Accelerating lead development by microwave-enhanced medicinal chemistry

Optimizing the Synthetic Route of Chromone-2-carboxylic Acids: A Step forward to Speed-Up the Discovery of Chromone-Based Multitarget-Directed Ligands

6-Bromochromone-2-carboxylic acid (3) was synthesized by a microwave-assisted process. The optimization of the reaction was performed varying parameters, such as type of base/number of reagent equivalents, solvent, temperature and reaction time. The yield of the reaction was improved to 87%. The new synthetic route is versatile as several chromone-2-carboxylic acids (compounds 4B-10B) were obtained with good yields (54-93%). Only in the case of the nitro substituent (compound 11B), an ester was obtained instead of the desired carboxylic acid. Following this synthetic route chromone carboxylic acids can be attained with a high degree of purity, without the need of the tedious and expensive purification processes through column chromatography. The reaction is safe, cost-effective, fast and robust, and can be used in the development of concise and diversity-oriented libraries based on chromone scaffold. The overall study can be looked as a step forward to speed-up the discovery of chromone-based multitarget-directed ligands.

Microwave-assisted cyclizations promoted by polyphosphoric acid esters: a general method for 1-aryl-2-iminoazacycloalkanes

The first general procedure for the synthesis of 5 to 7-membered 1-aryl-2-iminoazacycloalkanes is presented, by microwave-assisted ring closure of ω-arylaminonitriles promoted by polyphosphoric acid (PPA) esters. 1-Aryl-2-iminopyrrolidines were easily prepared from the acyclic precursors employing a chloroformic solution of ethyl polyphosphate (PPE). The use of trimethylsilyl polyphosphate (PPSE) in solvent-free conditions allowed for the synthesis of 1-aryl-2-iminopiperidines and hitherto unreported 1-aryl-2-iminoazepanes. The cyclization reaction involves good to high yields and short reaction times, and represents a novel application of PPA esters in heterocyclic synthesis.

Novel microwave-assisted synthesis of the immunomodulator organotellurium compound ammonium trichloro(dioxoethylene-O,O')tellurate (AS101)

Ammonium trichloro[1,2-ethanediolato-O,O′]-tellurate (AS101) is the most important synthetic Te compound from the standpoint of its biological activity. It is a potent immunomodulator with a variety of potential therapeutic applications and antitumoral action in several preclinical and clinical studies. An experimental design has been used to develop and optimize a novel microwave-assisted synthesis (MAOS) of the AS101. In comparison to the results observed in the literature, refluxing Te(IV) chloride and ethylene glycol in acetonitrile (Method A), or by refluxing Te(IV) chloride and ammonium chloride in ethylene glycol (Method B), it was found that the developed methods in the present work are an effective alternative, because although performance slightly decreases compared to conventional procedures (75% vs. 79% by Method A, and 45% vs. 51% by Method B), reaction times decreased from 4 h to 30 min and from 4 h to 10 min, by Methods A and B respectively. MAOS is proving to be of value in the rapid synthesis of compounds with new and improved biological activities, specially based on the benefit of its shorter reaction times.

A facile and efficient synthesis of diaryl amines or ethers under microwave irradiation at presence of KF/Al2O3 without solvent and their anti-fungal biological activities against six phytopathogens

A series of diaryl amines, ethers and thioethers were synthesized under microwave irradiation efficiently at presence of KF/Al2O3 in 83%-96% yields without any solvent. The salient characters of this method lie in short reaction time, high yields, general applicability to substrates and simple workup procedure. At the same time, their antifungal biological activities against six phytopathogen were evaluated. Most of the compounds (3b, 3c, 3g-o) are more potent than thiophannate-methyl against to Magnaporthe oryzae. This implies that diaryl amine or ether moiety may be helpful in finding a fungicide against Magnaporthe oryzae.

High regioselective ultrasonic-assisted synthesis of 2,7-diaryl-4,7-dihydropyrazolo[1,5-a]pyrimidine-5-carboxylic acids

New and high regioselective method of the synthesis of 2,7-diaryl-4,7-dihydropyrazolo[1,5-a]pyrimidine-5-carboxylic acids by reaction of 3-aryl-5-aminopyrazoles with arylidenpyruvic acid at room temperature under ultrasonication was developed and discussed.

