Cystic fibrosis and diabetes: isoLAB and isoDAB, enantiomeric carbon-branched pyrrolidine iminosugars

A concise synthetic approach for isoiminosugars

Isoiminosugars are highly biological active substances. Herein, we report a concise synthetic approach for this class of compounds. The key step relies on a stereospecific 1,2-hydride shift in O-2 tosylated glycopyranosides leading to C-2 branched glycofuranosides. This approach enables a 4-step synthesis of powerful β-galactosidase inhibitor 4-epi-isofagomine starting from a simple d-glucopyranoside.

Synthesis of novel azasugar-containing 2'β-C-Me 9-deaza nucleosides as potential anti-hepatitis C virus agents

As a part of our ongoing discovery efforts exploring azasugar as agents for treating various unmet medical needs, we prepared analogs of azasugar as potential anti-hepatitis C virus (HCV) agents. Herein we describe the synthesis of novel 2'β-C-Me 9-deazanucleoside azasugar analogs.

Synthesis and Anti-Hepatitis B Activities of 3′-Fluoro-2′-Substituted Apionucleosides

Nucleoside analogues have excellent records as anti-HBV drugs. Chronic infections require long-term administration ultimately leading to drug resistance. Therefore, the search for nucleosides with novel scaffolds is of high importance. Here we report the synthesis of novel 2′-hydroxy- and 2′-hydroxymethyl-apionucleosides, 4 and 5, corresponding triphosphates and phosphoramidate prodrugs. Triphosphate 38 of 2′-hydroxymethyl-apionucleoside 5 exhibited potent inhibition of HBV polymerase with an IC₅₀ value of 120 nM. In an HBV cell-based assay, the phosphoramidate prodrug 39 demonstrated potent activity with an EC₅₀ value of 7.8 nM.

N-Nonyloxypentyl-l-Deoxynojirimycin Inhibits Growth, Biofilm Formation and Virulence Factors Expression of Staphylococcus aureus

Staphylococcus aureus is one of the major causes of hospital- and community-associated bacterial infections throughout the world, which are difficult to treat due to the rising number of drug-resistant strains. New molecules displaying potent activity against this bacterium are urgently needed. In this study, d- and l-deoxynojirimycin (DNJ) and a small library of their N-alkyl derivatives were screened against S. aureus ATCC 29213, with the aim to identify novel candidates with inhibitory potential. Among them, N-nonyloxypentyl-l-DNJ (l-NPDNJ) proved to be the most active compound against S. aureus ATCC 29213 and its clinical isolates, with the minimum inhibitory concentration (MIC) value of 128 μg/mL. l-NPDNJ also displayed an additive effect with gentamicin and oxacillin against the gentamicin- and methicillin-resistant S. aureus isolate 00717. Sub-MIC values of l-NPDNJ affected S. aureus biofilm development in a dose-dependent manner, inducing a strong reduction in biofilm biomass. Moreover, real-time reverse transcriptase PCR analysis revealed that l-NPDNJ effectively inhibited at sub-MIC values the transcription of the spa, hla, hlb and sea virulence genes, as well as the agrA and saeR response regulator genes.

Synthesis and Therapeutic Applications of Iminosugars in Cystic Fibrosis

Iminosugars are sugar analogues endowed with a high pharmacological potential. The wide range of biological activities exhibited by these glycomimetics associated with their excellent drug profile make them attractive therapeutic candidates for several medical interventions. The ability of iminosugars to act as inhibitors or enhancers of carbohydrate-processing enzymes suggests their potential use as therapeutics for the treatment of cystic fibrosis (CF). Herein we review the most relevant advances in the field, paying attention to both the chemical synthesis of the iminosugars and their biological evaluations, resulting from in vitro and in vivo assays. Starting from the example of the marketed drug NBDNJ (N-butyl deoxynojirimycin), a variety of iminosugars have exhibited the capacity to rescue the trafficking of F508del-CFTR (deletion of F508 residue in the CF transmembrane conductance regulator), either alone or in combination with other correctors. Interesting results have also been obtained when iminosugars were considered as anti-inflammatory agents in CF lung disease. The data herein reported demonstrate that iminosugars hold considerable potential to be applied for both therapeutic purposes.

