Thanh-Hau Huynh

Chemical investigation of an actinomycete isolated from forest soil near a royal tomb site in the Republic of Korea (Streptomyces sp. YNK18) led to the discovery of two peptides: sadoamides A (1) and B (2). Spectroscopic analysis established 1 and 2 as all-aromatic tripeptides composed of phenylalanine (Phe) and two nonproteinogenic amino acids, 4-hydroxyphenylglycine (Hpg) and β-methyltryptophan (β-MeTrp). The relative configuration of the β-MeTrp residue was determined by J-based configuration analysis utilizing coupling constants and diagnostic ROESY correlations. The absolute configurations of sadoamides were determined using the advanced Marfey's method. Both compounds effectively inhibited the proteolytic activity of purified proteasomes in vitro and cellular proteasomes in HeLa cells, with 1 exhibiting greater potency. Sadoamide A (1) stabilized the short-lived antiapoptotic protein MCL1 and exerted significant cytoprotective effects against apoptosis-inducing chemical stimuli. These findings identify sadoamides as new microbial peptides that modulate the ubiquitin-proteasome system and highlight the potential of microbial metabolites to regulate critical eukaryotic signaling pathways, including apoptosis.

A targeted method for discovering cinnamoyl-containing nonribosomal peptides (CCNPs), a unique class of bioactive compounds, was devised by using cinnamoyl isomerase, a key enzyme in the biosynthesis of the cinnamoyl moiety, as a genome mining probe. A total of 39 hit strains were obtained, including 35 from polymerase chain reaction-based screening of the in-house bacterial library (2.5% of 1400 strains) targeting the cinnamoyl isomerase-encoding gene and 4 from the genome mining of online databases. Sequence similarity networking and phylogenetic analyses of the isomerase amplicons (∼530 bp) classified the CCNPs into three major substructure-based groups (Z-, E-, and M-type CCNPs) and revealed distinct clade-structure relationships (13 clades). To overcome the challenge of silent biosynthetic gene clusters, we activated these clusters by overexpressing conserved cluster-situated LuxR regulators combined with extensive culture optimization. CCNP production was metabolomically detected in the bacterial extracts by using the characteristic UV absorption and MS/MS fragments of cinnamoyl moieties. CCNP production was observed in 20 of the 39 hit strains, resulting in the isolation of 6 new CCNPs, including oxy-skyllamycin B (2), gwanacinnamycin (3), and luxocinnamycins A-D (4-7), with high structural novelty. Their structures were elucidated using comprehensive spectroscopic analyses and multiple-step chemical derivatizations, and the putative biosynthetic pathways were bioinformatically proposed. Gwanacinnamycin (3) exhibited significant antimycobacterial activity, whereas luxocinnamycin A (4) displayed moderate antiproliferative activity against stomach cancer cells. Our findings highlight a targeted metabologenomic approach combined with transcriptional regulator overexpression as a logical and efficient platform for the discovery of bioactive compounds from nature.

Dendropanax morbifera Leveille is a traditional medicine used to treat migraine headache and dysmenorrhea. In this study, three polyacetylenes, methyl (10E,9R,16R)-16-acetoxy-9-hydroxyoctadeca-10,17-dien-12,14-diynoate (1), methyl (10E,9R,16S)-9,16-dihydroxyoctadeca-10-en-12,14-diynoate (2), and methyl (10Z,9R,16S)-9,16-dihydroxyoctadeca-10,17-dien-12,14-diynoate (3), were isolated from the aerial parts of D. morbifera, together with seven known compounds (4–10). Importantly, the isolates (6 and 8) were found in the family Araliaceae for the first time in this study. Compounds 1−10 were evaluated for their binding affinity to AMPK and CTSS receptors using in silico docking simulations. Only compound 7 increased the protein expression levels of PPAR-α, Sirt1, and AMPK when administered to HepG2 cells as a PPAR-α agonist. On the other hand, 7 did not produce any significant reduction in CTSS activity. This study could pave the way for the discovery of novel treatments from D. morbifera targeting PPAR-α and AMPK.

