A new β-class milbemycin derivative from a mutant of genetically engineered strain Streptomyces avermitilis AVE-H39

A new β-class milbemycin, 13α-hydroxy milbemycin β₆ (1), was isolated from the fermentation broth of a mutant of genetically engineered strain Streptomyces avermitilis AVE-H39. Its structure and absolute configuration were elucidated by extensive spectroscopic methods and confirmed by single crystal X-ray diffraction.

Anulamycins A-F, Cinnamoyl-Containing Peptides from a Lake Sediment Derived Streptomyces

Bioinformatics analysis of a whole genome sequence coupled with HPLC-DAD analysis revealed that Streptomyces sp. Hu103 has the capacity to produce skyllamycin analogues. A subsequent chemical investigation of this strain yielded four new cinnamoyl-containing cyclopeptides, anulamycins A-D (1-4), two new cinnamoyl-containing linear peptides, anulamycins E and F (5 and 6), and two known cyclopeptides, skyllamycins A (7) and B (8). Their structures including absolute configurations were elucidated by detailed analysis of NMR and HRESIMS/MS spectroscopic data and the advanced Marfey's method. Compounds 1-4 exhibited antibacterial activity comparable to those of skyllamycins A and B.

A novel spiro-heterocycle milbemycin metabolite from a genetically engineered strain of Streptomyces bingchenggensis

Milbemycin R, a novel spiro-heterocycle milbemycin, was obtained from the metabolites produced by the mutant strain S. bingchenggensis BCJ60B11. Its structure was determined by spectroscopic and spectrometric analyses including 1 D, 2 D NMR, IR, HR-ESI-MS data. The acaricidal and nematicidal activities of milbemycin R against Tetranychus cinnabarinus and Bursaphelenchus xylophilus were tested. Milbemycin R possessed better acaricidal activity than milbemycins A3/A4.

Two new cyclopentenone metabolites from Streptomyces sp. HU119

Two previously undescribed cyclopentenone metabolites, (S)-2-(3-acetylamino-2-methyl)propyl-3-butyl-2-cyclopenten-1-one (1) and (S)-2-(3-acetylamino-2-ethyl)propyl-3-butyl-2-cyclopenten-1-one (2), were isolated from the fermentation broth of the strain Streptomyces sp. HU119. The structures of 1 and 2 were determined by the comprehensive spectroscopic analysis, including 1 D, 2 D NMR, MS spectral analysis and the comparison with data from the literature. The absolute configurations were elucidated by experimental and calculated optical rotations (OR). Compounds 1 and 2 displayed weak cytotoxic activity.

Sarubicinols A-C, Cytotoxic Benzoxazoles from a Streptomyces

A chemical investigation of Streptomyces sp. Hu186 afforded two known quinone antibiotics, sarubicin A (1) and sarubicin B (2), together with three unusual variants, sarubicinols A-C (3-5), and two new 1,4-naphthoquinone metabolites, sarubicin B₁ (6) and sarubicin B₂ (7). Compounds 3-5 possess a rare 2-oxabicyclo [2.2.2] substructure and a benzoxazole ring system. Their structures were elucidated using 1D and 2D nuclear magnetic resonance and high-resolution electrospray ionization mass spectrometry data. The absolute configurations of the side-chain moieties in 4 and 5 were solved by electronic circular dichroism calculations. Compounds 1-7 showed moderate cytotoxic activity against four tumor cell lines.

A facile preparation and crystal structure of romipeptide A

A double disulfide tethering depsipeptide dimer, romipeptide A (1) was prepared by NaOH catalyzed dimerization of romidepsin. Its structure was determined by analysis of NMR and HR-ESI-MS data as well as single crystal X-ray diffraction. Bioassay results showed that 1 exhibited good cytotoxic activity against two tumor cell lines B16 and HCT116. This study reported the single crystal data of 1 for the first time. The facile preparation of 1 afforded enough amount for its further biological evaluations.

