Fatty acid profiling and multivariate analysis in the genus Leucas reveals its nutritional, pharmaceutical and chemotaxonomic significance

Abstract

Genus Leucas with about 41 species found in India, is an Asian genus with separation from its close relatives in Africa based on phylogenetic evidence. Present study represents the only comprehensive phytochemical investigation on this genus. We have analyzed the seed fatty acid compositions of 26 species and five varieties of Leucas for nutritional, pharmaceutical and chemotaxonomic perspectives. The fatty acids and their composition in seeds of Leucas species, collected from different geographical regions in India, were analyzed by gas chromatography and mass spectrometry. Significant variations have been observed in fatty acid profiles among species and their varieties. We observed major fatty acids as palmitic, stearic, oleic, linoleic and laballenic acid; whereas myristic, palmitoleic, cis-vaccenic, linolenic, eicosanoic, eicosenoic, phlomic and docosanoic acid were detected in minor quantities. Laballenic and phlomic acids are unusual allenic fatty acids found in few Lamiaceae members from order Lamiales. Laballenic acid, a proven molecule of pharmaceutical importance, was observed in all the Leucas species studied. Three species of Leucas; L. helianthimifolia, L. ciliata var. vestita and L. hirta were found to contain ≥40% laballenic acid and can act as potential source for isolation of pharmaceutical compounds. This study also reports the presence of another allenic fatty acid, phlomic acid, in several Leucas species. Principal component analysis and hierarchical cluster analysis showed a distinct separation among the species based on abundance of similar fatty acids. The fatty acid profile appears to be overlapping at higher level and does not support separation of Asian Leucas from its African relatives and the inclusion of Asian taxa in morphologic sections. However, hierarchical clustering of L. helianthimifolia, L. ciliata var. vestita and L. hirta supported treatment under the morphologic section Astrodon. Multivariate analysis on the chemometric data also supported this cluster as the most prominent source of medicinally useful laballenic acid. Based on the FAs profile, a reconsideration of species boundaries in L. ciliata and L. marrubioides species complex is proposed.