New secondary metabolites produced by an engineered strain Streptomyces sp. XZQH13OEΔastC

Two previously undescribed alkaloids (1-2), five known alkaloids (3-7) and five cyclodipeptides (8-12) were obtained from an ansatrienin-producing mutant strain Streptomyces sp. XZQH13OEΔ astC. Their structures were elucidated by analysis of the 1D, 2D NMR and ESI HRMS data and by comparison with the reported data. The antibacterial activities of compounds 1-12 were evaluated.

Structural diversity and biological relevance of benzenoid and atypical ansamycins and their congeners

Covering: 2011 to 2021The structural division of ansamycins, including those of atypical cores and different lengths of the ansa chains, is presented. Recently discovered benzenoid and atypical ansamycin scaffolds are presented in relation to their natural source and biosynthetic routes realized in bacteria as well as their muta and semisynthetic modifications influencing biological properties. To better understand the structure-activity relationships among benzenoid ansamycins structural aspects together with mechanisms of action regarding different targets in cells, are discussed. The most promising directions for structural optimizations of benzenoid ansamycins, characterized by predominant anticancer properties, were discussed in view of their potential medical and pharmaceutical applications. The bibliography of the review covers mainly years from 2011 to 2021.

Ansafurantrienins, Unprecedented Ansatrienin Derivatives Formed via Photocatalytic Intramolecular [3 + 2] Oxidative Cycloaddition

Ansafurantrienins A-H, bearing a unique 5/6/8 dihydrofuran-fused benzo[b]azocine chromophore, were isolated from Streptomyces flaveolus. Their structures, especially in the dihydrofuran unit, were unambiguously established by spectroscopic analyses, molecular modeling, and TDDFT/ECD calculations. The ansafurantrienins were proposed to be generated via intramolecular [3 + 2] oxidative cycloaddition, which was achieved by photocatalytic reaction with UV light and oxygen and found to have solvent-dependent stereoselectivity. Ansafurantrienins showed significant antiproliferative effects against pancreatic cancer cells. The results led to a structural revision of strecacansamycins.

Three new polyketides from vasR2 gene over-expressed mutant strain of Verrucosispora sp. NS0172

Over-expression of the pathway specific positive regulator gene is an effective way to activate silent gene cluster. In the curret study, the SARP family regulatory gene, vasR2, was over-expressed in strain Verrucosispora sp. NS0172 and the cryptic gene cluster responsible for the biosynthesis of pentaketide ansamycin was partially activated. Two tetraketides (1 and 2) and a triketide (3) ansamycins, together with five known compounds (4-8), were isolated and elucidated from strain NS0172OEvasR2. Their NMR data were completely assigned by analysis of their HR-ESI-MS and ¹H, ¹³C NMR, HMQC, HMBC and ¹H-¹H COSY spectra.

Molecular networking-based for the target discovery of potent antiproliferative polycyclic macrolactam ansamycins from Streptomyces cacaoi subsp. asoensis

Molecular networking-based for the target discovery of potent antiproliferative polycyclic macrolactam ansamycins.

Refining and expanding nonribosomal peptide synthetase function and mechanism

Nonribosomal peptide synthetases (NRPSs) are involved in the biosynthesis of numerous peptide and peptide-like natural products that have been exploited in medicine, agriculture, and biotechnology, among other fields. As a consequence, there have been considerable efforts aimed at understanding how NRPSs orchestrate the assembly of these natural products. This review highlights several recent examples that continue to expand upon the fundamental knowledge of NRPS mechanism and includes (1) the discovery of new NRPS substrates and the mechanism by which these sometimes structurally complex substrates are made, (2) the characterization of new NRPS activities and domains that function during the process of peptide assembly, and (3) the various catalytic strategies that are utilized to release the NRPS product. These findings continue to strengthen the predictive power for connecting genes to products, thereby facilitating natural product discovery and development in the Genomics Era.

Ansamycins with Antiproliferative and Antineuroinflammatory Activity from Moss-Soil-Derived Streptomyces cacaoi subsp. asoensis H2S5

Three new 21-membered macrocyclic benzenoid ansamycins, trienomycins J-L (1-3), together with seven known analogues, trienomycins A-G (4-10), were isolated from liquid culture of the moss soil-derived actinomycete Streptomyces cacaoi subsp. asoensis H2S5. The structures of the new compounds were elucidated by extensive NMR spectroscopic analysis and HRESIMS data. The absolute configurations of trienomycins were established by Marfey's method. Antiproliferative assays showed that compound 1 had the greatest activity against HepG2 cells, with an IC₅₀ value of 0.1 μM. The induction of apoptosis of HepG2 cells by 1 was investigated by flow cytometry and evaluation of nuclear morphology. In addition, all of the compounds inhibited nitric oxide production with IC₅₀ values of 0.02 to 8.3 μM, and compounds 1, 4, and 7 were the most potent inhibitors. These findings will facilitate the development of new antineuroinflammatory agents.

New Ansamycins from the Deep-Sea-Derived Bacterium Ochrobactrum sp. OUCMDZ-2164

Two new ansamycins, trienomycins H (1) and I (2), together with the known trienomycinol (3), were isolated from the fermentation broth of the deep-sea-derived bacterium Ochrobactrum sp. OUCMDZ-2164. Their structures, including their absolute configurations, were elucidated based on spectroscopic analyses, ECD spectra, and Marfey’s method. Compound 1 exhibited cytotoxic effects on A549 and K562 cell lines with IC₅₀ values of 15 and 23 μM, respectively.

Diversity of Polyketide Chains Achieved by Deleting the Tailoring Genes in the Biosynthesis of Ansatrienins

The ast gene cluster (GenBank accession numbers KF813023.1 and KP284551) was characterized to be responsible for the biosynthesis of ansatrienins in Streptomyces sp. XZQH13, which contains astC, astF1, and astF2 genes involved in the assembly of the N-cyclohexanoyl d-alanyl side chain and the hydroxylation of C-19, respectively. Further to investigating the biosynthetic mechanism of ansatrienins, herein we constructed the mutant strains XZQH13OEΔastF2 and XZQH13OEΔastCΔastF2. Three new ansatrienin analogues, namely, ansatrienols I-K (1-3), along with trienomycinol (4) and 3-O-demethyltrienomycinol (5), were isolated from the XZQH13OEΔastCΔastF2 strain, and trienomycin A (6) and trienomycin G (7) were isolated from the XZQH13OEΔastF2 strain. Their structures were determined by a combination of high-resolution MS (ESI) and 1D and 2D NMR spectroscopy. Accordingly, a pathway for the biosynthesis of these new ansatrienins was proposed.

Ansavaricins A–E: five new streptovaricin derivatives from Streptomyces sp. S012

Five new polyketides of the ansamycin class, named ansavaricins A–E (1–5), together with three known streptovaricins 6–8, were isolated from the Streptomyces sp. S012 strain.

Ansavaricins F–I, new DNA topoisomerase inhibitors produced by Streptomyces sp. S012

Ansamycins are a family of macrolactams characterized by an aromatic chromophore with an aliphatic chain (ansa chain) connected back to a nonadjacent position through an amide bond.

Neoansamycins from Streptomyces sp. LZ35

Neoansamycins D–I with unusual extender units and diverse post-PKS modifications were isolated from the Streptomyces sp. SR201nam1OE strain.