Essential oils were extracted from the culm and leaf of Cymbopogon citratus collected from different regions of Vietnam and analyzed using GC/MS. The results showed that citral is the major component accounting for 61.20%–76.46% of the essential oils. The citral content was higher in the essential oil obtained from the leaf than in that from the culm of lemongrass in all regions. In particular, camphene, valerianol, and epi‐α‐muurolol can be used to differentiate essential oils originating from leaves versus culms. The cytotoxic effects of the essential oils on various lung cancer cell lines were evaluated in the present study. All essential oils exhibited cytotoxicity in the tested cells. The Ha Loc leaf essential oil (HLL) exhibited the most potent effects on A549 and H1975 cells, with IC₅₀ values of 1.73 ± 0.37 and 4.01 ± 0.30 μg/mL, respectively. The Hy Cuong leaf essential oil (HCL) showed the strongest effect on H1299 cells, with an IC₅₀ value of 2.45 ± 0.21 μg/mL. The Kim Duc culm (KDC) essential oil exerted the strongest cytotoxic effects against H1650 cells, with an IC₅₀ value of 4.86 ± 0.29 μg/mL. The HLL induced apoptosis and cycle arrest in A549 cells according to flow cytometric analysis and fluorescent nuclear staining assays. The western blot analysis indicated that HLL induced the apoptotic effect by altering the regulating proteins of the apoptosis process such as caspase‐3, Bcl‐2, and Bax. The data strongly suggested that the intrinsic pathway may play an important role in the apoptotic effects of HLL.

A screening of our actinomycete fraction library against the NCI-60 SKOV3 human tumor cell line led to the isolation of isopimara-2-one-3-ol-8,15-diene (1), lagumycin B (2), dehydrorabelomycin (3), phenanthroviridone (4), and WS-5995 A (5). These secondary metabolites were produced by a Micromonospora sp. isolated from sediment collected off the Cát Bà peninsula in the East Sea of Vietnam. Compound 1 is a novel Δ^8,9-pimarane diterpene, representing one of approximately 20 actinomycete-produced diterpenes reported to date, while compound 2 is an angucycline antibiotic that has yet to receive formal characterization. The structures of 1 and 2 were elucidated by combined NMR and MS analysis and the absolute configuration of 1 was assigned by analysis of NOESY NMR and CD spectroscopic data. Compounds 2–5 exhibited varying degrees of cytotoxicity against a panel of cancerous and non-cancerous cell lines. Overall, this study highlights our collaborative efforts to discover novel biologically active molecules from the large, underexplored, and biodiversity-rich waters of Vietnam’s East Sea.

Three new lavandulylated flavonoids, (2S,2″S)-6-lavandulyl-7,4′-dimethoxy-5,2′-dihydroxylflavanone (1), (2S,2″S)-6-lavandulyl-5,7,2′,4′-tetrahydroxylflavanone (2), and (2″S)-5′-lavandulyl-2′-methoxy-2,4,4′,6′-tetrahydroxylchalcone (3), along with seven known compounds 4–10 were isolated from culture broth of Streptomyces sp. G248. Their structures were established by spectroscopic data analysis, including 1D and 2D nuclear magnetic resonance (NMR), and high-resolution electrospray ionization mass spectrometry (HR-ESI-MS). The absolute configurations of 1–3 were resolved by comparison of their experimental and calculated electronic circular dichroism spectra. Compounds 1–3 exhibited remarkable antimicrobial activity. Whereas, two known compounds 4 and 5 exhibited inhibitory activity against Mycobacterium tuberculosis H37Rv with minimum inhibitory concentration (MIC) values of 6.0 µg/mL and 11.1 µg/mL, respectively.

Analysis of an antimicrobial culture broth extract of the sponge-derived actinomycete Streptomyces sp. (strain G246) led to the isolation of two new lavandulylated flavonoids, 6-lavandulyl-7-methoxy-5,2′,4′-trihydroxylflavanone (1) and 5′-lavandulyl-4′-methoxy-2,4,2′,6′-tetrahydroxylchalcone (2), along with eight known compounds 3–10. Their structures were established by spectral data analysis, including MS, 1D, 2D-NMR and CD. The absolute configurations of 1 and 2 were suggested by comparison of their experimental and calculated electronic circular dichroism spectra. All the isolated compounds were evaluated for their antimicrobial activity against a panel of clinically significant microorganisms. Compounds 1 and 2 had a broad-spectrum of antimicrobial activity. Additionally, except the strain Escherichia coli, compound 2 exhibited remarkable inhibitory activity against Pseudomonas aeruginosa, Salmonella enterica, Enterococcus faecalis, Staphylococcus aureus, Bacillus cereus, and Candida albicans strains. Graphical Abstract

Marine microorganisms are an invaluable source of novel active secondary metabolites possessing various biological activities. In this study, the extraction and isolation of the marine sediment Penicillium species collected in Vietnam yielded ten secondary metabolites, including sporogen AO-1 (1), 3-indolecarbaldehyde (2), 2-[(5-methyl-1,4-dioxan-2-yl)methoxy]ethanol (3), 2-[(2R-hydroxypropanoyl)amino]benzamide (4), 4-hydroxybenzandehyde (5), chrysogine (6), 3-acetyl-4-hydroxycinnoline (7), acid 1H-indole-3-acetic (8), cyclo (Tyr-Trp) (9), and 2’,3’-dihydrosorbicillin (10). Their structures were identified by the analysis of 1D and 2D NMR data. Among the isolated compounds, 2-[(5-methyl-1,4-dioxan-2-yl)methoxy]ethanol (3) showed a strong inhibitory effect against Enterococcus faecalis with a minimum inhibitory concentration value of 32 µg/mL. Both 2-[(2R-hydroxypropanoyl)amino]benzamide (4) and 4-hydroxybenzandehyde (5) selectively inhibited E. coli with minimum inhibitory concentration values of 16 and 8 µg/mL, respectively. 2’,3’-Dihydrosorbicillin (10) potentially inhibited α-glucosidase activity at a concentration of 2.0 mM (66.31%).