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Abstract
Throughout the ages, human has relied on nature to get the essentials of life, e.g. food, medicines, clothes, flavors and fragrances, fertilizers, means of transportation and some raw materials needed to satisfy all his requirements.
During the last decades, there has been an increasingly search for active compounds from many sources which have been termed ”natural products” to use them either as drugs or for industrial purposes.
Among a wide range of natural products classes, the phenolic class represents the most heterogeneous one \ This property comes from the fact that phenolics are those substances which possess in common an aromatic ring bearing one or more hydroxyl substituent(s)2.
Among the natural phenolic compounds, of which several thousand structures are known, the flavonoids (Fig. 1) form one of the largest groups. Flavonoids arc constituents of fruits, vegetables, nuts, plant-derived beverages such as tea and wine, traditional Eastern medicines such as Ginkgo biloba, as well as components present in a plethora of herbal-containing dietary supplements. Human have consumed flavonoids and other dietary phenolics since the arrival of human life on earth. Over 4000 different naturally occurring flavonoids have been described 3 and the list is still growing.
Simple monocyclic phenols, phenolic quinines 4 (Fig.2) and phenyl propanoids, including their dimers, lignans (Fig.3), minor neolignans 5 (Fig.4) are of rare occurrence, all exist in considerable numbers together with several important groups in plants such as lignins6 (Fig.S) and tannins7 (Fig.6) which are polyphcnolics. Occasionally, phenolic units are also encountered in proteins, alkaloids8 (Fig.7) and terpenoids 9 (Fig.8) existing in few plants.