Synthesis and Glycosidase Inhibition of Broussonetine M and Its Analogues

Cross-metathesis (CM) and Keck asymmetric allylation, which allows access to defined stereochemistry of a remote side chain hydroxyl group, are the key steps in a versatile synthesis of broussonetine M (3) from the d-arabinose-derived cyclic nitrone 14. By a similar strategy, ent-broussonetine M (ent-3) and six other stereoisomers have been synthesized, respectively, starting from l-arabino-nitrone (ent-14), l-lyxo-nitrone (ent-3-epi-14), and l-xylo-nitrone (2-epi-14) in five steps, in 26%–31% overall yield. The natural product broussonetine M (3) and 10’-epi-3 were potent inhibitors of β-glucosidase (IC₅₀ = 6.3 μM and 0.8 μM, respectively) and β-galactosidase (IC₅₀ = 2.3 μM and 0.2 μM, respectively); while their enantiomers, ent-3 and ent-10’-epi-3, were selective and potent inhibitors of rice α-glucosidase (IC₅₀ = 1.2 μM and 1.3 μM, respectively) and rat intestinal maltase (IC₅₀ = 0.29 μM and 18 μM, respectively). Both the configuration of the polyhydroxylated pyrrolidine ring and C-10’ hydroxyl on the alkyl side chain affect the specificity and potency of glycosidase inhibition.

Exploring the effect of chirality on the therapeutic potential of N-alkyl-deoxyiminosugars: anti-inflammatory response to Pseudomonas aeruginosa infections for application in CF lung disease

In the frame of a research program aimed to explore the relationship between chirality of iminosugars and their therapeutic potential, herein we report the synthesis of N-akyl l-deoxyiminosugars and the evaluation of the anti-inflammatory properties of selected candidates for the treatment of Pseudomonas aeruginosa infections in Cystic Fibrosis (CF) lung disease. Target glycomimetics were prepared by the shortest and most convenient approach reported to date, relying on the use of the well-known PS-TPP/I₂ reagent system to prepare reactive alkoxyalkyl iodides, acting as key intermediates. Iminosugars ent-1-3 demonstrated to efficiently reduce the inflammatory response induced by P. aeruginosa in CuFi cells, either alone or in synergistic combination with their d-enantiomers, by selectively inhibiting NLGase. Surprisingly, the evaluation in murine models of lung disease showed that the amount of ent-1 required to reduce the recruitment of neutrophils was 40-fold lower than that of the corresponding d-enantiomer. The remarkably low dosage of the l-iminosugar, combined with its inability to act as inhibitor for most glycosidases, is expected to limit the onset of undesired effects, which are typically associated with the administration of its d-counterpart. Biological results herein obtained place ent-1 and congeners among the earliest examples of l-iminosugars acting as anti-inflammatory agents for therapeutic applications in Cystic Fibrosis.

Regiospecific formation of sugar-derived ketonitrone towards unconventional C-branched pyrrolizidines and indolizidines

The synthesis of unprecedented branched pyrrolizidines and indolizidines was accomplished via nitrone chemistry.

Synthesis and glycosidase inhibition evaluation of (3S,4S)-3-((R)-1,2-dihydroxyethyl)pyrrolidine-3,4-diol

A new azasugar (3S,4S)-3-((R)-1,2-dihydroxyethyl)pyrrolidine-3,4-diol (1) was obtained from commercially available d-glucose using one-pot reductive cyclization as a key step. The target product, i.e., the iminosugar isomer, was obtained in 10 steps and 24.3% overall yield. Only three column chromatography purifications were needed in this synthesis. The biological activity of the target molecule as glycosidase inhibitor was studied, but the inhibitory activity against four glycosidases was not good (IC₅₀ > 100 μM).

Triacetonide of Glucoheptonic Acid in the Scalable Syntheses of d-Gulose, 6-Deoxy-d-gulose, l-Glucose, 6-Deoxy-l-glucose, and Related Sugars

Ease of separation of petrol-soluble acetonides derived from the triacetonide of methyl glucoheptonate allows scalable syntheses of rare sugars containing the l-gluco or d-gulo structural motif with any oxidation level at the C6 or C1 position of the hexose, usually without chromatography: meso-d-glycero-d-guloheptitol available in two steps is an ideal entry point for the study of the biotechnological production of heptoses.

