Synthesis and biological activity of hydroxylated analogues of KRN7000 (α-galactosylceramide)

Diversity-Oriented Synthesis of a Molecular Library of Immunomodulatory α-Galactosylceramides with Fluorous-Tag-Assisted Purification and Evaluation of Their Bioactivities in Regard to IL-2 Secretion

Structural variants of α-galactosylceramide (α-GalCer) that stimulate invariant natural killer T (iNKT) cells constitute an emerging class of immunomodulatory agents in development for numerous biological applications. Variations in lipid chain length and/or fatty acids in these glycoceramides selectively trigger specific pro-inflammatory responses. Studies that would link a specific function to a structurally distinct α-GalCer rely heavily on the availability of homogeneous and pure materials. To address this need, we report herein a general route to the diversification of the ceramide portion of α-GalCer glycolipids. Our convergent synthesis commences from common building blocks and relies on the Julia–Kocienski olefination as a key step. A cleavable fluorous tag is introduced at the non-reducing end of the sugar that facilitates quick purification of products by standard fluorous solid-phase extraction. The strategy enabled the rapid generation of a focused library of 61 α-GalCer analogs by efficiently assembling various lipids and fatty acids. Furthermore, when compared against parent α-GalCer in murine cells, many of these glycolipid variants were found to have iNKT cell stimulating activity similar to or greater than KRN7000. ELISA assaying indicated that glycolipids carrying short fatty N-acyl chains (1fc and 1ga), an unsubstituted (1fh and 1fi) or CF3-substituted phenyl ring at the lipid tail, and a flexible, shorter fatty acyl chain with an aromatic ring (1ge, 1gf, and 1gg) strongly affected the activation of iNKT cells by the glycolipid-loaded antigen-presenting molecule, CD1d. This indicates that the method may benefit the design of structural modifications to potent iNKT cell-binding glycolipids.

Polyhydroxylated Cyclopentane β-Amino Acids Derived from d-Mannose and d-Galactose: Synthesis and Protocol for Incorporation into Peptides

A stereoselective synthesis of polyhydroxylated cyclopentane β-amino acids from hexoses is reported. The reaction sequence comprises, as key steps, ring-closing metathesis of a polysubstituted diene intermediate followed by the stereoselective aza-Michael functionalization of the resulting cyclopent-1-ene-1-carboxylic acid ester. Examples of synthesis of polysubstituted 2-aminocyclopentanecarboxylic acid derivatives starting from protected d-mannose and d-galactose are presented. A general protocol for the incorporation of these highly functionalized alicyclic β-amino acids into peptides is also reported.

Synthesis of a Highly Branched Nonasaccharide Chlorella Virus N-Glycan Using a "Counterclockwise" Assembly Approach

Chloroviruses produce a capsid protein containing N-linked glycans differing in structure from those found in all other organisms. These species feature a core "hyper-branched" fucose residue in which every hydroxyl group is glycosylated. We describe the synthesis of a nonasaccharide from Paramecium bursaria chlorella virus 1, one of most complex chlorovirus N-glycans reported, using a "counterclockwise" strategy involving the sequential addition of trisaccharide, disaccharide, and monosaccharide motifs to a trisaccharide containing the core fucose residue.

3,4-Dideoxy-3,3,4,4-tetrafluoro- and 4-OH epimeric 3-deoxy-3,3-difluoro-α-GalCer analogues: Synthesis and biological evaluation on human iNKT cells stimulation

iNKT cells recognize CD1d/α-galactosylceramide (α-GalCer) complexes via their invariant TCR receptor and stimulate the immune response. Many α-GalCer analogues have been investigated to interrogate this interaction. Following our previous work related to the modification of the hydrogen bond network between α-GalCer and CD1d, we have now focused our attention on the synthesis of 3-deoxy-3,3-difluoro- and 3,4-dideoxy-3,3,4,4-tetrafluoro-α-GalCer analogues, and studied their ability to stimulate human iNKT cells. In each case, deoxygenation at the indicated positions was accompanied by difluoro introduction in order to evaluate the resulting electronic effect on the stability of the ternary CD1d/Galcer/TCR complex which has been rationalized by modeling study. With deoxy-difluorination at the 3-position, the two epimeric 4-OH analogues were investigated to establish their capacity to compensate for the lack of the hydrogen bond donating group at the 3-position. The 3,4-dideoxytetrafluoro analogue was of interest to highlight the amide NH-bond hydrogen bond properties.

