Abstract
The emergence of pathogenic bacteria-resistant strains is a major public health issue. In this regard, natural product scaffolds offer a promising source of new antimicrobial drugs. In the present study, we report the antimicrobial activity against Gram-positive and Gram-negative bacteria and the yeast Candida albicans of five phenolic nor-triterpenes (1–5) isolated from Maytenus blepharodes and Maytenus canariensis in addition to four derivatives (6–9), three of them reported for the first time. Their stereostructures have been elucidated on the basis of spectroscopic analysis, including one-dimensional (1D) and two-dimensional (2D) NMR techniques, spectrometric methods, and comparison with data reported in the literature. To understand the structural basis for the antimicrobial activity of this type of compounds, we have performed an in-depth study of the structure–activity relationship (SAR) of a series of previously reported phenolic nor-triterpenes. The SAR analysis was based on the skeleton framework, oxidation degree, functional groups, and regiosubstitution patterns, revealing that these aspects modulate the antimicrobial activity.
Highlights
The resistance of common pathogens to standard antibiotic therapies is rapidly becoming a major public health problem all over the world [1], and there is a need to develop new structural and mechanistic classes of antibiotic agents
The semisynthesis of 6 was achieved by acetylation derivatives 6–9 were prepared from pristimerin (Scheme 1)
The antimicrobial activity of five phenolic nor-triterpenes isolated from two Maytenus
Summary
The resistance of common pathogens to standard antibiotic therapies is rapidly becoming a major public health problem all over the world [1], and there is a need to develop new structural and mechanistic classes of antibiotic agents. Sci. 2019, 9, 2957; doi:10.3390/app9152957 www.mdpi.com/journal/applsci products shows a wide range of bioactivities, including cytotoxic [10,11], anti-inflammatory [12], antioxidant [13], antiparasitic [14], and insecticidal [15] properties Concerning their antimicrobial activity, pristimerin, tingenone, celastrol, and netzahualcoyone (Figure 1) exhibit inhibitory activity against Gram-positive bacteria [8,16,17], and the mode of action of netzahualcoyone against Bacillus subtilis and Escherichia coli has been investigated [18,19]. Celastraceae species, products shows wide range of bioactivities, including cytotoxic [10,11], anti-inflammatory [12], we report on the minimal concentrations (MICs)Concerning of five natural norantioxidant [13], antiparasitic [14], inhibitory and insecticidal [15] properties Their phenolic antimicrobial triterpenes (1–5) and tingenone, four derivatives (6–9), three of them reported for the first time, againstactivity. Spectra were measured in CHCl 3 on a Bruker IFS 55 the structural spectrophotometer. 1H (400 or 500 MHz) and 13C (100 or 125 MHz) NMR spectra were recorded on
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