Synthetic deoxynojirimycin derivatives bearing a thiolated, fluorinated or unsaturated N-alkyl chain: identification of potent α-glucosidase and trehalase inhibitors as well as F508del-CFTR correctors

Synthetic DNJs bearing a thiolated, fluorinated or unsaturated N-substituent exhibit trehalase inhibition or F508del-CFTR correction.

Searching for combinations of small-molecule correctors to restore f508del-cystic fibrosis transmembrane conductance regulator function and processing

The mutated protein F508del-cystic fibrosis transmembrane conductance regulator (CFTR) failed to traffic properly as a result of its retention in the endoplasmic reticulum and functions as a chloride (Cl(-)) channel with abnormal gating and endocytosis. Small chemicals (called correctors) individually restore F508del-CFTR trafficking and Cl(-) transport function, but recent findings indicate that synergistic pharmacology should be considered to address CFTR defects more clearly. We studied the function and maturation of F508del-CFTR expressed in HeLa cells using a combination of five correctors [miglustat, IsoLAB (1,4-dideoxy-2-hydroxymethyl-1,4-imino-l-threitol), Corr4a (N-[2-(5-chloro-2-methoxy-phenylamino)-4'-methyl-[4,5']bithiazolyl-2'-yl]-benzamide), VX-809 [3-(6-(1-(2,2-difluorobenzo[d][1,3]dioxol-5-yl)cyclopropanecarboxamido)-3-methylpyridin-2-yl)benzoic acid], and suberoylamilide hydroxamic acid (SAHA)]. Using the whole-cell patch-clamp technique, the current density recorded in response to CFTR activators (forskolin + genistein) was significantly increased in the presence of the following combinations: VX-809 + IsoLAB; VX-809 + miglustat + SAHA; VX-809 + miglustat + IsoLAB; VX-809 + IsoLAB + SAHA; VX-809 + miglustat + IsoLAB + SAHA. These combinations restored the activity of F508del-CFTR but with a differential effect on the appearance of mature c-band of F508del-CFTR proteins. Focusing on the VX-809 + IsoLAB cocktail, we recorded a level of correction higher at 37°C versus room temperature, but without amelioration of the thermal instability of CFTR. The level of functional rescue with VX-809 + IsoLAB after 4 hours of incubation was maximal and similar to that obtained in optimal conditions of use for each compound (i.e., 24 hours for VX-809 + 4 hours for IsoLAB). Finally, we compared the stimulation of F508del-CFTR by forskolin or forskolin + VX-770 [N-(2,4-di-tert-butyl-5-hydroxyphenyl)-4-oxo-1,4-dihydroquinoline-3-carboxamide] with cells corrected by VX-809 + IsoLAB. Our results open new perspectives for the development of a synergistic polypharmacology to rescue F508del-CFTR and show the importance of temperature on the effect of correctors and on the level of correction, suggesting that optimized combination of correctors could lead to a better rescue of F508del-CFTR function.

N- and C-alkylation of seven-membered iminosugars generates potent glucocerebrosidase inhibitors and F508del-CFTR correctors

The synthesis and biological evaluation of a library of novel seven-membered iminosugars is reported.

Rescue of functional CFTR channels in cystic fibrosis: a dramatic multivalent effect using iminosugar cluster-based correctors

Cystic fibrosis is caused by a mutation in the gene for the cystic fibrosis transmembrane conductance regulator (CFTR) protein. N-butyl 1-deoxynojirimycin (N-Bu DNJ), a clinical candidate for the treatment of cystic fibrosis, is able to act as a CFTR corrector by overcoming the processing defect of the mutant protein. To explore the potential of multivalency on CFTR correction activity, a library of twelve DNJ click clusters with valencies ranging from 3 to 14 were synthesized. Significantly, the trivalent analogues were found to be up to 225-fold more potent than N-Bu DNJ and up to 1000-fold more potent than the corresponding monovalent models. These results provide the first description of a multivalent effect for correcting protein folding defects in cells and should have application for the treatment of a number of protein folding disorders. Preliminary mechanistic studies indicated that CFTR correction activity enhancement was not due to a multivalent effect in ER-glucosidase inhibition or to a different mode of action of the multivalent iminosugars.

