A new derivative of ionone from aerial parts of Viola odorata Linn. and its antibacterial role against respiratory pathogens

Viola odorata, widely distributed in Eastern and Western Himalaya region is extensively used in treatment of various respiratory ailment, calculous affections and nervous disorders. It is a rich source of alkaloids, terpenes, flavonoids, glycosides, tannins as well as viola-quercitin and salicyclic acid known as natural aspirin. The present study was aimed to isolate bioactive compounds from the aerial parts of V. odorata. The isolated compound from aerial parts of V. odorata was identified grounded on observed spectral data including ultraviolet–visible (UV–vis), Fourier-transform infrared, gas chromatography-mass spectroscopy, 1H and 13C-nuclear magnetic resonance. The antibacterial efficacy of isolated compound was determined by disc diffusion method against five bacterial strains namely, Haemophilus influenzae (MTCC 3826), Pseudomonas aeruginosa (MTCC 2474), Staphylococcus aureus (MTCC 1144), Streptococcus pyogenes (MTCC 422) and Streptococcus pneumoniae (MTCC 655) and Minimum inhibitory concentrations (MICs) by a serial dilution method by using 96 well microtiter plates. Based on spectral data analysis, one new structurally related ionone-like compound known as 3-(2′,4′,6′,6′-tetramethylcyclohexa-1′,4′-dienyl)acrylic acid (1) has been isolated from aerial parts of V. odorata, with significant bioactivity. The antibacterial efficacy of compound 1 ranged between 7.3 ± 0.28 to 9.3 ± 0.28 mm against selected respiratory bacteria at 6 mg/disc concentration. The MICs were recorded at 32–128 μg/ml. Streptococcus pyogenes was fairly resistant and Haemophilus influenzae more sensitive than others. By this study, it can be concluded that compound 1 has significant bioactive properties against tested microorganisms. It validates its use as a new potential source of natural drug for curing the respiratory diseases caused by selected microorganisms.