Preface

Flavonoids are abundant secondary metabolites found in plants and fungi that have various roles in these organisms, including pigmentation, cell signalling, plant defence and inter-or‐ ganism communication. Due to their abundance in nature, flavonoids are also important components of the human diet, and the last four decades have seen an intense study focused on the structure characterization of flavonoids and on their roles in mammal metabolism.

Initially, flavonoids were identified as being potent antioxidants, capable of inhibiting many oxidative and nitrosative stress-induced lesions to biomolecules, which are considered to be at the onset of a number of human pathologies. They are also good chelating agents, and as they are partly planar, it has been shown that they are able to interfere with processes that involve DNA.

These antioxidant and chelating activities were present in both aglycones and glycosides but, most importantly, in the metabolites found in circulation in humans. This research area has evolved to include, first, the anti- and pro-inflammatory activities of flavonoids and, more recently, many other aspects of human biology, including modulation of neuronal signalling.

In this book, most of the well-established activities of flavonoids are reviewed, and recent research studies on the area of flavonoids are presented. Section 1 reviews the chemical as‐ pects of structure characterization of flavonoids, also focusing on isoflavonoids and homoi‐ soflavonoids. Section 2 addresses the biosynthesis of flavonoids in model plants as well as their role in abiotic stress situations and in agriculture and also presents a biomimetic ap‐ proach to Diels-Alder flavonoid compounds. Section 3 deals with the role of flavonoids in metabolism and health, from their antioxidant and chelating action to their anticancer and neuronal modulation activities. Section 4 addresses the importance of flavonoids in foods, from consumption to their use as bioactive components.

Finally, a special thanks to Pedro Pinheiro for his invaluable contributions to this work.

**Gonçalo C. Justino** Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal

**The Chemistry of Flavonoids**
