Leaf surface flavonoids in Iranian species of Nepeta (Lamiaceae) and some related genera

A HPLC survey of the leaf surface flavonoids of 38 species of Nepeta (Lamiaceae) and four species of the related genera Agastache, Dracocephalum and Lallemantia revealed 14 different flavones, one of which is new (8-hydroxycirsiliol or 5,8;3',4'-tetrahydroxy-6,7-dimethoxyflavone). In addition, two flavonols (methyl ethers-of kaempferol) were found in Dracocephalum kotschyii. The most frequently encountered flavones in Nepeta were cirsimaritin (5,4'-dihydroxy-6,7-dimethoxyflavone); 8-hydroxycirsimaritin (5,8,4'-trihydroxy-6,7-dimethoxyflavone, also called isothymusin) and genkwanin (5,4'-dihydroxy-7-methoxyflavone). Apigenin and the 4'-methyl ethers of cirsimaritin and 8-hydroxycirsimaritin (salvigenin and 8-hydroxysalvigenin, respectively) were also relatively common. The distribution of surface flavones in the four genera provided some valuable data for the phylogenetic relationships at generic level. The presence of surface flavones with. a 5-hydroxy-6,7-dimethoxy A-ring (as found in cirsimaritin and salvigenin) and the unusual 5;8-dihydroxy-6,7-dimethoxy A-ring substitution pattern (as found in 8-hydroxycirsimaritin, 8-hydroxysalvigenin and 8-hydroxycirsiliol), can be considered as a characteristic chemotaxonomic feature typical of the genus Nepeta. Cirsimaritin and 8-hydroxycirsimaritin were also detected in the one species examined for Agastache, but the absence of genkwanin and the presence of acacetin in A. barberi and in ten Agastache species studied previously, distinguished Agastache from Nepeta. The presence of methoxylated flavonols and absence of 8-hydroxycirsimaritin and related compounds distinguished species of Dracocephalum and Nepeta, whereas lack of flavonoids with 6- and 8-oxygenation of the A-ring characterised species of the genus Lallemantia. (C) 2002 Elsevier Science Ltd. All rights reserved.