Phytochemical investigation of crude methanol extracts of different species of Swertia from Nepal

BACKGROUND: The genus Swertia is reported to contain potent bitter compounds like iridoids, xanthones and c-glucoflavones that are known to heal many human disorders. In contrast to high ethnomedicinally valued Swertia chirayita, its other species have not been studied extensively, in spite of their common use in traditional medicinal system in Nepalese communities. So, the present study attempts to investigate the content of total polyphenols, flavonoids, antioxidant activity and estimate the rough content of amarogentin, swertiamarin and mangiferin from different species of Swertia from Nepalese Himalayas. METHODS: Whole plant parts of S. chirayita (SCH), S. angustifolia (SAN), S. paniculata (SPA), S. racemosa (SRA), S. nervosa (SNE), S. ciliata (SCI) and S. dilatata (SDI) were collected; total phenolic and flavonoid contents were quantified spectrophotometrically and in vitro DPPH free radical scavenging assay was measured. Thin layer chromatography was performed on TLC aluminium plates pre-coated with silica gel for identification of swertiamarin, amarogentin and mangiferin from those species and semi quantitative estimation was done using GelQuant.NET software using their standard compounds. RESULTS: The phenolic content was highest in the methanol extract of SCH (67.49 ± 0.5 mg GAE/g) followed by SDI, SRA, SNE, SCI, SPA and SAN. The contents of flavonoids were found in the order of SCH, SPA, SRA, SNE, SDI, SCI and SAN. Promising concentration of phenolics and flavonoids produced promising DPPH free radical scavenging values. The IC50 values for the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging test was lowest in SCH (23.35 ± 0.6 μg/ml), even lower than the standard ascorbic acid among the seven studied species. A significant correlation of 0.977 was observed between the polyphenol content and antioxidant values. The TLC profile showed the presence of all three major phytochemicals; amarogentin, swertiamarin and mangiferin in all of the plant samples. CONCLUSION: Among the seven studied species, SCH showed anticipating results in total phenol content, flavonoid content and DPPH radical scavenging test. The less considered species of Swertia can be a potential source of bioactive amarogentin, and other useful therapeutic compounds in the alarming status of Swertia chirayita as shown by the phytochemical analysis. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s13104-015-1753-0) contains supplementary material, which is available to authorized users.