Characterization of essential oil from Ocimum gratissimum leaves: Antibacterial and mode of action against selected gastroenteritis pathogens.

Essential oil of fresh leaves of Ocimum gratissimum (OGEO) was water-steam distilled and analyzed by GC-MS. Thirty-seven compounds were identified, with eugenol (55.6%) as the major component followed by cis-ocimene (13.9%), γ-muurolene (11.6%), (Z,E)-α-farnesene (5.6%), α-trans-bergamotene (4.1%), and ß-caryophyllene (2.7%). Antimicrobial activity of OGEO was tested against four gastroenteritis pathogens (Staphylococcus aureus, Escherichia coli, Salmonella Typhimurium, and Shigella flexneri). OGEO exhibited antibacterial effect, with MICs of 1-2 mg ml-1, against the tested species. OGEO also displayed rapid killing effect within 5 s at four times of MIC against both E. coli and S. Typhimurium. Various assays were performed to investigate the mode of action of the oil. OGEO increased the permeability of microbial cell membrane as evidenced by LIVE/DEAD BacLight assay. Analyses of the release of absorbing materials at 260 nm, protein leakage, SDS-PAGE, and SEM strongly suggested the disruptive action of the oil on the cytoplasmic membrane of the tested microorganisms. Results revealed that the antibacterial property of OGEO could be due to membrane disruption.

Grewiifopenes A-K, bioactive clerodane diterpenoids from Casearia grewiifolia Vent.

Eleven novel clerodane-type diterpenoids, grewiifopenes A-K (1-4 and 12-18), along with nine known compounds (5-11, 19, and 20) were purified from the dichloromethane extract of the twigs and stems of Casearia grewiifolia Vent. (Salicaceae). Their spectroscopic data, including the NMR, HRESIMS, and electronic circular dichroism calculations were employed to completely characterize and elucidate the chemical structures and absolute configurations. The clerodane diterpenoids possessing a 6-OH group and no substitution at C-7 exhibited greater cytotoxic activity than others, with their IC50 values ranging from 0.3 to 2.9 µM. Isocaseamembrin E (7) exhibited antibacterial activity against Staphylococcus aureus, while isocaseamembrin E (7), corymbulosin X (8), caseargrewiin A (9), kurzipene A (10), and balanspene F (11) exhibited antibacterial activity against Bacillus cereus.

Albiflorenes A-L, polyoxygenated cyclohex(a/e)ne diterpene esters from Kaempferia albiflora.

Twelve polyoxygenated cyclohex(a/e)ne diterpene esters, named albiflorenes A-L (1-12), were isolated from the whole plants of Kaempferia albiflora, known as "Prao Mang Mum." Their structures and relative stereochemistry were determined by extensive spectroscopic analysis. Furthermore, the comparison of experimental electronic circular dichroism (ECD) curves with the curves predicted by TDDFT was used to determine the absolute configurations. Albiflorenes contain polyoxygenated cyclohexane (or cyclohexene) derivatives, which are linked to either isopimarane or abietane diterpene acid units. The discovery marks the first occurrence of a conjugate between polyoxygenated cyclohexane (or cyclohexene) rings and diterpenoids. Among the isolates, albiflorene C specifically exhibited antibacterial activity against Bacillus cereus with MIC and MBC values of 3.13 and 6.25 µg/mL, respectively.

Diterpenoids and p-methoxycinnamic acid diol esters from Kaempferia saraburiensis Picheans. (Zingiberaceae): Structural assignment of saraburol and their biological activities.

Five undescribed compounds, including three diterpenoids namely, saraburol, saraburanes A and B, and two p-methoxycinnamic acid monoterpene diol esters, named E/Z-saraburinic esters, together with ten known oxygenated isopimarane diterpenoids, were isolated from the whole plant of Kaempferia saraburiensis Picheans. Among these compounds, saraburol possesses an unusual 6/9/6 tricyclic ring system bearing a 1,3-dioxonane-4-one scaffold, which is rarely found in natural products. The structure of isolated compounds was elucidated by spectroscopic methods, including HRESIMS, FTIR, 1D and 2D-NMR, and by comparison with published data, and their absolute configurations were determined by comparison of experimental with calculated ECD spectra and hydrolysis reaction. Using gauge-independent atomic orbital (GIAO) NMR shift calculations coupled with DP4+ probability analyses, biogenetic considerations, and optical rotation allowed for the complete characterization of saraburol. A plausible biosynthetic pathway for saraburol and saraburane A was proposed. The cytotoxicity result indicated that E-saraburinic ester exhibited the most potent activity with an IC50 value of 12.0 µM against MOLT-3 cells with a selectivity index of 12.5. Saraburane B exhibited the most potent activity against Gram-positive bacteria strain Staphylococcus epidermidis with MIC (MBC) value of 25 (50) µg/mL.

Roscotanes and roscoranes: Oxygenated abietane and pimarane diterpenoids from Kaempferia roscoeana.

Eight previously undescribed ditepenoids, including four oxygenated abietanes (roscotanes A-D) and four oxygenated pimaranes (roscoranes A-D), along with twelve known diterpenoids were isolated from the whole plants of Kaempferia roscoeana. Their structures were elucidated by extensive spectroscopic analysis, and the structure of roscotane A was further confirmed by single crystal X-ray diffraction analysis. Most isolated compounds were evaluated for their antimicrobial and antimalarial activities.

Antimicrobial activity of coronarin D and its synergistic potential with antibiotics.

Coronarin D is a labdane-type diterpene from the rhizomes of Hedychium coronarium. In the view of our ongoing effort to explore its novel biological activity, antimicrobial activity study of coronarin D was performed. The results showed that coronarin D was active against tested Gram-positive bacteria, inactive for tested Gram-negative bacteria, and weakly active against tested fungi. The antibacterial effect of the combination of coronarin D with nine classical antibiotics against four Gram-positive bacteria was also evaluated. The fractional inhibitory concentration indices (FICI) of coronarin D-antibiotics combinations, calculated from the checkerboard assay, were used as synergism indicator. Out of 36 combinations, 47% showed total synergism, 33% had partial synergistic interaction, 17% showed no effect, and 3% showed antagonism. By combination with coronarin D at concentration of 0.25 minimal inhibitory concentration (MIC), the activities of antibiotics were boosted to 4- to 128-fold. These finding suggested an attractive approach to combat the infectious diseases by using coronarin D-antibiotic drug combination.