1-O-Benzyl-2,3-O-iso-propyl-idene-6-O-tosyl-α-l-sorbo-furan-ose

IN THE TITLE COMPOUND (SYSTEMATIC NAME

{(3aS,5S,6R,6aS)-3a-[(benz-yloxy)meth-yl]-6-hy-droxy-2,2-di-methyl-tetra-hydro-furo[2,3-d][1,3]dioxol-5-yl}methyl 4-methyl-benzene-sulfonate), C23H28O8S, the absolute structure and relative stereochemistry of the four chiral centres have been established by X-ray crystallography, with the absolute configuration inferred from the use of l-sorbose as the starting material. The central furan-ose ring adopts a slightly twisted envelope conformation (with the C atom bearing the methyl-benzene-sulfonate substituent as the flap) from which three substituents depart pseudo-axially (-CH2-O-benzyl, -OH and one acetonide O atom) and two substituents pseudo-equatorially (-CH2-O-tosyl and second acetonide O atom). The dioxalane ring is in a flattened envelope conformation with the fused CH C atom as the flap. In the crystal, mol-ecules pack in columns along [010] linked by O-H⋯O hydrogen bonds involving the furan-ose hy-droxy group and furan-ose ether O atom.

C-branched iminosugars: α-glucosidase inhibition by enantiomers of isoDMDP, isoDGDP, and isoDAB-L-isoDMDP compared to miglitol and miglustat

The Ho crossed aldol condensation provides access to a series of carbon branched iminosugars as exemplified by the synthesis of enantiomeric pairs of isoDMDP, isoDGDP, and isoDAB, allowing comparison of their biological activities with three linear isomeric natural products DMDP, DGDP, and DAB and their enantiomers. L-IsoDMDP [(2S,3S,4R)-2,4-bis(hydroxymethyl)pyrrolidine-3,4-diol], prepared in 11 steps in an overall yield of 45% from d-lyxonolactone, is a potent specific competitive inhibitor of gut disaccharidases [K(i) 0.081 μM for rat intestinal maltase] and is more effective in the suppression of hyperglycaemia in a maltose loading test than miglitol, a drug presently used in the treatment of late onset diabetes. The partial rescue of the defective F508del-CFTR function in CF-KM4 cells by L-isoDMDP is compared with miglustat and isoLAB in an approach to the treatment of cystic fibrosis.

Chemo-enzymatic synthesis and glycosidase inhibitory properties of DAB and LAB derivatives

A chemo-enzymatic strategy for the preparation of 2-aminomethyl derivatives of (2R,3R,4R)-2-(hydroxymethyl)pyrrolidine-3,4-diol (also called 1,4-dideoxy-1,4-imino-D-arabinitol, DAB) and its enantiomer LAB is presented. The synthesis is based on the enzymatic preparation of DAB and LAB followed by the chemical modification of their hydroxymethyl functionality to afford diverse 2-aminomethyl derivatives. This strategy leads to novel aromatic, aminoalcohol and 2-oxopiperazine DAB and LAB derivatives. The compounds were preliminarily explored as inhibitors of a panel of commercial glycosidases, rat intestinal disaccharidases and against Mycobacterium tuberculosis, the causative agent of tuberculosis. It was found that the inhibitory profile of the new products differed considerably from the parent DAB and LAB. Furthermore, some of them were active inhibiting the growth of M. tuberculosis.

2-N-Benzyl-2,6-dide-oxy-2,6-imino-3,4-O-isopropyl-idene-3-C-methyl-d-allono-nitrile

X-ray crystallography firmly established the relative stereochemistry of the title compound, C₁₇H₂₂N₂O₃. The absolute configuration was determined by use of 2-C-methyl-d-ribonolactone as the starting material. The compound exists as O—H⋯N hydrogen-bonded chains of mol­ecules running parallel to the a-axis.

6-De-oxy-3,4-O-isopropyl-idene-2-C-methyl-l-galactono-1,5-lactone

X-ray crystallography unequivocally confirmed the stereochemistry of the 2-C-methyl group in the title mol­ecule, C₁₀H₁₆O₅, in which the 1,5-lactone ring exists in a boat conformation. The absolute stereochemistry was determined by the use of d-ribose in the synthesis. The crystal exists as O—H⋯O hydrogen bonded chains of mol­ecules running parallel to the a axis with each mol­ecule acting as a donor and acceptor for one hydrogen bond.

