Expeditious synthesis of Mycobacterium tuberculosis sulfolipids SL-1 and Ac2SGL analogues

Asymmetric Total Synthesis and Structural Revision of DAT2, an Antigenic Glycolipid from Mycobacterium tuberculosis

DAT2 is a member of the diacyl trehalose family (DAT) of antigenic glycolipids located in the mycomembrane of Mycobacterium tuberculosis (Mtb). Recently it was shown that the molecular structure of DAT2 had been incorrectly assigned, but the correct structure remained elusive. Herein, the correct molecular structure of DAT2 and its methyl-branched acyl substituent mycolipanolic acid is determined. For this, four different stereoisomers of mycolipanolic acid were prepared in a stereoselective and unified manner, and incorporated into DAT2. A rigorous comparison of the four isomers to the DAT isolated from Mtb H37Rv by NMR, HPLC, GC, and mass spectrometry allowed a structural revision of mycolipanolic acid and DAT2. Activation of the macrophage inducible Ca2+-dependent lectin receptor (Mincle) with all four stereoisomers shows that the natural stereochemistry of mycolipanolic acid / DAT2 provides the strongest activation, which indicates its high antigenicity and potential application in serodiagnostics and vaccine adjuvants.

Versatile approach towards fully desymmetrized trehalose with a novel set of orthogonal protecting groups

Trehalose-containing glycans play an essential role in bacterial pathogenesis, host-pathogen interaction, and cell signaling. The investigation of trehalose uptake and metabolism in Mycobacteria using synthetic desymmetrized trehalose probes is an important approach for the development of diagnostic tools and potential therapeutics for tuberculosis. Trehalose-derived mycobacterial glycolipids activate the innate immune response through recognition by the C-type lectin Mincle, justifying efforts to develop novel trehalose-based Mincle-dependent adjuvants. The chemical synthesis of trehalose-based glycoconjugates, glycolipids, and small-molecule trehalose probes requires the challenging chemical desymmetrization of eight hydroxyl groups in a C 2-symmetric disaccharide αGlc(1↔1)αGlc. Using a novel set of orthogonal protecting groups, we developed a flexible multiscale synthetic approach to a collection of differently and variably protected fully desymmetrized trehalose derivatives, ready for final chemical modification with relevant functional or reporter groups. Using a regioselective and site-specific protecting group strategy, we performed multiple symmetry-breaking operations, resulting in a library of trehalose-derived orthogonally protected building blocks as a versatile source for the synthesis of complex trehalose-containing glycans.

In silico Screening of Food and Drug Administration-approved Compounds against Trehalose 2-sulfotransferase (Rv0295c) in Mycobacterium tuberculosis: Insights from Molecular Docking and Dynamics Simulations

BACKGROUND

Tuberculosis (TB) remains a prominent global health challenge, distinguished by substantial occurrences of infection and death. The upsurge of drug-resistant TB strains underscores the urgency to identify novel therapeutic targets and repurpose existing compounds. Rv0295c is a potentially druggable enzyme involved in cell wall biosynthesis and virulence. We evaluated the inhibitory activity of Food and Drug Administration (FDA)-approved compounds against Rv0295c of Mycobacterium tuberculosis, employing molecular docking, ADME evaluation, and dynamics simulations.

METHODS

The study screened 1800 FDA-approved compounds and selected the top five compounds with the highest docking scores. Following this, we subjected the initially screened ligands to ADME analysis based on their dock scores. In addition, the compound exhibited the highest binding affinity chosen for molecular dynamics (MD) simulation to investigate the dynamic behavior of the ligand-receptor complex.

RESULTS

Dihydroergotamine (CHEMBL1732) exhibited the highest binding affinity (-12.8 kcal/mol) for Rv0295c within this set of compounds. We evaluated the stability and binding modes of the complex over extended simulation trajectories.

CONCLUSION

Our in silico analysis demonstrates that FDA-approved drugs can serve as potential Rv0295c inhibitors through repurposing. The combination of molecular docking and MD simulation offers a comprehensive understanding of the interactions between ligands and the protein target, providing valuable guidance for further experimental validation. Identifying Rv0295c inhibitors may contribute to new anti-TB drugs.

Sulfoglycolipids and Related Analogues of Mycobacterium tuberculosis: Chemical Synthesis and Immunological Studies

Mycobacterium tuberculosis (Mtb) causes tuberculosis as one major threat to human health, which has been deteriorated owing to the emerging multidrug resistance. Mtb contains a complex lipophilic cell wall structure that is important for bacterial persistence. Among the lipid components, sulfoglycolipids (SGLs), known to induce immune cell responses, are composed of a trehalose core attached with a conserved sulfate group and 1-4 fatty acyl chains in an asymmetric pattern. At least one of these acyl chains is polymethylated with 3-12 methyl branches. Although Mtb SGL can be isolated from bacterial culture, resulting SGL is still a homologous mixture, impeding accurate research studies. This up-to-date review covers the chemical synthesis and immunological studies of Mtb SGLs and structural analogues, with an emphasis on the development of new glycosylation methods and the asymmetric synthesis of polymethylated scaffolds. Both are critical to advance further research on biological functions of these complicated SGLs.

