Flavonoids, defined as plant-derived secondary metabolites, have been widely found in nature with more than 10,000 different species, since their discovery. They are divided into subclasses based on the oxidative state of the ring, such as flavones, flavonols, flavanones, isoflavones, flavandiols, dihydroflavonols, and anthocyanidins. They are promising compounds with a wide variety of biological activities including antioxidant, antitumor, antigen-toxicity properties. Furthermore, flavonoids are seen as promising tools in the development of new drug assets, and they have been the subject of studies for the development of high-efficiency formulations for the treatment of a variety of future-threatening diseases. Molecular modeling studies play an important role in identifying the most stable molecular configurations and conformations of these molecules. This chapter focuses on the structural and functional properties of flavonoids, their biological activities, bioavailability, use in cancer, use in the development of new drugs, and molecular modeling studies on these molecules.
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Flavonoids, which are polyphenolic compounds, are widely found in plants in nature and the main source of yellow, blue and red pigments in plants (Harborne & Mabry, 1982), also affect the flavor of foods by given the astringent or bitter tastes in the mouth (Hufnagel & Hofmann, 2008). Plant-derived flavonides are produced secondary metabolites to attract insect pollinators by providing the formation of flower pigments, to form signal molecules for beneficial microorganisms, and as antimicrobial defense compounds for plants (Wasmann & VanEtten, 1996; Enkerli, Bhatt, & Covert, 1998).
The Interest in flavonoids, of which approximately 10000 varieties are known today, has started to accelerate since the 1940s (Middleton Jr, 1993), and today the research on evaluation of the new functions of flavonoid compounds continues. As a result of extensive research, it has been determined that flavonoids have versatile biochemical and pharmacological activities. (Holiman, Hertog, & Katan, 1996).
Flavonoids and isoflavonoids were discovered as probably the best characterized natural product pathway in plants, and there has been an explosion of interest in them as components of the human diet for their beneficial health-promoting effects. (Dixon & Steele, 1999). Flavonoids, which are found in many parts of the plant, are generally found in fruits, vegetables, seeds, flowers, leaves and branches (Cook & Samman, 1996; Havsteen, 2002). Flavonoids have two phenyl rings (A and B) linked by a heteracyclic ring composed of three carbon chain that contain oxygen (C ring). Thus, their structure is also referred to as C6-C3-C6. Depending on the carbon of the C ring on which B ring is attached, and the degree of unsaturation and oxidation of the C ring, they classified in six subgroups, namely; flavones, flavonols, flavanones, isoflavones, flavanols, flavandiols, dihydroflavonols and anthocyanidins (Kumar & Pandey, 2013; Wang et al., 2018; Jucá et al., 2020). The structural and functional diversity of flavonoids, the largest class of polyphenols, is enormous. (Rice-Evans, Miller, & Paganga, 1997; Guliyev, 1999). Flavonoids are considered essential for human health both as active components of medicinal plants and as bioactive food components (Winkel-Shirley, 2002; Shuvendu Das & Rosazza, 2006) and are an integral part of our diet as they are naturally found in fruits, vegetables, seeds and herbal products. They have been proven to be safe for the human organism and their daily intake is estimated to be around 1g per day. (Cook & Samman, 1996; Hollman & Katan, 1999; Havsteen, 2002). Flavonoids, due to their many bioactive properties including antioxidant, antiflamatuar, hepatoprotective, antimicrobial, antiviral anticancer properties (Kumar & Pandey, 2013), they have been proven by scientific studies having beneficial effects in many pathological conditions such as obesity, Parkinson's disease, Alzheimer's disease, viral infections, coronavirus infections and cancer (So, Guthrie, Chambers, Moussa, & Carroll, 1996; Youdim & Joseph, 2001; Havsteen, 2002; Pavanato et al., 2003; Crowe et al., 2011; Wedick et al., 2012). Flavonoids are also known as health-promoting “nutraceuticals” (Madhujith & Shahidi, 2006), which makes them interesting. As plant-derived natural chemicals they are biosynthesized from the phenylalanine amino acid (Winkel-Shirley, 2002; Shuvendu Das & Rosazza, 2006).