Isoflavones are a relatively small, structurally well defined, group of plant secondary metabolites (natural products), which are of particular interest as biologically active, non-nutrient constituents of animal feed and human food. Chronologically, they were noticed at the beginning of XIXth century phytochemical studies as a class of plant pigments of considerable practical importance, but gained more significance after discovery of their estrogenic activity and interference with hormonal homeostasis of sheep, during 1940s. Contemporary studies of isoflavones are inseparably connected with soy, which is not only one of the principal agricultural crops of global significance, but also the richest source of genistein, daidzein and glycitein, which can occur as glycosides, aglycones or partly acylated glycosides. The presence of isoflavones in food products, which are derived from processing of soybean are generally considerd safe and beneficial for human health. Relatively recently, sufficiently selective and accurate analytical methods have been developed. These techniques have enabled the study of metabolic fates of isoflavones in experimental animals, as well as human patients, at the nanomolar levels which result from soy products ingestion or administration of pure isoflavones preparations. Although isoflavones share many physicochemical and biochemical characteristics with more numerous groups of natural products: flavonoids and polyphenolics (which are recognized as antioxidants, scavengers of the reactive oxygen species and antiinflammatory agents), they also feature some selective activities, like estrogenicity or multitarget and pluripotent anticancer action. The large amount of isoflavone pharmacological data accumulated tend to become less consistent as we advance from molecular level, through animal models, to human clinical trials, which indicates shortcomings of traditional approaches and the need for including systems biology methods and interpretations. Natural isoflavones remain interesting molecular probes, and lead compounds for several therapeutic directions; their presence in certain food products and variety of dietary supplements seems to be generally accepted, but it becomes evident that prospective drug development must take into account considerable differences in individual metabolism, which results in large part from very different microbiota which harbors in human intestines. On the other hand, synthetic chemistry of phenylpropanoids in general, and isoflavones in particular, is well developed and capable of delivering modified structures in both: form of structurally diverse dedicated libraries, and also in form of a scalable process for manufacturing of an active pharmaceutical ingredient featuring selected structure.
Keywords: Isoflavones, secondary metabolites, natural products, plant polyphenolics, flavonoids, isoflavone biosynthesis, isoflavone metabolism, soy isoflavones, phytoestrogens, genistein, daidzein, equol, puerarin, isoflavone glycosides, synthesis of isoflavones.