosomal recessive diseases caused by the defect in the lysosomal β-galactosidase (β-Gal), frequently related to misfolding and subsequent endoplasmic reticulum-associated degradation. Pharmacological chaperone (PC) therapy is a newly developed molecular therapeutic approach by using small molecule ligands of the mutant enzyme that are able to promote the correct folding and prevent endoplasmic reticulum-associated degradation and promote trafficking to the lysosome. In this report, we describe the enzymological properties of purified recombinant human β-Gal(WT) and two representative mutations in GM1 gangliosidosis Japanese patients, β-Gal(R201C) and β-Gal(I51T). We have also evaluated the PC effect of two competitive inhibitors of β-Gal. Moreover, we provide a detailed atomic view of the recognition mechanism of these compounds in comparison with two structurally related analogues. All compounds bind to the active site of β-Gal with the sugar-mimicking moiety making hydrogen bonds to active site residues. Moreover, the binding affinity, the enzyme selectivity, and the PC potential are strongly affected by the mono- or bicyclic structure of the core as well as the orientation, nature, and length of the exocyclic substituent. These results provide understanding on the mechanism of action of β-Gal selective chaperoning by newly developed PC compounds.

Targeted delivery of pharmacological chaperones for Gaucher disease to macrophages by a mannosylated cyclodextrin carrier

Efficient delivery of pharmacological chaperones for Gaucher disease to macrophages has been achieved.

Stereoselective synthesis of 2-acetamido-1,2-dideoxyallonojirimycin (DAJNAc), a new potent hexosaminidase inhibitor

A practical synthesis of the previously unreported N-acetyl-D-allosamine glycomimetic DAJNAc is described. The reaction sequence involves Pd-catalyzed allylic substitution by phthalimide in an azaheterobicyclic scaffold as the key step. The new iminosugar resulted in being a stronger β-N-acetylglucosaminidase (human placenta) competitive inhibitor than the D-gluco (DNJNAc) and D-galacto (DGJNAc) stereoisomers.

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

New human β-glucocerebrosidase (GCase) ligands with rigid 1,6-anhydro-β-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.

Conformationally-locked N-glycosides with selective β-glucosidase inhibitory activity: identification of a new non-iminosugar-type pharmacological chaperone for Gaucher disease

A series of conformationally locked N-glycosides having a cis-1,2-fused pyranose-1,3-oxazoline-2-thione structure and bearing different substituents at the exocyclic sulfur has been prepared. The polyhydroxylated bicyclic system was built in only three steps by treatment of the corresponding readily available 1,2-anhydrosugar with KSCN using TiO(TFA)(2) as catalyst, followed by S-alkylation and acetyl deprotection. In vitro screening against several glycosidase enzymes showed highly specific inhibition of mammalian β-glucosidase with a marked dependence of the potency upon the nature of the exocyclic substituent. The most potent representative, bearing an S-(ω-hydroxyhexadecyl) substituent, was further assayed as inhibitor of the human lysosomal β-glucocerebrosidase and as pharmacological chaperone in Gaucher disease fibroblasts. Activity enhancements in N370S/N370S mutants analogous to those achieved with the reference compound ambroxol were attained with a more favorable chaperone/inhibitor balance.