Development of α-GalCer Analogues with an α-Fluorocarbonyl Moiety as Th2-Selective Ligands of CD1d

A series of α-GalCer analogues containing an α-fluorocarbonyl moiety at the terminal position of the acyl chain were designed for targeting polar residues in the hydrophobic cavity of CD1d using a structure-based approach. The acyl chain length was efficiently adjusted by an asymmetric alkyne-alkyne cross coupling strategy, and the newly synthesized α-GalCer analogues showed the high Th2-selective activity of iNKT cells. The biased activity of ligands could be caused by the hydrogen-bonding interaction between ligands and CD1d according to the Th2-selective cytokine secretion and molecular docking studies.

Innate, innate-like and adaptive lymphocytes in the pathogenesis of MS and EAE

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) in which the immune system damages the protective insulation surrounding the nerve fibers that project from neurons. A hallmark of MS and its animal model, experimental autoimmune encephalomyelitis (EAE), is autoimmunity against proteins of the myelin sheath. Most studies in this field have focused on the roles of CD4⁺ T lymphocytes, which form part of the adaptive immune system as both mediators and regulators in disease pathogenesis. Consequently, the treatments for MS often target the inflammatory CD4⁺ T-cell responses. However, many other lymphocyte subsets contribute to the pathophysiology of MS and EAE, and these subsets include CD8⁺ T cells and B cells of the adaptive immune system, lymphocytes of the innate immune system such as natural killer cells, and subsets of innate-like T and B lymphocytes such as γδ T cells, natural killer T cells, and mucosal-associated invariant T cells. Several of these lymphocyte subsets can act as mediators of CNS inflammation, whereas others exhibit immunoregulatory functions in disease. Importantly, the efficacy of some MS treatments might be mediated in part by effects on lymphocytes other than CD4⁺ T cells. Here we review the contributions of distinct subsets of lymphocytes on the pathogenesis of MS and EAE, with an emphasis on lymphocytes other than CD4⁺ T cells. A better understanding of the distinct lymphocyte subsets that contribute to the pathophysiology of MS and its experimental models will inform the development of novel therapeutic approaches.

Synthesis of the Highly Branched Hexasaccharide Core of Chlorella Virus N-Linked Glycans

Chlorella viruses produce N-linked glycoproteins with carbohydrate moieties that differ in structure from all other N-linked glycans. In addition, unlike most viruses, these organisms do not hijack the biosynthetic machinery of the host to make glycocoproteins; instead, they produce their own carbohydrate-processing enzymes. A better understanding of the function and assembly of these fascinating and structurally-unprecedented glycans requires access to probe molecules. This work describes the first synthesis of a chlorella virus N-linked glycan, a highly branched hexasaccharide that contains the pentasaccharide present in all of the >15 structures reported to date. The target molecule includes a glucosyl-asparagine linkage and a "hyperbranched" fucose residue in which all of the hydroxyl groups are glycosylated. Both convergent and linear approaches were investigated with the latter being successful in providing the target in 16 steps and 13 % overall yield.