Two new 13-hydroxylated milbemycin metabolites from the genetically engineered strain Streptomyces avermitilis AVE-H39

Two new milbemycin metabolites, 13α-hydroxymilbemycin β₁₃ (1) and 26-methyl-13α-hydroxymilbemycin β₁₃ (2), were isolated from the fermentation broth of a genetically engineered strain Streptomyces avermitilis AVE-H39. Their structures were determined by the comprehensive spectroscopic data, including 1 D, 2 D NMR, MS spectral analysis and the comparison with data from the literature. Compounds 1 and 2 not only exhibited potent acaricidal activities against Tetranychus cinnabarinus, but also had nematocidal activity against Bursaphelenchus xylophilus.

Two new milbemycin derivatives from a genetically engineered strain Streptomyces bingchenggensis

Two new milbemycin derivatives, milbemycin M (1) and milbemycin N (2), were isolated from the culture of a genetically engineered strain Streptomyces bingchenggensis BCJ60. Their structures were elucidated through the interpretation of NMR and HR-ESI-MS spectroscopic data, as well as comparison with previous reports. The acaricidal and nematicidal activities of them against Tetranychus cinnabarinus and Bursaphelenchus xylophilus were tested. The results showed that compounds 1-2 possessed potent acaricidal and nematocidal activities.

Two novel milbemycin derivatives from the genetically engineered strain Streptomyces avermitilis AVE-H39

Two novel milbemycin derivatives, 5,27-epoxy-13α-hydroxy milbemycin β₁₁ (1) and 5,27-epoxy-13α-hydroxy-25-ethyl milbemycin β₁₁ (2), were isolated from the genetically engineered strain Streptomyces avermitilis AVE-H39. Their structures were elucidated through the interpretation of HR-ESIMS and extensive NMR spectroscopic data. Compounds 1 and 2 exhibited moderate acaricidal and nematicidal activities.

Two new compounds from Streptomyces sp. HS-NF-813

Two new derivatives of cytotoxic substance BE-52211, designed as BE-52211D (1) and BE-52211E (2), were isolated from the fermentation broth of the strain Streptomyces sp. HS-NF-813. Their structures were determined by 1D and 2D NMR techniques, ESI-MS and comparison with data from the literature. The absolute stereochemistry of 1 was elucidated by NMR data of the Mosher ester derivatives. Compounds 1 and 2 showed moderate cytotoxic activity against three human tumor cell lines.

Bioactive naphthoquinone and anthrone derivatives from endophytic Micromonospora sp. NEAU-gq13

Two new naphthalenone derivatives, 5-hydroxy-4-oxo-2-(2-oxopropyl)-1,2,3,4-tetrahydronaphthalen-1-yl acetate (1) and 5-hydroxy-2-(2-hydroxypropyl)naphthalene-1,4-dione (2), together with two new anthrone derivatives, (S)-2,5-dihydroxy-2-methyl-1,2,3,4-tetrahydroanthracene-9,10-dione (3) and 4,5-dihydroxy-2-methyl-9H-xanthen-9-one (4), were isolated from the fermentation broth of endophytic Micromonospora sp. NEAU-gq13. Their structures were determined by 1D-NMR, 2D-NMR, and HR-ESI-MS analysis. Compounds 2 and 3 exhibited strong cytotoxic activity against human central nervous system cancer (SF-268) with the IC₅₀ values of 3.04 and 5.66 μg/ml, respectively. Moreover, compound 2 also displayed potent activity against human liver cancer (HepG2) with an IC₅₀ value of 1.01 μg/ml.

Characterization of the N-methyltransferases involved in the biosynthesis of toxoflavin, fervenulin and reumycin from Streptomyces hiroshimensis ATCC53615

Toxoflavin (1), fervenulin (2), and reumycin (3), known to be produced by plant pathogen Burkholderia glumae BGR1, are structurally related 7-azapteridine antibiotics. Previous biosynthetic studies revealed that N-methyltransferase ToxA from B. glumae BGR1 catalyzed the sequential methylation at N6 and N1 in pyrimido[5,4-e]-as-triazine-5,7(6H,8H)-dione (4) to generate 1. However, the N8 methylation of 4 in the biosynthesis of fervenulin remains unclear. To explore the N-methyltransferases required for the biosynthesis of 1 and 2, we identified and characterized the fervenulin and toxoflavin biosynthetic gene clusters in S. hiroshimensis ATCC53615. On the basis of the structures of intermediates accumulated from the four N-methyltransferase gene inactivation mutants and systematic enzymatic methylation reactions, the tailoring steps for the methylation order in the biosynthesis of 1 and 2 were proposed. The N-methylation order and routes for the biosynthesis of fervenulin and toxoflavin in S. hiroshimensis are more complex and represent an obvious departure from those in B. glumae BGR1.

