Therapeutic Applications of Iminosugars: Current Perspectives and Future Opportunities

Molecular networking-guided investigation of the secondary metabolome of four Morus species and their in vivo neuroprotective potential for the mitigation of Alzheimer's disease

Alzheimer's Disease (AD) is a fatal age-related neurodegenerative condition with a multifactorial etiology contributing to 70% of dementia globally. The search for a multi-target agent to hit different targets involved in the pathogenesis of AD is crucial. In the present study, the neuroprotective effects of four Morus extracts were assessed in LPS-induced AD in mice. Among the studied species, M. macroura exhibited a profound effect on alleviating the loss of cognitive function, improved the learning ability, restored the acetylcholine esterase (AChE) levels to normal, and significantly reduced the tumor necrosis factor alpha (TNF-α) brain content in LPS-treated mice. To investigate the secondary metabolome of the studied Morus species, ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-HRMS/MS), aided with feature-based molecular networking, was employed. Among the annotated features, aryl benzofurans and prenylated flavonoids were suggested as being responsible for the observed neuroprotective effect. Furthermore, some of the detected metabolites were proposed as new natural products such as moranoline di-O-hexoside (1), isomers of trimethoxy-dihydrochalcone-O-dihexoside (59 & 76), (hydroxy-dimethoxyphenyl)butenone-O-hexoside (82), and O-methylpreglabridin-O-sulphate (105). In conclusion, our findings advocate the potential usage of M. macroura leaves for the management of AD, yet after considering further clinical trials.

Stereoselective Synthesis of Heavily Hydroxylated Azepane Iminosugars via Osmium-Catalyzed Tethered Aminohydroxylation

A novel stereoselective synthetic approach to pentahydroxyazepane iminosugars is described. The strategy relies on a key osmium-catalyzed aminohydroxylation reaction of allylic alcohols obtained via addition of vinylmagnesium bromide to a d-mannose-derived aldehyde, which forms the new C-N bond with complete regio- and stereocontrol according to the tethering approach. Subsequent intramolecular reductive amination afforded the desired azepanes. This method represents the first application of the osmium-catalyzed tethered aminohydroxylation reaction to the synthesis of iminosugars.

Synthesis, α-mannosidase inhibition studies and molecular modeling of 1,4-imino-ᴅ-lyxitols and their C-5-altered N-arylalkyl derivatives

A synthesis of 1,4-imino-ᴅ-lyxitols and their N-arylalkyl derivatives altered at C-5 is reported. Their inhibitory activity and selectivity toward four GH38 α-mannosidases (two Golgi types: GMIIb from Drosophila melanogaster and AMAN-2 from Caenorhabditis elegans, and two lysosomal types: LManII from Drosophila melanogaster and JBMan from Canavalia ensiformis) were investigated. 6-Deoxy-DIM was found to be the most potent inhibitor of AMAN-2 (K _i = 0.19 μM), whose amino acid sequence and 3D structure of the active site are almost identical to the human α-mannosidase II (GMII). Although 6-deoxy-DIM was 3.5 times more potent toward AMAN-2 than DIM, their selectivity profiles were almost the same. N-Arylalkylation of 6-deoxy-DIM resulted only in a partial improvement as the selectivity was enhanced at the expense of potency. Structural and physicochemical properties of the corresponding inhibitor:enzyme complexes were analyzed by molecular modeling.

GANAB and N-Glycans Substrates Are Relevant in Human Physiology, Polycystic Pathology and Multiple Sclerosis: A Review

Glycans are one of the four fundamental macromolecular components of living matter, and they are highly regulated in the cell. Their functions are metabolic, structural and modulatory. In particular, ER resident N-glycans participate with the Glc3Man9GlcNAc2 highly conserved sequence, in protein folding process, where the physiological balance between glycosylation/deglycosylation on the innermost glucose residue takes place, according GANAB/UGGT concentration ratio. However, under abnormal conditions, the cell adapts to the glucose availability by adopting an aerobic or anaerobic regimen of glycolysis, or to external stimuli through internal or external recognition patterns, so it responds to pathogenic noxa with unfolded protein response (UPR). UPR can affect Multiple Sclerosis (MS) and several neurological and metabolic diseases via the BiP stress sensor, resulting in ATF6, PERK and IRE1 activation. Furthermore, the abnormal GANAB expression has been observed in MS, systemic lupus erythematous, male germinal epithelium and predisposed highly replicating cells of the kidney tubules and bile ducts. The latter is the case of Polycystic Liver Disease (PCLD) and Polycystic Kidney Disease (PCKD), where genetically induced GANAB loss affects polycystin-1 (PC1) and polycystin-2 (PC2), resulting in altered protein quality control and cyst formation phenomenon. Our topics resume the role of glycans in cell physiology, highlighting the N-glycans one, as a substrate of GANAB, which is an emerging key molecule in MS and other human pathologies.

