Cinnamoyl-containing nonribosomal peptides (CCNPs) form a unique family of actinobacterial secondary metabolites and display various biological activities. A new CCNP named epoxinnamide (1) was discovered from intertidal mudflat-derived Streptomyces sp. OID44. The structure of 1 was determined by the analysis of one-dimensional (1D) and two-dimensional (2D) nuclear magnetic resonance (NMR) data along with a mass spectrum. The absolute configuration of 1 was assigned by the combination of advanced Marfey’s method, ³J_HH and rotating-frame overhauser effect spectroscopy (ROESY) analysis, DP4 calculation, and genomic analysis. The putative biosynthetic pathway of epoxinnamide (1) was identified through the whole-genome sequencing of Streptomyces sp. OID44. In particular, the thioesterase domain in the nonribosomal peptide synthetase (NRPS) biosynthetic gene cluster was proposed as a bifunctional enzyme, which catalyzes both epimerization and macrocyclization. Epoxinnamide (1) induced quinone reductase (QR) activity in murine Hepa-1c1c7 cells by 1.6-fold at 5 μM. It also exhibited effective antiangiogenesis activity in human umbilical vein endothelial cells (IC₅₀ = 13.4 μM).

Aminomalonic acid (Ama) is found in various natural products and protein hydrolysates of multiple organisms, but the understanding of its biosynthetic origin remains largely limited. By exploiting a biosynthetic gene cluster for ribosomally synthesized and post-translationally modified peptides (RiPPs), which are rich sources of new enzyme chemistry, we identified a novel two-enzyme pathway for Ama biosynthesis. This biosynthetic pathway, mediated by an Fe(II)/2-oxoglutarate-dependent oxygenase (Fe(II)/2OG), SmaO, and an atypical Fe(II)-dependent histidine-aspartate (HD) domain enzyme, SmaX, converts aspartate (Asp) to β-hydroxyaspartic acid (Hya) intermediate and ultimately to Ama. These tandem enzymatic reactions─hydroxylation of the carbon next to an acid functional group and subsequent four-electron oxidative bond cleavage in α-hydroxy acid─are similar to those associated with other known HD domain oxygenases, PhnZ and TmpB. However, SmaX also exhibits unique features, such as C-C bond cleavage in α-hydroxycarboxylate using a single Fe cofactor, in contrast to the C-P bond cleavage using a mixed-valent diiron cofactor in PhnZ and TmpB. Bioinformatic analysis reveals that this two-enzyme cascade may be present in various biosynthetic pathways for peptide natural products, including RiPPs and nonribosomal peptides (NRPs). Collectively, our study demonstrates the presence of a novel Ama biosynthetic pathway and suggests its widespread distribution in peptide natural product biosynthesis.

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.

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.