Phytotoxic triterpene saponins from Bellis longifolia, an endemic plant of Crete

Abstract

In a study of 62 plant species of the Cretan flora for their phytotoxic activity, plants were extracted successively with CH₂Cl₂, MeOH and H₂O. Phytotoxicity evaluation of the 240 extracts was performed against Lactuca sativa L. and Agrostis stolonifera L.. The MeOH extract of Bellis longifolia was the most phytotoxic. Bioassay-guided fractionation revealed that a fraction consisting mainly of saponins was the most effective. Separation of the saponins was performed using initially a step-gradient Centrifugal Partition Chromatography (CPC). Investigation of the active fraction led to the isolation and structure elucidation of three previously undescribed triterpene saponins, 3-O-β-D-fucopyranosyl polygalacic acid, 28-O-α-L-rhamnopyranosyl-(1 → 2)-β-D-fucopyranosyl polygalacic acid and 3-O-β-D-fucopyranosyl-2α,3β,23-trihydroxyolean-12-en-28-oic acid, which were present as the main phytotoxic compounds of the methanol extract. Two triterpenes, polygalacic acid and bellisonic acid and four kaempferol glucosides, as well as chlorogenic acid were also isolated. 3-O-β-D-fucopyranosyl polygalacic acid and 3-O-β-D-fucopyranosyl-2α,3β,23-trihydroxyolean-12-en-28-oic acid had phytotoxic activity similar to some commercial herbicides (IC₅₀ values of ca. 25 μM) against duckweed (Lemna paucicostata).

Keywords: Asteraceae; Bellis longifolia; Centrifugal Partition Chromatography; Flavonoids; Phytotoxicity; Saponins.