Serratiomycins D1-D3, Antibacterial Cyclic Peptides from a Serratia sp. and Structure Revision of Serratiomycin.

Serratiomycin (1) is an antibacterial cyclic depsipeptide, first discovered from a Eubacterium culture in 1998. This compound was initially reported to contain l-Leu, l-Ser, l-allo-Thr, d-Phe, d-Ile, and hydroxydecanoic acid. In the present study, 1 and three new derivatives, serratiomycin D1-D3 (2-4), were isolated from a Serratia sp. strain isolated from the exoskeleton of a long-horned beetle. The planar structures of 1-4 were elucidated by using mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy. Comparison of the NMR chemical shifts and the physicochemical data of 1 to those of previously reported serratiomycin indeed identified 1 as serratiomycin. The absolute configurations of the amino units in compounds 1-4 were determined by the advanced Marfey's method, 2,3,4,6-tetra-O-acetyl-ß-d-glucopyranosyl isothiocyanate derivatization, and liquid chromatography-mass spectrometric (LC-MS) analysis. Additionally, methanolysis and the modified Mosher's method were used to determine the absolute configuration of (3R)-hydroxydecanoic acid in 1. Consequently, the revised structure of 1 was found to possess d-Leu, l-Ser, l-Thr, d-Phe, l-allo-Ile, and d-hydroxydecanoic acid. In comparison with the previously published structure of serratiomycin, l-Leu, l-allo-Thr, and d-Ile in serratiomycin were revised to d-Leu, l-Thr, and l-allo-Ile. The new members of the serratiomycin family, compounds 2 and 3, showed considerably higher antibacterial activities against Staphylococcus aureus and Salmonella enterica than compound 1.

Retinestatin, a Polyol Polyketide from a Termite Nest-Derived Streptomyces sp.

A new polyol polyketide, named retinestatin (1), was obtained and characterized from the culture of a Streptomyces strain, which was isolated from a subterranean nest of the termite Reticulitermes speratus kyushuensis Morimoto. The planar structure of 1 was elucidated on the basis of the cumulative analysis of ultraviolet, infrared, mass spectrometry, and nuclear magnetic resonance spectroscopic data. The absolute configuration of 1 at 12 chiral centers was successfully assigned by employing a J-based configuration analysis in combination with ROESY correlations, a quantum mechanics-based computational approach to calculate NMR chemical shifts, and a 3 min flash esterification by Mosher's reagents followed by NMR analysis. Biological evaluation of retinestatin (1) using an in vitro model of Parkinson's disease revealed that 1 protected SH-SY5Y dopaminergic cells from MPP+-induced cytotoxicity, indicating its neuroprotective effects.

Hamuramicin C, a Cytotoxic Bicyclic Macrolide Isolated from a Wasp Gut Bacterium.

A new bicyclic macrolide, hamuramicin C (1), was isolated from Streptomyces sp. MBP16, a gut bacterial strain of the wasp Vespa crabro flavofasciata. Its 22-membered macrocyclic lactone structure was determined by NMR and mass spectrometry. The relative configurations of hamuramicin C (1) were assigned by J-based configuration analysis utilizing 1H rotating frame Overhauser effect spectroscopy and heteronuclear long-range coupling NMR spectroscopy. Genomic and bioinformatic analyses of the bacterial strain enabled identification of the type-I polyketide synthase pathway, which employs a trans-acyltransferase system. The absolute configurations of 1 were proposed based on the analysis of the sequences of ketoreductases in the modular gene cluster. Moreover, hamuramicin C (1) demonstrated significant inhibitory activity against diverse human cancer cell lines (HCT116, A549, SNU-638, SK-HEP-1, and MDA-MB-231).

Formicolides A and B, Antioxidative and Antiangiogenic 20-Membered Macrolides from a Wood Ant Gut Bacterium.

Two new macrolides, formicolides A (1) and B (2), were isolated from Streptomyces sp. BA01, a gut bacterial strain of the wood ant (Formica yessensis). Their 20-membered macrocyclic lactone structures were established using NMR and mass spectrometric data. The relative configurations of the formicolides were determined by J-based configuration analysis utilizing ROESY, HETLOC, and HECADE NMR spectroscopic data. Genomic and bioinformatics analysis of the bacterial strain enabled us to identify the type-I polyketide synthase pathway employing a trans-acyltransferase system. The absolute configurations of 1 and 2 are proposed based on detailed analysis of the sequences of the ketoreductases in the modular gene cluster and statistical comparative analysis of the experimental NMR chemical shifts and quantum mechanical calculations. Formicolides A and B (1 and 2) induced quinone reductase activity in murine Hepa-1c1c7 cells and antiangiogenic activity by suppression of tube formation in human umbilical vein endothelial cells.

Formicins, N-Acetylcysteamine-Bearing Indenone Thioesters from a Wood Ant-Associated Bacterium.

Formicins A-C (1-3) were discovered from Streptomyces sp. associated with wood ants. The structures of 1 and 2 were elucidated as indenone thioesters bearing N-acetylcysteamine based on spectroscopic analysis. The configurations of 1-3 were determined by the analysis of ROESY correlations, the phenylglycine methyl ester method, and chemical derivatization from 3 to 2. Formicin A inhibited the growth of human triple-negative breast cancer cells by regulating the liver kinase B1-mediated AMPK signaling pathway.

Camporidines A and B: Antimetastatic and Anti-inflammatory Polyketide Alkaloids from a Gut Bacterium of Camponotus kiusiuensis.

Chemical studies of gut bacteria of the carpenter ant Camponotus kiusiuensis led to the discovery of two new alkaloids, camporidines A and B (1 and 2), from Streptomyces sp. STA1. The structures of 1 and 2 were established as new polyketide alkaloids bearing a piperidine-cyclopentene-epoxide 6/5/3 tricyclic system based on NMR spectroscopic and mass spectrometric analysis. The relative configurations of the camporidines were determined by their 1H-1H NOESY/ROESY and 1D NOE NMR correlations. The experimental ECD spectra of 1 and 2 were compared with their calculated ECD spectra to assign their absolute configurations. Camporidine A (1) displayed antimetastatic activity by suppression of cell invasion against the metastatic breast cancer cell line MDA-MB-231 and showed an anti-inflammatory effect by suppressing nitric oxide production induced by lipopolysaccharide. In addition, the putative biosynthetic gene cluster of the camporidines was identified, and the biosynthetic pathway of the camporidines was proposed based on bioinformatic analysis of the full genome of Streptomyces sp. STA1. Camporidines A and B (1 and 2) could be biosynthesized by a modular type I PKS containing an acyl transferase domain that accepts an unusual extender unit, which becomes the (C1'-C6') hexyl side chain. The post-PKS modification enzymes were predicted to perform an amination and an oxidation along with spontaneous Schiff base formation and generate the unique piperidine-cyclopentene-epoxide 6/5/3 tricyclic framework.