Four new macrolides, spirosnuolides A-D (1-4, respectively), were discovered from the termite nest-derived Kitasatospora sp. INHA29. Spirosnuolides A-D are 18-membered macrolides sharing an embedded [6,6]-spiroketal functionality inside the macrocycle and are conjugated with structurally uncommon side chains featuring cyclopentenone, 1,4-benzoquinone, hydroxyfuroic acid, or butenolide moieties. Structure elucidation was achieved using a combination of spectroscopic analyses, multiple chemical derivatizations (methylation, methanolysis, Luche reduction, and Mosher's reaction), X-ray diffraction analysis, and computational ECD calculations. Interestingly, genome sequencing analysis suggests that spirosnuolides were biosynthesized through a rare type I/III hybrid polyketide synthase. Importantly, spirosnuolide B displayed potent antiproliferative effects against various cancer cell lines at nanomolar concentrations, particularly against HCC827 cells, an EGFR mutant non-small-cell lung cancer (NSCLC) cell line, with a high safety index value. Based on in vitro studies, the antiproliferative mechanism of spirosnuolide B involved the activation of AMPK signaling, leading to cell cycle arrest and apoptosis in HCC827 cells. Its potent efficacy was also proven in vivo by the effective inhibition of tumor growth in mouse xenograft studies. Moreover, cotreatment with spirosnuolide B and gefitinib, synergistically enhanced the antiproliferative activity and apoptosis, suggesting a potential strategy to overcome gefitinib resistance in EGFR mutant NSCLC.

Dendropanax morbifera Leveille is a traditional medicine used to treat migraine headache and dysmenorrhea. In this study, a new phenolic glycoside, morbiferoside A (1), and three polyacetylenes, methyl (10E,9R,16R)-16-acetoxy-9-hydroxyoctadeca-10,17-dien-12,14-diynoate (2), methyl (10E,9R,16S)-9,16-dihydroxyoctadeca-10-en-12,14-diynoate (3), and methyl (10Z,9R,16S)-9,16-dihydroxyoctadeca-10,17-dien-12,14-diynoate (4), were isolated from the aerial parts of D. morbifera, together with seven known compounds (5–11). Importantly, the isolates, 7 and 9 were found in the family Araliaceae for the first time in this study. Compounds 1−11 were evaluated for their binding affinity to AMPK and CTSS receptors using in silico docking simulations. Only compound 8 increased the protein expression levels of PPAR-α, Sirt1, and AMPK when administered to HepG2 cells as a PPAR-α agonist. On the other hand, 8 did not produce any significant reduction in CTSS activity. This study could pave the way for the discovery of novel treatments from D. morbifera targeting PPAR-α and AMPK.

Two new proton-deficient metabolites, tandocyclinones A and B (1 and 2), were discovered via the chemical profiling of the Streptomyces sp. strain TDH03, which was isolated from a marine sediment sample collected from the intertidal mudflat in Tando Port, the Republic of Korea. The structures of 1 and 2 were elucidated as new ether-bridged C-glycosyl benz[a]anthracenes by using a combination of spectroscopic analyses of ultraviolet (UV) and mass spectrometry (MS) data, along with nuclear magnetic resonance (NMR) spectra, which were acquired in tetrahydrofuran (THF)-d₈ selected after an extensive search for a solvent, resulting in mostly observable exchangeable protons in the ¹H NMR spectrum. Their configurations were successfully assigned by applying a J-based configuration analysis, rotating-frame Overhauser enhancement spectroscopy (ROESY) NMR correlations, chemical derivatization methods based on NMR (a modified version of Mosher’s method) and circular dichroism (CD) (Snatzke’s method using Mo₂(OAc)₄-induced CD), as well as quantum-mechanics-based computational methods, to calculate the electronic circular dichroism (ECD). Tandocyclinones A and B (1 and 2) were found to have weak antifungal activity against Trichophyton mentagrophytes IFM40996 with an MIC value of 128 μg/mL (244 and 265 μM for 1 and 2, respectively). A further biological evaluation revealed that tandocyclinone A (1) displayed inhibitory activity against Mycobacterium avium (MIC₅₀ = 40.8 μM) and antiproliferative activity against SNU638 and HCT116 cancer cells, with IC₅₀ values of 31.9 µM and 49.4 µM, respectively.