MAOS and medicinal chemistry: some important examples from the last years

This review aims to highlight microwave-assisted organic synthesis as applied to medicinal chemistry in the last years, showing some reactions performed under microwave irradiation for the synthesis of distinct structurally molecules of biological interest, divided into the following groups: antineoplastics, anti-inflammatory, antimicrobial agents, antivirals, agents for the treatment of neglected diseases and central nervous system-acting prototypes.

Microwave-assisted syntheses of nucleosides and their precursors

In recent decades, nucleosides analogs have been the cornerstone in the treatment of various diseases, such as AIDS, herpes and hepatitis. More than 40 modified nucleosides are officially approved by the US FDA and represent the major compound class for inhibition of viral replication. By comparison with traditional conditions, microwave irradiation offers a powerful tool that can increase yields and decrease reaction time, with simple manipulation and an environmentally friendly way. Here, we report the latest progress in nucleoside synthesis using microwave irradiation.

(3-Cyano-5-fluorophenyl)biaryl negative allosteric modulators of mGlu(5): Discovery of a new tool compound with activity in the OSS mouse model of addiction

Glutamate is the major excitatory transmitter in the mammalian CNS, exerting its effects through both ionotropic and metabotropic glutamate receptors. The metabotropic glutamate receptors (mGlus) belong to family C of the G-protein-coupled receptors (GPCRs). The eight mGlus identified to date are classified into three groups based on their structure, preferred signal transduction mechanisms, and pharmacology (Group I: mGlu(1) and mGlu(5); Group II: mGlu(2) and mGlu(3); Group III: mGlu(4), mGlu(6), mGlu(7), and mGlu(8)). Non-competitive antagonists, also known as negative allosteric modulators (NAMs), of mGlu(5) offer potential therapeutic applications in diseases such as pain, anxiety, gastroesophageal reflux disease (GERD), Parkinson's disease (PD), fragile X syndrome, and addiction. The development of SAR in a (3-cyano-5-fluorophenyl)biaryl series using our functional cell-based assay is described in this communication. Further characterization of a selected compound, 3-fluoro-5-(2-methylbenzo[d]thiazol-5-yl)benzonitrile, in additional cell based assays as well as in vitro assays designed to measure its metabolic stability and protein binding indicated its potential utility as an in vivo tool. Subsequent evaluation of the same compound in a pharmacokinetic study using intraperitoneal dosing in mice showed good exposure in both plasma and brain samples. The compound was efficacious in a mouse marble burying model of anxiety, an assay known to be sensitive to mGlu(5) antagonists. A new operant model of addiction termed operant sensation seeking (OSS) was chosen as a second behavioral assay. The compound also proved efficacious in the OSS model and constitutes the first reported example of efficacy with a small molecule mGlu(5) NAM in this novel assay.

Recent advances in the design and development of novel negative allosteric modulators of mGlu(5)

Negative allosteric modulators (NAMs) of metabotropic glutamate receptor subtype 5 (mGlu(5)) have remained attractive to researchers as potential therapies for a number of central nervous system related diseases, including anxiety, pain, gastroesophageal reflux disease (GERD), addiction, Parkinson's disease (PD), and fragile X syndrome (FXS). In addition to the many publications with supportive preclinical data with key tool molecules, recent positive reports from the clinic have bolstered the confidence in this approach. During the two year time span from 2009 through 2010, a number of new mGlu(5) NAM chemotypes have been disclosed and discussed in the primary and patent literature. A summary of several efforts representing many diverse chemotypes are presented here, along with a discussion of representative structure activity relationships (SAR) and synthetic approaches to the templates where possible.

Synthesis of a drug-like focused library of trisubstituted pyrrolidines using integrated flow chemistry and batch methods

A combination of flow and batch chemistries has been successfully applied to the assembly of a series of trisubstituted drug-like pyrrolidines. This study demonstrates the efficient preparation of a focused library of these pharmaceutically important structures using microreactor technologies, as well as classical parallel synthesis techniques, and thus exemplifies the impact of integrating innovative enabling tools within the drug discovery process.