A new spectinabilin derivative with cytotoxic activity from ant-derived Streptomyces sp. 1H-GS5

A new spectinabilin derivative (1) was isolated from the fermentation broth of the ant-derived Streptomyces sp. 1H-GS5, and the structure was elucidated by extensive spectroscopic analysis. Compound 1 showed cytotoxicity against human tumor cell lines A549, HCT-116, and HepG2 with IC₅₀ values of 9.7, 12.8, and 9.1 μg/ml, respectively, which was relative higher than that of spectinabilin.

A new naphthalenepropanoic acid analog from the marine-derived actinomycetes Micromonospora sp. HS-HM-036

A new naphthalenepropanoic acid analog (1) was isolated from the broth of the actinomycetes Micromonospora sp. HS-HM-036. The structure of compound 1 was determined based on MS and extensive NMR analysis. A preliminary investigation of the biological activity of compound 1 was also described.

New macrocyclic lactones with acaricidal and nematocidal activities from a genetically engineered strain Streptomyces bingchenggensis BCJ60

Two new macrocyclic lactones, 4,25-diethyl-4,25-demethyl-milbemycin β₃ (1) and 27-formaldehyde-milbemycin β₁₄ (2), were isolated from a genetically engineered strain Streptomyces bingchenggensis BCJ60. Their structures were determined on the basis of spectroscopic analysis, including 1D and 2D NMR techniques as well as ESI-MS and comparison with data from the literature. The acaricidal and nematocidal capacities of compounds 1 and 2 were evaluated against Tetranychus cinnabarinus and Bursaphelenchus xylophilus, respectively. The results showed that the two new macrocyclic lactones 1 and 2 possessed potent acaricidal and nematocidal activities.

A new tetrahydrobenzofuranone metabolite from Streptomyces sp. HS-NF-853

A new tetrahydrobenzofuranone derivative, strefuranone A (1), was isolated from Streptomyces sp. HS-NF-853. The structure of the compound was elucidated on the basis of MS and extensive NMR analysis.

Combined application of plasma mutagenesis and gene engineering leads to 5-oxomilbemycins A3/A4 as main components from Streptomyces bingchenggensis

Milbemycin oxime has been commercialized as effective anthelmintics in the fields of animal health, agriculture, and human infections. Currently, milbemycin oxime is synthesized by a two-step chemical reaction, which involves the ketonization of milbemycins A3/A4 to yield the intermediates 5-oxomilbemycins A3/A4 using CrO3 as catalyst. Due to the low efficiency and environmental unfriendliness of the ketonization of milbemycins A3/A4, it is imperative to develop alternative strategies to produce 5-oxomilbemycins A3/A4. In this study, the atmospheric and room temperature plasma (ARTP) mutation system was first employed to treat milbemycin-producing strain Streptomyces bingchenggensis, and a mutant strain BC-120-4 producing milbemycins A3, A4, B2, and B3 as main components was obtained, which favors the construction of genetically engineered strains producing 5-oxomilbemycins. Importantly, the milbemycins A3/A4 yield of BC-120-4 reached 3,890 ± 52 g/l, which was approximately two times higher than that of the initial strain BC-109-6 (1,326 ± 37 g/l). The subsequent interruption of the gene milF encoding a C5-ketoreductase responsible for the ketonization of milbemycins led to strain BCJ60 (∆milF) with the production of 5-oxomilbemycins A3/A4 and the elimination of milbemycins A3, A4, B2, and B3. The high 5-oxomilbemycins A3/A4 yield (3,470 ± 147 g/l) and genetic stability of BCJ60 implied the potential use in industry to prepare 5-oxomilbemycins A3/A4 for the semisynthesis of milbemycins oxime.