Total Synthesis and Structure Confirmation of Fusaroside

Recently, we synthesized the proposed structure of the fungal glycolipid fusaroside and suggested corrections in its structure with respect to the positions of the double bonds in the lipid portion. Herein, we report the first total synthesis of the proposed revised structure of fusaroside and thereby confirm its structure. The synthesis involved Julia-Kocienski olefination for the construction of fatty acid and its coupling with trehalose at the O4 position followed by late-stage gem-dimethylation as key steps.

Total Synthesis of a Trehalose-Containing Lipooligosaccharide Analogue from Mycobacterium linda

A short and efficient methodology has been developed to synthesize an analogue of a lipooligosaccharide from Mycobacterium linda isolated from Crohn's disease. The total synthesis of the tetrasaccharide was achieved via a convergent [2 + 2] glycosylation approach. The key features of the synthesis involve the selective functionalization of a trehalose core via highly regioselective acylations and regioselective glycosylations. The synthesis was completed via a longest linear sequence of 14 steps in a 14.2% overall yield.

Advancement of the Cleavage Methods of Carbohydrate-derived Isopropylidene and Cyclohexylidene Ketals

Abstract:

Carbohydrates, amino acids, and nucleosides, the fundamental building blocks of complex biomolecules in nature, are essential starting materials for the fabrication of natural and unnatural structural entities, which necessitate the masking and demasking of various functional groups with the utmost chemoselectivity, mildness, and efficiency to avoid unintended bond breaking and formation, as well as associated reactions. Ketals, benzylidene, methoxymethyl, p-methoxybenzyl, silyl ethers, trityl, tert-butyl carbamate, and other functional groups are widely used in modern organic synthesis. In carbohydrate chemistry, the commonly used protecting functionality of isopropylidene and cyclohexylidene ketals necessitates effective methods for selective cleavage. This review summarises different methods for deblocking isopropylidene and cyclohexylidene ketals using inorganic acids, Lewis acid, silica-supported inorganic acids, Amberlite-120 (H+) resin, phosphotungstic acid, Nafion-H, NaBArF4.2H2O, montmorillonite clay, Dowex 50W-X8, camphorsulphonic acid (CSA), ceric ammonium nitrate, molecular iodine, ionic liquids, zeolites and so on.

Total Synthesis and Structure Revision of a Fungal Glycolipid Fusaroside

Herein, we report a strategy for the total synthesis of a structurally unique fungal glycolipid fusaroside. The first total synthesis of the proposed structure involved construction of the complex, branched lipid chain having a variety of alkenes with E stereochemistry and attachment of the masked α,β-unsaturated β-keto acid at the O-4 position of trehalose as key steps. We propose a revision in the structure of fusaroside, particularly the position of olefins in the lipid chain.

A Virulence-Associated Glycolipid with Distinct Conformational Attributes: Impact on Lateral Organization of Host Plasma Membrane, Autophagy, and Signaling

Mycobacterium tuberculosis (Mtb) serves as the epitome of how lipids-next to proteins-are utilized as central effectors in pathogenesis. It synthesizes an arsenal of structurally atypical lipids (C60-C90) to impact various membrane-dependent steps involved in host interactions. There is a growing precedent to support insertion of these exposed lipids into the host membrane as part of their mode of action. However, the vital role of specific virulence-associated lipids in modulating cellular functions by altering the host membrane organization and associated signaling pathways remain unanswered questions. Here, we combined chemical synthesis, biophysics, cell biology, and molecular dynamics simulations to elucidate host membrane structure modifications and modulation of membrane-associated signaling using synthetic Mycobacterium tuberculosis sulfoglycolipids (Mtb SL). We reveal that Mtb SL reorganizes the host cell plasma membrane domains while showing higher preference for fluid membrane regions. This rearrangement is governed by the distinct conformational states sampled by SL acyl chains. Physicochemical assays with SL analogues reveal insights into their structure-function relationships, highlighting specific roles of lipid acyl chains and headgroup, along with effects on autophagy and cytokine profiles. Our findings uncover a mechanism whereby Mtb uses specific chemical moieties on its lipids to fine-tune host lipid interactions and confer control of the downstream functions by modifying the cell membrane structure and function. These findings will inspire development of chemotherapeutics against Mtb by counteracting their effects on the host-cell membrane.

Synthesis of trehalose glycolipids

Chemical synthesis of trehalose glycolipids such as DAT, TDM, SL-1, SL-3, and Ac₂SGL from MTb, emmyguyacins from fungi, succinoyl trehalose from rhodococcus, and maradolipids from worms, as well as mycobacterial oligosaccharides is reviewed.

