Review on Structural Trends and Chemotaxonomical Aspects of Pharmacologically Evaluated Flavonoids

INTRODUCTION: This work provides statistical analyses of bibliographic data on pharmacologically evaluated flavonoids from different plant families. By opposition to structural elucidations benefitting from full data aspects, pharmacological evaluations are concerned with partial investigations resulting in sparse information. METHODS: The limited data availability was overcome by extensive consideration of several small sets of pharmacologically evaluated flavonoids in several plant taxa, alternatively to the traditional intensive analysis of big dataset of a given metabolic family in a given plant taxon. Statistical analyses were carried out using correspondence analysis, cluster analysis, box plots and fisher exact test to highlight structure-structure, structure-plant and structure-activity trends. RESULTS: Different aglycone types showed opposite trends between hydroxylation (flavonols, anthocyanidins, flavanols), and methoxylation (isoflavones, isoflavanes, neoflavones). Moreover, different carbons showed differential substitution levels in different aglycones: C3 in flavonols, C6, C8 in flavones, flavonols, C2' in flavanones, C6' in isoflavanes. Plant families were well differentiated by different relative occurrences of aglycones: flavones in Lamiaceae, flavanones in Rutaceae, neoflavones in Rubiaceae, flavonols in Asteraceae, isoflavones in Fabaceae. Relatively more hydroxylated flavonoids occurred in Asteraceae, Lamiaceae and Fabaceae vs. more methoxylated ones in Rutaceae and Rubiaceae. Concerning structure-activity trends, flavanols and isoflavones were relatively more concerned with anti-diabetic and anti-inflammatory activities, respectively, vs. balanced distribution of flavones. Anti-inflammatory activity showed significant association with substitution position of same chemical groups (OH, OCH3), whereas anti-diabetic activity was revealed to be mainly influenced by the type of chemical groups (positive effect of OH and glycosyls). CONCLUSION: These results call for regular updates and further investigations.