Synthesis of novel 2-pyrrolidinone and pyrrolidine derivatives and study of their inhibitory activity against autotaxin enzyme
Graphical abstract
General structure of potent ATX inhibitors.
Introduction
Autotaxin (ATX, also known as ENPP2) is an enzyme originally isolated in 1992 as an autocrine motility factor from A2058 melanoma cells and is characterized as a 125 kDa glycoprotein1. It belongs to a seven-membered family of ectonucleotide pyrophosphatases/phosphodiesterases (ENPPs), which are characterized by their ability to catalyze the hydrolysis of pyrophosphate or phosphodiester bonds in nucleotides.2 ATX is unique among the ENPPs since it acts as a lysophospholipase D (lysoPLD), catalyzing the hydrolysis of lysophosphatidylcholine (LPC) into the signaling lysophosphatidic acid (LPA) and choline.3, 4 The bioactive lipid mediator LPA binds to specific G-protein-coupled receptors and activates the migration, proliferation and survival of various cell types.5, 6 ATX is produced in various tissues and is essential for vascular development, but it has also been involved in a variety of chronic inflammatory conditions, such as arthritis and cancer, as summarized in a number of review articles.7, 8, 9, 10, 11, 12 ATX consists of two N-terminal somatomedin B-like domains (SMB1 and SMB2), a central catalytic phosphodiesterase (PDE) domain, and a C-terminal nuclease-like domain (NUC). A threonine (T210) residue in the active site located in the PDE domain, along with two zinc ions, are responsible for its hydrolytic catalytic activity.13 The crystal structure of mouse ATX was presented in 2011,14 while in the same year the structural basis of substrate discrimination and integrin binding by ATX was reported.15 Several synthetic ATX inhibitors have been developed both in academia and pharmaceutical industry, the majority of which are derivatives of various heterocycles and have been summarized in a number of review articles.16, 17, 18, 19 Recently, a comprehensive overview of the most important series of ATX inhibitors appeared in the literature,20 in which the structure activity relationship and the mode of binding studies was carried out for the identification of advanced leads. Among the most active ATX inhibitors, we refer to the boronic acid derivatives and especially the most representative member (HA155),21, 22, 23 piperidine and piperazine derivatives,24, 25, 26, 27 2-oxo-pyrrolidine derivatives28 as well as hydroxamic acid derivatives.29 Lastly, it was reported that the ATX inhibitor (GLPG1690) was well tolerated in the phase I clinical trials and the results support its continued clinical development as a novel treatment for idiopathic pulmonary fibrosis (IPF).30
The aim of our work was to develop novel ATX inhibitors, optically active derivatives of 2-pyrrolidinone and pyrrolidine heterocycles, taking into consideration the generally accepted standards that should be fulfilled for potentially pharmacologically interesting compounds.31, 32, 33 The 2-pyrrolidinone template considered as an essential pharmacophore group is present in known drugs for patients with seizures, Alzheimer’s, senile dementia and other neurological problems (piracetam), 34 for patients with respiratory failure (doxapram) 35 and other conditions. Moreover, 2-pyrrolidinones incorporated in more complicated chemical structures have shown significant pharmacological properties, including those associated with the central nervous system.36 In recent years, we have designed and synthesized optically active 2-pyrrolidinones, based on natural S-pyroglutamic acid, some of which exhibited antihypertensive and anti-inflammatory activity. 37, 38, 39, 40 S-pyroglutamic acid is considered a unique chiral synthon and its asymmetric use is based on its two differentiated carbonyls, the properties of which allow an extended derivatization on the 5-membered ring of the starting compound and lead to a plethora of natural products, e. g. domoic acid,41 an inhibitor of angiotensin converting enzyme (ACE) for the treatment of hypertension,42 as well as to chemical auxiliaries in asymmetric synthesis.43 The properties and applications of pyroglutamic acid as a versatile building block in asymmetric synthesis have been extensively reviewed in the literature.44, 45, 46
Section snippets
Chemistry
In this paper we present the synthesis of twenty nine, optically active compounds derivatives of 2-pyrrolidinone, starting from the naturally derived S pyroglutamic acid (2-oxotetrahydro pyrrol-5S-carboxylic acid) or its enantiomer (Table 1), as well as the synthesis of six optically active compounds derivatives of pyrrolidine, starting from the natural amino acid S proline or its enantiomer (Table 2). In these derivatives, the 2-pyrrolidinone heterocycle ring of the (S/R)-pyroglutamic acid or
Conclusions
In this study we describe the synthesis of a new class of optically active compounds that possess a 2-pyrrolidinone and pyrrolidine template and assess their in vitro inhibitory activity against ATX. Among the 2-pyrrolidinone derivatives, three compounds bearing the acidic 4,4,5,5 tetramethyl-1,2,3-dioxoborolane moiety, namely 3k (IC50 0.05 μΜ), 3l (IC50 0.12 μΜ), 3m (IC50 0.18 μΜ) and especially the boronic acid derivative 21(IC50 0.035 μΜ), presented inhibitory potency for ATX at the
Instruments and materials
All chemicals and solvents were reagent grade and used without purification. Dry THF and extra dry DMF (99.8%) over molecular sieves were purchased from Acros. Chromatographic purification of products was accomplished using Merck Silica Gel 60 (70–230 or 230–400 mesh). Thin layer chromatography (TLC) was performed on Silica Gel 60 F254 aluminum plates. TLC spots were visualized with UV light or phosphomolybdic acid in EtOH. Melting points were determined on a Büchi 530 apparatus and are
Acknowledgements
Τhe research work was supported by the Hellenic Foundation for Research and Innovation (HFRI) and the General Secretariat for Research and Technology (GSRT), under the HFRI PhD Fellowship grant (GA. no. 2313).
Financial support from the Special Research Account of the University of Athens is highly appreciated.
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