Characterization and analysis of an industrial strain of Streptomyces bingchenggensis by genome sequencing and gene microarray

Streptomyces bingchenggensis is a soil bacterium that produces milbemycins, a family of macrolide antibiotics that are commercially important in crop protection and veterinary medicine. In addition, S. bingchenggensis produces many other natural products including the polyether nanchangmycin and novel cyclic pentapeptides. To identify the gene clusters involved in the biosynthesis of these compounds, and better clarify the biochemical pathways of these gene clusters, the whole genome of S. bingchenggensis was sequenced, and the transcriptome profile was subsequently investigated by microarray. In comparison with other sequenced genomes in Streptomyces, S. bingchenggensis has the largest linear chromosome consisting of 11 936 683 base pairs (bp), with an average GC content of 70.8%. The 10 023 predicted protein-coding sequences include at least 47 gene clusters correlated with the biosynthesis of known or predicted secondary metabolites. Transcriptional analysis demonstrated an extremely high expression level of the milbemycin gene cluster during the entire growth period and a moderately high expression level of the nanchangmycin gene cluster during the initial hours that subsequently decreased. However, other gene clusters appear to be silent. The genome-wide analysis of the secondary metabolite gene clusters in S. bingchenggensis, coupled with transcriptional analysis, will facilitate the rational development of high milbemycins-producing strains as well as the discovery of new natural products.

Three new cyclopentenone derivatives from Actinoalloteichus nanshanensis NEAU 119

Three new cyclopentenone derivatives (1-3) were isolated from the rare actinomycete Actinoalloteichus nanshanensis NEAU 119. Their structures were elucidated by extensive spectroscopic analysis. Compound 1 showed moderate cytotoxic activity against human lung adenocarcinoma cell line A549, human leukemia cell line K562, and human renal carcinoma cell line ACHN with an IC50 of 14.67, 11.87, and 23.36 μg ml(-1), respectively.

A new prenylated indole derivative from endophytic actinobacteria Streptomyces sp. neau-D50

A new prenylated indole derivative 3-acetonylidene-7-prenylindolin-2-one (1) was isolated from the endophytic actinobacterium Streptomyces sp. neau-D50, together with four known hybrid isoprenoids, 7-isoprenylindole-3-carboxylic acid (2), 3-cyanomethyl-6-prenylindole (3), 6-isoprenylindole-3-carboxylic acid (4) and 7,4'-dihydroxy-5-methoxy-8-(γ,γ-dimethylallyl)-flavanone (5). The structures of these compounds were elucidated on the basis of extensive spectroscopic analysis and comparison with data from the literature. Compounds 1 and 2 demonstrated strong cytotoxic activities against human lung adenocarcinoma cell line A549 with an IC50 of 3.3 and 5.1 μg mL(- 1), respectively, which are comparable to that of the positive control doxorubicin (4.2 μg mL(- 1)). Furthermore, compounds 1-4 exhibited potent antifungal activity against phytopathogenic fungi Colletotrichum orbiculare, Phytophthora capsici, Corynespora cassiicola and Fusarium oxysporum.

Genetic engineering of Streptomyces bingchenggensis to produce milbemycins A3/A4 as main components and eliminate the biosynthesis of nanchangmycin

