Isolation, antifungal activity, and structure elucidation of the glutarimide antibiotic, streptimidone, produced by Micromonospora coerulea

The Genomic-Driven Discovery of Glutarimide-Containing Derivatives from Burkholderia gladioli

Glutarimide-containing polyketides exhibiting potent antitumor and antimicrobial activities were encoded via conserved module blocks in various strains that favor the genomic mining of these family compounds. The bioinformatic analysis of the genome of Burkholderia gladioli ATCC 10248 showed a silent trans-AT PKS biosynthetic gene cluster (BGC) on chromosome 2 (Chr2C8), which was predicted to produce new glutarimide-containing derivatives. Then, the silent polyketide synthase gene cluster was successfully activated via in situ promoter insertion and heterologous expression. As a result, seven glutarimide-containing analogs, including five new ones, gladiofungins D-H (3-7), and two known gladiofungin A/gladiostatin (1) and 2 (named gladiofungin C), were isolated from the fermentation of the activated mutant. Their structures were elucidated through the analysis of HR-ESI-MS and NMR spectroscopy. The structural diversities of gladiofungins may be due to the degradation of the butenolide group in gladiofungin A (1) during the fermentation and extraction process. Bioactivity screening showed that 2 and 4 had moderate anti-inflammatory activities. Thus, genome mining combined with promoter engineering and heterologous expression were proved to be effective strategies for the pathway-specific activation of the silent BGCs for the directional discovery of new natural products.

Natural products from marine fungi as a source against agricultural pathogenic fungi

There are many kinds of agricultural pathogenic fungi, which may belong to pathogenic fungi in different species, such as Fusarium, Alternaria, Colletotrichum, Phytophthora, and other agricultural pathogens. Pathogenic fungi from different sources are widely distributed in agriculture, which threaten the lives of crops around the world and caused great damage to agricultural production and economic benefits. Due to the particularity of the marine environment, marine-derived fungi could produce natural compounds with unique structures, rich diversities, and significant bioactivities. Since marine natural products with different structural characteristics could inhibit different kinds of agricultural pathogenic fungi, secondary metabolites with antifungal activity could be used as lead compounds against agricultural pathogenic fungi. In order to summarize the structural characteristics of marine natural products against agricultural pathogenic fungi, this review systematically overview the activities against agricultural pathogenic fungi of 198 secondary metabolites from different marine fungal sources. A total of 92 references published from 1998 to 2022 were cited. KEY POINTS: • Pathogenic fungi, which could cause damage to agriculture, were classified. • Structurally diverse antifungal compounds from marine-derived fungi were summarized. • The sources and distributions of these bioactive metabolites were analyzed.

Micromonospora: A Prolific Source of Bioactive Secondary Metabolites with Therapeutic Potential

Micromonospora, one of the most important actinomycetes genera, is well-known as the treasure trove of bioactive secondary metabolites (SMs). Herein, together with an in-depth genomic analysis of the reported Micromonospora strains, all SMs from this genus are comprehensively summarized, containing structural features, bioactive properties, and mode of actions as well as their biosynthetic and chemical synthesis pathways. The perspective enables a detailed view of Micromonospora-derived SMs, which will enrich the chemical diversity of natural products and inspire new drug discovery in the pharmaceutical industry.

Chemical constituents from the Streptomyces morookaensis strain Sm4-1986

Three new compounds, including 6-methoxy-3,4,5,7-tetramethylisochromane-3,8-diol (1), 3,4,5,7-tetramethylisochromane-3,6,8-triol (2), streptimidone derivative (3), along with ten known compounds (4-13) were isolated from the Streptomyces morookaensis strain Sm4-1986. Their chemical structures were established based on the information from UV, IR, NMR (¹H NMR, ¹³C NMR, ¹H-¹H COSY, HSQC, HMBC, NOESY), and mass spectroscopic. Moreover, all the isolated new compounds were evaluated for antibacterial activities (S. aureus, B. cereus, S. epidermids and methicillin-resistant S. aureus) and their cytotoxicities against MCF-7, A549, Hela tumor cell lines and Marc-145 normal cell line.

Design and Synthesis of N-Substituted 3,4-Pyrroledicarboximides as Potential Anti-Inflammatory Agents

In the present paper, we describe the biological activity of the newly designed and synthesized series N-substituted 3,4-pyrroledicarboximides 2a-2p. The compounds 2a-2p were obtained in good yields by one-pot, three-component condensation of pyrrolo[3,4-c]pyrrole scaffold (1a-c) with secondary amines and an excess of formaldehyde solution in C2H5OH. The structural properties of the compounds were characterized by 1H NMR, 13C NMR FT-IR, MS, and elemental analysis. Moreover, single crystal X-ray diffraction has been recorded for compound 2h. The colorimetric inhibitor screening assay was used to obtain their potencies to inhibit COX-1 and COX-2 enzymes. According to the results, all of the tested compounds inhibited the activity of COX-1 and COX-2. Theoretical modeling was also applied to describe the binding properties of compounds towards COX-1 and COX-2 cyclooxygenase isoform. The data were supported by QSAR study.

