Phytochemical Analysis of Bangladeshi Medicinal Plants Led to the Isolation of Anti-Staphylococcal Compounds

Antibacterial resistance is a major threat to global health. Due to its new resistance mechanisms, it is spreading and emerging widely, thereby threatening the treatment of common infectious diseases. Ancient history and ethnopharmacological studies highlighted the importance of natural sources in treating resistance infections. This study involved bioassay-directed phytochemical investigation on Bangladeshi medicinal plants selected by an ethnopharmacological survey to explore antibacterial compounds against Methicillin resistance Staphylococcus aureus (MRSA). In 2016, an ethnopharmacological survey conducted in Bangladesh led to the recommendation of 71 medicinal plants by 127 respondents (71 Ayurvedic/Unani practitioners, 21 Ayurvedic patients and 35 local inhabitants) for the treatment of infectious diseases. Based on the literature review, data analysis of the ethnopharmacological survey and ease of availability of the plants, 18 plants were initially selected and collected from Bangladesh. After the initial antibacterial screening of 18 plants, five plants with Minimum Inhibitory Concentration (MIC) of 32–512 μg/mL were chosen based on potential antibacterial activity. These are (Zingiber montanum, Uraria picta, Diospyros malabarica, Cynometra ramiflora, Swertia chirayita. Extensive phytochemical work using different chromatographic and spectroscopic techniques on five Bangladeshi medicinal plants led to the isolation and identification of 24 compounds. Eight terpenes (zerumbol (3), zerumbone (4), buddledone A (5), germacrone (6), furanodienone (7), (−) borneol (1), camphor (2) and 8(17), 12-labdadiene-15, 16-dial) (8) were isolated from Zingiber montanum with the MIC (32– >128 μg/mL). Eugenol (14) and steroids were isolated from Uraria picta (MIC 64– >128 μg/mL). Lupane-type triterpenoids (Lupeol (20), betulin (21), betulinaldehyde (23), betulone (24) and messagenin (22) were isolated and identified from Diospyros malabarica with the MIC (64– >128 μg/mL), while pentacyclic triterpene (glutinol (10), glutinone (11)), simple phenolic (ethyl 4-ethoxybenzoate (9)) and steroids were isolated from Cynometra ramiflora with MIC (64– >128 μg/mL). A series of xanthones (swerchirin (16), swertiaperenin (17), bellidifolin (18) and decussatin (19)) were identified from Swertia chirayita with MIC (>128 μg/mL). 4-ethoxybenzoate (9) and messagenin (22) were identified as new natural compounds among these compounds. In terms of activity, 8(17), 12-labdadiene-15, 16-dial (8) (32 μg/mL against ATCC 5941) and zerumbol (3) (32 μg/mL against EMRSA 15) exhibited potential antibacterial activity. Phytochemical discoveries of Bangladeshi medicinal plants gave a new dimension to exploring anti-staphylococcal compounds.