Identification of indole inhibitors of human hematopoietic prostaglandin D2 synthase (hH-PGDS)

The "cesium effect" magnified: exceptional chemoselectivity in cesium ion mediated nucleophilic reactions

Chemodivergent construction of structurally distinct heterocycles from the same precursors by adjusting specific reaction parameters is an emergent area of organic synthesis; yet, understanding of the processes that underpin the reaction divergence is lacking, preventing the development of new synthetic methods by systematically harnessing key mechanistic effects. We describe herein cesium carbonate-promoted oxadiaza excision cross-coupling reactions of β-ketoesters with 1,2,3-triazine 1-oxides that form pyridones in good to high yields, instead of the sole formation of pyridines when the same reaction is performed in the presence of other alkali metal carbonates or organic bases. The reaction can be further extended to the construction of synthetically challenging pyridylpyridones. A computational study comparing the effect of cesium and sodium ions in the oxadiaza excision cross-coupling reactions reveals that the cesium-coordinated species changes the reaction preference from attack at the ketone carbonyl to attack at the ester carbon due to metal ion-specific transition state conformational accommodation, revealing a previously unexplored role of cesium ions that may facilitate the development of chemodivergent approaches to other heterocyclic systems.

The mercapturic acid pathway

The mercapturic acid pathway is a major route for the biotransformation of xenobiotic and endobiotic electrophilic compounds and their metabolites. Mercapturic acids (N-acetyl-l-cysteine S-conjugates) are formed by the sequential action of the glutathione transferases, γ-glutamyltransferases, dipeptidases, and cysteine S-conjugate N-acetyltransferase to yield glutathione S-conjugates, l-cysteinylglycine S-conjugates, l-cysteine S-conjugates, and mercapturic acids; these metabolites constitute a "mercapturomic" profile. Aminoacylases catalyze the hydrolysis of mercapturic acids to form cysteine S-conjugates. Several renal transport systems facilitate the urinary elimination of mercapturic acids; urinary mercapturic acids may serve as biomarkers for exposure to chemicals. Although mercapturic acid formation and elimination is a detoxication reaction, l-cysteine S-conjugates may undergo bioactivation by cysteine S-conjugate β-lyase. Moreover, some l-cysteine S-conjugates, particularly l-cysteinyl-leukotrienes, exert significant pathophysiological effects. Finally, some enzymes of the mercapturic acid pathway are described as the so-called "moonlighting proteins," catalytic proteins that exert multiple biochemical or biophysical functions apart from catalysis.

Amelioration of mechanism-based inactivation of CYP3A4 by a H-PGDS inhibitor

This work describes the rational amelioration of mechanism-based inactivation (MBI) of Cytochrome P450 (CYP) 3A4 in a human hematopoietic prostaglandin D synthase (hH-PGDS) inhibitor (cpd 1). We utilized metabolism reports in order to check if patterns in the metabolism of 1 and similar compounds by CYP3A4 could be deciphered. Then we used structure based design, first modifying the CYP3A4 crystal structure (pdb code: 4NY4) by adding an oxyferryl moiety to the heme, followed by validating the modified structure to obtain the 1' and 4 position oxidation products of midazolam and then recapitulating the metabolism patterns deciphered previously for 1 and analogs. We checked if the pattern deciphered could lead to a putative reactive moiety. Finally we used the docking pose of 1 into this model of the modified CYP3A4 crystal structure to guide transformation of 1 into MBI-free H-PGDS inhibitors.

Prostaglandins and Their Receptors in Eosinophil Function and As Therapeutic Targets

Of the known prostanoid receptors, human eosinophils express the prostaglandin D₂ (PGD₂) receptors DP1 [also D-type prostanoid (DP)] and DP2 (also chemoattractant receptor homologous molecule, expressed on Th2 cells), the prostaglandin E₂ receptors EP2 and EP4, and the prostacyclin (PGI₂) receptor IP. Prostanoids can bind to either one or multiple receptors, characteristically have a short half-life in vivo, and are quickly degraded into metabolites with altered affinity and specificity for a given receptor subtype. Prostanoid receptors signal mainly through G proteins and naturally activate signal transduction pathways according to the G protein subtype that they preferentially interact with. This can lead to the activation of sometimes opposing signaling pathways. In addition, prostanoid signaling is often cell-type specific and also the combination of expressed receptors can influence the outcome of the prostanoid impulse. Accordingly, it is assumed that eosinophils and their (patho-)physiological functions are governed by a sensitive prostanoid signaling network. In this review, we specifically focus on the functions of PGD₂, PGE₂, and PGI₂ and their receptors on eosinophils. We discuss their significance in allergic and non-allergic diseases and summarize potential targets for drug intervention.

Regulation of inflammation by lipid mediators in oral diseases

Lipid mediators (LM) of inflammation are a class of compounds derived from ω-3 and ω-6 fatty acids that play a wide role in modulating inflammatory responses. Some LM possess pro-inflammatory properties, while others possess proresolving characteristics, and the class switch from pro-inflammatory to proresolving is crucial for tissue homeostasis. In this article, we review the major classes of LM, focusing on their biosynthesis and signaling pathways, and their role in systemic and, especially, oral health and disease. We discuss the detection of these LM in various body fluids, focusing on diagnostic and therapeutic applications. We also present data showing gender-related differences in salivary LM levels in healthy controls, leading to a hypothesis on the etiology of inflammatory diseases, particularly Sjögren's syndrome. We conclude by enumerating open areas of research where further investigation of LM is likely to result in therapeutic and diagnostic advances.

Development of a scintillation proximity binding assay for high-throughput screening of hematopoietic prostaglandin D2 synthase

Prostaglandin D2 synthase (PGDS) catalyzes the isomerization of prostaglandin H2 (PGH2) to prostaglandin D2 (PGD2). PGD2 produced by hematopoietic prostaglandin D2 synthase (H-PGDS) in mast cells and Th2 cells is proposed to be a mediator of allergic and inflammatory responses. Consequently, inhibitors of H-PGDS represent potential therapeutic agents for the treatment of inflammatory diseases such as asthma. Due to the instability of the PGDS substrate PGH2, an in-vitro enzymatic assay is not feasible for large-scale screening of H-PGDS inhibitors. Herein, we report the development of a competition binding assay amenable to high-throughput screening (HTS) in a scintillation proximity assay (SPA) format. This assay was used to screen an in-house compound library of approximately 280,000 compounds for novel H-PGDS inhibitors. The hit rate of the H-PGDS primary screen was found to be 4%. This high hit rate suggests that the active site of H-PGDS can accommodate a large diversity of chemical scaffolds. For hit prioritization, these initial hits were rescreened at a lower concentration in SPA and tested in the LAD2 cell assay. 116 compounds were active in both assays with IC50s ranging from 6 to 807 nM in SPA and 82 nM to 10 μM in the LAD2 cell assay.