Letizia Giampietro

Benzothiazole-based N-(phenylsulfonyl)amides as a novel family of PPARα antagonists.

The discovery of PPAR antagonists is emerging as an useful tool for elucidating the biological role of the receptor. Here we report the identification of N-(phenylsulfonyl)amides containing the benzothiazole scaffold, a novel class of potent PPARα antagonists obtained from chemical modification of carboxylic acid agonists. In this work, a group of phenylsulfonamides were synthesized and in vitro evaluated against the agonistic effect of GW7647; they showed an inhibitory effect on PPARα activation, with best compounds revealing a dose-dependent antagonistic profile. Some of these antagonists showed also an inhibitory effect on CPT1A pattern expression.

N-Substituted acetamidines and 2-methylimidazole derivatives as selective inhibitors of neuronal nitric oxide synthase.

A series of N-substituted acetamidines and 2-methylimidazole derivatives structurally related to W1400 were synthesized and evaluated as Nitric Oxide Synthase (NOS) inhibitors. Analogs with sterically hindering isopropyl and phenyl substituents on the benzylic carbon connecting the aromatic core of W1400 to the acetamidine nitrogen, showed good inhibitory potency for nNOS (IC(50)=0.2 and 0.3 μM) and selectivity over eNOS (500 and 1166) and to a lesser extent over iNOS (50 and 100). A molecular modeling study allowed to shed light on the effects of the structural modifications on the selectivity of the designed inhibitors toward the different NOS isoforms.

Synthesis, Biological Evaluation, and Docking Studies of N-Substituted Acetamidines as Selective Inhibitors of Inducible Nitric Oxide Synthase

New acetamidines structurally related to N-(3-(aminomethyl)benzyl)acetamidine (1, W1400) were designed as inhibitors of inducible nitric oxide synthase (iNOS). Six compounds were found to be selective for iNOS over endothelial nitric oxide synthase (eNOS), and among them, the most active and selective compound was the N-benzylacetamidine 2. A docking study was also performed to shed light on the effects of the structural modifications on the interaction of the designed inhibitors with the NOS.

Synthesis and Biological Evaluation of 2-Heteroarylthioalkanoic Acid Analogues of Clofibric Acid as Peroxisome Proliferator-Activated Receptor α Agonists

A series of 2-heteroarylthioalkanoic acids were synthesized through systematic structural modifications of clofibric acid and evaluated for human peroxisome proliferator-activated receptor alpha (PPARalpha) transactivation activity, with the aim of obtaining new hypolipidemic compounds. Some thiophene and benzothiazole derivatives showing a good activation of the receptor alpha were screened for activity against the PPARgamma isoform. The gene induction of selected compounds was also investigated in the human hepatoma cell line.

Asymmetric synthesis of (S)-ibuprofen by esterification with amides of (S)-lactic acid as chiral auxiliaries: experimental and theoretical results

A novel synthesis of chiral ibuprofen by a dynamic kinetic resolution process is described. The racemic ibuprofen was converted into the corresponding diastereomeric mixtures of esters with amides of (S)-lactic acid as chiral auxiliaries, using dicyclohexylcarbodiimide (DCC) and 4-dimethylaminopyridine (DMAP) as condensation agents. The reactions afforded predominantly one of the two diastereomers with good diastereomeric ratios. The reasons of the stereoselectivity were also investigated by molecular mechanic calculations, using MM2 force fields.

Blocking the Peroxisome Proliferator‐Activated Receptor (PPAR): An Overview

Peroxisome proliferator‐activated receptors (PPARs) have been studied extensively over the last few decades and have been assessed as molecular targets for the development of drugs against metabolic disorders. A rapid increase in understanding of the physiology and pharmacology of these receptors has occurred, together with the identification of novel chemical structures that are able to activate the various PPAR subtypes. More recent evidence suggests that moderate activation of these receptors could be favorable in pathological situations due to a decrease in the side effects brought about by PPAR agonists. PPAR partial agonists and antagonists are interesting tools that are currently used to better elucidate the biological processes modulated by this family of nuclear receptors. Herein we present an overview of the various molecular structures that are able to block each of the PPAR subtypes, with a focus on promising therapeutic applications.

Structural development studies of PPARs ligands based on tyrosine scaffold.

PPARs are nuclear receptors with a critical physiological role in lipid and glucose metabolism. As part of our effort to develop new and selective PPAR agonists containing stilbene and its bioisoster phenyldiazene, novel analogs were synthesized starting from tyrosine and evaluated as PPAR agonists. We tested the effects of phenyloxazole replacement of GW409544, a well-known PPARα/γ dual agonist, with stilbene or phenyldiazene moiety, spaced by an ether bridge to tyrosine portion. These structural modifications provided potent and selective PPARγ agonists. Molecular docking studies performed on these new compounds complemented the experimental results and allowed to gain some insights into the nature of binding of the ligands.