Stereoselective Access to Iminosugar C,C-Glycosides from 6-Azidoketopyranoses

We report the synthesis of iminosugar C,C-glycosides starting from 6-azidoketopyranoses. Their Staudinger-azaWittig-mediated cyclization provided bicyclic N,O-acetals, which were stereoselectively opened with AllMgBr to afford β-hydroxyazepanes with a quaternary carbon α to the nitrogen. Their ring contraction via a β-aminoalcohol rearrangement produced the six-membered l-iminosugars with two functional handles at the pseudoanomeric position. Inversion of the free OH at the azepane level furnished the d-iminosugars.

Design, synthesis, and preliminary immunopotentiating activity of new analogues of nojirimycin

Three new classes of nojirimycin analogues viz. N-alkyl with C1-substituent (4-phenylbutyl), N-substituted 1-deoxynojirimycin and its congener δ-lactam, and a 4-phenylbutyl-β-C-glycoside were designed and synthesized for immunological studies. The resulting diverse compound library exhibited proliferation of B Cells and T cells induced by LPS and Con A, respectively. The majority of the analogues augmented the secretion of IL-12 in dendritic cells and TNF-α secretion in murine peritoneal macrophages compared to LPS (10 μg/ml). A deoxynojirimycin-triazole conjugate of phytosphingosine analogue was superior in the responses mentioned above and exhibited nitric oxide response equal to LPS. In comparison to findings on its congeners with immunosuppressive action, early immunological tests show that the novel nojirimycin analogues have immunopotentiating effect. Hence, nojirimycin analogues offer tremendous potential in tuning the immunomodulatory activity of iminosugars by subtle to substantial structural variations.

Piperidine Azasugars Bearing Lipophilic Chains: Stereoselective Synthesis and Biological Activity as Inhibitors of Glucocerebrosidase (GCase)

We report a straightforward synthetic strategy for the preparation of trihydroxypiperidine azasugars decorated with lipophilic chains at both the nitrogen and the adjacent carbon as potential inhibitors of the lysosomal enzyme glucocerebrosidase (GCase), which is involved in Gaucher disease. The procedure relies on the preparation of C-erythrosyl N-alkylated nitrones 10 through reaction of aldehyde 8 and primary amines 13 followed by oxidation of the imines formed in situ with the methyltrioxorhenium catalyst and urea hydrogen peroxide. The addition of octylMgBr to nitrone 10e provided access to both epimeric hydroxylamines 21 and 22 with opposite configuration at the newly created stereocenter in a stereodivergent and completely stereoselective way, depending on the absence or presence of BF₃·Et₂O. Final reductive amination and acetonide deprotection provided compounds 14 and 15 from low-cost d-mannose in remarkable 43 and 32% overall yields, respectively, over eight steps. The C-2 R-configured bis-alkylated trihydroxypiperidine 15 was the best ligand for GCase (IC₅₀ = 15 μM), in agreement with MD simulations that allowed us to identify the chair conformation corresponding to the best binding affinity.

A Convenient Approach towards the Synthesis of ADMDP Type Iminosugars and Nojirimycin Derivatives from Sugar-Derived Lactams

An efficient method for the synthesis of nojirimycin- and pyrrolidine-based iminosugar derivatives has been developed. The strategy is based on the partial reduction in sugar-derived lactams by Schwartz’s reagent and tandem stereoselective nucleophilic addition of cyanide or a silyl enol ether dictated by Woerpel’s or diffusion control models, which affords amino-modified iminosugars, such as ADMDP or higher nojirimycin derivatives.

