Research paper
Antiproliferative activity and mode of action analysis of novel amino and amido substituted phenantrene and naphtho[2,1-b]thiophene derivatives

https://doi.org/10.1016/j.ejmech.2019.111833Get rights and content

Highlights

  • Substituted phenantrene and naphtho[2,1-b]thiophene derivatives.

  • antiproliferative activity on a panel of human cancer cell lines.

  • Cyano derivatives with a pronounced and selective activity against HeLa and HepG2 cells.

  • Mode of biological action analysis for the most active compounds performed in silico and in vitro.

  • Western blot analysis of HIF-1-α relative expression for most active compounds.

Abstract

Herein we present and describe the design and synthesis of novel phenantrene derivatives substituted with either amino or amido side chains and their biological activity. Antiproliferative activities were assessed in vitro on a panel of human cancer cell lines. Tested compounds showed moderate activity against cancer cells in comparison with 5-fluorouracile. Among all tested compounds, some compounds substituted with cyano groups showed a pronounced and selective activity in the nanomolar range of inhibitory concentrations against HeLa and HepG2. The strongest selective activity against HeLa cells was observed for acrylonitriles 8 and 11 and their cyclic analogues 15 and 17 substituted with two cyano groups with a corresponding IC50 = 0.33, 0.21, 0.65 and 0.45 μM, respectively. Compounds 11 showed the most pronounced selectivity being almost non cytotoxic to normal fibroblasts. Additionally, mode of biological action analysis was performed in silico and in vitro by Western blot analysis of HIF-1-α relative expression for compounds 8 and 11.

Introduction

Natural products may serve as drugs or templates for design of novel molecules and thus, play a crucial role in the drug discovery and development process. This fact is again gaining interest among researchers in recent years. For example, phenanthrene is a polycyclic aromatic naturally occurring ring system of many biologically active compounds that occur in more than 10 plant families [1]. Hence, natural differently substituted phenantrene derivatives were isolated from Combretaceae, Orchidaceae, Dioscoreaceae and Betulaceae families possessing various biological activities including antitumor [[2], [3], [4]], antibacterial [5] or anti-inflammatory activities [6]. Most natural phenanthrenes occur in the monomeric form consisting of more than 200 compounds substituted mainly with hydroxy and methoxy groups placed at different positions on the tetracyclic skeleton. Pettit et al. [7] have isolated and structurally characterized a series of active phenanthrenes present in the African willow tree Combretum caffrum. Their antitumor activity was confirmed on murine P388 lymphocytic leukemia cell (Fig. 1, I). Furthermore, Lusianthridin (Fig. 1, II) and Denbinobin which were isolated from Dendrobium nobile were found to exert cytotoxic effects both in vitro and in vivo on several cancer cells [8]. Phenantrenes isolated from D. thyrsiflorum which has been used in Chinese ethnomedicine, also showed antitumor activity on several cancer cell [9]. Additionally, derivatives isolated from Domohinea perrieri displayed significant activity towards cancer cells with some cell-type selectivity (Fig. 1, III). Obtained results revealed that unsubstituted methyl group placed at the C-7 position is very important for the antitumor activity [10].

Phenantrene derivatives could be usually prepared by oxidative coupling of the aromatic rings of stilbene precursors. Besides, due to the high biologically potential of substituted phenantrene derivatives and the fact that the synthesis of phenanthrenes is of highly importance in medicinal chemistry, several synthetic methods were published for the preparation of suchlike compounds. The synthetic strategies for their preparation thus include benzyne-alkyne-benzyne insertion [11], intramolecular cyclizations [12], [4 + 2] benzannulation reactions [13,14] or Pd catalyzed insertion of alkynes into cyclic diaryliodoniums [15].

It is well known that heterocyclic derivatives, both those of natural occurrence and widely distributed in nature or those of synthetic origin, are essential for many life processes and have an important role in medicinal chemistry due to the large variety of their possible chemical, pharmacological and biological properties [16,17]. A large number of biologically important compounds belong to a major class of heterocycles containing sulphur. For example, thiophenes and its fused derivatives as benzothiophenes, naphthothiophenes ot thienothiophenes have been classified as highly-privileged structures and valuable building blocks in organic and medicinal chemistry [18,19]. Thiophene nuclei could be found in the structure of numerous medicinal agents including Raloxifene as selective estrogen receptor modulator or Zileuton for asthma treatment. Naphthothiophene derivatives display a wide range of biological activities like antitumor [20], antibacterial [21], antifungal [22], analgestic [23] or anti-inflammatory [24] and may be additionally exploited as photographic materials [25] or for the purpose of aqueous cold bleaching of textiles [26]. At last, benzothiophenes have been recently proposed also as MAO-B inhibitors with a potential in treatment of neurodegenerative disease as well [27].

Taking into account that both phenantrene and naphthothiophene derivatives are promising and expanding groups of potentially biologically active compounds whose potential has not yet been thoroughly investigated sufficiently, we have designed and synthesized their novel amino and amido substituted derivatives. As part of the initial evaluation of their biological activity profile, their antiproliferative activity was determined. Besides, the structure activity relationships are discussed in this work to correlate between the substituent effects and the activities that aid in drug design. Furthermore, mode of biological action analysis was performed based on obtained results in silico and in vitro.

Section snippets

Chemistry

All newly prepared compounds were synthesized according to the main experimental synthetic procedure presented in Scheme 1.

Acyclic precursors 611 were prepared in the reaction of aldol condensation of corresponding benzaldehydes 35 and benzylcyanide 1 or 2-(thiophen-2-yl)acetonitrile 2 in absolute methanol using sodium methoxide as a base. Cyclic derivatives of phenanthrene 1214 and naphtho[2,1-b]thiophene 1517 were prepared by photochemical dehydrocyclization in ethanolic solution with the

Conclusion

Herein we described the design and synthesis of novel phenantrene and naphtho[2,1-b]thiophene derivatives bearing either different amino or amido side chains. In addition, their antiproliferative activity and mode of biological action are presented and described.

Targeted cyclic derivatives were obtained by using photochemical dehydrocyclization. Amino substituted derivatives were prepared by uncatalyzed microwave assisted amination while amide substituted derivatives obtained by reaction of

General methods

All chemicals and solvents were purchased from commercial suppliers Aldrich and Acros. Melting points were recorded on SMP11 Bibby and Büchi 535 apparatus. All NMR spectra were measured in DMSO‑d6 solutions using TMS as an internal standard. The 1H and 13C NMR spectra were recorded on a Varian Gemini 300 or Varian Gemini 600 at 300, 600 and 150 and 75 MHz, respectively. Chemical shifts are reported in ppm (δ) relative to TMS. All compounds were routinely checked by TLC with Merck silica gel

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We greatly appreciate the financial support of the Croatian Science Foundation under the projects 4379 entitled Exploring the antioxidative potential of benzazole scaffold in the design of novel antitumor agents. ects We would like to thank Croatian Government and the European Union (European Regional Development Fund—the Competitiveness and Cohesion Operational Programme - KK.01.1.1.01) for funding this research through project Bioprospecting of the Adriatic Sea (KK.01.1.1.01.0002) granted to

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