Wenjun Zhang

Spiroindimicins A-D: new bisindole alkaloids from a deep-sea-derived actinomycete.

A PCR-based screening approach led to the identification of a deep-sea-derived Streptomyces sp. SCSIO 03032 capable of producing new bisindole alkaloids spiroindimicins A-D (1-4). Structural elucidation of these compounds revealed the presence of unusual [5,6] or [5,5] spiro-ring containing skeletons. Spiroindimicins B-D (2-4) with a [5,5] spiro-ring exhibited moderate cytotoxicities against several cancer cell lines.

Mechanistic Insights into Polycycle Formation by Reductive Cyclization in Ikarugamycin Biosynthesis

Ikarugamycin is a member of the polycyclic tetramate macrolactams (PTMs) family of natural products with diverse biological activities. The biochemical mechanisms for the formation of polycyclic ring systems in PTMs remain elusive. The enzymatic mechanism of constructing an inner five-membered ring in ikarugamycin is reported. A three-gene-cassette ikaABC from the marine-derived Streptomyces sp. ZJ306 is sufficient for conferring ikarugamycin production in a heterologous host. IkaC catalyzes a reductive cyclization reaction to form the inner five-membered ring by a Michael addition-like reaction. This study provides the first biochemical evidence for polycycle formation in PTMs and suggests a reductive cyclization strategy which may be potentially applicable in general to the corresponding ring formation in other PTMs.

Fluostatins I-K from the South China Sea-Derived Micromonospora rosaria SCSIO N160

The strain SCSIO N160 was isolated from a South China Sea sediment sample and was characterized as a Micromonospora rosaria species on the basis of its 16S rRNA gene sequence. Three new fluostatins, I-K (1-3), were isolated from the culture of M. rosaria SCSIO N160, together with six known compounds, fluostatins C-F (4-7), rabelomycin (8), and phenanthroviridone (9). The structure of fluostatin D (5) was confirmed by an X-ray crystallographic study. The absolute configuration of 1 and 3 was assigned by electronic circular dichroism calculations. Compounds 8 and 9 exhibited good antimicrobial activities against Staphylococcus aureus ATCC 29213 with MIC values of 1.0 and 0.25 μg/mL, respectively. Compound 9 also exhibited significant in vitro cytotoxic activities toward SF-268 (IC50 0.09 μM) and MCF-7 (IC50 0.17 μM).

Heronamides D-F, Polyketide Macrolactams from the Deep-Sea-Derived Streptomyces sp SCSIO 03032

Three new macrolactams, heronamides D-F (1-3), were isolated from the deep-sea-derived Streptomyces sp. SCSIO 03032 upon changing cultivation conditions. The planar structures of heronamides D-F (1-3) were elucidated by extensive MS and NMR spectroscopic analyses and comparisons with the closely related heronamides A-C. The relative configurations of 1-3 were deduced by detailed analysis of (3)JHH values and NOESY data. The absolute configurations of 1 and 2 were determined by chemical modifications and application of the modified Moshers method. None of the compounds exhibited obvious antimicrobial or cytotoxic activities.

Indimicins A-E, Bisindole Alkaloids from the Deep-Sea-Derived Streptomyces sp. SCSIO 03032.

Five new bisindole alkaloids, indimicins A-E (1-5), bearing a unique 1,3-dimethyl-2-hydroindole moiety, were isolated from the marine-derived Streptomyces sp. SCSIO 03032, along with two new compounds, lynamicins F and G (6 and 7). Their planar structures were elucidated by detailed interpretation of their MS and NMR spectroscopic data, and the absolute configurations were determined by X-ray crystallographic analysis (for 1), comparison of CD spectra (for 2-4), and quantum chemical calculations (for 5). Indimicin B (2) exhibited moderate cytotoxic activity toward the MCF-7 cell line.

Characterization of Heronamide Biosynthesis Reveals a Tailoring Hydroxylase and Indicates Migrated Double Bonds.

