Farnesane-Type Sesquiterpenoids with Antibiotic Activity from Chiliadenus lopadusanus

Abstract

Chiliadenus lopadusanus Brullo is an Asteraceae plant species endemic to Lampedusa island, the largest island of the Pelage archipelago, Italy. The organic extract of its whole aerial parts, showing antibiotic activity against Staphylococcus aureus and Acinetobacter baumannii, wasfractionated employing bioguided purification procedures affording three main farnesane-type sesquiterpenoids. They were identified by spectroscopic methods (NMR and ESIMS data) as the (E)-3,7,11-trimethyldodeca-1,6,10-triene-3,9-diol, (E)-10-hydroxy-2,6,10-trimethyldodeca-2,6,11- trien-4-one and (E)-10-hydroxy-2,6,10-trimethyl-dodeca-6,11-dien-4-one, commonly named 9-hydroxynerolidol, 9-oxonerolidol, and chiliadenol B, respectively. These three sesquiterpenes, isolated for the first time from C. lopadusanus, were tested on methicillin-resistant S. aureus and A. baumannii showing antibacterial and antibiofilm activities. This plant could be used as a source to isolate secondary metabolites as potential new antibiotics.

Keywords: Chiliadenus lopadusanus; antibacterial activity; antibiofilm activity; sesquiterpenes.

Figure 1

Chiliadenus lopadusanus in Conigli bay, Lampedusa island, Italy.

Figure 2

The chemical structures of camphor, borneol, 1,8-cineole, t-cadinol, t-muurolol, and torreyol.

Figure 3

Structures of 9-hydroxynerolidol, 9-oxonerolidol, and chiliadenol B (1–3).

Figure 4

In vitro biofilm formation of S. aureus following an overnight treatment with serial dilutions of compound 3. Biofilm formation was determined by the cristal violet assay. Biofilm biomass values are presented as the mean percentage ± standard deviation (SD) and S. aureus biofilm biomass without a treatment is assumed to be 100%. Each pair of means was compared using a Tukey’s multiple comparisons test; no significant differences were detected between the following pairs: 150℃9.37 μg/mL; 37.5℃18.7 μg/mL.

Figure 5

In vitro biofilm formation of A. baumannii following an overnight treatment with serial dilutions of compound 3. Biofilm formation was determined by the cristal violet assay. Biofilm biomass values are presented as the mean percentage ± SD and A. baumannii biofilm biomass without a treatment is assumed to be 100%. Each pair of means was compared using a Tukey’s multiple comparisons test; no significant differences were detected between the following pairs: 150℃9.37 μg/mL; 37.5℃18.7 μg/mL.

Figure 6

Chromatographic purification diagram of the metabolites extracted from C. lopadusanus.