Cell viability assay as a tool to study activity and inhibition of hepatitis C p7 channels

The p7 viroporin of the hepatitis C virus (HCV) forms an intracellular proton-conducting transmembrane channel in virus-infected cells, shunting the pH of intracellular compartments and thus helping virus assembly and release. This activity is essential for virus infectivity, making viroporins an attractive target for drug development. The protein sequence and drug sensitivity of p7 vary between the seven major genotypes of the hepatitis C virus, but the essential channel activity is preserved. Here, we investigated the effect of several inhibitors on recombinant HCV p7 channels corresponding to genotypes 1a-b, 2a-b, 3a and 4a using patch-clamp electrophysiology and cell-based assays. We established a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)-based cell viability assay for recombinant p7 expressed in HEK293 cells to assess channel activity and its sensitivity to inhibitors. The results from the cell viability assay were consistent with control measurements using established assays of haemadsorption and intracellular pH, and agreed with data from patch-clamp electrophysiology. Hexamethylene amiloride (HMA) was the most potent inhibitor of p7 activity, but possessed cytotoxic activity at higher concentrations. Rimantadine was active against p7 of all genotypes, while amantadine activity was genotype-dependent. The alkyl-chain iminosugars NB-DNJ, NN-DNJ and NN-DGJ were tested and their activity was found to be genotype-specific. In the current study, we introduce cell viability assays as a rapid and cost-efficient technique to assess viroporin activity and identify channel inhibitors as potential novel antiviral drugs.

Selective Golgi α-mannosidase II inhibitors: N-alkyl substituted pyrrolidines with a basic functional group

Enzymatic assays, molecular modeling and NMR studies of novel 1,4-dideoxy-1,4-imino-l-lyxitols provided new information on the GH38 family enzyme inhibitors and their selectivity.

Contributing to the Study of Enzymatic and Chemical Glycosyl Transfer Through the Observation and Mimicry of Glycosyl Cations

This account describes our efforts dedicated to: 1) the design of glycomimetics aimed at targeting therapeutically relevant carbohydrate processing enzymes, and 2) the observation, characterization, and exploitation of glycosyl cations as a tool for studying the glycosylation reaction. These findings have brought important data regarding this key ionic species as well as innovative strategies to access iminosugars of interest.

1 Introduction

2 The Glycosyl Cation, A Central Species in Glycosciences

2.1 A Selection of the Strategies Developed so far to Gain Insights into Glycosyl Cations Structure

2.2 When Superacids Meet Carbohydrates

3 Chemical Probes to Gain Insights into the Pseudorotational Itinerary of Glycosides During Glycosidic Bond Hydrolysis

3.1 Conformationally Locked Glycosides

3.1.1 The Xylopyranose Case

3.1.2 The Mannopyranose Case

3.2 Conformationally Flexible Iminosugars

3.2.1 Nojirimycin Ring Homologues

3.2.2 Noeuromycin Ring Homologues

3.2.3 Seven-Membered Iminosugar C-Glycosides

4 N-Acetyl-d-glucosamine Mimics

5 Ring Contraction: A Useful Tool to Increase Iminosugar’s Structural Diversity

6 Regioselective Deprotection of Iminosugar C-Glycosides to Introduce Diversity at C2 Position

7 Conclusion

Substituent Position of Iminocyclitols Determines the Potency and Selectivity for Gut Microbial Xenobiotic-Reactivating Enzymes

Selective inhibitors of gut bacterial β-glucuronidases (GUSs) are of particular interest in the prevention of xenobiotic-induced toxicities. This study reports the first structure-activity relationships on potency and selectivity of several iminocyclitols (2-7) for the GUSs. Complex structures of Ruminococcus gnavus GUS with 2-7 explained how charge, conformation, and substituent of iminocyclitols affect their potency and selectivity. N1 of uronic isofagomine (2) made strong electrostatic interactions with two catalytic glutamates of GUSs, resulting in the most potent inhibition (K_i ≥ 11 nM). C6-propyl analogue of 2 (6) displayed 700-fold selectivity for opportunistic bacterial GUSs (K_i = 74 nM for E. coli GUS and 51.8 μM for RgGUS). In comparison with 2, there was 200-fold enhancement in the selectivity, which was attributed to differential interactions between the propyl group and loop 5 residues of the GUSs. The results provide useful insights to develop potent and selective inhibitors for undesired GUSs.