A novel chresdihydrochalcone from Streptomyces chrestomyceticus exhibiting activity against Gram-positive bacteria

Microbial-derived natural products provide unique bioactivities and serve as a unique source of drug leads. In the present study, we isolated one new chresdihydrochalcone (1), one new chresphenylacetone (2), and one known streptimidone (3) from Streptomyces chrestomyceticus BCC 24770 using antibacterial activity-guided isolation and purification procedures. We determined their molecular weights using MS and HRMS and elucidated their chemical structures from their 1D and 2D NMR and electronic circular dichroism (ECD) spectra. Compound 1 showed moderate inhibitory activities against the Gram-positive bacteria Methicillin-resistant Staphylococcus aureus, Bacillus subtilis, and Micrococcus luteus. Cytotoxicity and hemolytic activity were not observed at a concentration of up to 100 μg ml^-1. The specific antimicrobial activity and low toxicity of compound 1 indicate this compound to be a potential antibiotic candidate, especially as antibiotic resistance has become a significant public health threat.

Isolation of new streptimidone derivatives, glutarimide antibiotics from Streptomyces sp. W3002 using LC-MS-guided screening

A LC-MS-guided screening led to the isolation of two new streptimidone derivatives (2 and 3) containing a glutarimide ring and two glutarimide ring-opened compounds (4 and 5) along with a known glutarimide-containing polyketide, streptimidone (1) from Streptomyces sp. W3002 strain. Their structures were elucidated by MS and NMR spectroscopic analyses and by comparison with data from the literature. Compound 2 is a non-hydroxylated analog at the C-5 position of streptimidone. The structure of 3 was determined as a streptimidone derivative possessing the α, β-unsaturated ketone moiety at positions C-5 and C-6. Compound 4 had similar chemical shifts and splitting patterns with 3, but the glutarimide ring is opened. Compound 5 closely resembles that of 4 with the only difference being the existence of an additional methoxy group instead of an amide group. Streptimidone (1) and 3 showed weak cytotoxic activity against three human cancer cell lines, respectively.

Coumarin tethered cyclic imides as efficacious glucose uptake agents and investigation of hit candidate to probe its binding mechanism with human serum albumin

A series of novel coumarin-cyclic imide conjugates (1a-1j) were designed and synthesized to evaluate their glucose uptake activity by insulin resistant liver hepatocyte carcinoma (HepG2) cells through 2-NBDG uptake assay. Compounds (1a-1j) were characterised using various analytical methods such as ¹H NMR, ¹³C NMR, IR, GC-MS, elemental and single-crystal X-ray diffraction techniques. Compounds (1a-1j) exhibited 85.21 - 65.80% of glucose uptake and showed low level of cytotoxicity towards human embryonic kidney cells (HEK-293) indicating good selectivity and safety profile. Compound 1f was identified as a hit candidate exhibiting 85.21% of glucose uptake which was comparable with standard antidiabetic drug Metformin (93.25% glucose uptake). Solution stability study under physiological pH conditions ≈ (3.4 - 8.7), indicates that compound 1f is sufficiently stable at varied pH conditions and thereby compatible with bio-physiological environments. Interaction of 1f with human serum albumin (HSA) were also studied which quantifies that compound 1f binds with HSA efficiently through facile binding reaction in solution. Fluorescence, UV-vis spectrophotometry and molecular modeling methodologies were employed for studying the interaction mechanism of compound 1f with protein.

Two new glutarimide antibiotics from Streptomyces sp. HS-NF-780

Two new glutarimide antibiotics, 9-methylstreptimidone 2-α-D-glucopyranoside (1), and hydroxyiso-9-methylstreptimidone (2), along with a known compound, 9-methylstreptimidone (3), have been isolated from the broth of Streptomyces sp. HS-NF-780. 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. By modified Mosher's method and acid hydrolysis, the absolute configurations of compounds 1 and 2 were established. Compounds 1 and 2 exhibited moderate cytotoxic activity.

Antifungal activity of rimocidin and a new rimocidin derivative BU16 produced by Streptomyces mauvecolor BU16 and their effects on pepper anthracnose

AIMS

The objective of this study was to explore antifungal metabolites targeting fungal cell envelope and to evaluate the control efficacy against anthracnose development in pepper plants.