Milbemycins A3/A4 are important 16-membered macrolides which have been commercialized and widely used as pesticide and veterinary medicine. However, similar to other milbemycin producers, the production of milbemycins A3/A4 in Streptomyces bingchenggensis is usually accompanied with undesired by-products such as C5-O - methylmilbemycins B2/B3 (α-class) and β1/β2 (β-class) together with nanchangmycin. In order to obtain high yield milbemycins A3/A4-producing strains that produce milbemycins A3/A4 as main components, milD, a putative C5-O-methyltransferase gene of S. bingchenggensis , was biofunctionally investigated by heterologous expression in Escherichia coli . Enzymatic analysis indicated that MilD can catalyze both α-class (A3/A4) and β-class milbemycins (β11) into C5-O-methylmilbemycins B2/B3 and β1, respectively, suggesting little effect of furan ring formed between C6 and C8a on the C5-O-methylation catalyzed by MilD. Deletion of milD gene resulted in the elimination of C5-Omethylmilbemycins B2/B3 and β1/β2 together with an increased yield of milbemycins A3/A4 in disruption strain BCJ13. Further disruption of the gene nanLD encoding loading module of polyketide synthase responsible for the biosynthesis of nanchangmycin led to strain BCJ36 that abolished the production of nanchangmycin. Importantly, mutant strain BCJ36 (ΔmilDΔnanLD) produced milbemycins A3/A4 as main secondary metabolites with a yield of 2312 ± 47 μg/ml, which was approximately 74 % higher than that of the initial strain S. bingchenggensis BC-109-6 (1326 ± 37 μg/ml).

Two new piperidine alkaloids from Streptomyces sp. NEAU-Z4

Two new piperidine alkaloids, streptazones E (1) and F (2), were isolated from Streptomyces sp. NEAU-Z4. Their structures were elucidated on the basis of MS and NMR analysis.

Borrelidin, a potent antifungal agent: insight into the antifungal mechanism against Phytophthora sojae

Borrelidin has high and specific antifungal activity against Phytophthora sojae . To explore the antifungal mechanism of borrelidin against P. sojae , the relationship between the antifungal activity of borrelidin and the concentration of threonine was evaluated. The results demonstrated that the growth-inhibitory effect of borrelidin on the growth of P. sojae was antagonized by threonine in a dose-dependent manner, suggesting that threonyl-tRNA synthetase (ThrRS) may be the potential target of borrelidin. Subsequently, the inhibition of the enzymatic activity of ThrRS by borrelidin in vitro was confirmed. Furthermore, the detailed interaction between ThrRS and borrelidin was investigated using fluorescence spectroscopy and circular dichroism (CD), implying a tight binding of borrelidin to ThrRS. Taken together, these results suggest that the antifungal activity of borrelidin against P. sojae was mediated by inhibition of ThrRS via the formation of the ThrRS-borrelidin complex.

Four new doramectin congeners with acaricidal and insecticidal activity from Streptomyces avermitilis NEAU1069

Four new doramectin congeners, 1-4, were isolated from Streptomyces avermitilis NEAU1069. The structures of 1-4 were elucidated on the basis of spectroscopic analysis, including 1D- and 2D-NMR as well as HR-ESI-MS, ESI-MS, UV, and IR, and comparison with literature data. All compounds exhibited noticeable acaricidal and insecticidal activities. Especially compound 2 was found to be the most potent pesticide of the compounds evaluated with the IC(50) values of 10.2, 65.1 and 124.4 μg/ml against adult two-spotted spider mites (Tetranychus urticae Koch), two-spotted spider mite eggs, and Mythimna separata, respectively, which are comparable to those of commercial pesticide milbemycin A(3)/A(4) as positive reference.

Neaumycin: a new macrolide from Streptomyces sp. NEAU-x211

Neaumycin, a new 30-membered macrolide featuring an internal diester bridge, a molecular architecture that is unprecedented among known macrolide natural products, was isolated from a soil actinomycete strain Streptomyces sp. NEAU-x211. The structure of neaumycin was elucidated on the basis of comprehensive mass and NMR spectroscopic interpretation, including the relative stereochemistry of four independent coupling systems.

Antifungal activity of borrelidin produced by a Streptomyces strain isolated from soybean

In this study, an endophytic Streptomyces sp. neau-D50 with strong antifungal activity against Phytophthora sojae was isolated from healthy soybean root, using an in vitro screening technique. A bioactivity-guided approach was then employed to isolate and determine the chemical identity of bioactive constituents with antifungal activity from strain neau-D50. The structure of the antifungal metabolite was elucidated as borrelidin on the basis of spectral analysis. To our knowledge, this is the first report that borrelidin has strong antifungal activity against dominant race 1 of P. sojae with EC(50) and EC(95) of 0.0056 and 0.026 mg/L, respectively. The values were respectively 62.5- and 262.3-fold lower than those of the commercial fungicide metalaxyl, which has been used to treat soybean seed for the control of P. sojae . The in situ bioassays demonstrated that borrelidin at 10 mg/L reduced P. sojae race 1 lesions on soybean seedlings by 94.72% without affecting root growth. Thus, borrelidin might be a promising candidate for new antifungal agents against P. sojae.

