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

Stereoselective Synthesis of Nojirimycin α-C-Glycosides from a Bicyclic Acyliminium Intermediate: A Convenient Entry to N,C-Biantennary Glycomimetics

A simple and efficient method for the stereoselective synthesis of nojirimycin α-C-glycoside derivatives has been developed using a bicyclic carbamate-type sp2-iminosugar, whose preparation on a gram scale has been optimized, as the starting material. sp2-iminosugar O-glycosides or anomeric esters serve as excellent precursors of acyliminium cations, which can add nucleophiles, including C-nucleophiles. The stereochemical outcome of the reaction is governed by stereoelectronic effects, affording the target α-anomer with total stereoselectivity. Thus, the judicious combination of C-allylation, carbamate hydrolysis, cross-metathesis, and hydrogenation reactions provides a very convenient entry to iminosugar α-C-glycosides, which have been transformed into N,C-biantennary derivatives by reductive amination or thiourea-forming reactions. The thiourea adducts undergo intramolecular cyclization to bicyclic iminooxazolidine iminosugar α-C-glycosides upon acid treatment, broadening the opportunities for molecular diversity. A preliminary evaluation against a panel of commercial glycosidases validates the approach for finely tuning the inhibitory profile of glycomimetics.

The Lysozyme Inhibitor Thionine Acetate Is Also an Inhibitor of the Soluble Lytic Transglycosylase Slt35 from Escherichia coli

Lytic transglycosylases such as Slt35 from E. coli are enzymes involved in bacterial cell wall remodelling and recycling, which represent potential targets for novel antibacterial agents. Here, we investigated a series of known glycosidase inhibitors for their ability to inhibit Slt35. While glycosidase inhibitors such as 1-deoxynojirimycin, castanospermine, thiamet G and miglitol had no effect, the phenothiazinium dye thionine acetate was found to be a weak inhibitor. IC₅₀ values and binding constants for thionine acetate were similar for Slt35 and the hen egg white lysozyme. Molecular docking simulations suggest that thionine binds to the active site of both Slt35 and lysozyme, although it does not make direct interactions with the side-chain of the catalytic Asp and Glu residues as might be expected based on other inhibitors. Thionine acetate also increased the potency of the beta-lactam antibiotic ampicillin against a laboratory strain of E. coli.

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.

Integrating thin film microfluidics in developing a concise synthesis of DGJNAc: A potent inhibitor of α-N-acetylgalctosaminidases

A simple synthesis, which utilizes a thin film microfluidic reactor for a problematic step, of a potent inhibitor of α-N-acetylhexosaminidases, DGJNAc, has been developed.

Stereodivergent Synthesis of Pseudotabersonine Alkaloids

An eight-step stereodivergent synthesis of enantiomerically pure (-)-14-epi-pseudotabersonine and (+)-pseudotabersonine has been developed from a common N-tert-butanesulfinyl ketimine key intermediate.

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.

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.

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.

Stereoselective synthesis of 2-acetamido-1,2-dideoxynojirimycin (DNJNAc) and ureido-DNJNAc derivatives as new hexosaminidase inhibitors

A novel approach to the synthesis of 2-acetamido-1,2-dideoxynojirimycin (DNJNAc) and ureido-DNJNAc derivatives as potent hexosaminidase inhibitors is reported.

Exploring NAG-thiazoline and its derivatives as inhibitors of chitinolytic β-acetylglucosaminidases

NAG-thiazoline (NGT) and its derivatives are well-known inhibitors against most β-acetylglucosaminidases (β-GlcNAcases) except for insect and bacterial chitinolytic β-GlcNAcases, including the molting-indispensable OfHex1 from the insect Ostrinia furnacalis. Here, we report the co-crystal structure of OfHex1 in complex with NGT. This structure reveals a large active pocket in OfHex1 that may account for the poor inhibitory activity of NGT. To test this hypothesis, a bulky substituent was designed and synthesized on the thiazoline ring of NGT. The resulting compound (NMAGT) was determined to be a submicromolar inhibitor of OfHex1 with a Ki value of 0.13 μM, which is 600-fold lower than Ki value of NGT. Molecular dynamics simulation analysis supported the good fit of NMAGT to the active pocket.