Tlc Flavonoid

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16 Application of TLC in the Isolation and
Analysis of Flavonoids
Marica Medi-Šari, Ivona Jasprica, c c Ana Mornar, and Željan Maleš CONTENTS
Introduction ................................................................................................ 405 16.1.1 Chemistry, Biochemistry, and Medicinal Significance of the Flavonoids.......................................................................... 405 16.1.2 Brief Overview of Use of TLC in the Analysis of Flavonoids in Plants ................................................................ 406 16.2 TLC Techniques......................................................................................... 407 16.2.1 Basic Principles for Flavonoid Separations ................................. 407 16.2.2 Sample Preparation ...................................................................... 409 16.2.3 Separation of Flavonoid Aglycones and Glycosides on Silica Gel and Reversed-Phase TLC....................................... 410 16.2.4 Use of Mathematical Methods for the Optimization of Chromatographic Conditions for Flavonoid Separations ........ 413 16.2.5 Multidimensional Planar Chromatography (Unidimensional Multiple Development and Two-Dimensional Development)..... 415 16.2.6 Quantitative Evaluation................................................................ 418 16.3 Modern TLC Techniques in the Separation of Flavonoids ....................... 418 16.3.1 Overpressured-Layer Chromatography ........................................ 418 16.3.2 Rotation Planar Chromatography................................................. 419 16.4 Use of TLC in the Isolation of Flavonoids from Plant Extracts ............... 419 16.4.1 Future Trends ............................................................................... 420 References ............................................................................................................. 420 16.1

16.1 INTRODUCTION 16.1.1 CHEMISTRY, BIOCHEMISTRY, AND MEDICINAL SIGNIFICANCE OF THE FLAVONOIDS Flavonoids constitute one of the largest and recently very popular group of phytochemicals. They are virtually ubiquitous in green plants and as such are likely to be 405

406

Thin Layer Chromatography in Phytochemistry
13 8 7 6 5 A 10 1 9 O C 4 O 17 12 2 11 3 B 15 16 14

FIGURE 16.1 Basic flavonoid nucleus. Subdivision to different groups is primarily based on the presence (or absence) of a carbonyl substituent on the position C4, the presence (or absence) of a double bond between carbon atoms 2 and 3, and a phenyl substitution at the positions 2 or 3 of the pyrone ring.

encountered in any work involving plant extracts. The term flavonoid is a collective term for plant pigments, mostly derived from benzo-g-pyrone, which is synonymous with chromone.1 In plants, flavonoid aglycones (flavonoids without attached sugars) occur in a variety of structures, all containing 15 carbon atoms arranged in a C6–C3– C6 configuration (flavonoid nucleus is depicted in Figure 16.1). Until now, more than 4000 flavonoids have been identified and this number is constantly growing because of the great structural diversity arising from the various hydroxylation, metoxylation, glycosylation, and acylation patterns. Most frequently encountered groups of flavonoid aglycones include flavones, flavonols, anthocyanidins, isoflavones, flavanones, dihydroflavonols, biflavonoids, calchones, and aurones. Flavonoid aglycones possess the chemical properties of phenolics, and thus they are slightly acidic. Those possessing a number of unsubstituted hydroxyl groups, or sugar moieties, are polar substances and soluble in polar organic solvents. The presence of sugar makes flavonoid more water soluble, while less polar aglycones like isoflavones, flavanones, and highly methoxylated flavones and flavonols tend to be more soluble in ether or chloroform.2 Flavonoids have important roles in plant physiology and are components of the diet of numerous herbivores and omnivores,...
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