ABSTRACT
Due to the rapidly growing bacterial antibiotic-resistance and the scarcity of novel agents in development, bacterial infection is still a global problem. Therefore, new types of antibacterial agents, which are effective both alone and in combination with traditional antibiotics, are urgently needed. In this paper, a series of antibacterial ocotillol-type C-24 epimers modified from natural 20(S)-protopanaxadiol were synthesized and evaluated for their antibacterial activity. According to the screening results of Gram-positive bacteria (B. subtilis 168 and MRSA USA300) and Gram-negative bacteria (P. aer PAO1 and A. baum ATCC19606) in vitro, the derivatives exhibited good antibacterial activity, particularly against Gram-positive bacteria with an minimum inhibitory concentrations (MIC) value of 2-16 µg/mL. The subsequent synergistic antibacterial assay showed that derivatives 5c and 6c enhanced the susceptibility of B. subtilis 168 and MRSA USA300 to chloramphenicol (CHL) and kanamycin (KAN) (FICI < 0.5). Our data showed that ocotillol-type derivatives with long-chain amino acid substituents at C-3 were good leads against antibiotic-resistant pathogens MRSA USA300, which could improve the ability of KAN and CHL to exhibit antibacterial activity at much lower concentrations with reduced toxicity.
Subject(s)
Anti-Bacterial Agents/chemical synthesis , Anti-Bacterial Agents/pharmacology , Ginsenosides/chemical synthesis , Ginsenosides/pharmacology , Anti-Bacterial Agents/chemistry , Drug Synergism , Ginsenosides/chemistry , Microbial Sensitivity Tests , Molecular Structure , Structure-Activity RelationshipABSTRACT
Nitric oxide (NO) and its auto-oxidation products are known to disrupt normal bacterial function and NO releasing molecules have the potential to be developed as antibacterial leads in drug discovery. We have designed and synthesized a series of novel nitrated compounds by combining NO releasing groups with ocotillol-type triterpenoids, which have previously demonstrated activity only against Gram-positive bacteria. The in vitro NO release capacity and antibacterial activity were sequentially evaluated and the data showed that most of the synthesized compounds could release nitric oxide. Compound 16a, 17a and 17c, with nitrated aliphatic esters at C-3 position, displayed higher NO release than other analogues, correlating to their good antibacterial activity, in which 17c demonstrated broad-spectrum activity against both Gram positive and -negative bacteria, as well as excellent synergism at sub-minimum inhibitory concentration when using with kanamycin and chloramphenicol. Furthermore, the epifluorescent microscopic study indicated that the ocotillol-type triterpenoid core may induce NO release on the bacterial membrane. Our results demonstrate that nitrated substitutions at C-3 of ocotillol-type derivatives could provide an approach to expand their antibacterial spectrum, and that ocotillol-type triterpenoids may also be developed as appropriate carriers for NO donors in antibacterial agent discovery with low cytotoxicity.
Subject(s)
Anti-Bacterial Agents/chemical synthesis , Anti-Bacterial Agents/pharmacology , Drug Design , Ginsenosides/chemistry , Ginsenosides/pharmacology , Gram-Negative Bacteria/drug effects , Gram-Positive Bacteria/drug effects , Nitric Oxide/metabolism , Anti-Bacterial Agents/chemistry , Cell Line , Cell Survival/drug effects , Dose-Response Relationship, Drug , Ginsenosides/chemical synthesis , Gram-Negative Bacteria/metabolism , Gram-Positive Bacteria/metabolism , Humans , Microbial Sensitivity Tests , Molecular Structure , Structure-Activity RelationshipABSTRACT
A novel class of ocotillol-type triterpenoid derivatives have been synthesized and evaluated for their in vitro antibacterial activity against several representative pathogenic bacterial strains. Compounds 20(S)-protopanaxadiol (PPD), 3, 5, 16 and 24 exhibited potent antibacterial activity against Gram-positive bacteria. Compounds 3 and 5 also displayed promising antibacterial activity against a community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA; strain USA300). Furthermore, compounds PPD, 3 and 16 combined with two commercially available antibiotics kanamycin and chloramphenicol showed strong synergistic inhibitory effects at their sub-MIC concentrations against S. aureus USA300 and Bacillus subtilis 168. Additionally, cytotoxic activity assay showed that the compounds tested did not affect cell viability of the human epithelial kidney (HEK-293) and human cervical (HeLa) cells at their MICs.
