Solution-phase microwave assisted parallel synthesis, biological evaluation and in silico docking studies of N,N′-disubstituted thioureas derived from 3-chlorobenzoic acid

doi:10.1016/j.bmc.2016.07.042

Bioorganic & Medicinal Chemistry

Volume 24, Issue 18, 15 September 2016, Pages 4452-4463

https://doi.org/10.1016/j.bmc.2016.07.042 Get rights and content

Abstract

A facile and robust microwave-assisted solution phase parallel synthesis protocol was exercised for the development of a 38-member library of N,N′-disubstituted thiourea analogues (1–38) by using an identical set of conditions. The reaction time for synthesis of N,N′-disubstituted thiourea analogues was drastically reduced from a reported duration of 8–12 h for conventional methods to only 1.5–2.0 min. All the derivatives (1–38) were characterized by physico-analytical techniques such as elemental analysis in combination with FT-IR, ¹H, ¹³C NMR and by single crystal XRD analysis have also been performed. These compounds were screened for their in vitro urease inhibition activities. Majority of compounds exhibited potent urease inhibition activities, however, the most significant activity was found for 16, with an IC₅₀ value of 1.23 ± 0.1 μM. Furthermore, the synthesized compounds were screened for their cytotoxic potential against lungs cancer cell lines. Cell culture studies demonstrated significant toxicity of the compounds on the cell lines, and the levels of toxicity were altered in the presence of various side groups. The molecular docking studies of the most potent inhibitors were performed to identify the probable binding modes in the active site of the urease enzymes. These compounds have a great potential and significance for further investigations.

Graphical abstract

Introduction

Urease (urea amidohydrolase; E.C.3.5.1.5), a nickel-containing metalloenzyme with an ability to catalyze the hydrolysis of urea to ammonia and carbamates, is considered as an important virulence factor in the pathogenesis of several diseases.1, 2 It is predominantly found in numerous living organisms, such as bacteria, fungi, higher plants, and some invertebrates.3, 4 Urease is important for human and animal health due to its involvement in the development of several infections associated with stones and plays a vibrant role in pathogenesis of urolithiasis, pyelonephritis, and hepatic encephalopathy.⁴ In addition, high concentration of ammonia from the hydrolysis reaction as well as elevated pH level also imparts several negative effects in the fields of medicine and agriculture.5, 6, 7, 8 To counteract these negative effects, inhibition of urease is an attractive strategy and a diverse variety of urease inhibitors have been reported1, 9, 10, 11, 12, however, due to their toxicity or instability, the development of potent urease inhibitors with fewer toxic effects is highly needed.

Similarly, cancer still remains a potentially life-threatening disease and is the second cause of death in the US, with an expected 1,665,540 cancer cases in 2014. The high volume of data related to cancer deaths indicates that 90% of the patients die due to chronic tumor metastases.¹³ Cancer is chronic disease, initiated by complex processes, which are directly associated to a fundamental cycle of life, i.e., cell division and may be induced by exogenous agents and is characterized by uncontrolled cell proliferation leading to tumor formation.13, 14 Several external (chemicals, radiation, infectious microorganisms, and tobacco) and internal (hormones, mutations and immune conditions) factors contribute enormously to the eruption of cancers.14, 15 Despite the development of several anticancer drugs, the continued efforts to identify new anticancer agents with less side effects and toxicity is the subject of current medicinal chemistry research.16, 17

Aryl/aroyl substituted thioureas have found potential applications for the structural developments in heterocyclic chemistry and modifications with remarkable pharmacological and biological implications. In the past few decades, in vitro studies have shown that polyfunctional thioureas are potential herbicides,¹⁸ insecticides,¹⁹ plant-growth regulators²⁰ and antihypertensive agents,²¹ antitubercular, antimalarial, anticancer,²² antithyroid, antihelmintic and TRPV1 receptor antagonists.²³ Thioureas may be used as precursors to yield active compounds of pharmacological importance by treating with other intermediates bearing different functionalities. For example, thioureas condense with α-halocarbonyl compounds to produce 2-amino-1,3-thiazoles²⁴ and arylthioureas can be converted into benzothiazoles in the presence of bromine as an oxidizing agent.²⁵ The synthesis of iminothiazolines,²⁶ thiohydantoins,²⁷ 1,3,5-triazines²⁸ and 2-amino-oxazolidines²⁹ from thioureas has been well explored.