A novel macrocyclic lactone with insecticidal bioactivity from Streptomyces microflavus neau3

A novel macrocyclic lactone (1) was isolated from the fermentation broth of Streptomycesmicroflavus neau3, and the structure was elucidated by extensive spectroscopic analysis. Compound 1 showed high acaricidal activity against adult mites (IC(50)=11.1 μg mL(-1)), and nematocidal activity against Caenorhabditis elegans (IC(50)=17.4 μg mL(-1)), especially the acaricidal activity against mite eggs with an IC(50) of 37.1 μg mL(-1), which was relative higher than that of the commercial acaricide and nematocide milbemycins A(3)/A(4).

Comparative studies on the interaction of genistein, 8-chlorogenistein, and 3',8-dichlorogenistein with bovine serum albumin

Chlorination can significantly enhance the antioxidant and antitumor activity of genistein. In this paper, genistein, 8-chlorogenistein, and 3',8-dichlorogenistein were selected to investigate the binding to bovine serum albumin (BSA) using fluorescence spectroscopy and circular dichroism (CD). The results showed that chlorination, especially at position 3', had significant effects on the binding constant value of chlorinated genistein derivatives to BSA; however, the binding site and the binding number were slightly affected. The thermodynamic parameters indicated that hydrophobic and electrostatic forces played important roles in the binding process and the enhanced binding affinity mainly associated with the increase of the hydrophobicity caused by the chlorine atom substitution. Furthermore, the CD data demonstrated that the conformation of BSA was slightly altered in the presence of genistein, 8-chlorogenistein, and 3',8-dichlorogenistein, with different reduced α-helix contents. The results obtained herein will be of biological significance in toxicology investigation and genistein derivative drug design.

Isolation and identification of 5-hydroxyl-5-methyl-2-hexenoic acid from Actinoplanes sp. HBDN08 with antifungal activity

A bioactivity-guided approach was employed to isolate and determine the chemical identity of bioactive constituents with antifungal activity from Actinoplanes sp. HBDN08. The structure of the antifungal metabolite was elucidated as 5-hydroxyl-5-methyl-2-hexenoic acid on the basis of spectral analysis. This compound showed strong in vitro antifungal activity against Botrytis cinerea, Cladosporium cucumerinum and Corynespora cassiicola, with an IC(50) of 32.45, 27.17, and 30.66 mg/L, respectively; however, it only moderately inhibited hyphal growth of Rhizoctonia solani with an IC(50) of 61.64 mg/L. The in vivo antifungal activity under greenhouse conditions demonstrated that 5-hydroxyl-5-methyl-2-hexenoic acid could effectively control the diseases caused by B. cinerea, C. cucumerinum and C. cassiicola with 71.42%, 78.63% and 65.13% control values at 350 mg/L, respectively. This strong antifungal activity suggests that 5-hydroxyl-5-methyl-2-hexenoic acid might be a promising candidate for new antifungal agents.

Isolation and identification of novel macrocyclic lactones from Streptomyces avermitilis NEAU1069 with acaricidal and nematocidal activity

Bioactivity-guided fractionation of Streptomyces avermitilis NEAU1069 fermentation broth was used to isolate and determine the chemical identity of bioactive constituents with acaricidal and nemotocidal activity. The structures of novel compounds 1 and 2 were determined on the basis of spectroscopic analysis, including 1D and 2D NMR as well as HRESI-MS, ESI-MS of spectrometry analysis, UV and IR spectroscopic analyses, and comparison with data from the literature. The acaricidal activities of the isolated compounds against adult mites and mite eggs were evaluated by mortality and unhatched eggs. The nematocidal activity of the isolated compounds against Caenorhabditis elegans was calculated according to the immobilized rates against the total number of tested nematodes. The results indicated that compounds 1 and 2 exhibited potent acaricidal activity against adult mites, with a mortality of >90% at a concentration of 30 microg/mL. However, compounds 1 and 2 showed only weak acaricidal activity against mite eggs, with unhatched mite egg rates of <60% at a concentration of 100 microg/mL. Compound 2, a hydroxylated derivative at C-23 of 1, possessed a high nematocidal activity against C. elegans, with an immobility of >90% at a concentration of 10 microg/mL. These results demonstrate that compounds 1 and 2, especially compound 2, have potential as pesticides with acaricidal and nematocidal activity.