Iminosugars as therapeutic agents: recent advances and promising trends

For the purpose of this article, iminosugars are polyhydroxylated secondary and tertiary amines in which the molecules resemble monosaccharide sugars in which the ring oxygen is replaced by the nitrogen. The bicyclic structures may biologically resemble disaccharides. Very few iminosugars have been available up to now for evaluation of their pharmaceutical applications. The early compounds were discovered and selected for study due to glycosidase inhibition, which is now known to not be necessary for pharmacological activity and may cause off-target effects. Glyset® and Zavesca®, derived from the glucosidase-inhibiting natural product 1-deoxynojirimycin, are the first two examples of iminosugar drugs. Since the discovery of this first generation, many new natural products have been identified with a wide range of biological activities but few are widely available. Among the biological properties of these compounds are good oral bioavailability and very specific immune modulatory and chaperoning activity. Although the natural products from plants and microorganisms can have good specificity, modifications of the template natural products have been very successful recently in producing bioactive compounds with good profiles. The field of iminosugars continues to open up exciting new opportunities for therapeutic agent discovery and offers many new tools for precisely modifying carbohydrate structures and modulating glycosidase activity in vivo. Current efforts are directed towards a greater range of structures and a wider range of biochemical targets.

Looking-glass synergistic pharmacological chaperones: DGJ and L-DGJ from the enantiomers of tagatose

The enantiomers of tagatose are converted to L-DGJ [a noncompetitive inhibitor of human lysosome α-galactosidase A (α-Gal A), K(i) 38.5 μM] and DGJ [a competitive inhibitor of α-Gal A, K(i) 15.1 nM] in 66% yield. L-DGJ and DGJ provide the first examples of pharmacological chaperones that (a) are enantiomeric iminosugars and (b) have synergistic activity with implications for the treatment of lysosomal storage disorders and other protein deficiencies.

C-3 branched δ-3,5-cis- and trans-THF sugar amino acids: synthesis of the first generation of branched homooligomers

This article describes the efficient synthesis of the first generation of branched sugar amino acid (SAA) oligomers in solution phase via two main routes: by the use of a standard coupling reagent and via the use of active ester intermediates. Benzyl-protected dimeric carbopeptoid and methyl-protected dimeric and tetrameric, hexameric and octameric carbopeptoids were obtained from a branched δ-3,5-trans-tetrahydrofuran (THF) SAA and methyl-protected dimeric and tetrameric carbopeptoids were synthesised from a branched δ-3,5-cis-THF SAA. These systems are of interest because of their potential to display foldameric properties reminiscent of those observed in α-peptides and proteins. Amongst their many uses, foldamers provide simpler models in the study of the factors which induce the folding and unfolding of proteins and, ultimately, potential insights into their functioning.

4-C-Me-DAB and 4-C-Me-LAB - enantiomeric alkyl-branched pyrrolidine iminosugars - are specific and potent α-glucosidase inhibitors; acetone as the sole protecting group

The syntheses of 4-C-Me-DAB [1,4-dideoxy-1,4-imino-4-C-methyl-d-arabinitol] from l-erythronolactone and of 4-C-Me-LAB [from d-erythronolactone] require only a single acetonide protecting group. The effect of pH on the NMR spectra of 4-C-Me-DAB [pK(a) of the salt around 8.4] is discussed and illustrates the need for care in analysis of both coupling constants and chemical shift. 4-C-Me-DAB (for rat intestinal sucrase K(i) 0.89 μM, IC(50) 0.41 μM) is a competitive - whereas 4-C-Me-LAB (for rat intestinal sucrase K(i) 0.95 μM, IC(50) 0.66 μM) is a non-competitive - specific and potent α-glucosidase inhibitor. A rationale for the α-glucosidase inhibition by DAB, LAB, 4-C-Me-DAB, 4-C-Me-LAB, and isoDAB - but not isoLAB - is provided. Both are inhibitors of endoplasmic reticulum (ER) resident α-glucosidase I and II.