Mostly, N,N′-disubstituted thioureas are synthesized by treating primary and secondary amines with Na⁺/K⁺/NH₄⁺ thiocyanates,²¹ aroyl isothiocyanates with primary and secondary amines followed by acid hydrolysis³⁰ and isothiocyanates with ammonia or amines.³¹ The de-benzoylation of N-substituted and N,N′-disubstituted thioureas with hydrazine hydrate under solvent-free conditions yields mono- and N,N′-disubstituted thioureas³² and a synthesis of unsubstituted thioureas with primary alkyl amines at high temperature have also been reported.³³ In the recent decades, numerous new methodologies have been exercised for the design and synthesis of N,N′-substituted thioureas.³⁴ However, many of these methods are not very popular due to some disadvantages, specifically, long reaction time under high thermal conditions and the use of large quantity of solvents. The development of efficient, mild and environment friendly protocols are still need of the day. The microwave supported organic syntheses have received great attention in the recent years that greatly facilitated the organic chemists to increase the number and purity of the products. It has also inherent advantages of high chemical yield and shorter reaction time. Recently, solvent free microwave assisted synthesis of substituted thioureas have been reported.35, 36, 37 These solvent free syntheses have many objections regarding purity of the products due to the presence of inorganic byproducts, non-uniform heating and restricted molecular activities in the viscous phase. Keeping in view these issues and in perpetuation to our previous work on different types of thioureas, their coordination and medicinal chemistry,38, 39 we report here the microwave assisted solution-phase parallel synthesis of N,N′-disubstituted thioureas and their biological activities such as urease inhibition both in vitro & in virtual and anticancer activities because of their inherent drug like significance. We speculated that our designed thiourea compounds could effectively inhibit the urease due to structural similarity with the natural substrate of urease, i.e., urea and the diverse structural features introduced on both diversity points of thiourea would probably exert positive effects on activity through the binding of molecules to active site of the enzyme. The results of this study are presented in the subsequent discussion.

Section snippets

Materials and methods

All experiments were carried out under the specified conditions of temperature and normal pressure. Solvents were purified and distilled from the drying agents, stored over molecular sieves 4 Å and degassed before use. Microwave syntheses were carried out using a CEM MARS 6 microwave synthesizer with low absorption power settings. The experiments were carried out in standard Pyrex capable glass vials (20 mL).

NMR spectra were recorded on a Bruker ARX, 300 MHz spectrometer. ¹H NMR (300.13 MHz):

Chemistry

Solution-phase microwave assisted parallel synthesis of N,N′-disubstituted thioureas was performed using CEM MARS 6 microwave reactor, specifically for organic synthesis. A small library of thirty eight members (1–38) was successfully developed and fully characterized by modern analytical techniques. The purity level of the compounds was established by TLC with Merck Kieselgel GF 254 plates and elemental analysis. Their structures were investigated by FT-IR, ¹H- and ¹³C-NMR (Bruker ARX, 300 MHz

Conclusion

A series of N,N′-disubsituted thiourea analogues were prepared using facile microwave-assisted solution phase parallel synthesis. The synthesized compounds were evaluated for in vitro urease inhibitory activity. Most of the compounds exhibited excellent urease inhibition, among which, compound 16 shows potent urease inhibitory activity with an IC₅₀ value 1.23 ± 0.1 μM. All the synthesized derivatives were screened for their anticancer activities. Compound 12 was the potent compound against H157

Acknowledgements

The M. Khawar Rauf is thankful to the Quaid-i-Azam University, Islamabad, Pakistan for the grant of funds for Post-doctoral Fellowship. Jamshed Iqbal is thankful to the Organization for the Prohibition of Chemical Weapons (OPCW), The Hague, The Netherlands and the Higher Education Commission of Pakistan for the financial support through Project No. 20-3733/NRPU/R&D/14/520.

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Citation Excerpt :
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Solution-phase microwave assisted parallel synthesis, biological evaluation and in silico docking studies of N,N′-disubstituted thioureas derived from 3-chlorobenzoic acid

Abstract

Graphical abstract

Introduction

Section snippets

Materials and methods

Chemistry

Conclusion

Acknowledgements

Bioorg. Med. Chem.

Eur. J. Med. Chem.

Eur. J. Med. Chem.

J. Org. Chem.

J. Chem. Soc., Perkin Trans. 1

Green Chem.

Synthesis

Org. Synth. Coll. III

Chinese J. Chem.

Eur. J. Med. Chem.

Anal. Chem.

Arch. Pharm. Chem. Life Sci.

J. Am. Chem. Soc.

J. Enzym. Inhib. Med. Chem.

J. Enzym. Inhib. Med. Chem.

Plant Physiol.

Mol. Microbiol.

Nat. Rev. Mol. Cell Biol.

Biol. Fertil. Soils

Indian J. Biotechnol.

Expert. Opin. Ther. Pat.

Curr. Med. Chem.

J. Clin. Pathol.

Chem. Soc. Rev.

Res. Chem. Intermed.

Huaxueshiji

J. Indian Chem. Soc.