SYNTHESIS AND BIOLOGICAL APPLICATIONS OF FLAVONOID BASED NATURAL PRODUCTS

Abstract

The thesis entitled “Synthesis and Biological Applications of Flavonoid Based Natural Products” is reported in six chapters. The present work is aimed to design and synthesis of novel flavonoids-based derivatives involving C-C, C-O, C-N bonds formation using different reactions like Ullmann coupling, Aza-Michael ring opening and cyclization, C-H amination, dehalogenation reaction. The novel synthesized compounds were characterized through different spectral techniques such as 1H NMR, 13C NMR, IR, LC-MS, HRMS and x-ray diffraction and their biological evaluations were reported as anti-proliferative applications. The thesis has been divided into six chapters for the sake of convenience and clarity and organized as follows: Chapter 1: Introduction Flavonoids are found in most of the higher plants as secondary metabolites and are water soluble due to polyphenolic nature. These naturally occurring compounds are widely distributed in plants like vegetables, tea, soya bean, berries and other citrus fruits as dietary sources. They have exhibited antioxidant and chelating properties so have many health promoting effects. Some of the activities attributed to flavonoids include anti-allergic, anti-cancer, antioxidant, anti-inflammatory and anti-viral. Flavonoids as central core containing compounds are used as drugs such as xanthokeismins A-C and dime fine for the treatment of bronchial asthma. Chromene and quinoline based conjugates belong to important class of natural and synthetic compounds displaying a broad spectrum of pharmacological activities including anticancer, antitubercular, anti-inflammatory, antimicrobial, antihistaminic, antihypertensive and anti-HIV activity. Natural product is a substance or compound, created via living organism such as - plants, fruits and microorganisms, etc. exclusively found in nature, formed with metabolism. For the development in the field of organic chemistry, natural products have participated a vital role by providing confronting synthetic targets in drug development and drug synthesis. Directly and indirectly, a huge percentage of drugs in modern medicine are originated from natural sources. Traditionally significant concept for the natural products is that it is applied as a therapeutic agent in different disease such as cancer infectious disease and reduced pain flavonoids, carotenoids, chromones, coumarins, alkaloids and quinolines etc. are considered as a significant part of natural products and usually utilized around the world due to their assorted pharmacological properties. In general, flavonoids, chromenes and quinolines have occupied a ABSTRACT ii considerable amount of research space owing to their diverse pharmacological, therapeutic and chemo-sensor applications. Chapter 2. Route to Highly Functionalized stereospecific-Aminated Aurones from 3-bromo flavones with aniline and N-phenyl urea via a Domino- Aza Michael- ring opening-cyclization reaction In this chapter, We describe the synthesis and characterization stereospecific aminated aurone scaffold by cascade Domino reaction (Aza Michael addition, ring opening and cyclization reaction) between 3-bromoflavone and aniline or N- phenyl urea is make known to continue economically in the presence of potassium tertiary but-oxide as a base and copper Iodide as a catalyst. Optimization of the reaction conditions and screening of copper Iodide 5 mol % best catalyst and 3 equivalents of KOtBu best base and DMF is suitable solvent for the stereospecific aminated aurone which gave products in good yields to excellent yields (62-84%). This protocol is operationally successful with ease, avoids the requirement of additives and ligand, less reaction time, and offers broad substrate scope with high yielding. Scheme: 1 Synthesis of stereospecific aminated aurone from 3-bromo flavone and aniline and N-phenyl urea. All synthesized compounds were fully characterized by 1H-NMR, 13C-NMR, FTIR, HR-MS and single crystal X-ray analysis. Chapter 3: CuI mediated synthesis of heterocyclic flavone-benzofuran fused derivatives In this chapter, A copper iodide catalyzed the coupling reaction of substituted 2- (2-chlorophenyl)-3-hydroxy-4H-chromen-4-ones with base i.e. K2CO3 followed by intramolecular cyclization between -OH (hydroxy) and -Cl (Chloro) group leads to ABSTRACT iii assembling of functionalized Flavone fused benzofuran derivative with good to excellent yield (75–90%), a natural product with a broad range of biological activities. This protocol involves less reaction time, low catalyst loading, ligand free, fast conversion and mild reaction condition. Scheme: 2 Synthesis of flavone fused benzofuran derivative. All Synthesized compounds were fully characterized by 1H NMR, 13C NMR, FTIR and