METHODS AND RESULTS

A natural product library comprising 3000 microbial culture extracts was screened via an adenylate kinase (AK)-based cell lysis assay to detect antifungal metabolites targeting the cell envelope of plant-pathogenic fungi. The culture extract of Streptomyces mauvecolor strain BU16 displayed potent AK-releasing activity. Rimocidin and a new rimocidin derivative, BU16, were identified from the extract as active constituents. BU16 is a tetraene macrolide containing a six-membered hemiketal ring with an ethyl group side chain instead of the propyl group in rimocidin. Rimocidin and BU16 showed broad-spectrum antifungal activity against various plant-pathogenic fungi and demonstrated potent control efficacy against anthracnose development in pepper plants.

CONCLUSIONS

Antifungal metabolites produced by S. mauvecolor strain BU16 were identified to be rimocidin and BU16. The compounds displayed potent control efficacy against pepper anthracnose.

SIGNIFICANCE AND IMPACT OF THE STUDY

Rimocidin and BU16 would be active ingredients of disease control agents disrupting cell envelope of plant-pathogenic fungi. The structure and antifungal activity of rimocidin derivative BU16 is first described in this study.

Streptomyces sanglieri which colonised and enhanced the growth of Elaeis guineensis Jacq. seedlings was antagonistic to Ganoderma boninense in in vitro studies

Actinomycete strain AUM 00500 was 99.5 % similar to Streptomyces sanglieri NBRC 100784(T) and was evaluated for antagonistic activity towards Ganoderma boninense, the causative fungus of basal stem rot of oil palm. The strain showed strong antifungal activity towards G. boninense in in vitro and SEM analysis showed various modes of inhibition of the fungus. Ethyl acetate extracts of single culture and inhibition zone of cross-plug culture by HPLC indicated that strain AUM 00500 produced two different antibiotics of the glutarimide group namely cycloheximide and actiphenol. In greenhouse trials, oil palm seed treated with spores of S. sanglieri strain AUM 00500 at 10(9) cfu/ml showed significant (P < 0.05) increase in oil palm seedlings growth when compared to the control. Streptomyces sanglieri strain AUM 00500 successfully colonised the epidermal surface of the roots of treated oil palm seedlings and it was recovered from root fragments plated on starch casein agar.

Antiproliferative and antibacterial activity of some glutarimide derivatives

Antiproliferative and antibacterial activities of nine glutarimide derivatives (1-9) were reported. Cytotoxicity of compounds was tested toward three human cancer cell lines, HeLa, K562 and MDA-MB-453 by MTT assay. Compound 7 (2-benzyl-2-azaspiro[5.11]heptadecane-1,3,7-trione), containing 12-membered ketone ring, was found to be the most potent toward all tested cell lines (IC50 = 9-27 μM). Preliminary screening of antibacterial activity by a disk diffusion method showed that Gram-positive bacteria were more susceptible to the tested compounds than Gram-negative bacteria. Minimum inhibitory concentration (MIC) determined by a broth microdilution method confirmed that compounds 1, 2, 4, 6-8 and 9 inhibited the growth of all tested Gram-positive and some of the Gram-negative bacteria. The best antibacterial potential was achieved with compound 9 (ethyl 4-(1-benzyl-2,6-dioxopiperidin-3-yl)butanoate) against Bacillus cereus (MIC 0.625 mg/mL; 1.97 × 10(-3 )mol/L). Distinction between more and less active/inactive compounds was assessed from the pharmacophoric patterns obtained by molecular interaction fields.

Identification of antifungal niphimycin from Streptomyces sp. KP6107 by screening based on adenylate kinase assay

Microbial culture extracts are used for natural product screening to find antifungal lead compounds. A microbial culture extract library was constructed using 343 actinomycete isolates to examine the value of the adenylate kinase (AK) assay for screening to identify antifungal metabolites that disrupt cell integrity in plant pathogenic fungi. A culture extract of Streptomyces sp. strain KP6107 lysed cells of Fusarium oxysporum f.sp. lycopersici which resulted in high AK activity. The active ingredient N-1 was purified from the culture extract using various chromatographic procedures and identified to be the guanidyl-polyol macrolide antibiotic, niphimycin, which is a potent fungal cell membrane disruptor. Niphimycin showed broad-spectrum antifungal activity against Alternaria mali, Aspergillus oryzae, Colletotrichum coccodes, Colletotrichum gloeosporioides, Cercospora canescens, Cylindrocarpon destructans, F. oxysporum f.sp. cucumerinum, F. oxysporum f.sp. lycopersici, and Rhizoctonia solani at concentrations of 8-64 µg ml(-1). Anthracnose development in pepper plants was completely inhibited by treatment with 50 µg ml(-1) niphimycin, which was as effective as chlorothalonil. These results show that the AK assay is an efficient and selective tool in screening for cell membrane/wall disruptors of plant pathogenic fungi.