Microwave assisted synthesis of some new fused 1,2,4-triazines bearing thiophene moieties with expected pharmacological activity

Rapid and efficient solvent-free synthesis of 4-amino-3-mercapto-6-[2-(2-thienyl)vinyl]-1,2,4-triazin-5(4H)-one 1 under microwave irradiation is described. Some new fused heterobicyclic nitrogen systems such as 1,2,4-triazino[3,4-b][1,3,4]thiadiazinones, 1,3,4-thiadiazolo[2,3-c][1,2,4]triazinone and pyrazolo[5,1-c]-[1,2,4]triazine-7-carbonitrile, have been synthesized by treatment of 1 with bifunctional oxygen and halogen compounds, CS₂/KOH and malononitrile via heterocyclization reactions, in addition to some uncondensed triazines. Structures of the products have been deduced from their elemental analysis and spectral data (IR, ¹H-NMR, ¹³C-NMR). Select new synthesized compounds were screened as anticancer agents, with some showing activity as cytotoxic agents against different cancer cell lines.

The flow synthesis of heterocycles for natural product and medicinal chemistry applications

This article represents an overview of recent research from the Innovative Technology Centre in the field of flow chemistry which was presented at the FROST2 meeting in Budapest in October 2009. After a short introduction of this rapidly expanding field, we discuss some of our results with a main focus on the synthesis of heterocyclic compounds which we use in various natural product and medicinal chemistry programmes.

A short and facile synthesis of 2-(1Z)-(3-hydroxy-3,7-dimethylocta-1,6-dienyl)-1,4-benzenediol and 1-(3'-methoxypropanoyl)-2,4,5-trimethoxybenzene isolated from Cordia alliodora

A novel synthesis of 2-(1Z)-(3-hydroxy-3,7-dimethylocta-1,6-dienyl)-1,4-benzenediol and 1-(3'-methoxypropanoyl)-2,4,5-trimethoxybenzene has been carried out by making use of an easily available starting material, acceleration by MW irradiation and the use of water as a green solvent in the key steps.

Discovery and SAR of 6-substituted-4-anilinoquinazolines as non-competitive antagonists of mGlu5

A high-throughput cell-based screen identified a series of 6-substituted-4-anilinoquinazolines as non-competitive antagonists of metabotropic glutamate receptor 5 (mGlu(5)). This Letter describes the SAR of this series and the profile of selected compounds in selectivity and radioligand binding assays.

Synthesis of gamma-nitro aliphatic methyl esters via Michael additions promoted by microwave irradiation

A simple and efficient protocol has been developed for the direct synthesis of γ-nitrobutyric acid methyl esters under microwave irradiation. This methodology reduces reaction times from days to minutes, compared to conventional conditions. Additionally, these conditions increased yields and provided cleaner reactions.

On the energy efficiency of microwave-assisted organic reactions

The energy consumed for four different organic transformations carried out under microwave and conventional heating under otherwise identical reaction conditions was measured with the aid of a Wattmeter. In the case of open-vessel reflux processing, microwave dielectric heating required significantly more energy than conventional techniques using oil baths or heating mantles. This is a consequence of the comparably low energy efficiency of the magnetron in converting electrical to microwave energy. Significant savings in energy were experienced by taking advantage of sealed-vessel microwave processing at high temperatures. When comparing a conventionally heated reflux experiment with a microwave-heated experiment using a superheated solvent in a sealed vessel, reaction times were reduced significantly from hours to minutes. The energy savings in these instances are, however, largely connected to the reduced reaction time and are not an inherent feature of microwave heating.

Microwave-assisted, one-pot syntheses and fungicidal activity of polyfluorinated 2-benzylthiobenzothiazoles

Polyfluorinated 2-benzylthiobenzothiazoles 3a-l are prepared via a microwave-assisted, one-pot procedure. The advantages, such as good to excellent yields, shorter reaction time (14-21min), readily available starting material, and simple purification procedure, distinguish the present protocol from other existing methods used for the synthesis of 2-benzylthiobenzothiazoles. Bioassay indicated that most of the compounds showed significant fungicidal activity against Rhizoctonia solani, Botrytis cinereapers, and Dothiorella gregaria at a dosage of 50microg/mL. Interestingly, compared to the control of commercial fungicide, triadimefon, compound 3c exhibited much higher activities against R. solani, B. cinereapers, and D. gregaria, which showed that the polyfluorinated 2-benzylthiobenzothiazoles can be used as lead compound for developing novel fungicides.

Novel and Expeditious Microwave-Assisted Three-Component Reactions for the Synthesis of Spiroimidazolin-4-ones

Highly efficient methods for the syntheses of spiroimidazolinones via microwave-assisted three-component one-pot sequential reactions or one-pot domino reactions are described. The efficiency and utility of the methods have been demonstrated by quickly accessing the antihypertensive drug irbesartan (2).