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Fermentation of the marine-derived fungus Trichoderma asperellum, collected from the sediment of the Antarctic Penguin Island, resulted in the isolation of six new peptaibols named asperelines A-F (1-6), which are characterized by an acetylated N-terminus and a C-terminus containing an uncommon prolinol residue. Structures were determined by extensive 1D and 2D NMR ((1)H-(1)H COSY, HMQC, HMBC, NOESY) spectroscopic data analysis combined with ESIMS/MS fragmentation. The absolute configurations of the amino acid residues possessing a chiral alpha-carbon and of the prolinol residue were determined to be L and S, respectively, using a new method of (1)H NMR spectroscopic comparison of complexes formed between the chiral reagent Ru(D(4)-Por*)CO and amino acids derived from the peptaibols with those formed with reference standards.

Hypertrophic scarring is a common disease affecting millions of people around the world, but there are currently no satisfactory drugs to treat the disease. Exaggerated inflammation and mechanical stress have been shown to be two main mechanisms of excessive fibrotic diseases. Here we found that a benzopyran natural product, xiamenmycin, could significantly attenuate hypertrophic scar formation in a mechanical stretch-induced mouse model. The compound suppressed local inflammation by reducing CD4+ lymphocyte and monocyte/macrophage retention in fibrotic foci and blocked fibroblast adhesion with monocytes. Both in vivo and in vitro studies found that the compound inhibited the mechanical stress-induced profibrotic effects by suppressing proliferation, activation, fibroblast contraction, and inactivating FAK, p38, and Rho guanosine triphosphatase signaling. Taken together, the compound could simultaneously suppress both the inflammatory and mechanical stress responses, which are the two pivotal pathological processes in hypertrophic scar formation, thus suggesting that xiamenmycin can serve as a potential agent for treating hypertrophic scar formation and other excessive fibrotic diseases.

The pyran ring is a very common structural unit of many natural, bioactive molecules that are widely found in plants, bacteria, and fungi. However, the enzymatic processes by which many of these pyran-containing molecules are formed are unclear. Herein, we report the construction of the pyran ring catalyzed by the cooperation of a flavin-dependent monooxygenase, XimD, and a SnoaL-like cyclase, XimE, in the biosynthesis of xiamenmycins. XimD catalyzes the formation of an epoxide intermediate that spontaneously transforms to furan and pyran products (43:1) in vitro. XimE then catalyzes the formation of the pyran ring in a 6-endo configuration from the epoxide to yield a benzopyran, xiamenmycin B. Further, we obtained the crystallographic structure of XimE, with and without product, which suggests a synergistic mechanism in which a group of four residues (Y46–Y90–H102–E136) acts cooperatively as the general acid and base. Subsequent structure-based analysis of possible viable substrates indicates that both XimD and XimE exhibit high promiscuity in their catalysis. Overall, this study reveals the mechanism of pyran ring formation in xiamenmycin biosynthesis and demonstrates the potential application of XimD and XimE in the biosynthesis of other benzoheterocycle scaffolds, including furano- and pyranocoumarins.

Polycyclic tetramate macrolactams (PTMs) were identified as distinct secondary metabolites of the mangrove-derived Streptomyces xiamenensis 318. Together with three known compounds—ikarugamycin (1), capsimycin (2) and capsimycin B (3)—two new compounds, capsimycin C (4) with trans-diols and capsimycin D (5) with trans-configurations at C-13/C-14, have been identified. The absolute configurations of the tert/tert-diols moiety was determined in 4 by NMR spectroscopic analysis, CD spectral comparisons and semi-synthetic method. The post-modification mechanism of the carbocyclic ring at C-14/C-13 of compound 1 in the biosynthesis of an important intermediate 3 was investigated. A putative cytochrome P450 superfamily gene, SXIM_40690 (ikaD), which was proximally localized to the ikarugamycin biosynthetic pathway, was characterized. In vivo gene inactivation and complementation experiment confirmed that IkaD catalysed the epoxide-ring formation reaction and further hydroxylation of ethyl side chain to form capsimycin G (3′). Binding affinities and kinetic parameters for the interactions between ikarugamycin (1) and capsimycin B (3) with IkaD were measured with Surface Plasmon Resonance. The intermediate compound 3′ was isolated and identified as 30-hydroxyl-capsimycin B. The caspimycins 2 and 3, were transferred to methoxyl derivatives, 6 and 7, under acidic and heating conditions. Compounds 1–3 exhibited anti-proliferative activities against pancreatic carcinoma with IC50 values of 1.30–3.37 μM.

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A new 24-membered macrolide macrolactin T (1), and a new polyene d-lactone macrolactin U (2), along with macrolactins A, B, D, O, and S, were isolated from the cultured broth of the bacterium Bacillus marinus, which was isolated from Suaeda salsa collected in the coastline of Bohai Sea of China. The structures of 1 and 2 were elucidated on the basis of extensive spectroscopic data analyses. The inhibitory activity of macrolactins T, B and D against fungi Pyricularia oryzae and Alternaria solani, and bacteria Staphylococcus aureus is reported.

Xiamenmycin (1) is a prenylated benzopyran derivative with anti-fibrotic activity. To investigate the genetic basis of xiamenmycin biosynthesis, we performed genome mining in the xiamenmycin-producing Streptomyces xiamenensis wild-type strain 318 to identify a candidate gene cluster. The complete gene cluster, consisting of five genes, was confirmed by a series of gene inactivations and heterologous expression. Based on bioinformatics analyses of each gene and feeding experiments, we found that the structure of an intermediate xiamenmycin B (3) accumulated in a ximA inactivation mutant, allowing us to propose a biosynthetic pathway. All five of the genes in the pathway were genetically and biochemically characterized. XimA was biochemically characterized as an ATP-dependent amide synthetase, catalyzing an amide bond formation in the presence of ATP as the final step in Xiamenmycin biosynthesis. The K m value of XimA was determined to be 474.38 µM for the substrate xiamenmycin B. These studies provide opportunities to use genetic and chemo-enzymatic methods to create new benzopyran derivatives as potential therapeutic agents.