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Background and Purpose Experimental Approach Key Results Conclusion and Implications Most inhibitors of histone deacetylases (HDACs) are not selective and are cytotoxic. Some have anti‐inflammatory activity in disease models, but cytotoxicity prevents long‐term uses in non‐fatal diseases. Inhibitors selective for class IIa HDACs are much less cytotoxic and may have applications in management of chronic inflammatory diseases.LL87 is a novel HDAC inhibitor examined here for HDAC enzyme selectivity. It was also investigated in macrophages for cytotoxicity and for inhibition of lipopolysaccharide (LPS)‐stimulated cytokine secretion. In a rat model of collagen‐induced arthritis, LL87 was investigated for effects on joint inflammation in Dark Agouti rats. Histological, immunohistochemical, micro‐computed tomography and molecular analyses characterise developing arthritis and anti‐inflammatory efficacy.LL87 was significantly more inhibitory against class IIa than class I or IIb HDAC enzymes. In macrophages, LL87 was not cytotoxic and reduced both LPS‐induced secretion of pro‐inflammatory cytokines, and IL6‐induced class IIa HDAC activity. In rats, LL87 attenuated paw swelling and clinical signs of arthritis, reducing collagen loss and histological damage in ankle joints. LL87 decreased immune cell infiltration, especially pro‐inflammatory macrophages and osteoclasts, into synovial joints and significantly reduced expression of pro‐inflammatory cytokines and tissue‐degrading proteases.A novel inhibitor of class IIa HDACs has been shown to have an anti‐inflammatory and anti‐arthritic profile distinct from current therapies. It is efficacious in reducing macrophage infiltration and joint inflammation in a chronic model of rat arthritis. [ABSTRACT FROM AUTHOR]

The introduction of an amide bond linking side chains of the first and fifth amino acids forms a cyclic pentapeptide that optimally stabilizes the smallest known α‐helix in water. The origin of the stabilization is unclear. The observed dependence of α‐helicity on the solvent and cyclization linker led us to discover a novel long‐range n to π* interaction between a main‐chain amide oxygen and a uniquely positioned carbonyl group in the linker of cyclic pentapeptides. CD and NMR spectra, NMR and X‐ray structures, modelling, and MD simulations reveal that this first example of a synthetically incorporated long‐range n to π* CO⋅⋅⋅Cγ=Ο interaction uniquely enforces an almost perfect and remarkably stable peptide α‐helix in water but not in DMSO. This unusual interaction with a covalent amide bond outside the helical backbone suggests new approaches to synthetically stabilize peptide structures in water. [ABSTRACT FROM AUTHOR]

5‐(2‐Oxopropylideneamino)‐6‐d‐ribitylaminouracil (5‐OP‐RU) is a natural product formed during bacterial synthesis of vitamin B2. It potently activates mucosal associated invariant T (MAIT) cells and has immunomodulatory, inflammatory, and anticancer properties. This highly polar and unstable compound forms a remarkably stable Schiff base with a lysine residue in major histocompatibility complex class I–related protein (MR1) expressed in antigen‐presenting cells. Inspired by the importance of the ribityl moiety of 5‐OP‐RU for binding to both MR1 and the T cell receptor (TCR) on MAIT cells, each OH was removed in silico. DFT calculations and MD simulations revealed a very stable hydrogen bond between the C3′−OH and uracil N1H, which profoundly restricts flexibility and positioning of each ribityl‐OH, potentially impacting their interactions with MR1 and TCR. By using deoxygenation strategies and kinetically controlled imine formation, four monodeoxyribityl and four monohydroxyalkyl analogues of 5‐OP‐RU were synthesised as new tools for probing T cell activation mechanisms. [ABSTRACT FROM AUTHOR]

