Selective and Bioavailable HDAC6 2-(Difluoromethyl)-1,3,4-oxadiazole Substrate Inhibitors and Modeling of Their Bioactivation Mechanism.

Histone deacetylase 6 (HDAC6) is a unique member of the HDAC family mainly targeting cytosolic nonhistone substrates, such as α-tubulin, cortactin, and heat shock protein 90 to regulate cell proliferation, metastasis, invasion, and mitosis in tumors. We describe the identification and characterization of a series of 2-(difluoromethyl)-1,3,4-oxadiazoles (DFMOs) as selective nonhydroxamic acid HDAC6 inhibitors. By comparing structure-activity relationships and performing quantum mechanical calculations of the HDAC6 catalytic mechanism, we show that potent oxadiazoles are electrophilic substrates of HDAC6 and propose a mechanism for the bioactivation. We also observe that the inherent electrophilicity of the oxadiazoles makes them prone to degradation in water solution and the generation of potentially toxic products cannot be ruled out, limiting the developability for chronic diseases. However, the oxadiazoles demonstrate high oral bioavailability and low in vivo clearance and are excellent tools for studying the role of HDAC6 in vitro and in vivo in rats and mice.

Discovery of AZD8154, a Dual PI3Kγδ Inhibitor for the Treatment of Asthma.

Starting from our previously described PI3Kγ inhibitors, we describe the exploration of structure-activity relationships that led to the discovery of highly potent dual PI3Kγδ inhibitors. We explored changes in two positions of the molecules, including macrocyclization, but ultimately identified a simpler series with the desired potency profile that had suitable physicochemical properties for inhalation. We were able to demonstrate efficacy in a rat ovalbumin challenge model of allergic asthma and in cells derived from asthmatic patients. The optimized compound, AZD8154, has a long duration of action in the lung and low systemic exposure coupled with high selectivity against off-targets.

An Angle on MK2 Inhibition-Optimization and Evaluation of Prevention of Activation Inhibitors.

The mitogen-activated protein kinase p38α pathway has been an attractive target for the treatment of inflammatory conditions such as rheumatoid arthritis. While a number of p38α inhibitors have been taken to the clinic, they have been limited by their efficacy and toxicological profile. A lead identification program was initiated to selectively target prevention of activation (PoA) of mitogen-activated protein kinase-activated protein kinase 2 (MK2) rather than mitogen- and stress-activated protein kinase 1 (MSK1), both immediate downstream substrates of p38α, to improve the efficacy/safety profile over direct p38α inhibition. Starting with a series of pyrazole amide PoA MK2 inhibitor leads, and guided by structural chemistry and rational design, a highly selective imidazole 9 (2-(3'-(2-amino-2-oxoethyl)-[1,1'-biphenyl]-3-yl)-N-(5-(N,N-dimethylsulfamoyl)-2-methylphenyl)-1-propyl-1H-imidazole-5-carboxamide) and the orally bioavailable imidazole 18 (3-methyl-N-(2-methyl-5-sulfamoylphenyl)-2-(o-tolyl)imidazole-4-carboxamide) were discovered. The PoA concept was further evaluated by protein immunoblotting, which showed that the optimized PoA MK2 compounds, despite their biochemical selectivity against MSK1 phosphorylation, behaved similarly to p38 inhibitors in cellular signaling. This study highlights the importance of selective tool compounds in untangling complex signaling pathways, and although 9 and 18 were not differentiated from p38α inhibitors in a cellular context, they are still useful tools for further research directed to understand the role of MK2 in the p38α signaling pathway.

A class of highly selective inhibitors bind to an active state of PI3Kγ.

We have discovered a class of PI3Kγ inhibitors exhibiting over 1,000-fold selectivity over PI3Kα and PI3Kß. On the basis of X-ray crystallography, hydrogen-deuterium exchange-mass spectrometry and surface plasmon resonance experiments we propose that the cyclopropylethyl moiety displaces the DFG motif of the enzyme away from the adenosine tri-phosphate binding site, inducing a large conformational change in both the kinase- and helical domains of PI3Kγ. Site directed mutagenesis explained how the conformational changes occur. Our results suggest that these cyclopropylethyl substituted compounds selectively inhibit the active state of PI3Kγ, which is unique to these compounds and to the PI3Kγ isoform, explaining their excellent potency and unmatched isoform selectivity that were confirmed in cellular systems. This is the first example of a Class I PI3K inhibitor achieving its selectivity by affecting the DFG motif in a manner that bears similarity to DFG in/out for type II protein kinase inhibitors.

Evolution of PI3Kγ and δ Inhibitors for Inflammatory and Autoimmune Diseases.

Phosphoinositol 3-kinases (PI3Ks) γ and δ are key enzymes in hematopoietic cells and have been seen as high-value targets for the treatment of diseases with inflammatory and immunomodulatory components since their discovery and the identification of their roles. In this Perspective we review progress in the application of inhibitors of PI3Kγ and δ to inflammatory and immunological conditions over the past 6 years. We consider progress in the understanding of the roles of PI3Kγ and PI3Kδ in immunology and inflammation, the experience from clinical trials where inhibitors have been tested, and what has been learned about the safety of their use. The extensive medicinal chemistry efforts to discover both isoform selective and dual PI3Kγδ inhibitors are analyzed and detailed. Developments in understanding the structural chemistry of the PI3K enzymes and the factors that govern isoform selectivity are discussed. The effects observed with the known inhibitor compounds in animal models are described.

