Holarrhena mitis (Vahl) R.Br. ex Roem. & Schult. which is an endemic plant growing mainly in the dry regions of the low-country has been used in the treatment of dysentery in Ayurvedic medicine. During the present study, we tested antibacterial, antifungal, antioxidant activities and brine shrimp lethality, as well as the total phenolic content of the dichloromethane, ethyl acetate and methanol extracts of the bark and leaves of H. mitis. The methanol extract of bark produced a measurable zone of inhibition against two Candida species, namely Candida albicans, Candida krusei among all five tested species and against both dermatophytes, Microsporum gypseum and Tricophyton mentagrophytes. In addition, the methanol extract of bark showed very strong antifungal activity against C. krusei (20 mm), which is very close to that of the positive control ketoconazole (22 mm). Both dicholoromethane extracts of bark and leaves and methanol extracts of leaves showed an activity against both tested strains of Staphylococcus aureus but were negative against Escherichia coli and Salmonella enteritidis. However, the rest of the extracts exerted an active against all the tested bacterial strains. In the brine shrimp cytotoxicity assay, the dichloromethane extracts of both leaves and bark showed lower LC 50 values (27.13 ppm and 9.38 ppm, respectively) than that of positive control, K 2 Cr 2 O 7 , (35.74 ppm) indicating cell toxicity. Compared to the positive control, DL-α-tocopherol (IC 50 : 12.2 ppm), the antioxidant activity of the ethyl acetate and methanol extracts of leaves exhibited comparable activity (IC 50 :16.9 ppm and 29.8 ppm, respectively). Antioxidant activity correlated well with the polyphenol content of methanol and ethyl acetate extracts (473.25 and 138.74 mg (GAE) /g, respectively) of leaves, with respect to gallic acid. These empirical results revealed that methanol extract of bark of H. mitis showed strong antifungal activity as well as very low brine shrimp lethality indicating that it would be a potential nontoxic anti-fungal natural product. The dichloromethane extracts exhibited strong brine shrimp lethality and may contain potential natural anticancer lead compounds. Ethyl acetate extracts of both leaves and bark having significant antibacterial activity, would be source of potential antibacterial lead compounds.
Highlights• β-Sitosterol was isolated from ripen fruits of Avocado with a relatively good yield.• Four derivatives were synthesized and C6 hydroxy β-sitosterol was reported for the first time.• The anti-bacterial activity was reduced for derivatives with increasing lipophilicity.• Hydroxyl groups at C3 and C6 are significant towards the antibacterial activity.
The scarcity of novel drugs has prompted scientific research to re-evaluate natural products as drug lead compounds with high chemical and biological potential. Among the many phytochemicals, alkaloids are an important group of natural products consisting of an extensive list of bioactivities such as antitumor, anti-inflammatory, antiviral, antihypertensive, antiulcer, diuretic and analgesic. The alkaloid mixture from the bark of Holarrhena mitis, which is an endemic plant to Sri Lanka, consists of 11 known compounds. This alkaloid mixture was assessed for its antibacterial, antifungal, antioxidant and acetylcholinesterase (AChE) inhibitory activities and brine shrimp lethality. Significant antifungal activity against standard strains of five Candida sp. mainly against C. krusei and C. glabrata, with inhibition diameter of 21 mm was identified. In addition, it showed moderate antibacterial activity (MIC 6.7±0.1 mg mL -1 ) against both Escherichia coli and Staphylococcus aureus, and AChE inhibitory activity (IC 50 value of 58±0.5 μg mL -1 ) and non-toxicity to brine shrimp lethality assay (LC 50 value of 1410.11±2.05 mg L -1 ). However, the alkaloid mixture did not exhibit potential antioxidant activity (IC 50 399±1.3 mg L -1 ). These empirical results suggest that alkaloids isolated from this plant could be good potential candidates for further development of new antifungal and antibacterial lead compounds, and AChE inhibitors.
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