Synergistic broad-spectrum antibacterial activity of Hypoxis hemerocallidea-derived silver nanoparticles and streptomycin against respiratory pathobionts

Respiratory tract infections arise due to the introduction of microbes into the airway, disrupting the normal, healthy, complex interdependent microbiome. The selective disruption of this community can be either beneficial or dangerous. Nanoparticles are a potential tool for modifying this population. Coated silver nanoparticles (AgNPs) were synthesized using ethanolic extracts of Hypoxis hemerocallidea (EEHH), a Southern African plant used extensively in traditional medicine and the source of many bioactive secondary metabolites. The room temperature reaction between silver nitrate and EEHH forms largely spherical AgNPs with an average diameter of 6-20 nm. These nanoparticles show similar levels of antibacterial activity as the broad-spectrum antibiotic streptomycin against Bacillus cereus, Streptococcus pneumonia, Escherichia coli, Pseudomonas aeuroginosa, and Moraxella catarrhalis. However, the AgNPs synergistically increase the antibacterial activity of streptomycin when they are applied in combination (30-52%). AgNPs are reiterated to be promising dual-function antibiotics, synergistically enhancing activity while also acting as delivery agents for small molecules.

Determination of radical scavenging activities of some pyrimidine derivatives

Purpose: To synthesize some pyrimidine derivatives and investigate their radical scavenging activities. Methods: A series of newly pyranopyrimidines derivatives and dithiopyridopyrimidinediones were synthesized by condensation of barbituric acid, malononitrile and different substituted benzaldehydes reacted with 1,4-Diazabicyclo[2.2.2] octane (DABCO) as a base. Compounds P1-7 (series 1),  S1-11 (series 2) Scheme 1 and 6-amino-2-thiouracil with aromatic aldehydes in glacial acetic acid under reflux J1-13 (series 3) Scheme 2. 1H & 13C NMR, CHN, GC-MS and IR were used to characterize the compounds and were also screened for radical scavenging activity using 2,2-diphenyl- 1-picrylhydrazyl (DPPH) radical scavenging activity (IC50 = 50 μg/ml). Results: The potency of radical scavenging activity was ranked as series 1 > series 3 > series 2. Compounds P3, J4, S10, P5, P7 with inhibitory  concentration at 50 % level (IC50) of 12, 40, 48, 50, and 54 μg/ml, respectively, showed radical scavenging activity equal or more potent than the standard antioxidant, ascorbic acid (IC50 = 50 μg/ml). Conclusion: Series of newly pyranopyrimidines and dithiopyridopyrimidinediones derivatives have been successfully synthesized, and they  demonstrate good radical scavenging activity. Keywords: Pyranopyrimidine, Dipyrimidines, Anti-oxidant, DPPH, Ascorbic acid, Radical scavenging