Abstract: Mucosal associated invariant T (MAIT) cells are restricted by the monomorphic MHC class I‐like molecule, MHC‐related protein‐1 (MR1). Until 2012, the origin of the MAIT cell antigens (Ags) was unknown, although it was established that MAIT cells could be activated by a broad range of bacteria and yeasts, possibly suggesting a conserved Ag. Using a combination of protein chemistry, mass spectrometry, cellular biology, structural biology and small molecule chemistry, we discovered MR1 ligands derived from folic acid (vitamin B9) and from an intermediate in the microbial biosynthesis of riboflavin (vitamin B2). While the folate derivative 6‐formylpterin generally inhibited MAIT cell activation, two riboflavin pathway derivatives, 5‐(2‐oxopropylideneamino)‐6‐D‐ribitylaminouracil and 5‐(2‐oxoethylideneamino)‐6‐D‐ribitylaminouracil, were potent MAIT cell agonists. Other intermediates and derivatives of riboflavin synthesis displayed weak or no MAIT cell activation. Collectively, these studies revealed that in addition to peptide and lipid‐based Ags, small molecule natural product metabolites are also ligands that can activate T cells expressing αβ T‐cell receptors, and here we recount this discovery. [ABSTRACT FROM AUTHOR]

Mycobacterium tuberculosis produces dideoxymycobactin-838 (DDM-838), a lipopeptide that potently activates T cells upon binding to the MHC-like antigen-presenting molecule CD1a. M. tuberculosis produces DDM-838 in only trace amounts and a previous solid-phase synthesis provided sub-milligram quantities. We describe a high-yielding solution-phase synthesis of DDM-838 that features a Mitsunobu substitution that avoids yield-limiting epimerization at lysine during esterification, and amidation conditions that prevent double-bond isomerization of the Z-C20:1 acyl chain, and provides material with equivalent antigenicity to natural DDM-838. Isomers of DDM-838 that varied in stereochemistry at the central lysine and the C20:1 acyl chain were compared for their ability to be recognised by CD1a-restricted T cell receptors (TCRs). These TCRs, derived from unrelated human donors, exhibited a similar spectrum of reactivity towards the panel of DDM-838 isomers, highlighting the exquisite sensitivity of lipopeptide-reactive T cells for the natural DDM stereochemistry. [ABSTRACT FROM AUTHOR]

Multiple serine proteases exert proinflammatory actions by signaling through protease-activated receptor-2 (PAR2) on the cell surface. Although inhibitors of individual proteases are anti-inflammatory, we sought to discover whether the first potent antagonist of their common target PAR2 might be beneficial in treating chronic arthritis-like inflammatory disease. Using a fluorescence assay, a novel compound, GB88, was shown to antagonize PAR2-induced intracellular Ca2+ release in human monocyte-derived macrophages, being 1000 times more potent than a control compound, ENMD-1068 (IC50 1.60±5 µM vs. 1.20±4 mM, respectively). In Wistar rats, GB88 was orally bioavailable (F55%, Tmax 4 h , Cmax 1.7 µM, 10 mg/kg). GB88 inhibited the acute paw edema induced in Wistar rats by intraplantar λ-carrageenan or PAR2 agonists 2-furoyl-LIGRLO-NH2 or mast cell β-tryptase, without inhibiting proteolytic activity of tryptase in vitro. In the chronic collagen-induced model of arthritis in rats, GB88 (10 mg/kg) was disease modifying and ameliorated pathological and histopathological changes (edema, pannus formation, synovial hyperplasia, collagen degradation, macrophage invasion, mast cell degranulation) compared to untreated arthritic controls. The results suggest that an orally active PAR2 antagonist is effective in treating chronic arthritis in rats through inhibiting macrophage infiltration, mast cell degranulation, and β-tryptase-PAR2 signaling in joint inflammation. [ABSTRACT FROM AUTHOR]

Small molecule heparan sulfate mimetics like (VI) and (X) are synthesized by the Ugi four-component condensation of mannopyranoside-derived isocyanides (I) and (VII) with a variety of carboxylic acids, e.g.(II), amines such as (III) and (VIII), and formaldehyde (IV) as the carbonyl component, followed by sulfonation. [ABSTRACT FROM AUTHOR]