Andrea Calcaterra

The market of chiral drugs: Chiral switches versus de novo enantiomerically pure compounds

Graphical abstract Figure. No Caption available. HighlightsAn overview of the current market of chiral drugs is proposed.The main techniques to assess the absolute configuration have been surveyed.A focus on the chiral drugs approved by the FDA in 2015 is given.All the chiral drugs approved in 2015 were single enantiomers, except for lesinurad. ABSTRACT This review article is aimed at providing an overview of the current market of chiral drugs by exploring which is the nowadays tendency, for the pharmaceutical industry, either to exploit the chiral switching practice from already marketed racemates or to develop de novo enantiomerically pure compounds. A concise illustration of the main techniques developed to assess the absolute configuration (AC) and enantiomeric purity of chiral drugs has been given, where greater emphasis was placed on the contribution of enantioselective chromatography (HPLC, SFC and UHPC). Afterwards, we focused our study on the cohort of 45 new drugs that have been approved by the US Food and Drug Administration (FDA) in 2015. We extracted the chemical structure of the new drugs from the FDA approval chemistry reviews available on the database of the agency’s Center for Drug Evaluation and Research (CDER), and we selected a subgroup (i.e., 44% of the cohort) of small‐molecule active pharmaceutical ingredients (APIs) containing one or more chirality centers. On the basis of the FDA dossiers examined, it emerged that all the chiral drugs approved by the FDA in 2015 are enantiomerically pure compounds with a well‐defined AC, with the exception of one, namely lesinurad, which has been licensed as the racemate of two enantiomeric atropoisomers, arising because of the hindered rotation around the single C–N bond in the naphthalene ring. Finally, none of the previously developed racemates has been switched to the single‐enantiomer version in 2015.

Kuwanon-L as a New Allosteric HIV-1 Integrase Inhibitor: Molecular Modeling and Biological Evaluation

HIV‐1 integrase (IN) active site inhibitors are the latest class of drugs approved for HIV treatment. The selection of IN strand‐transfer drug‐resistant HIV strains in patients supports the development of new agents that are active as allosteric IN inhibitors. Here, a docking‐based virtual screening has been applied to a small library of natural ligands to identify new allosteric IN inhibitors that target the sucrose binding pocket. From theoretical studies, kuwanon‐L emerged as the most promising binder and was thus selected for biological studies. Biochemical studies showed that kuwanon‐L is able to inhibit the HIV‐1 IN catalytic activity in the absence and in the presence of LEDGF/p75 protein, the IN dimerization, and the IN/LEDGF binding. Kuwanon‐L also inhibited HIV‐1 replication in cell cultures. Overall, docking and biochemical results suggest that kuwanon‐L binds to an allosteric binding pocket and can be considered an attractive lead for the development of new allosteric IN antiviral agents.

Antioxidant Properties of Aminoethylcysteine Ketimine Decarboxylated Dimer: A Review

Aminoethylcysteine ketimine decarboxylated dimer is a natural sulfur-containing compound detected in human plasma and urine, in mammalian brain and in many common edible vegetables. Over the past decade many studies have been undertaken to identify its metabolic role. Attention has been focused on its antioxidant properties and on its reactivity against oxygen and nitrogen reactive species. These properties have been studied in different model systems starting from plasma lipoproteins to specific cellular lines. All these studies report that aminoethylcysteine ketimine decarboxylated dimer is able to interact both with reactive oxygen and nitrogen species (hydrogen peroxide, superoxide anion, hydroxyl radical, peroxynitrite and its derivatives). Its antioxidant activity is similar to that of Vitamin E while higher than other hydrophilic antioxidants, such as trolox and N-acetylcysteine.

One Hundred Faces of Cyclopamine.

The natural steroidal alkaloid cyclopamine has been identified as the first inhibitor of the Hedgehog (Hh) signaling pathway, which is implicated in embryonic development and tumorigenesis, as well as is hyperactivated in cancer stem cells (CSCs). The list of Hh-dependent tumors is steadily growing, and it has been estimated that about 25% of all cancer deaths show signs of aberrant Hh pathway activation. Notably, cyclopamine has been found to exert anticancer activity against several types of human cancer and to inhibit CSCs proliferation, thus highlighting the druggability of the Hh pathway and paving new opportunities in anticancer drug discovery. The aim of the present work is to review the main synthetic strategies to cyclopamine and its derivatives, with particular emphasis on the challenging chemical modifications aimed at improving the biological activity of the molecule.

Natural Product Kuwanon-L Inhibits HIV-1 Replication through Multiple Target Binding

In recent years many advances have been made in the fight against HIV‐1 infection. However, the lack of a vaccine, together with the increasing resistance to the highly active anti‐retroviral therapy (HAART), make HIV‐1 infection still a serious global emergency. Thus, new compounds with original modes of action are continuously required, and natural products have ever been a very interesting class of pharmacologically active molecules. Some of them have been used since ancient times against viral infections. Here we present a work in which we suggest that kuwanon‐L, a natural product active as an HIV‐1 integrase (IN) inhibitor, might exert its overall antiviral activity through binding to multiple viral targets. Specific enzymatic tests, together with a time‐of‐addition (TOA) experiment, support our hypothesis of binding both to IN and to reverse transcriptase (RT). Overall, this compound can be considered an attractive lead for the development of new classes of antiviral agents able to overcome the problem of resistance, due to its ability to exert its action by binding simultaneously to multiple viral targets.