Synthesis, Conformational Analysis, and Complexation Study of an Iminosugar-Aza-Crown, a Sweet Chiral Cyclam Analog

A new family of chiral C₂ symmetric tetraazamacrocycles, coined ISAC for IminoSugar Aza-Crown, incorporating two iminosugars adopting a ⁴C₁ conformation is disclosed. Multinuclear NMR experiments on the corresponding Cd²⁺ complex show that the ISAC is a strong chelator in water and its tetramine cavity adopts a conformation similar to that of the parent Cd–cyclam complex. Similar behavior is observed with Cu²⁺ in solution, with enhanced stability compared to the Cu–cyclam complex.

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.

Design, synthesis and glycosidase inhibition studies of novel triazole fused iminocyclitol-δ-lactams

Synthesis of novel triazole fused iminocyclitol-δ-lactams, from tri-O-benzyl-d-glucal, involving intermolecular [3 + 2]cycloaddition and intramolecular lactamisation reactions as key steps is described.

Safety assessment of a standardized cucumber extract (Q-Actin™): Oral repeat-dose toxicity and mutagenicity studies

Cucumus sativus (cucumber) is one of the most widely consumed fruit vegetables worldwide. Recent discovery of iminosugars in commonly consumed fruits and vegetables has promoted the interest in isolating these compounds and understanding the potential benefits to human health. The objective of the present study was to investigate the general toxicity and mutagenic effects of an aqueous extract of cucumber (Q-Actin), standardized to ≥1% (1-2%) ido-BR1 iminosugar. Single dose of Q-Actin was well tolerated without mortality at 2000 mg/kg body weight (bw) in Sprague Dawley rats. Oral (gavage) administration of Q-Actin up to 1000 mg/kg bw/day was well tolerated followed by repeated administration for a maximum period of 90 days in Sprague-Dawley rats. There were no treatment related changes in clinical observations, ophthalmic examinations, body weights and body weight gains or feed consumption, clinical chemistry and pathological changes compared to control. The mutagenicity as evaluated by Ames assay, in vitro chromosomal aberration test and in vivo micronucleus assay did not reveal any potential of Q-Actin to induce genotoxicity. The results showed that Q-Actin is well tolerated in general toxicity studies and did not induce mutagenicity. The no-observed-adverse-effect level (NOAEL) of the standardized aqueous cucumber extract (Q-Actin) is considered to be ≥1000 mg/kg bw/day, followed by repeated administration for90 days.

Stereocontrolled synthesis of polyhydroxylated bicyclic azetidines as a new class of iminosugars

We report herein the development of a stereodivergent route towards polyhydroxylated bicyclic azetidine scaffolds, namely 6-azabicyclo[3.2.0]heptane derivatives. The strategy hinges on a common bicyclic β-lactam precursor, which is forged by way of a rare example of a cationic Dieckmann-type reaction, followed by IBX-mediated desaturation. Substrate-controlled diastereoselective oxidations then allow the divergent preparation of novel iminosugar mimics.

Structure-Activity Studies of N-Butyl-1-deoxynojirimycin (NB-DNJ) Analogues: Discovery of Potent and Selective Aminocyclopentitol Inhibitors of GBA1 and GBA2