New nemadectin congener from Streptomyces microflavus neau3: fermentation, isolation, structure elucidation and biological activities

Bioactivity-guided fractionation of Streptomyces microflavus neau3 fermentation broth was used to determine the chemical identity of bioactive constituents. The structure of the new compound 1 was determined on the basis of spectroscopic analysis, including 1D and 2D NMR, as well as HRESI-MS, ESI-MS, UV and IR, and compared with the data reported in the literature. The acaricidal and nematocidal activities of the isolated compound 1 and its previously reported analogs 2, 3, 4 and 5 were evaluated. The results demonstrate that compounds 1, 2, 3, 4 and 5, especially compound 1, have potential as antiparasitics with acaricidal and nematocidal activities. These lactones shed new insights into the structural diversity of nemadectin and milbemycin analog libraries that are potentially accessible by combinatorial biosynthesis.

Isolation and identification of chlorinated genistein from Actinoplanes sp. HBDN08 with antioxidant and antitumor activities

A strain Actinoplanes sp. HBDN08 was screened by PCR-guided method using primers derived from conserved regions of halogenase genes. A new chlorinated isoflavone, 3',8-dichlorogenistein (1), along with 8-chlorogenistein (2) were isolated from the fermentation broth of Actinoplanes sp. HBDN08. Their structures were elucidated on the basis of extensive 1D and 2D NMR as well as HRESI-MS, ESI-MS, UV, and IR spectroscopic analyses. The origin of the two compounds was also investigated by high-performance liquid chromatography (HPLC) analysis. The results demonstrated that they were not biosynthesized but derived from the biotransformation of genistein by Actinoplanes sp. HBDN08. The antioxidant activities of the isolated compounds 1 and 2 were evaluated by using the lipid peroxidation assay. Their antitumor activities were calculated according to the inhibitory rate of cell proliferation against the human breast cancer cell line MDA-MB-231. The results indicated that compounds 1 (IC(50) = 5.2 microM) and 2 (IC(50) = 7.5 microM) showed stronger antioxidant activities than genistein (IC(50) = 13.6 microM). In comparison with the antitumor activities of genistein, those of compounds 1 and 2 increased 7.7- and 2.6-fold, respectively. These results suggest that the PCR-guided screening strategy is a rapid method for obtaining halometabolite-producing strains. Moreover, these results reveal that chlorination has significant effects on the bioactivities of genistein. This could be important information for studying the structure-activity relationships of genistein.

Three new milbemycin derivatives from Streptomyces bingchenggensis

In the continuing study of the chemical compositions of the strain Streptomyces bingchenggensis, three new milbemycin derivatives, milbemycin alpha(31) (1), secomilbemycins C (2), and D (3), were isolated. Their structures were established on the basis of extensive spectroscopic analysis.

Role of nsdA in negative regulation of antibiotic production and morphological differentiation in Streptomyces bingchengensis

To investigate the function of nsdA in Streptomyces bingchengensis, it was cloned and sequenced, which presented an 89.89% identity with that of S. coelicolor. The lambdaRED-mediated PCR-targeting technique was used to create nsdA replacement in the S. bingchengensis_226541 chromosome. The nsdA disruption mutant, BC29, was obtained, which produced more pigment and spores than did the ancestral strain. HPLC analysis revealed that the disruption of nsdA efficiently increased milbemycin A(4) production and nanchangmycin production by 1.5-fold and 9-fold, respectively. Complementation of the nsdA mutation restored the phenotype and antibiotic production. These results showed that nsdA negatively affected sporulation and antibiotic production in S. bingchengensis.