Elsevier

Bioorganic Chemistry

Volume 91, October 2019, 103170
Bioorganic Chemistry

Bis-coumarins; non-cytotoxic selective urease inhibitors and antiglycation agents

https://doi.org/10.1016/j.bioorg.2019.103170Get rights and content

Highlights

  • Synthesis of forty four bis-coumarin derivatives.

  • Evaluation of synthetic compounds 144 for urease inhibitory and antiglycation activities.

  • Compound 17 was found to possess potent urease inhibitory activity.

  • Kinetic studies revealed the compound 17 as competitive inhibitor.

  • Several compounds showed good to moderate antiglycation potential.

Abstract

The current study is concerned with the identification of lead molecules based on the bis-coumarin scaffold having selective urease inhibitory and antiglycation activities. For that purpose, bis-coumarins (1-44) were synthesized and structurally characterized by different spectroscopic techniques. Eight derivatives 4, 8-10, 14, 17, 34, and 40 demonstrated urease inhibition in the range of IC50 = 4.4 ± 0.21–115.6 ± 2.13 μM, as compared to standard thiourea (IC50 = 21.3 ± 1.3 μM). Especially, compound 17 (IC50 = 4.4 ± 0.21 μM) was found to be five-fold more potent than the standard. Kinetic studies were also performed on compound 17 in order to identify the mechanism of inhibition. Kinetic studies revealed that compound 17 is a competitive inhibitor. Antiglycation activity was evaluated using glycation of bovine serum albumin by methylglyoxal in vitro. Compounds 2, 11-13, 16, 17, 1922, 35, 37, and 42 showed good to moderate antiglycation activities with IC50 values of 333.63–919.72 μM, as compared to the standard rutin (IC50 = 294.46 ± 1.5 μM). Results of both assays showed that the compounds with urease inhibitory activity did not show any antiglycation potential, and vice versa. Only compound 17 showed dual inhibition potential. All compounds were also evaluated for cytotoxicity. Compounds 17, 19, and 37 showed a weak toxicity towards 3 T3 mouse fibroblast cell line. All other compounds were found to be non-cytotoxic. Urease inhibition is an approach to treat infections caused by ureolytic bacteria whereas inhibition of glycation of proteins is a strategy to avoid late diabetic complications. Therefore, these compounds may serve as leads for further research.

Introduction

Bis-coumarins are biologically active pharmacophores, initially isolated from natural sources [1], [2]. Several biological activities are associated with bis-coumarins, such as α-glucosidase [3], urease [4], nucleotide pyrophosphatases-1 [5], and DNA polymerase β-lyase inhibitory activities [6]. Bis-coumarins are also reported to possess anticoagulant, and hemorrhagic properties [7]. However, there is still a need to explore this class for a wide spectrum of pharmacological activities.

Urease (amidohydrolase EC 3.5.1.5) is a metalloenzyme, contains nickel in its active site. It catalyzes the hydrolysis of urea into carbon dioxide and ammonia [8], [9]. This enzyme synthesizes by numerous plants, animals, bacteria, and other organisms [10]. Hyperactivity of urease is harmful to human and animal health, as well as for the agricultural sector. Urease is a key virulence in the pathogenesis of urolithiasis, urinary catheter encrustation, pyelonephritis, hepatic coma, and hepatic encephalopathy [11], [12]. It also participates in the pathologies caused by ureolytic bacteria Helicobacter pylori (HP). It facilitates bacteria to survive in stomach at acidic pH during initial colonization. Therefore, it plays an important role in the pathologies of ulcers (gastric and peptic), and cancer [13], [14], [15], [16]. In the agriculture sector, hyperactivity of urease leads to considerable economic and environmental damage by liberating aberrantly large quantities of ammonia into the atmosphere, during the process of urea fertilization [17]. Therefore, it is important to develop strategies based on urease inhibition to solve the problems caused by urease producing bacteria.