Analogues of N‐butyl‐1‐deoxynojirimycin (NB‐DNJ) were prepared and assayed for inhibition of ceramide‐specific glucosyltransferase (CGT), non‐lysosomal β‐glucosidase 2 (GBA2) and the lysosomal β‐glucosidase 1 (GBA1). Compounds 5 a–6 f, which carry sterically demanding nitrogen substituents, and compound 13, devoid of the C3 and C5 hydroxy groups present in DNJ/NB‐DGJ (N‐butyldeoxygalactojirimycin) showed no inhibitory activity for CGT or GBA2. Inversion of stereochemistry at C4 of N‐(n‐butyl)‐ and N‐(n‐nonyl)‐DGJ (compounds 24) also led to a loss of activity in these assays. The aminocyclopentitols N‐(n‐butyl)‐ (35 a), N‐(n‐nonyl)‐4‐amino‐5‐(hydroxymethyl)cyclopentane‐ (35 b), and N‐(1‐(pentyloxy)methyl)adamantan‐1‐yl)‐1,2,3‐triol (35 f), were found to be selective inhibitors of GBA1 and GBA2 that did not inhibit CGT (>1 mm), with the exception of 35 f, which inhibited CGT with an IC₅₀ value of 1 mm. The N‐butyl analogue 35 a was 100‐fold selective for inhibiting GBA1 over GBA2 (K_i values of 32 nm and 3.3 μm for GBA1 and GBA2, respectively). The N‐nonyl analogue 35 b displayed a K_i value of ≪14 nm for GBA1 inhibition and a K_i of 43 nm for GBA2. The N‐(1‐(pentyloxy)methyl)adamantan‐1‐yl) derivative 35 f had K_i values of ≈16 and 14 nm for GBA1 and GBA2, respectively. The related N‐bis‐substituted aminocyclopentitols were found to be significantly less potent inhibitors than their mono‐substituted analogues. The aminocyclopentitol scaffold should hold promise for further inhibitor development.

Square sugars: challenges and synthetic strategies

The synthesis of square sugars requires innovative strategies based on efficient stereoselective methodologies, from organocatalysis to metal carbene insertion.

Pushing the limits of catalytic C-H amination in polyoxygenated cyclobutanes

A synthetic route to a new class of conformationally constrained iminosugars based on a 5-azaspiro[3.4]octane skeleton has been developed by way of Rh(ii)-catalyzed C(sp(3))-H amination. The pivotal stereocontrolled formation of the quaternary C-N bond by insertion into the C-H bonds of the cyclobutane ring was explored with a series of polyoxygenated substrates. In addition to anticipated regioselective issues induced by the high density of activated α-ethereal C-H bonds, this systematic study showed that cyclobutane C-H bonds were, in general, poorly reactive towards catalytic C-H amination. This was demonstrated inter alia by the unexpected formation of a oxathiazonane derivative, which constitutes a very rare example of the formation of a 9-membered ring by way of catalyzed C(sp(3))-H amination. A complete stereocontrol could be however achieved by activating the key insertion position as an allylic C-H bond in combination with reducing the electron density at the undesired C-H insertion sites by using electron-withdrawing protecting groups. Preliminary biological evaluations of the synthesized spiro-iminosugars were performed, which led to the identification of a new class of correctors of the defective F508del-CFTR gating involved in cystic fibrosis.

Identification of Novel Human Breast Carcinoma (MDA-MB-231) Cell Growth Modulators from a Carbohydrate-Based Diversity Oriented Synthesis Library

The application of a cell-based growth inhibition on a library of skeletally different glycomimetics allowed for the selection of a hexahydro-2H-furo[3,2-b][1,4]oxazine compound as candidate inhibitors of MDA-MB-231 cell growth. Subsequent synthesis of analogue compounds and preliminary biological studies validated the selection of a valuable hit compound with a novel polyhydroxylated structure for the modulation of the breast carcinoma cell cycle mechanism.

A novel rare sugar inhibitor of murine herpes simplex keratitis

Purpose

To determine the therapeutic efficacy of a novel rare sugar, L-psicose, for the treatment of HSV-1 induced herpetic stromal keratitis (HSK) in a mouse eye model.

Methods

One rare sugar L-psicose was assayed for HSV-1 inhibition of in vitro virus adsorption. The IC₅₀ and IC₉₀ values of L-psicose were determined using plaque reduction assay (PRA) in CV-1 cell. Female Balb/c mice were corneally infected with HSV-1, strain KOS-GFP; A topical eye drop treatment of L-psicose was started 24 h after infection and continued four times daily for ten consecutive days. The severity of HSK was monitored by slit lamp examination in a masked fashion and Infectious HSV-1 shedding was determined by PRA.

Results

L-psicose was found to have anti-viral activity in vitro at an IC₅₀ dose of 99.5 mM and an IC₉₀ dose of 160 mM. Topical eye drop treatment with 200 mM L-psicose in PBS solution significantly reduced the severity of HSK compared to the mock treatment group. The in vivo mouse ocular model results of L-psicose therapy correlated with accelerated clearance of virus from eye swabs.

