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Abstract: A two-step procedure was applied to couple zerumbone, a natural sesquiterpene, with thiols 8a-k to obtain a small library of ten novel zerumbone derivatives 9a-k with full-length library data of spectra including 1H-, 13C-NMR, and HRMS. The tautomerization of 9a, 9b, and 9c was revealed in DMSO and discussed in the case of 9c. The series of 9a-k together with zerumbone 1 was evaluated for their in vitro cytotoxic activity using three human cancer cell lines, HepG2, A549 and HeLa. The results revealed that all zerumbone derivatives had cytotoxic activity against HepG2, A549, and HeLa cells that was 4-20 times stronger than zerumbone.

An indigenous effective bacterial strain has been isolated from soil samples of contaminated tea farming site in Northern Vietnam with chlorpyrifos degradability and plant growth promoting characteristics. The bacterial isolate was determined to belong to genus Ensifer (syn. Sinorhizobium), and its degrading property for OPP substrate chlorpyrifos in culture as well as in test soil were studied. The results open a prospect of applying the dual-effective bacterial strain in agriculture practices either to reduce the use of chemical fertilizer or to remediate OPP contaminated planting soils.

Sargassum is a widely distributed marine brown algal genus in Vietnam and has been considered a source of diverse bioactive metabolites. In this study, S. crassifolium collected from South Central region of Vietnam was chemically studied and bioactively evaluated. Fucosterol was isolated and identified from the methanolic extract of the alga by means of chemical fractionation and spectral analysis and showed no cytotoxic effect in Hep-G2 cells at the observed concentrations. In vitro assay for intracellular reactive oxygen species by dichlorofluorescein method revealed a potent scavenging effect of the isolated compound. Accordingly, the level of intracellular reactive oxygen species induced by hydrogen peroxide (H2O2) was reduced by 71.66% with the treatment of fucosterol at 10 µg.ml-1. The results indicated the ability of algal fucosterol in diffusing into cells and preventing the production of different ROS compounds and further suggested the therapeutic potential against diseases caused by oxidative stress of natural metabolites from S. crassifolium in Vietnam.

Arbuscular mycorrhizal (AM) fungi are soil eukaryotes that belong to phylum Glomeromycota and have symbiosis with the vast majority of higher plants’ roots. AM fungi are believed to be coevolved with terrestrial plants, the abundance and diversity of AM fungal communities as a result are host plant dependent. A survey of AM fungi from the rhizospheres of medicinal plants in Northern Vietnam including gurma Gymnema sylvestre and turmeric Curcuma longa was carried out. From the extracted total DNAs of the medicinal plants’ rhizosphere soil samples, 35 mycorrhizal fungal species were identified by analyzing small subunit rRNA gene sequences. Result revealed that genus Glomus is the most abundant in the AM communities of G. sylvestre and C. longa, followed by Gigaspora and Acaulospora. Besides, AM species belonging to genera Scutellospora, Diversispora and Rhizophagus were observed in almost all rhizosphere soil samples. The spore counting by wet sieving and decanting method uncovered a variation in AM spore density of gurma and turmeric rhizosphere. In general, AM species were found more abundantly and more diverse in collected rhizome soil samples of C. longa (27 species belonging to 10 genera) than of G. sylvestre (17 species found belonging to 7 genera). The observed difference in AM communities of G. sylvestre and C. longa supports evidence for the dependence of AM fungal species on host plants, and indicates that AM fungi may have relation to the host plants’ secondary metabolite production.

In the context of sources for natural products discovery are going scarcer, exploiting biotechnologically potential compounds from marine microbial symbionts is considered a relatively new trend. In our study a total of fifteen fungal strains were isolated from marine algal samples belonging to species Kappaphycus cottonii, K. striatus, Gracilaria eucheumatoides and Betaphycus gelatinus collected in Nha Trang in 2017. The in vitro biological activities, including antimicrobial, cytotoxic and hemolytic activities of ethyl acetate extracts of the fungal strains were determined. From fifteen fungal extracts, six displayed antimicrobial activity against at least one test strain. At 20 μg.ml-1, four fungal extracts were found to express cytotoxic activity on two human cancer cell lines hepatocellular carcinoma (Hep-G2) and breast adenocarcinoma (MCF-7), with G. eucheumatoides being the source of the highest number of producer strains. Hemolytic activity was observed in rabbit erythrocytes under almost all fungal extracts’ effect. No apparent relationship was observed between the biological activities of fungal isolates. The biological assessments uncovered several fungal candidates, such as Bge-1.1, Kco-2.1 and Geu-1.1 with relatively potent antimicrobial and cytotoxic activities while expressing less hemolytic effect at concentrations from 20 μg.ml-1 to 200 μg.ml-1. The results evidenced the potential of exploiting natural products from associated marine microorganisms, especially those for the purpose of pharmaceutical applications.

In recent years, a considerable number of studies on the role of microbes in agarwood production have been carried out in plants of the species Aquilaria. Based on the fact that there is a relationship between the microorganisms residing inside the plant and the agarwood formation, we isolated and characterized endophytic fungi associated with A. crassna samples collected from Southern Vietnam. Morphological identification and DNA barcoding analysis of the fungal endophytic isolates indicated that they were classified at least into three groups of diverse genera: Geotrichum, Fusarium and Colletotrichum belonging to families Dipodascaceae, Nectriaceae and Glomerellaceae, respectively. Noteworthy, Geotrichum candium strain SHTr1 isolated from a dark colored woody sample of agarwood was able to produce a fruity odor and exhibited a slight antimicrobial activity against the test bacterium Staphylococcus aureus. Another fungal isolate, Fusarium verticillioides SHTr3’s, showed a moderate antimicrobial activity against a test Gram positive bacteria Bacillus subtillis and S. aureus with MIC values at 50 μg.mL-1. At 200 μg.mL-1, the ethyl acetate extracts of fungal isolates F. verticillioides SHTr3 and Colletotrichum truncatum SHTrHc7 were found to have comparable scavenging abilities on DPPH-free radicals with 53.87 and 71.82%, respectively. The present results contribute to a depiction of a diverse fungal endophytic community in Vietnamese agarwood plant A. crassna and provide important information for further understanding of the role of endophytic fungi in agarwood formation and therapeutic applications of host plants in general.