**Author details**

flavonoid nucleus is 222 *a.m.u*. for flavones, isoflavone and aurone; 224 *a.m.u.* for flavanones and chalcones; 238 *a.m.u.* for flavonols; and 240 *a.m.u*. for the dihydroflavonols. The molecular weight of the unknown flavonoid could be deduced by addition of atomic mass units of

weights above. The loss of some ion-fragments from the molecular or pseudo-molecular ion is very characteristic in the mass spectra of flavonoids. Peaks obtained during this fragmentation process represent accurately the corresponding ion-fragments that are expressed as mass-to-charge ratio (m/z). The exact molecular weight for each fragment may be measured to the nearest 0.0001 mass unit if the mass spectrometer is operating in high resolution. This information enables calculation of precise molecular formula from the molecular ion peak and ion-fragments [54]. A prerequisite for successful mass spectrometry is that the flavonoid should be sufficiently volatile in the high vacuum within the mass spectrometer. Most aglycones are sufficiently volatile at probe temperature of 100–230°C, higher temperatures being required for the more polar polyhydroxyflavones and flavonols. Glycosides, anthocyanidins and biflavonoids, however, are not sufficiently volatile and should therefore be derivatized to improve their volatility. Some standard methods used for derivatization of compounds are

Natural products in general or flavonoids in particular remain an important source for drug discovery. Determination of their absolute configurations is one of the most challenging tasks in the structure elucidation of chiral flavonoids. It has been proven that the change in absolute configuration of secondary metabolites consequently affected the difference in pharmacological activity of both stereo-compounds. Methods such as chiroptical approaches, chemical synthesis, analytical chemistry, chiral derivatization and X-ray crystallography could be used to determine the absolute configuration of flavonoids. An important investigation was reported on the determination of absolute configuration of natural products and some flavonoids using experimental and calculated electronic circular dichroism (ECD) data [56].

The extraction, isolation and characterization of flavonoids from natural products have been carried out successfully by natural product chemists and phytochemists using relevant techniques and new methods. Some of these techniques and methods have been documented in this chapter with illustrations owing to some flavonoids recently reported. It is clear that the HPLC and its combination with other available techniques of isolation are being often used to obtain flavonoids from natural sources especially from plant species. The characterization of flavonoids remains basically focused on the analysis of their spectroscopic, mass and UV data and some chemical investigations depending on the nature of the structure under elucidation. The need of flavonoids in agriculture, food and drug industries still one of the worldwide up-to-date research interests. Natural resources and especially medicinal plants are still available to discover novel or efficient antioxidant flavonoids that could be used as drugs to fight against degenerative diseases one of the issues the global health is

), and so on] to one of the basic molecular

all its substituents [16 a.m.u (-OH), 30 a.m.u. (-OCH<sup>3</sup>

54 Flavonoids - From Biosynthesis to Human Health

**5. Conclusion**

facing today.

permethylation or perdeuteromethylation and trimethylsilylation [54].

Maurice D. Awouafack1,2\*, Pierre Tane<sup>1</sup> and Hiroyuki Morita2

\*Address all correspondence to: amauduc2@yahoo.com

1 Laboratory of Natural Products Chemistry, Department of Chemistry, Faculty of Science, University of Dschang, Dschang, Cameroon

2 Institute of Natural Medicine, University of Toyama, Toyama, Japan

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