LCMS. Chapter 4. Synthesis, estrogen receptor binding affinity and molecular docking of pyrimidine-piperazine-chromene and -quinoline conjugates In this chapter, we report a simple, mild and efficient multi-component reaction in one pot synthesis and characterization of substituted 2-amino-7-((6-(4-(2- hydroxyethyl) piperazin-1-yl)-2-methylpyrimidin-4-yl)oxy)-4-phenyl-4H-chromene-3- carbonitrile and 2-amino-7-((6-(4-(2-hydroxyethyl)piperazin-1-yl)-2-methylpyrimidin- 4-yl)oxy)-4-phenyl-1,4-dihydroquinoline-3-carbonitrile conjugates under mild reaction condition. The synthesised compounds (5a -5t) were assessed their antiproliferative activities against human embryonic kidney cells (HEK293) (Normal cell) and human breast cancer cell lines (MCF-7). Compounds 5f, 5g, 5o, 5q and 5s showed better cytotoxic activities as (48± 1.70, 65± 1.13, 92± 1.18, 30± 1.17 and 16± 1.10) with (IC50< 50 mM) against human breast cancer line than curcumin drug (48 ± 1.11) as compare to other compounds. We also perform molecular docking with compounds 5f, 5g and 5o against Bcl-2 protein which gave good binding affinity (G = -9.08 kcal/mol, -8.29 kcal/mol and -7.70 kcal/mol). Furthermore, the structure-activity relationship (SAR) study exposed that the optimal amalgamation enhanced anti-proliferative activities when quinoline and chromene moiety attached with pyrimidine and piperazine moiety. All synthesized compounds were fully characterized by 1H-NMR, 13C-NMR, FT-IR, LC-MS. ABSTRACT iv Scheme: 3 Synthesis of chromene and quinoline derivative with pyrimidine and piperazine and their biological evolution against human breast cancer cell line and human embryonic kidney cell line. Chapter-5: Design, Synthesis, Molecular docking and Molecular Insights Inhibition studies of Microtubule Affinity Regulating Kinase 4 of novel 3-N-aryl substituted-2-heteroarylchromones for Cancer Therapy In this chapter we describe a series of 3-N-aryl substituted-2- heteroarylchromones were designed and efficiently synthesized via Pd-mediated oxidative coupling using 2-heteroarylchromones and anilines as selective human Microtubule affinity regulating kinase 4 (MARK4) enzyme inhibitors, a recently identified anti-cancer drug target. Among 22 synthesized molecules, compounds para - iodo, para- nitro and para- methyl were identified as hit and exhibited excellent in vitro inhibitory effect against MARK4 with IC50 value (50% of ATPase activity) at 2.12± 0.22μM, 1.98 ± 0.34μM and 5.56 ± 0.42μM respectively. The fluorescence binding and dot blot assay were found in μM range for compounds para- iodo, para- nitro and paramethyl substituted derivative which indicates a better binding affinity. In vitro studies against the cancerous cells (MCF-7 and HepG2) revealed that the compounds para-iodo, para- nitro and para-methyl substituted derivative inhibit the cell viability, induce apoptosis and tau-phosphorylation. Cell viability studies gave the growth inhibition of cancerous cells with IC50 values of 3.22 ± 0.42, 4.32 ± 0.23 μM and 16.22 ± 1.33μM for human breast cancer cells (MCF-7) and 6.45 ± 1.12, 5.22 ± 0.72 μM and 19.12 ± 1.43μM for human liver carcinoma cells (HepG2) respectively. ABSTRACT v Scheme: 4 Synthesis of 3-N-aryl substituted-2-heteroarylchromones and their Microtubule Affinity Regulating Kinase 4for human breast cancer cell line, human liver carcinoma cells and human embryonic kidney cell line. Also, compounds para-iodo, para-nitro and para-methyl put the cancerous cells on oxidative stress as suggested by ROS quantification. Based on above studies, molecular docking of compounds para-iodo, para-nitro and para-methyl showed hydrogen bonding, charge or polar and van der Waals interactions by the active site residues of MARK4. These observations clearly showed that the compounds fit nicely in the active site with high binding affinity. Thus, compounds may be as potential inhibitors and further explored to design novel therapeutic molecules in the drug discovery against MARK4-related diseases. All synthesized compounds were fully characterized by 1HNMR, 13C-NMR, FT-IR, HRMS. Chapter 6. Regioselective Hydrodehalogenation of Aromatic α- and β- Halo carbonyl Compounds by CuI in Isopropanol An operationally simple copper-catalyzed hydro-dehalogenation of β’-halochalcone and α-halo-flavone has been developed with isopropanol used as a solvent and also serve as a hydride source in basic medium at 90 o C leads to the corresponding hydro dehalogenation chalcone and flavone products with high selectivity. By this reagent combination, Iodide, bromide and chloride can be reduced without any ligand involving good to excellent yield. The reduction is companionable with numerous electronwithdrawing or electron-donating groups. All synthesized compounds were fully characterized by 1H-NMR, 13C-NMR, FT-IR, HRMS.