Discovery of gemfibrozil analogues that activate PPARα and enhance the expression of gene CPT1A involved in fatty acids catabolism.

A new series of gemfibrozil analogues conjugated with α-asarone, trans-stilbene, chalcone, and their bioisosteric modifications were synthesized and evaluated to develop PPARα agonists. In this attempt, we have removed the methyls on the phenyl ring of gemfibrozil and introduced the above scaffolds in para position synthesizing two series of derivatives, keeping the dimethylpentanoic skeleton of gemfibrozil unaltered or demethylated. Four compounds exhibited good activation of the PPARα receptor and were also screened for their activity on PPARα-regulated gene CPT1A.

Different binding and recognition modes of GL479, a dual agonist of Peroxisome Proliferator-Activated Receptor α/γ

Peroxisome Proliferator-Activated Receptors (PPARs) are ligand-dependent transcription factors that control various functions in human organism, including the control of glucose and lipid metabolism. PPARγ is a target of TZD agonists, clinically used to improve insulin sensitivity whereas fibrates, PPARα ligands, lower serum triglyceride levels. We report here the structural studies of GL479, a synthetic dual PPARα/γ agonist, designed by a combination of clofibric acid skeleton and a phenyldiazenyl moiety, as bioisosteric replacement of stilbene group, in complex with both PPARα and PPARγ receptors. GL479 was previously reported as a partial agonist of PPARγ and a full agonist of PPARα with high affinity for both PPARs. Our structural studies reveal different binding modes of GL479 to PPARα and PPARγ, which may explain the distinct activation behaviors observed for each receptor. In both cases the ligand interacts with a Tyr located at helix 12 (H12), resulting in the receptor active conformation. In the complex with PPARα, GL479 occupies the same region of the ligand-binding pocket (LBP) observed for other full agonists, whereas GL479 bound to PPARγ displays a new binding mode. Our results indicate a novel region of PPARs LBP that may be explored for the design of partial agonists as well dual PPARα/γ agonists that combine, simultaneously, the therapeutic effects of the treatment of insulin resistance and dyslipidemia.

Selective Inhibition of iNOS by Benzyl‐ and Dibenzyl Derivatives of N‐(3‐Aminobenzyl)acetamidine

Nitric oxide (NO), one of the smallest known bioactive products of mammalian cells, can be produced by almost all cells. In mammals, NO is synthesized by a family of three NO synthases (NOS): neuronal nNOS, inducible iNOS and endothelial eNOS, that are products of three genes: NOS1, NOS2, and NOS3, respectively. The three isoforms generate NO by the conversion of l-arginine to l-citrulline; they differ in both structure and function but share about 50 % sequence homology and are differentially regulated making the catalytic activity distinct for each isoform. nNOS and eNOS are constitutive and primarily expressed in neurons and endothelial cells, respectively. These isoforms are calcium/calmodulin dependent and generate low levels of NO for short periods of time in a pulsative manner. iNOS was first identified and characterized in cytokine-activated murine macrophages. This isoform is not dependent upon calcium/calmodulin for its enzymatic action and is expressed in a wide array of cells and tissues, for example, macrophages, hepatocytes, neutrophils, pulmonary epithelium, colonic epithelium, and vasculature. After induction, iNOS continuously produces NO until the enzyme is degraded. The overproduction of NO by iNOS may have detrimental consequences, and this activity seems to be involved in the pathophysiology of several human diseases, such as asthma, arthritis, multiple sclerosis, colitis, psoriasis, neurodegenerative diseases, tumor development, transplant rejection, and septic shock. In recent years, considerable effort has been directed toward the selective inhibition of iNOS as a strategy for the prevention of excessive NO production, while maintaining the basal formation of NO from constitutive NOS that is required for normal physiological function. The first approach to NOS inhibitors included analogues of the natural substrate l-arginine that act competitively at the substrate binding site; however, these compounds are not selective enough over the eNOS and nNOS isoforms, which limits their application in vivo. More recent studies have focused on the design and synthesis of non-amino acid analogues, such as amino heterocycles, amidines, guanidines, isoquinolinamines, and isothioureas. We previously reported the synthesis, biological evaluation, and docking studies of a series of N-substituted acetamidines, structurally related to the leading scaffold W1400 (1), a potent and selective iNOS inhibitor. Starting from docking results previously obtained, and with the aim of extending the study of possible ligand–enzyme interactions, we have now evaluated the effect of the introduction of several substituents in ortho, meta or para positions of the leading scaffolds 2 and 3, differing from 1 by the amino substitution at the 3-aminomethyl group with one or two benzylic groups.