Discovery of Highly Isoform Selective Orally Bioavailable Phosphoinositide 3-Kinase (PI3K)-γ Inhibitors.

In this paper, we describe the discovery and optimization of a new chemotype of isoform selective PI3Kγ inhibitors. Starting from an HTS hit, potency and physicochemical properties could be improved to give compounds such as 15, which is a potent and remarkably selective PI3Kγ inhibitor with ADME properties suitable for oral administration. Compound 15 was advanced into in vivo studies showing dose-dependent inhibition of LPS-induced airway neutrophilia in rats when administered orally.

Solid-phase synthesis of serine-based glycosphingolipid analogues for preparation of glycoconjugate arrays.

Synthetic glycolipids with defined structures are important tools in the study of glycolipid biology. In this paper we describe a solid-phase synthesis of three galactosylated serine-based glycosphingolipid analogues using the novel linker 2-fluoro-4-(hydroxymethyl)-phenoxyacetic acid. Gel-phase (19)F-NMR spectroscopy was used to measure the yield and stereochemical outcome of the solid-phase glycosylations. Under NIS-TfOH promotion, alpha- and beta-selective glycosylations were performed at room temperature with thioglycoside donors carrying fluorine labelled protective groups. Finally, the glycolipids were covalently linked to microtiter plates and labelled lectins with different selectivity for alpha- and beta-galactosides could bind to the glycolipid arrays.

A fluorinated selenide linker for solid-phase synthesis of n-pentenyl glycosides.

[reaction: see text] A fluorine-labeled selenide linker for installing terminal isolated olefins has been synthesized in high overall yield. The resin-bound linker could be glycosylated both with glycosyl trichloroacetimidates and glycosyl fluorides. The linker did not decompose after oxidation with tBuOOH but underwent beta-elimination when it was subjected to heat. This allowed the released n-pentenyl glycoside 15 to be isolated in excellent yield and purity after filtration.

Gel-phase 19F NMR spectral quality for resins commonly used in solid-phase organic synthesis; a study of peptide solid-phase glycosylations.

The spectroscopic properties for seven different commercial resins used in solid-phase synthesis were investigated with (19)F NMR spectroscopy. A fluorine-labeled dipeptide was synthesized on each resin, and the resolution of the (19)F resonances in CDCl(3), DMSO-d(6), benzene-d(6) and CD(3)OD were measured with a conventional NMR spectrometer, i.e. without using magic angle spinning. In general, resins containing poly(ethylene glycol) chains (ArgoGel, TentaGel and PEGA) were found to be favorable for the (19)F NMR spectral quality. Three serine containing tri-, penta-, and heptapeptides were then prepared on an ArgoGel resin functionalized with a fluorine-labeled linker. The resin bound peptides were glycosylated utilizing a thiogalactoside glycosyl donor carrying fluorine-labeled protective groups. Monitoring of the glycosylations with gel-phase (19)F NMR spectroscopy allowed each glycopeptide to be formed in similar 80% yield, using a minimal amount of glycosyl donor (3 x 2 equivalents). In addition, it was found that the glycosylation yields were independent of peptide length.

Solid-phase synthesis of alpha-Gal epitopes: on-resin analysis of solid-phase oligosaccharide synthesis with 19F NMR spectroscopy.

A route for solid-phase synthesis of the alpha-Gal epitopes Gal(alpha1-3)Gal(beta1-4)Glc and Gal(alpha1-3)Gal(beta1-4)GlcNAc is described. These trisaccharide antigens are responsible for hyperacute rejection in xenotransplantation of porcine organs. Optimization of the solid-phase synthesis relied on use of fluorinated protective groups for the carbohydrate building blocks and use of a fluorinated linker. This allowed convenient on-resin analysis of the reactions with gel-phase (19)F NMR spectroscopy. Conditions were established which allowed reductive ring-opening of 4,6-O-benzylidene acetals to be performed on the solid phase with high regioselectivity to furnish the corresponding 6-O-benzyl ethers. It was found that glycosylations could be conveniently carried out by using thioglycosides as donors with N-iodosuccinimide and trifluoromethanesulfonic acid as the promoter system. With use of these conditions a challenging alpha-glycosidic linkage was successfully installed with complete stereoselectivity in the final glycosylation. It was also established that fluorinated benzoates, benzyl ethers, and benzylidene acetals display almost identical chemical properties as their nonfluorinated counterparts, a finding that is essential for future use of fluorinated protective groups in solid-phase oligosaccharide synthesis.

Influence of saccharide size on the cellular immune response to glycopeptides.

Glycopeptides that bind to MHC molecules on antigen presenting cells may elicit carbohydrate selective T cells. In order to investigate how the cellular immune response depends on the size of the carbohydrate moiety, a trigalactosylated derivative of an immunogenic peptide from hen egg-white lysozyme (HEL52-61) was prepared. Synthesis was accomplished by assembly of an alpha-1,4-linked trigalactose peracetate which was coupled to Fmoc serine. After activation as a pentafluorophenyl ester the resulting building block was used in solid-phase synthesis In contrast to the corresponding mono- and digalactosylated derivatives of HEL52-61, the trigalactosylated HEL52-61 was not immunogenic. Somewhat surprisingly, this was found to be because the trigalactosyl derivative bound approximately two orders of magnitude weaker to I-Ak MHC molecules than the mono- and digalactosyl peptides. Our observation suggests an explanation for previous findings, which show that glycopeptides isolated from MHC molecules in nature usually carry small saccharides.