Glycation is a non-enzymatic reaction in which reducing sugars non-enzymatically bind with the amino terminal of proteins via a nucleophilic addition reaction, ultimately giving rise to advanced glycation end products (AGEs). Haemoglobin, serum albumin, collagen, elastin, and crystalline are common proteins that undergo glycation. Changes in their structures and functions lead to different abnormalities such as atherosclerosis, neuropathy, diabetic retinopathy, diabetic nephropathy, etc. This process is cumulatively called glycation stress [18], [19]. In this process, reactive intermediates such as methylglyoxal (MG) are more prone to bind with amino groups as compared to their carbohydrate precursors. Eighty percent (80%) of blood proteins is serum albumin, which is more likely to be glycated [20]. As a result of complex rearrangements, substitution, and addition reactions of glycated proteins, AGEs are produced in the body which change the functions of proteins, and accumulate with time in different tissues [21], [22], [23]. Many late diabetic complications, such as retinopathy, nephropathy, cataracts, atherosclerosis, and osteoporosis are due to the glycation of vital proteins, and accumulation of AGEs [24]. The inhibition of glycation process plays a pivotal role in the prevention of many late diabetic complications. Therefore, it is important to find inhibitors for glycation.

Bis-coumarins have not yet been reported for their antiglycation activity. Fig. 1 showed that chromone ring, a positional isomer of coumarin, is the main scaffold of rutin which encouraged us to evaluate the compounds 144 for their antiglycation activity. Furthermore, we have previously reported bis-coumarins for urease inhibitory activity [4]. New members of this series were thus evaluated to identify more potent urease inhibitors [Fig. 1]. In brief, forty-four derivatives were synthesized and evaluated for their urease inhibitory, and antiglycation activities. After knowing the selective potential of compounds, cytotoxicity was also checked. To the best of our knowledge, except compounds 6, 14, 16, 17, 19, 20, 2326, 28, and 3032 [25], [26], [27], [28], [29], the rest of the compounds were identified as new.

Section snippets

Chemistry

Bis-coumarin derivatives 144 were synthesized by reacting 6-fluoro-4-hydroxy, 4-hydroxy, and 6-chloro-4-hydroxy coumarins with a variety of benzaldehydes in the presence of tetraethylammonium bromide (TEAB) as a catalyst. Reactions were performed in distilled water (Scheme 1) and checked periodically by TLC analysis. Precipitates of products were obtained in good yields (Table 1). Compounds were structurally identified by various spectroscopic analyses such as 1H- and 13C NMR as well as FAB-,

Conclusion

Synthetic bis-coumarins 144 were evaluated for their urease inhibitory and antiglycation activities. Seven derivatives 4, 810, 14, 34, and 40 showed selective urease inhibition, whereas, twelve analogs 2, 1113, 16, 17, 1922, 35, 37, and 42 demonstrated antiglycation potential. Only compound 17 showed dual inhibition. All compounds were largely found to be non-cytotoxic. Newly identified compounds, based on bis-coumarin scaffold, may serve as leads for future research for more powerful,

Materials and methods

Thin layer chromatography (TLC) was performed on pre-coated silica gel aluminum plates (Kieselgel 60 F-254, 0.20 mm, Merck, Darmstadt, Germany). Chromatograms were visualized by using a handhold UV lamp at 254, and 365 nm or placing in iodine vapors. Fast atom bombardement mass spectra (FAB MS) were recorded on a Finnigan MAT-311A (Germany) (70 eV) spectrometers, electrospray ionization mass spectra (ESI-MS, HRESI-MS) were recorded on a QSTAR XL LCMS-MS, and ABSciex (Germany) (50 kV) mass

Acknowledgement

The authors are thankful to the Higher Education Commission (HEC), Pakistan, for providing financial support under “National Research Program for Universities”, for Project No. 20-1910. One of us (Arsalan Nizamani) also acknowledges Higher Education Commission, Pakistan, for financial support through “Indigenous 5000 Scholarship Programme Batch-VII”.

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