Antifungalmycin, an antifungal macrolide from Streptomyces padanus 702

Two polyene macrolide antibiotics: antifungalmycin (1 ) and fungichromin (2 ) were isolated from the culture mycelia of Streptomyces padanus 702 via bioactivity-guided fractionation using various chromatographic procedures. Their structures were elucidated on the basis of spectral analysis, and 1 is a new polyene macrolide. Compounds 1 and 2 showed significant inhibition against Gibberella zeae with EC50 values of 26.71 and 2.21 µg/mL, Fusicoccum sp. (plantain head blight) with EC50 values of 23.4 and 3.17 µg/mL, Mucor ssp. 8894 with EC50 values of 28.80 and 2.11 µg/mL, Ustilaginoidea virens with EC50 values of 26.72 and 0.21 µg/mL, respectively. This shows that the microbial secondary metabolites 1 and 2 have the potential to be developed as agricultural fungicides for use against G. zeae, Fusicoccum sp., Mucor ssp. 8894, and U. virens .

Synthesis and antiviral activities of synthetic glutarimide derivatives

A series of novel glutarimide compounds were synthesized and their antiviral activities were evaluated. The compounds displaying the strongest antiviral activities included 5, 6f, 7e and 9 against coxsackievirus B3 (Cox B3), 10 and 6f against influenza virus A (influenza A) and 7a against herpes simplex virus 2 (HSV-2). However, most of the synthetic glutarimides showed comparatively much weaker activity against influenza A, Cox B3 and HSV-2 than the natural glutarimide compounds tested. Based on the results, it seemed likely that a conjugated system at the β-substituted moiety provides stronger antiviral activity.

Disease control effect of strevertenes produced by Streptomyces psammoticus against tomato fusarium wilt

During screening of microorganisms producing antifungal metabolites, Streptomyces psammoticus strain KP1404 was isolated. The culture extract of this strain showed potent disease control efficacy against Fusarium wilt on tomato plants. The antifungal metabolites ST-1 and ST-2 were isolated from the culture extract using a variety of chromatographic procedures. On the basis of MS and NMR spectrometric analysis, the structures of the antifungal active compounds ST-1 and ST-2 were determined to be the polyene antibiotics strevertene A and strevertene B, respectively. In vitro, strevertenes A and B showed inhibitory effects against the mycelial growth of Alternaria mali , Aspergillus oryzae , Cylindrocarpon destructans , Colletotrichum orbiculare , Fusarium oxysporum f.sp. lycopersici, and Sclerotinia sclerotiorum , even at concentrations of 4-16 μg/mL. Fusarium wilt development on tomato plants was strongly retarded by treatment with 1 μg/mL of these strevertenes. The disease control efficacies of strevertenes on Fusarium wilt were as remarkable as that of benomyl.

Evaluation of new migrastatin and dorrigocin congeners unveils cell migration inhibitors with dramatically improved potency

Lactimidomycin (LTM, 1), iso-migrastatin (iso-MGS, 2) and migrastatin (MGS, 3) are macrolide antitumor antibiotics differing in macrolide ring size but all bearing a glutarimide side chain. To further develop these natural products and related analogs as drug candidates we have produced and evaluated the biological activities of a small library of iso-MGS and LTM-derived agents; congeners evaluated bear either the MGS scaffold or related acyclic (dorrigocin) scaffolds. Scratch wound-healing (SWH) assays with 4T1 mouse and MDA-MB-231 human mammary tumor cell lines, respectively, reveal structural elements crucial to inhibition of cell migration by these compounds. Moreover, two substances, 14 and 17, with activity far superior to that of MGS are unveiled by SWH assays.

