Flavonoids, which possess a basic C15 phenyl‐benzopyrone skeleton, refer to a series of compounds in which two benzene rings (ring A and B) are connected to each other through three carbon atoms. Based on their core structure, flavonoids can be grouped into different flavonoid classes, such as flavonols, flavones, flavanones, flavanonols, anthocyanidins, isoflavones and chalcones. Flavonoids are often hydroxylated in positions 3, 5, 7, 3′, 4′ and/or 5′. Frequently, one or more of these hydroxyl groups are methylated, acetylated, prenylated or sulfated. In plants, flavonoids are often present as O‐ or C‐glycosides. The O‐glycosides have sugar substituents bound to a hydroxyl group of the aglycone, usually located at position 3 or 7, whereas the C‐glycosides have sugar groups bound to a carbon of the aglycone, usually 6‐C or 8‐C. The most common carbohydrates are rhamnose, glucose, galactose and arabinose. This chapter mainly introduces the methods of isolation and structure identification of flavonoids.
Part of the book: Flavonoids
The chemical constituents of plants are complicated, and monomeric compounds must be obtained via extraction and isolation before structure identification, bioactivity screening, and so on. In recent years, the new technologies and methods of the extraction, isolation, and structural identification have come forth, which promote the speed of extraction and analysis of phytochemicals. The chemical structures of compounds from plants must be identified or elucidated, which may provide the necessary basis for further study on the bioactivities, structure-activity relationships, metabolisms in vivo, structural modification, and synthesis of the active compounds. The amount of chemical constituents isolated from plants is often minor, so the structural studies are often difficult to carry out with classical methods. Therefore, spectral analysis is mainly used. This chapter describes the isolation and identification methods during the study of phytochemicals.
Part of the book: Phytochemicals in Human Health