Total syntheses of seminolipid and its analogues by using 2,6-bis(trifluoromethyl)phenylboronic acid as protective reagent

A concise total synthesis of seminolipid, a sulfoglycolipid, has been achieved; key features include regioselective, tin-free sulfation of allyl β-d-galactopyranoside using 2,6-bis(trifluoromethyl)phenylboronic acid as protective reagent, stereoselective epoxidation, and site-selective acylation. The utility of this divergent synthetic approach to introduce 2,2,2-trichloroethyl-protected sulfate group at an early stage without toxic and environmentally unfavorable tin reagents was demonstrated by the syntheses of three seminolipid analogues with different side-chains from the common intermediate.

Diarylborinic Acid-Catalyzed, Site-Selective Sulfation of Carbohydrate Derivatives

Sulfated carbohydrates have been implicated in diverse biological processes, with the position and extent of sulfation of a glycoside often playing important roles in determining the affinity and specificity of its binding to a biomolecular partner. Methods for the site-selective introduction of sulfate groups to carbohydrates are thus of interest. Here, we describe the development of a diarylborinic acid-catalyzed protocol for selective sulfation of pyranoside derivatives at the equatorial position of a cis-1,2-diol group. This method, which employs the sulfur trioxide-trimethylamine complex as the electrophile, has been employed for installation of a sulfate group at the 3-position of a range of galacto- and mannopyranosides, including substrates having a free primary OH group. By using a full equivalent of the diarylborinic acid, selective syntheses of more complex monosulfated glycosides, namely, a 3'-sulfolactose derivative and 3'-sulfo-β-galactosylceramide, have been accomplished. Preliminary kinetics experiments suggested that the catalyst resting state is a tetracoordinate diarylborinic ester that reacts with the SO₃ complex in the turnover-limiting step. Catalyst inhibition by the pyranoside sulfate product and trialkylamine byproduct of the reaction was demonstrated.

CD1b Tetramers Identify T Cells that Recognize Natural and Synthetic Diacylated Sulfoglycolipids from Mycobacterium tuberculosis

Mycobacterial cell wall lipids bind the conserved CD1 family of antigen-presenting molecules and activate T cells via their T cell receptors (TCRs). Sulfoglycolipids (SGLs) are uniquely synthesized by Mycobacterium tuberculosis, but tools to study SGL-specific T cells in humans are lacking. We designed a novel hybrid synthesis of a naturally occurring SGL, generated CD1b tetramers loaded with natural or synthetic SGL analogs, and studied the molecular requirements for TCR binding and T cell activation. Two T cell lines derived using natural SGLs are activated by synthetic analogs independently of lipid chain length and hydroxylation, but differentially by saturation status. By contrast, two T cell lines derived using an unsaturated SGL synthetic analog were not activated by the natural antigen. Our data provide a bioequivalence hierarchy of synthetic SGL analogs and SGL-loaded CD1b tetramers. These reagents can now be applied to large-scale translational studies investigating the diagnostic potential of SGL-specific T cell responses or SGL-based vaccines.

Tailoring Trehalose for Biomedical and Biotechnological Applications

Trehalose is a non-reducing sugar whose ability to stabilize biomolecules has brought about its widespread use in biological preservation applications. Trehalose is also an essential metabolite in a number of pathogens, most significantly the global pathogen Mycobacterium tuberculosis, though it is absent in humans and other mammals. Recently, there has been a surge of interest in modifying the structure of trehalose to generate analogues that have applications in biomedical research and biotechnology. Non-degradable trehalose analogues could have a number of advantages as bioprotectants and food additives. Trehalose-based imaging probes and inhibitors are already useful as research tools and may have future value in the diagnosis and treatment of tuberculosis, among other uses. Underlying the advancements made in these areas are novel synthetic methods that facilitate access to and evaluation of trehalose analogues. In this review, we focus on both aspects of the development of this class of molecules. First, we consider the chemical and chemoenzymatic methods that have been used to prepare trehalose analogues and discuss their prospects for synthesis on commercially relevant scales. Second, we describe ongoing efforts to develop and deploy detectable trehalose analogues, trehalose-based inhibitors, and non-digestible trehalose analogues. The current and potential future uses of these compounds are discussed, with an emphasis on their roles in understanding and combatting mycobacterial infection.

First total synthesis of trehalose containing tetrasaccharides from Mycobacterium smegmatis

Total synthesis of three important trehalose containing tetrasaccharides isolated fromMycobacterium smegmatisis reported for the first time, using regioselective opening of benzylidene acetals and stereoselective glycosylations as key steps.

Synthesis of Mycobacterium tuberculosis Sulfolipid-3 Analogues and Total Synthesis of the Tetraacylated Trehaloglycolipid of Mycobacterium paraffinicum

A novel methodology for the regioselective O6 acylation of the 2,3-diacyl trehaloses to access Mycobacterium tuberculosis sulfolipid SL-3 and related 2,3,6-triester glycolipid analogues is reported for the first time. The methodology was successfully extended to achieve the first total synthesis of the tetraacylated trehalose glycolipid from Mycobacterium paraffinicum. The corresponding 2,3,6'-triesters trehalose glycolipids were also synthesized starting from the common 2,3-diacyl trehalose. These synthetic glycolipids are potential candidates for serodiagnosis and vaccine development for tuberculosis.