In vitro antagonism of an actinobacterial Kitasatospora isolate against the plant pathogen Phytophthora citricola as elucidated with ultrahigh resolution mass spectrometry

Many soil microorganisms antagonistic to soil borne plant pathogens are well known for their ability to control diseases in situ. A variety of substances, like lytic enzymes, siderophores and antibiotics, produced by these organisms have the potential to protect roots against pathogens. Understanding the ecology and a functional assessment of antagonistic microbial communities in soil requires in-depth knowledge of the mechanisms involved in these interactions, a challenging task in complex systems if low-resolution methods are applied. We propose an information-rich strategy of general relevance, composed of adequate preconcentration in conjunction with ultrahigh resolution ion cyclotron resonance Fourier transform mass spectrometry (ICR-FT/MS) and nuclear magnetic resonance (NMR) spectroscopy to identify any bioactive substances in complex systems. This approach is demonstrated on the specific example of substance identification considered responsible for in vitro antagonism of an actinobacterial antagonist isolated from European beech (Fagus sylvatica) rhizosphere soil against the oomycetous root rot pathogen Phytophthora citricola. The isolate belonging to the genus Kitasatospora exhibited strong antibiosis against the oomycete in vitro. The bioactive substance was observed to exhibit a molar mass of 281.1699 g/mol in positive electrospray ionization mass spectra, and the high mass accuracy of the ICR-FT/MS measurements allowed a precise assignment of a molecular formula that was found identical to the macrolide polyketide cycloheximide C(15)H(23)NO(4)+H(+); its identity was then unequivocally confirmed by the information-rich atomic signature of proton NMR spectroscopy. In conclusion, the combination of the near orthogonal methods (pre)fractionation, ultrahigh-resolution ICR-FT mass spectrometry (yielding molecular and MS(n) fragment signatures) and nuclear magnetic resonance spectroscopy (providing atomic signatures) has been found capable of identifying a biocontrol active compound of Kitasatospora active against Phytophthora citricola expediently, quickly, and accurately. This straightforward approach is of general applicability to elucidate biocontrol mechanisms in any complex system with improved efficiency.

The synthesis of unsubstituted cyclic imides using hydroxylamine under microwave irradiation

Unsubstituted cyclic imides were synthesized from a series of cyclic anhydrides, hydroxylamine hydrochloride (NH₂OH∙HCl), and 4-N,N-dimethylamino-pyridine (DMAP, base catalyst) under microwave irradiation in monomode and multimode microwaves. This novel microwave synthesis produced high yields of the unsubstituted cyclic imides for both the monomode (61 - 81%) and multimode (84 - 97%) microwaves.

Isolation and antifungal and antioomycete activities of aerugine produced by Pseudomonas fluorescens strain MM-B16

The bacterial strain MM-B16, which showed strong antifungal and antioomycete activity against some plant pathogens, was isolated from a mountain forest soil in Korea. Based on the physiological and biochemical characteristics and 16S ribosomal DNA sequence analysis, the bacterial strain MM-B16 was identical to Pseudomonas fluorescens. An antibiotic active against Colletotrichum orbiculare and Phytophthora capsici in vitro and in vivo was isolated from the culture filtrates of P. fluorescens strain MM-B16 using various chromatographic procedures. The molecular formula of the antibiotic was deduced to be C(10)H(11)NO(2)S (M(+), m/z 209.0513) by analysis of electron impact mass spectral data. Based on the nuclear magnetic resonance and infrared spectral data, the antibiotic was confirmed to have the structure of a thiazoline derivative, aerugine [4-hydroxymethyl-2-(2-hydroxyphenyl)-2-thiazoline]. C. orbiculare, P. capsici, and Pythium ultimum were most sensitive to aerugine (MICs for these organisms were approximately 10 micro g ml(-1)). However, no antimicrobial activity was found against yeasts and bacteria even at concentrations of more than 100 micro g ml(-1). Treatment with aerugine exhibited a significantly high protective activity against development of phytophthora disease on pepper and anthracnose on cucumber. However, the control efficacy of aerugine against the diseases was in general somewhat less than that of the commercial fungicides metalaxyl and chlorothalonil. This is the first study to isolate aerugine from P. fluorescens and demonstrate its in vitro and in vivo antifungal and antioomycete activities against C. orbiculare and P. capsici.

Isolation and in vivo and in vitro antifungal activity of phenylacetic acid and sodium phenylacetate from Streptomyces humidus

The antifungal substances SH-1 and SH-2 were isolated from Streptomyces humidus strain S5-55 cultures by various purification procedures and identified as phenylacetic acid and sodium phenylacetate, respectively, based on the nuclear magnetic resonance, electron ionization mass spectral, and inductively coupled plasma mass spectral data. SH-1 and SH-2 completely inhibited the growth of Pythium ultimum, Phytophthora capsici, Rhizoctonia solani, Saccharomyces cerevisiae, and Pseudomonas syringae pv. syringae at concentrations from 10 to 50 microg/ml. The two compounds were as effective as the commercial fungicide metalaxyl in inhibiting spore germination and hyphal growth of P. capsici. However, the in vivo control efficacies of the two antifungal compounds against P. capsici infection on pepper plants were similar to those of H(3)PO(3) and fosetyl-AI but less than that of metalaxyl.