Nisachon Khunnawutmanotham

Labdane diterpenes from the rhizomes of Hedychium coronarium

A new labdane diterpenoid, (E)-labda-8(17),12-dien-15,16-olide (1) together with eight known compounds, coronarin D (2), coronarin D methyl ether (3), coronarin D ethyl ether (4), isocoronarin D (5), coronarin B (6), labda-8(17),11,13-trien-15,16-olide (7), (E)-labda-8(17),12-diene-15,16-dial (8) and 16-hydroxylabda-8(17),11,13-trien-15,16-olide (9), are isolated from the rhizomes of Hedychium coronarium. Compounds 2–4, 5 and 9 are isolated as mixtures of C-15, C-14 and C-16 epimers, respectively. Their structures are determined on the basis of their spectroscopic data. The epimeric mixtures of 2 and 3 have not been reported before. Some of them were evaluated for their cytotoxicity.

Cytotoxic and antimicrobial activities of aporphine alkaloids isolated from Stephania venosa (Blume) Spreng.

The cytotoxic activity of five alkaloids, namely 4,5-dioxo-dehydrocrebanine (1), dehydrocrebanine (2), crebanine (3), oxostephanine (4), and thailandine (5) isolated from the tuber and leaves of Stephania venosa (Blume) Spreng was investigated. Thailandine showed the strongest activity against lung carcinoma cells (A549) (IC50 of 0.30 µg/mL) with very low cytotoxicity against normal embryonic lung cells (MRC-5). Thailandine also demonstrated strong activity against Plasmodium falciparum, K1 strain (IC50 of 20 ng/mL), and Mycobacterium tuberculosis H(37)Ra (MIC of 6.25 µg/mL) as well as gram-positive bacteria such as Streptococcus pneumoniae and Staphylococcus aureus. Oxostephanine exhibited strong activity against breast cancer (BC) and acute lymphoblastic leukemia cells (MOLT-3) with an IC50 of 0.24 and 0.71 µg/mL, respectively, and exhibited very low cytotoxicity against MRC-5 cells. Dehydrocrebanine demonstrated strong activity against promyelocytic leukemia cells (HL-60) with an IC50 of 2.14 µg/mL whereas crebanine showed weak activity against cancer cell lines. However, both of them showed cytotoxicity against MRC-5 cells.

Synthesis and anti-acetylcholinesterase activity of scopoletin derivatives.

A series of scopoletin derivatives incorporated with the pyridinium moiety was synthesized and evaluated for their acetylcholinesterase (AChE) inhibitory activity by the colorimetric Ellmans method. A 2-fluorobenzylpyridinium derivative was the most potent among the tested compounds, with an IC50 value of 0.215±0.015μM, which was greatly improved from that of scopoletin. Docking studies revealed that the scopoletin portion of the mentioned compound was bound to the peripheral anionic site of the AChE, whereas the N-benzylpyridinium residue to the catalytic anionic site.

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.

Dipyridodiazepinone derivatives; synthesis and anti HIV-1 activity

Summary Ten dipyridodiazepinone derivatives were synthesized and evaluated for their anti HIV-1 reverse transcriptase activity against wild-type and mutant type enzymes, K103N and Y181C. Two of them were found to be promising inhibitors for HIV-1 RT.

Novel 2-Chloro-8-arylthiomethyldipyridodiazepinone Derivatives with Activity against HIV-1 Reverse Transcriptase

Based on the molecular modeling analysis against Y181C HIV-1 RT, dipyridodiazepinone derivatives containing an unsubstituted lactam nitrogen and 2-chloro-8-arylthiomethyl were synthesized via an efficient route. Some of them were evaluated for their antiviral activity against HIV-1 RT subtype E and were found to exhibit virustatic activity comparable to some clinically used therapeutic agents.

Three Lycopodium alkaloids from Thai club mosses

Phytochemical constituents in alkaloid extracts from three Thai club mosses Huperzia squarrosa, Huperzia phlegmaria and Phlegmariurus nummularifolius were investigated. Squarrosinoxide was an undescribed Lycopodium alkaloid from H. squarrosa possessing an unprecedented 6/5/7 tricyclic spiro system. Acetyllycophlegmarianol was an undescribed N-oxide lycopodine-type alkaloid isolated from H. phlegmaria. 4-Epilycopodine, an undescribed epimer of lycopodine, was first isolated from P. nummularifolius. The structural assignments were established through comprehensive spectroscopic techniques and chemical correlations. All compounds were assayed for their anti-acetylcholinesterase activity in vitro.

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 β-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.

Synthesis of 3-aminocoumarin-N-benzylpyridinium conjugates with nanomolar inhibitory activity against acetylcholinesterase

A series of 3-amino-6,7-dimethoxycoumarins conjugated with the N-benzylpyridinium moiety through an amide-bond linkage was synthesized and evaluated for their acetylcholinesterase inhibitory activity. A number of the benzylpyridinium derivatives exhibited potent activities with inhibitory concentration (IC50) values in the nanomolar concentration range. Among them, the 2,3-difluorobenzylpyridinium-containing compound was the most potent inhibitor with an IC50 value of 1.53 ± 0.01 nM. Docking studies revealed that the synthesized compounds inhibit the target enzyme by a dual binding site mechanism whereby the coumarin portion binds with the peripheral anionic site while the N-benzylpyridinium residue binds with the catalytic anionic site of the enzyme.

Coronarin D conjugated to methylene homologues of chlorambucil: synthesis and evaluation of their cytotoxicity

Methylene homologues of chlorambucil were synthesised and conjugated to the labdane diterpene coronarin D. The products were evaluated for their in vitro cytotoxicity, and were found to exhibit selective activity against MOLT-3 cell line. Two homologues of chlorambucil showed a comparable cytotoxic effect to their parent. However, as compared with the non-derivatised chlorambucil and its homologues, their conjugation with coronarin D through ester linkage did not enhance in vitro cytotoxicity against the tested cancer cell lines.