Reactions of Functionalized Sulfonamides: Application to Lowering the Lipophilicity of Cytosolic Phospholipase A2α Inhibitors

1-Benzylindoles as inhibitors of cytosolic phospholipase A2α: synthesis, biological activity, aqueous solubility, and cell permeability

Cytosolic phospholipase A2α (cPLA2α) is considered an interesting target for the development of new anti-inflammatory drugs, as it is significantly involved in the formation of pro-inflammatory lipid mediators. Recently, in a ligand-based virtual screening approach, 2,4-dichlorobenzyl-substituted 4-[2-(indol-3-ylmethylene)hydrazineyl]benzoic acid 7 was found to be an inhibitor of cPLA2α with micromolar activity. This compound has now been systematically varied to increase inhibitory potency. The studies performed led to 5-(1-benzylindol-3-ylmethyl)-2H-tetrazol-2-yl)pentanoic acid derivatives that exhibited submicromolar activity against the enzyme. The most potent compounds were also tested for their water solubility and for permeability in a Caco-2 model. Among other things, it was found that in Caco-2 cells, the pentanoic acid chain of the molecules can be metabolised to a considerable extent to propionic acid by β-oxidation.

Synthesis, activity and metabolic stability of propan-2-one substituted tetrazolylalkanoic acids as dual inhibitors of cytosolic phospholipase A2α and fatty acid amide hydrolase

The serine hydrolases cytosolic phospholipase A2α (cPLA2α) and fatty acid amide hydrolase (FAAH) are interesting targets for the development of new anti-inflammatory and analgesic drugs. Structural modifications of a potent dual inhibitor with a propan-2-one substituted tetrazolylpropionic acid moiety led to compounds with also nanomolar activity against both enzymes but better physicochemical properties. The structure-activity relationships showed that the variations had partially divergent effects on the inhibitory activity of the compounds towards cPLA2α and FAAH reflecting differences in the binding mode to the enzymes. Furthermore, the metabolic stability of the target structures was investigated in vitro.

N-Substituted 4-sulfamoylbenzoic acid derivatives as inhibitors of cytosolic phospholipase A2α

The N,N-disubstituted 4-sulfamoylbenzoic acid derivative 3, which was found to be an inhibitor of cytosolic phospholipase A2α (cPLA2α) with micromolar activity in a ligand-based virtual screening approach, was structurally modified to increase its enzyme inhibitory potency. Replacing the substituents on the sulfonamide nitrogen with other residues such as naphthyl, naphthylmethyl, indolylalkyl and differently substituted phenyl moieties did not lead to a significant increase in activity. Only strong structural convergence to the potent known benzhydrylindole-substituted benzoic acid derivatives that had served as templates in the virtual screening resulted in compounds with considerable potency. Thus, the sulfamoyl benzoic acid derivatives 85 and 88 showed submicromolar IC50 values against cPLA2α.

Discovery of substituted indole derivatives as allosteric inhibitors of m6 A-RNA methyltransferase, METTL3-14 complex

m⁶ A RNA methyltransferase (METTL3-14) catalyzes the methylation of adenosine in mRNA and plays important roles in mRNA functions, and it has been implicated in the progression of multiple cancers, including acute myeloid leukemia (AML). In this study, we describe the discovery of the first allosteric inhibitor of the METTL3-14 complex based on structure-activity relationship (SAR) and optimization studies of the hit compound, 4-[2-[5-chloro-1-(diphenylmethyl)-2-methyl-1H-indol-3-yl]-ethoxy]benzoic acid (CDIBA). Compound 43n was optimized throughout the modifications of 4 different regions of the structure, and it displayed potent enzyme inhibitory activity of the METTL3-14 complex (IC₅₀  = 2.81 μM) and an antiproliferative effect in the AML cell lines by suppressing the m⁶ A level of mRNA. The inhibition mechanism and binding mode of 43n were based on the interaction of the reversible and noncompetitive inhibitory profile at the allosteric site along with selectivity for the METTL3-14 complex relative to each subunit enzyme or truncated complex enzyme.

2-Oxoamide inhibitors of cytosolic group IVA phospholipase A2 with reduced lipophilicity

Cytosolic GIVA phospholipase A2 (GIVA cPLA2) initiates the eicosanoid pathway of inflammation and thus inhibitors of this enzyme constitute novel potential agents for the treatment of inflammatory diseases. Traditionally, GIVA cPLA2 inhibitors have suffered systemically from high lipophilicity. We have developed a variety of long chain 2-oxoamides as inhibitors of GIVA PLA2. Among them, AX048 was found to produce a potent analgesic effect. We have now reduced the lipophilicity of AX048 by replacing the long aliphatic chain with a chain containing an ether linked aromatic ring with in vitro inhibitory activities similar to AX048.

Inhibitors of Cytosolic Phospholipase A2α as Anti-inflammatory Drugs

Arachidonic acid derivatives, like prostaglandins and leukotrienes, as well as the alkyl-ether phospholipid platelet-activating factor (PAF) are highly active substances with diverse biological actions. Elevated levels of these lipid mediators in response to a variety of stimuli have been implicated in the pathology of many inflammatory diseases. The rate-limiting step in the generation of prostaglandins, leukotrienes and PAF, respectively, is the cleavage of the sn-2-ester of membrane phospholipids by a phospholipase A2 (PLA2). Among the superfamily of PLA2 enzymes, cytosolic PLA2α (cPLA2α, also referred to as group IVA PLA2) is thought to play the primary role in this biochemical reaction. Therefore, inhibition of cPLA2α activity is an attractive approach to the control of inflammatory disorders.

In this chapter the main groups of cPLA2α inhibitors are described and the problems associated with the development of clinical active drug candidates are discussed. Furthermore, in-vivo data obtained with such compounds in pre-clinical animal models of inflammation will be presented.