Anti-quorum sensing compound from Nerium oleander roots

Nerium oleander L. (Apocynaceae) is a poisonous plant rich in cardenolides. Many researchers investigated its aerial parts but little work has been carried out concerning the roots. The phytochemical investigation of different fractions of N. oleander roots resulted in isolation of 17 compounds. Strospeside (1) and 3β-O- (4-O- gentiobiosyl-D-digitalopyranoside)-14β-hydroxy-16α-acetoxy-5β- card-20 (22)-enolide (2) were isolated for the first time from N. oleander. In addition to other compounds reported for first time in Nerium roots; uzarigenin (3), 3-epidigitoxigenin (4), 3β-O-(β-D-diginosyl)-14β-hydroxy-5α-card-20(22)-enolide (5), odoroside-H (6), 3β-O-(β-D-digitalosyl)-14β-hydroxy-5α-card-20(22)-enolide (7), uzarigenin-3-O-β-D-glucopyranosyl-(1→4)-O-β-D-digitalopyranoside (8), 3β-O-(4-O- gentiobiosyl-D-digitalopyranoside)-14β-hydroxy- 5β, 14β- card-20 (22)-enolide (9), odoroside-K (10) and 2,4-di-OH-acetophenone (11). Structures of all these compounds were elucidated mainly by the analysis of their NMR and MS data. In a previous study we evaluated the anti-quorum sensing activity of N. oleander root extract but it showed no activity. The reassessment of anti-QS sensing activity revealed that one compound (11) has anti-QS sensing activity. This activity was tested by disc diffusion assay for anti-QS activity using Chromo bacterium violaceum ATCC 12472 and C. violaceum CV026. The activities were measured through violacein pigment production inhibition. This compound; 2,4-di-OH-acetopheneone showed inhibition zones of 19 ± 0.5 and 25 ± 0.3 for C. violaceum CV026 and C. violaceum ATCC 12472, respectively.