Chemical, computational and functional insights into the chemical stability of the Hedgehog pathway inhibitor GANT61

Abstract This work aims at elucidating the mechanism and kinetics of hydrolysis of GANT61, the first and most-widely used inhibitor of the Hedgehog (Hh) signalling pathway that targets Glioma-associated oncogene homologue (Gli) proteins, and at confirming the chemical nature of its bioactive form. GANT61 is poorly stable under physiological conditions and rapidly hydrolyses into an aldehyde species (GANT61-A), which is devoid of the biological activity against Hh signalling, and a diamine derivative (GANT61-D), which has shown inhibition of Gli-mediated transcription. Here, we combined chemical synthesis, NMR spectroscopy, analytical studies, molecular modelling and functional cell assays to characterise the GANT61 hydrolysis pathway. Our results show that GANT61-D is the bioactive form of GANT61 in NIH3T3 Shh-Light II cells and SuFu−/− mouse embryonic fibroblasts, and clarify the structural requirements for GANT61-D binding to Gli1. This study paves the way to the design of GANT61 derivatives with improved potency and chemical stability. Graphical Abstract

Ultraviolet and infrared spectroscopy of neutral and ionic non-covalent diastereomeric complexes in the gas phase

Non-covalent intermolecular interactions responsible for chiral discrimination have been investigated in the gas phase both in neutral and ionic complexes. Mass-selected resonant two-photon ionization (R2PI) as well as infrared depleted R2PI (IR–R2PI) techniques have been applied to investigate the role of fluorine substitution in the chiral recognition process between (R)-1-phenyl 1-ethanol (ER), (S)-1-(4-fluorophenyl)-ethanol (pFES), (R)-1-phenyl-2,2,2-trifluoroethanol (FER) and the two enantiomers of butan-2-ol (BR/S), generated in a supersonic molecular beam. The results have been interpreted with the aid of theoretical predictions at the D-B3LYP/6-31G** level of theory. The diastereomeric complexes of ER and pFES with R- and S-butan-2-ol are structurally similar, and dispersive interactions between the aliphatic chain of the alcohol and the π system of the chromophore as well repulsive interactions are mainly responsible for chiral recognition. FER forms, predominantly with S-butan-2-ol, also stable complexes in which the alcohol is oriented away from the aromatic ring. The ionic complexes between pure enantiomers of the bis (diamido)-bridged basket resorcin[4]arene and cytarabine are generated in the gas phase by electrospray ionization and investigated by IRMPD. The proton-bound diastereomers show clearly different IRMPD spectra which, in light of ONIOM (B3LYP/6-31(d):UFF) calculations, are consistent with the occurrence of several isomeric structures, in which the N(3)-protonated guest is either accommodated inside the host cavity or outside it. The spectral differences are attributed to the effects of the intramolecular hydrogen bonding between the C(2′)_OH group and the aglycone oxygen atom of the nucleosidic guest upon repulsive interactions between the same oxygen atom and the aromatic rings of the host.

Covalently assembled resorcin[4]arenes and molecular tweezers: a chiral recognition rationale by NMR

Abstract Chiral diamides and tetramidic resorcin[4]arenes deriving from (R,R)-1,2-diaminocyclohexane and (S,S)-1,2-diphenylethylendiamine, and a valine containing resorcin[4]arene have been compared by NMR in the enantiodiscrimination of mandelic acid. The relevance of cooperation between side arms and external surface of resorcin[4]arene core has been ascertained.

Metal Free Graphene Oxide (GO) Nanosheets and Pristine-Single Wall Carbon Nanotubes (p-SWCNTs) Biocompatibility Investigation: A Comparative Study in Different Human Cell Lines

The in vitro biocompatibility of Graphene Oxide (GO) nanosheets, which were obtained by the electrochemical exfoliation of graphite electrodes in an electrolytic bath containing salts, was compared with the pristine Single Wall Carbon Nanotubes (p-SWCNTs) under the same experimental conditions in different human cell lines. The cells were treated with different concentrations of GO and SWCNTs for up to 48 h. GO did not induce any significant morphological or functional modifications (demonstrating a high biocompatibility), while SWNCTs were toxic at any concentration used after a few hours of treatment. The cell viability or cytotoxicity were detected by the trypan blue assay and the lactate dehydrogenase LDH quantitative enzymatic test. The Confocal Laser Scanning Microscopy (CLSM) and transmission electron microscopy (TEM) analysis demonstrated the uptake and internalization of GO sheets into cells, which was localized mainly in the cytoplasm. Different results were observed in the same cell lines treated with p-SWCNTs. TEM and CLSM (Confocal Laser Scanning Microscopy) showed that the p-SWCNTs induced vacuolization in the cytoplasm, disruption of cellular architecture and damage to the nuclei. The most important result of this study is our finding of a higher GO biocompatibility compared to the p-SWCNTs in the same cell lines. This means that GO nanosheets, which are obtained by the electrochemical exfoliation of a graphite-based electrode (carried out in saline solutions or other physiological working media) could represent an eligible nanocarrier for drug delivery, gene transfection and molecular cell imaging tests.