Deep Profiling of Immunosuppressive Glycosphingolipids and Sphingomyelins in Wild Cordyceps

Deep profiling of glycosphingolipids and sphingomyelins in wild Cordyceps was carried out by using offline chromatographic enrichment followed by ultrahigh performance liquid chromatography-ultrahigh definition-quadrupole time-of-flight mass spectrometry (UHPLC-UHD-Q-TOF-MS). A total of 119 glycosphingolipids (72 new ones) and 87 sphingomyelins (43 new ones) were identified from wild Cordyceps on the basis of the accurate mass and MS/MS fragmentations, isotope patterns, sphingolipid (SPL) database matching, confirmation by SPL standards, and the reversed-phase liquid chromatographic retention rule. This study is the most comprehensive report on the identification of glycosphingolipids and sphingomyelins from fungus. A subsequent lipopolysaccharide-induced mouse splenic lymphocyte proliferation assay showed that the Cordyceps glycosphingolipid fraction exhibits higher immunosuppressive activity compared to that of Cordyceps sphingomyelins. Our findings provided insight into the chemical diversity of sphingolipids in Cordyceps and chemical evidence for the therapeutic application of wild Cordyceps.

Isolation and Synthesis of Misszrtine A: A Novel Indole Alkaloid From Marine Sponge-Associated Aspergillus sp. SCSIO XWS03F03

A novel indole alkaloid, misszrtine A (1), was isolated from marine sponge-derived fungus Aspergillus sp. SCSIO XWS03F03. The planar structure of 1 was assigned by analysis of spectroscopic data, the absolute configuration of which was unambiguously determined by total synthesis. Compound 1 represents the first example of N-isopentenyl tryptophan methyl ester with a phenylpropanoic amide arm, which exhibited a potent antagonistic activity on HL60 (IC₅₀ = 3.1 μM) and LNCaP (IC₅₀ = 4.9 μM) cell lines. Bioactivity evaluation reveals that functional group on indole nitrogen of 1 has a great effect on its cytotoxity, which provides a mean to probe the structure-activity relationships of 1.

Natural killer T cells in multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is a chronic inflammatory disease that causes demyelination of neurons in the central nervous system. Traditional therapies for MS have involved anti-inflammatory and immunosuppressive drugs with significant side effects that often only provide short-term relief. A more desirable outcome of immunotherapy would be to protect against disease before its clinical manifestation or to halt disease after its initiation. One attractive approach to accomplish this goal would be to restore tolerance by targeting immunoregulatory cell networks. Although much of the work in this area has focused on CD4(+) Foxp3(+) regulatory T cells, other studies have investigated natural killer T (NKT) cells, a subset of T cells that recognizes glycolipid antigens in the context of the CD1d glycoprotein. Studies with human MS patients have revealed alterations in the numbers and functions of NKT cells, which have been partially supported by studies with the experimental autoimmune encephalomyelitis model of MS. Additional studies have shown that activation of NKT cells with synthetic lipid antigens can, at least under certain experimental conditions, protect mice against the development of MS-like disease. Although mechanisms of this protection remain to be fully investigated, current evidence suggests that it involves interactions with other immunoregulatory cell types such as regulatory T cells and immunosuppressive myeloid cells. These studies have provided a strong foundation for the rational design of NKT-cell-based immunotherapies for MS that induce tolerance while sparing overall immune function. Nevertheless, additional pre-clinical and clinical studies will be required to bring this goal to fruition.

Design and Evaluation of ω-Hydroxy Fatty Acids Containing α-GalCer Analogues for CD1d-Mediated NKT Cell Activation

CD1d molecules recognize glycolipid antigens with straight chain fatty acid moieties. Although most of the residues in the CD1d binding groove are hydrophobic, some of the amino acids can form hydrogen bonds. Consequently, we have designed ω-hydroxy fatty acid-containing glycolipid derivatives of the prototypical CD1d ligand α-GalCer. The potency of the ω-hydroxy analogues of the proper length is comparable to that of α-GalCer. We propose, based on the biological results and molecular modeling studies, that a hydrogen bonding interaction is involved between the ω-hydroxy group and a polar amino acid residue in the hydrophobic binding groove.