Volatile‐Oils Composition, and Bioactivity of the Essential Oils of Plectranthus barbatus, P. neochilus, and P. ornatus Grown in Portugal

Abstract

Volatile-oils chemical composition and bioactivity of the essentail oils from Plectranthus barbatus, P. neochilus, and P. ornatus (Lamiaceae) were assessed. Aerial parts from these three related Plectranthus species were collected from cultivated plants grown in Portugal, during vegetative and flowering phases. Volatiles, isolated by distillation-extraction, were analyzed by GC and GC/MS. Monoterpene hydrocarbons (12-74%) and sesquiterpene hydrocarbons (4-45%) constituted the main fractions in all volatiles. α-Pinene (3; 12-67%), oct-1-en-3-ol (6; traces-28%), β-pinene (7; 0.1-22%), and β-caryophyllene (50; 7-12%) dominated P. barbatus volatiles. P. neochilus major volatile components were α-terpenyl acetate (41; traces-48%), α-thujone (2; 2-28%), β-caryophyllene (50; 2-28%), β-pinene (7; 1-25%), and α-pinene (3; 1-19%). Oct-1-en-3-ol (6; 13-31%), β-pinene (7; 11-24%), α-pinene (3; 11-19%), and β-caryophyllene (50; traces-11%) were the main constituents from P. ornatus volatiles. These chemical compositions were rather different from those previously found for specimens harvested in Africa and Brazil. Moreover, the volatiles from the flowers are herewith reported for the first time. Essential oils, isolated by hydrodistillation from leaves and stems, showed a yellowish color and unpleasant odor, with yields ranging from 0.08% to 0.84% (v/dry weight). Antioxidant and antimicrobial activities of the essential oils were evaluated by DPPH· and TBARS assays, and agar disc-diffusion method, respectively. Results showed low or moderate antioxidant capacity and significant antimicrobial activity against Gram-positive bacteria.

Thujone, a widely debated volatile compound: What do we know about it?

“…It should be mentioned that thujone may accumulate in some less frequently used and investigated species of the Lamiaceae family, too. For example, higher amounts were detected in Plectranthus species, where a-thujone accumulated up to 28% of the EO (Mota et al 2014) and in Phlomis ferruginea in 5.5% (Formisano et al 2006). Similarly, a-thujone was detected by Kaurinovic et al (2010) in 2.1-3.3% in samples of Marrubium peregrinum, nevertheless even the accumulation rate of total volatiles was very low (0.09-0.14% DW.…”

A Survey of Chemical Compositions and Biological Activities of Yemeni Aromatic Medicinal Plants

“…The essential oil of Plectranthus barbatus from Taiz region of Yemen has been found to have α-terpinene (2.8%), p -cymene (9.3%), γ-terpinene (20.0%), thymol (48.7%), β-caryophyllene (6.4%) and β-selinene (2.1%) as the major constituents [ 16 ]. The chemical composition of Yemeni Plectranthus barbatus was very different from a Plectranthus barbatus sample from Portugal, which was devoid of thymol [ 93 ]. The Taiz oil sample was subjected to antimicrobial, antifungal, and cytotoxic assays against MCF-7 and MDA-MB-231 cancer cells.…”

Antimicrobial Activity of the Essential Oil ofPlectranthus neochilusagainst Cariogenic Bacteria

“…The essential oil of P. neochilus displays antischistosomal [ 12 ] and insecticidal [ 15 ] activities. Recently, researchers have applied diffusion in agar disc to assess the antimicrobial activity of the essential oil of a specimen of P. neochilus collected in Portugal against Bacillus cereus , Bacillus subtilis , Staphylococcus aureus , Listeria monocytogenes , Escherichia coli , Pseudomonas aeruginosa , Helicobacter pylori , and Saccharomyces cerevisiae [ 16 ]. The authors reported that the activity of this essential oil against the selected microorganisms was between low and moderate.…”