Heronamides belong to a growing family of β‐amino acid polyketide macrolactams (βPMs) with an unsaturated side chain. The biosynthetic gene cluster for heronamideu2005F was identified from the deep‐sea‐derived Streptomyces sp. SCSIO 03032. The involvement of the gene cluster in heronamide biosynthesis was confirmed by the functional characterization of the P450 enzyme HerO as an 8‐hydroxylase for tailoring heronamide biosynthesis. The presence of migrated double bonds in the conjugated diene‐containing side chain of heronamides was confirmed by feeding experiments with labeled small carboxylic acid molecules. This study is the first demonstration of migrated double bonds in βPMs with an unsaturated side chain.

α-Pyrones with Diverse Hydroxy Substitutions from Three Marine-Derived Nocardiopsis Strains

Eight new α-pyrones 1-8 and three known α-pyrones 9-11 were isolated from three marine-derived Nocardiopsis strains SCSIO 10419, SCSIO 04583, and SCSIO KS107. The structures of compounds 1-8 were elucidated by comprehensive spectral analyses. The absolute configurations of 4-deoxyphomapyrone C (1), 4-deoxy-11-hydroxyphomapyrone C (3), 4-deoxy-7R-hydroxyphomapyrone C (5), and phomapyrone C (11) were determined by TDDFT-ECD calculations for the solution conformers, which revealed that the conformation of the side chain was decisive for the sign of the characteristic high-wavelength ECD transition. (-)-4-Deoxy-8-hydroxyphomapyrone C (4) was isolated from SCSIO 10419 and was deduced as a diastereomeric mixture containing (8S)- and (8R)-4-deoxy-8-hydroxyphomapyrone C in a ratio of 2.6:1 (8R:8S), by chiral-phase HPLC analysis and Moshers ester analysis. Interestingly, 7-hydroxymucidone (9) was isolated from both SCSIO 04583 and SCSIO KS107, as an enantiomeric mixture containing (7S)-hydroxymucidone (major in 9 from SCSIO 04583) and (7R)-hydroxymucidone (major in 9 from SCSIO KS107). α-Pyrones 3-5 were identified as three isomers of phomapyrone C (11) with diverse hydroxy substitutions. α-Pyrones 10-hydroxymucidone (6), 4-hydroxymucidone (8), and 9, differed in the position of the hydroxy group. Several α-pyrones exhibited moderate growth inhibitory activity against Micrococcus luteus and Bacillus subtilis.

Heterologous Expression of Fluostatin Gene Cluster Leads to a Bioactive Heterodimer.

The biosynthesis gene cluster (fls) for atypical angucycline fluostatins was identified from the marine derived Micromonospora rosaria SCSIO N160 and was confirmed by gene knockouts and the biochemical characterization of a bifunctional oxygenase FlsO2. The absolute configuration of the key biosynthetic intermediate prejadomycin was determined for the first time by Cu Kα X-ray analysis. Heterologous expression of the intact fls-gene cluster in Streptomyces coelicolor YF11 in the presence of 3% sea salts led to the isolation of two new compounds: fluostatin L (1) and difluostatin A (2). Difluostatin A (2), an unusual heterodimer, exhibited antibacterial activities.

Elucidating Hydroxylation and Methylation Steps Tailoring Piericidin A1 Biosynthesis

The piericidin A1 (1) gene cluster was identified from the deep-sea derived Streptomyces sp. SCSIO 03032. Our in vivo and in vitro experiments verified PieE as a 4-hydroxylase and PieB2 as a 4-O-methyltransferase, allowing the elucidation of the post-PKS modification steps involved in 1 biosynthesis. In addition, the shunt metabolite piericidin E1 (7) was identified as a novel analogue featuring a C-2/C-3 epoxy ring.

Pyrazolofluostatins A–C, Pyrazole-Fused Benzo[a]fluorenes from South China Sea-Derived Micromonospora rosaria SCSIO N160

Pyrazolofluostatins A-C (1-3), three new benzo[a]fluorenes with an unprecedented carbon skeleton, were obtained from the South China Sea-derived Micromonospora rosaria SCSIO N160. Their structures were elucidated by extensive spectroscopic analyses. The structure of pyrazolofluostatin A (1) was confirmed by X-ray crystallographic analysis. Notably, 1-3 possessed a benzo[cd]indeno[2,1-f]indazol skeleton with a pyrazole-fused 6/5/6/6/5 pentacyclic ring system. Pyrazolofluostatin A (1) showed moderate antioxidation activity (EC50 48.6 μM).