Conclusion

The results suggest that topical treatment with rare sugar L-psicose has efficacy against HSK through inhibition of HSV-1.

Aglycone mimics for tuning of glycosidase inhibition: design, synthesis and biological evaluation of bicyclic pyrrolidotriazole iminosugars

Various fuco-configured bicyclic pyrrolidotriazole aglycone mimics were synthesised using copper-catalysed coupling of allyl bromides with terminal alkynes and Sonogashira–Hagihara reaction followed by intramolecular azide-alkyne ‘click’ reaction.

[1,4]-sigmatropic rearrangement of chiral nitrones and their utilization in the synthesis of new iminosugars

A new mechanism of nitrone epimerization via [1,4]-sigmatropic rearrangement was proposed and a set of epimeric iminosugars was synthesized.

Synthesis of a new class of iminosugars based on constrained azaspirocyclic scaffolds by way of catalytic C-H amination

The synthesis of the first examples of a new class of iminosugars based on constrained spirocyclic scaffolds has been achieved via Rh-catalyzed C(sp(3))-H amination. In this process, the needed electronic control in securing high regioselectivity from substrates with a high density of activated C-H bonds was achieved by using a combination of activating and electron-withdrawing groups.

Design, synthesis and photochemical properties of the first examples of iminosugar clusters based on fluorescent cores

The synthesis and photophysical properties of the first examples of iminosugar clusters based on a BODIPY or a pyrene core are reported. The tri- and tetravalent systems designed as molecular probes and synthesized by way of Cu(I)-catalysed azide-alkyne cycloadditions are fluorescent analogues of potent pharmacological chaperones/correctors recently reported in the field of Gaucher disease and cystic fibrosis, two rare genetic diseases caused by protein misfolding.

Gold nanoparticles are suitable cores for building tunable iminosugar multivalency

Inhibition in the low micromolar range towards amyloglucosidase.

Stereoconvergent synthesis of 1-deoxynojirimycin isomers by using the 3 component 4 centred Ugi reaction

A new reductive cyclization/Ugi multicomponent reaction sequence for the synthesis of 1-deoxyallonojirimycin and 1-deoxyaltronojirimycin has been developed.

Azetidine- and N-carboxylic azetidine-iminosugars as amyloglucosidase inhibitors: synthesis, glycosidase inhibitory activity and molecular docking studies

Azetidine and an unprecedented N-carboxylic azetidine iminosugars were synthesized from d-glucose, which showed prominent amyloglucosidase inhibitory activity.

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.

Asymmetric syntheses of (-)-3-epi-Fagomine, (2R,3S,4R)-dihydroxypipecolic acid, and several polyhydroxylated homopipecolic acids

A range of enantiopure polyhydroxylated piperidines, including (2R,3S,4R)-dihydroxypipecolic acid, (-)-3-epi-fagomine, (2S,3S,4R)-dihydroxyhomopipecolic acid, (2S,3R,4R)-dihydroxyhomopipecolic acid, and two trihydroxy-substituted homopipecolic acids, have been prepared using diastereoselective olefinic oxidations of a range of enantiopure tetrahydropyridines as the key step. The requisite substrates were readily prepared from tert-butyl sorbate using our diastereoselective hydroamination or aminohydroxylation protocols followed by ring-closing metathesis. After diastereoselective olefinic oxidation of the resultant enantiopure tetrahydropyridines and deprotection, enantiopure polyhydroxylated piperidines were isolated as single diastereoisomers (>99:1 dr) in good overall yield.

Iminosugar C-glycoside analogues of α-D-GlcNAc-1-phosphate: synthesis and bacterial transglycosylase inhibition

We herein describe the first synthesis of iminosugar C-glycosides of α-d-GlcNAc-1-phosphate in 10 steps starting from unprotected d-GlcNAc. A diastereoselective intramolecular iodoamination–cyclization as the key step was employed to construct the central piperidine ring of the iminosugar and the C-glycosidic structure of α-d-GlcNAc. Finally, the iminosugar phosphonate and its elongated phosphate analogue were accessed. These phosphorus-containing iminosugars were coupled efficiently with lipophilic monophosphates to give lipid-linked pyrophosphate derivatives, which are lipid II mimetics endowed with potent inhibitory properties toward bacterial transglycosylases (TGase).