Qingbo 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.

Identification and Characterization of Xiamycin A and Oxiamycin Gene Cluster Reveals an Oxidative Cyclization Strategy Tailoring Indolosesquiterpene Biosynthesis

Xiamycin A (XMA) and oxiamycin (OXM) are bacterial indolosesquiterpenes featuring rare pentacyclic ring systems and are isolated from a marine-derived Streptomyces sp. SCSIO 02999. The putative biosynthetic gene cluster for XMA/OXM was identified by a partial genome sequencing approach. Eighteen genes were proposed to be involved in XMA/OXM biosynthesis, including five genes for terpene synthesis via a non-mevalonate pathway, eight genes encoding oxidoreductases, and five genes for regulation and resistance. Targeted disruptions of 13 genes within the xia gene cluster were carried out to probe their encoded functions in XMA/OXM biosynthesis. The disruption of xiaK, encoding an aromatic ring hydroxylase, led to a mutant producing indosespene and a minor amount of XMA. Feeding of indosespene to XMA/OXM nonproducing mutants revealed indosespene as a common precursor for XMA/OXM biosynthesis. Most notably, the flavin dependent oxygenase XiaI was biochemically characterized in vitro to convert indosespene to XMA, revealing an unusual oxidative cyclization strategy tailoring indolosesquiterpene biosynthesis.

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.

New diketopiperazine derivatives from a deep-sea-derived Nocardiopsis alba SCSIO 03039

The strain SCSIO 03039 was isolated from a sediment sample in the Indian Ocean and was characterized as a Nocardiopsis alba species on the basis of its 16S rRNA gene sequence. Seven diketopiperazines (DKPs), including two new DKPs nocazines D (2a) and E (2b), and five known DKPs (1, 3–6), were isolated from N. alba SCSIO 03039, along with two known compounds 2-methoxy-1,4-naphthoquinone (7) and 1-hydroxy-4-methoxy-2-naphthoic acid (8). Their structures were elucidated by mass and NMR spectroscopic analyses. The structure of methoxyneihumicin (1), previously proposed in a conference poster lacking publicly available experimental data, was validated for the first time by detailed NMR analyses and X-ray diffraction study. The two enantiomers nocazines D (2a) and E (2b) were isolated as a mixture. Compounds 3 and 4 were only known as synthetic compounds before. Methoxyneihumicin (1) exhibited in vitro cytotoxicities against MCF-7 and SF-268 with IC50 values of 4.6 and 12.7 μM, respectively, better than those of 6 (22.0 and 20.6 μM). The other compounds showed less pronounced cytotoxities against three tested human cancer cell lines and no compounds displayed antibacterial activities toward four indicator strains.

Carboxyl formation from methyl via triple hydroxylations by XiaM in xiamycin A biosynthesis.

The P450 enzyme XiaM was identified as a candidate to form the C-24 carboxyl group in xiamycin A (1). Alteration of medium composition led to the discovery of four new compounds from the ΔxiaM and the ΔxiaK (encoding an aromatic ring hydroxylase) mutants. Biotransformation experiments revealed that XiaM was capable of converting a methyl group to a carboxyl group through diol and aldehyde intermediates.

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 heronamide F 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.

Elucidating the cyclization cascades in xiamycin biosynthesis by substrate synthesis and enzyme characterizations.

Indolosesquiterpene xiamycin A features a pentacyclic core structure. The chemical synthesis of two key precursors, 3-farnesylindole and 3-(epoxyfarnesyl)-indole, allowed elucidation of the enzymatic cascades forming the pentacyclic ring system of xiamycin A by XiaO-catalyzed epoxidation and the membrane protein XiaH-catalyzed terpene cyclization. The substrate flexibility of XiaI, an indole oxygenase for assembly of the central ring, was also demonstrated.

Antibacterial and cytotoxic new napyradiomycins from the marine-derived Streptomyces sp. SCSIO 10428.

Three new napyradiomycins (1–3) were isolated from the culture broth of a marine-derived actinomycete strain SCSIO 10428, together with six known related analogues napyradiomycin A1 (4), 18-oxonapyradiomycin A1 (5), napyradiomycin B1 (6), napyradiomycin B3 (7), naphthomevalin (8), and napyradiomycin SR (9). The strain SCSIO 10428 was identified as a Streptomyces species by the sequence analysis of its 16S rRNA gene. The structures of new compounds 1–3, designated 4-dehydro-4a-dechloronapyradiomycin A1 (1), 3-dechloro-3-bromonapyradiomycin A1 (2), and 3-chloro-6,8-dihydroxy-8-α-lapachone (3), respectively, were elucidated by comparing their 1D and 2D NMR spectroscopic data with known congeners. None of the napyradiomycins 1–9 showed antioxidative activities. Napyradiomycins 1–8 displayed antibacterial activities against three Gram-positive bacteria Staphylococcus and Bacillus strains with MIC values ranging from 0.25 to 32 μg mL−1, with the exception that compound 3 had a MIC value of above 128 μg mL−1 against Staphylococcus aureus ATCC 29213. Napyradiomycins 2, 4, 6, and 7 exhibited moderate cytotoxicities against four human cancer cell lines SF-268, MCF-7, NCI-H460, and HepG-2 with IC50 values below 20 μM, while the IC50 values for other five napyradiomycins 1, 3, 5, 8 and 9 were above 20 μM.

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.

Two new polyketides from a marine sediment-derived fungus Eutypella scoparia FS26

Two new polyketides, 7,8-dihydroxy-3,5,7-trimethyl-8,8a-dihydro-1H-isochromen-6(7H)-one (1) and 6-(hydroxymethyl)-2,2-dimethyl-3,4-dihydro-2H-chromene-3,4-diol (2), together with a known nitrogen-containing polyketide (cytochalasin-type of metabolites), [12]-cytochalasin (3), have been isolated from the fermentation broth of a marine sediment-derived fungus Eutypella scoparia FS26 obtained from the South China Sea. Their structures were elucidated by spectroscopic methods, mainly 1D and 2D NMR spectroscopic techniques. The absolute configurations of compound 1 were determined by NOESY analysis and the literature data were compared with circular dichroism (CD) spectroscopy. The cytotoxic effects on MCF-7, NCI-H460 and SF-268 cell lines of all compounds were evaluated by the sulforhodamine B method.