Asperazine

Two new alkaloids from the endophytic fungus Aspergillus fumigatus SAS10 isolated from the mangrove tree Sonneratia apetala.[Pubmed:37874626]

Nat Prod Res. 2023 Oct 24:1-6.

Two new alkaloids designated aspernigrin E (1) and pyranonigrin L (2) were isolated from mangrove endophytic fungus Aspergillus fumigatus SAS10, together with the known alkaloid compounds pyranonigrin A (3), Asperazine (4), (+)-iso-pestalazine A (5), pestalazine A (6), and pestalazine B (7). The planar structures of the new compounds were elucidated by HR-MS and NMR spectroscopic data analyses. The absolute configurations of compounds 1 and 2 were determined by comparison of the electronic circular dichroic (ECD) spectra with the calculated ECD spectra. All these compounds were tested for anti-bacterial activity.

A one-step gram-scale protocol for stereoselective domino dimerization to asperazine A analogs.[Pubmed:36861828]

STAR Protoc. 2023 Mar 17;4(1):102114.

Here, we present an efficient protocol for stereoselective 4N-based domino dimerization in one single step, establishing a 22-membered library of Asperazine A analogs. We describe steps for performing a gram-scale 2N-monomer to access the unsymmetrical 4N-dimer. We detail the synthesis of the desired dimer 3a as a yellow solid in 78% yield. This process demonstrates the 2-(iodomethyl)cyclopropane-1,1-dicarboxylate to be an iodine cation source. The protocol is limited to unprotected aniline of 2N-monomer. For complete details on the use and execution of this protocol, please refer to Bai et al. (2022).(1).

Copper-Mediated Single-Electron Approach to Indoline Amination: Scope, Mechanism, and Total Synthesis of Asperazine A.[Pubmed:35876810]

J Org Chem. 2022 Aug 5;87(15):9907-9914.

Pyrroloindolines bearing a C3-N linkage comprise the core of many biologically active natural products, but many methods toward their synthesis are limited by the sterics or electronics of the product. We report a single electron-based approach for the synthesis of this scaffold and demonstrate high-yielding aminations, regardless of electronic or steric demands. The transformation uses copper wire and isopropanol to promote the reaction. The broad synthetic utility of this heterogeneous copper-catalyzed approach to access pyrroloindolines, diketopiperazine, furoindoline, and (+)-Asperazine is included, along with experiments to provide insight into the mechanism of this new process.

In Vitro Phytobiological Investigation of Bioactive Secondary Metabolites from the Malus domestica-Derived Endophytic Fungus Aspergillus tubingensis Strain AN103.[Pubmed:35744888]

Molecules. 2022 Jun 11;27(12):3762.

Endophytic fungi including black aspergilli have the potential to synthesize multiple bioactive secondary metabolites. Therefore, the search for active metabolites from endophytic fungi against pathogenic microbes has become a necessity for alternative and promising strategies. In this study, 25 endophytic fungal isolates associated with Malus domestica were isolated, grown, and fermented on a solid rice medium. Subsequently, their ethyl acetate crude extracts were pretested for biological activity. One endophytic fungal isolate demonstrated the highest activity and was chosen for further investigation. Based on its phenotypic, ITS ribosomal gene sequences, and phylogenetic characterization, this isolate was identified as Aspergillus tubingensis strain AN103 with the accession number (KR184138). Chemical investigations of its fermented cultures yielded four compounds: Pyranonigrin A (1), Fonsecin (2), TMC 256 A1 (3), and Asperazine (4). Furthermore, 1H-NMR, HPLC, and LC-MS were performed for the identification and structure elucidation of these metabolites. The isolated pure compounds showed moderate-to-potent antibacterial activities against Pseudomonas aeruginosa and Escherichia coli (MIC value ranged from 31 and 121 to 14.5 and 58.3 mug/mL), respectively; in addition, the time-kill kinetics for the highly sensitive bacteria against isolated compounds was also investigated. The antifungal activity results show that (3) and (4) had the maximum effect against Fusarium solani and A. niger with inhibition zones of 16.40 +/- 0.55 and 16.20 +/- 0.20 mm, respectively, and (2) had the best effect against Candida albicans, with an inhibition zone of 17.8 +/- 1.35 mm. Moreover, in a cytotoxicity assay against mouse lymphoma cell line L5178Y, (4) exhibited moderate cytotoxicity (49% inhibition), whereas (1-3) reported weak cytotoxicity (15, 26, and 19% inhibition), respectively. Our results reveal that these compounds might be useful to develop potential cytotoxic and antimicrobial drugs and an alternative source for various medical and pharmaceutical fields.

Antifeedant and Antifungal Activities of Metabolites Isolated from the Coculture of Endophytic Fungus Aspergillus tubingensis S1120 with Red Ginseng.[Pubmed:34786852]

Chem Biodivers. 2022 Jan;19(1):e202100608.

A new globoscinic acid derivative, aspertubin A (1) along with four known compounds, were obtained from the co-culture of Aspergillus tubingensis S1120 with red ginseng. The chemical structures of compounds were characterized by using spectroscopic methods, the calculated and experimental electronic circular dichroism. Panaxytriol (2) from red ginseng, and asperic acid (4) showed significant antifeedant effect with the antifeedant rates of 75 % and 80 % at the concentrations of 50 mug/cm(2) . Monomeric carviolin (3) and Asperazine (5) displayed weak attractant activity on silkworm. All compounds were assayed for antifungal activities against phytopathogens A. tubingensis, Nigrospora oryzae and Phoma herbarum and the results indicated that autotoxic aspertubin A (1) and panaxytriol (2) possessed selective inhibition against A. tubingensis with MIC values at 8 mug/mL. The co-culture extract showed higher antifeedant and antifungal activities against P. herbarum than those of monoculture of A. tubingensis in ordinary medium. So the medicinal plant and endophyte showed synergistic effect on the plant disease resistance by active compounds from the coculture of A. tubingensis S1120 and red ginseng.

Diversity within Aspergillus niger Clade and Description of a New Species: Aspergillus vinaceus sp. nov.[Pubmed:33348541]

J Fungi (Basel). 2020 Dec 17;6(4):371.

Diversity of species within Aspergillus niger clade, currently represented by A. niger sensu stricto and A. welwitshiae, was investigated combining three-locus gene sequences, Random Amplified Polymorphic DNA, secondary metabolites profile and morphology. Firstly, approximately 700 accessions belonging to this clade were investigated using calmodulin gene sequences. Based on these sequences, eight haplotypes were clearly identified as A. niger (n = 247) and 17 as A. welwitschiae (n = 403). However, calmodulin sequences did not provide definitive species identities for six haplotypes. To elucidate the taxonomic position of these haplotypes, two other loci, part of the beta-tubulin gene and part of the RNA polymerase II gene, were sequenced and used to perform an analysis of Genealogical Concordance Phylogenetic Species Recognition. This analysis enabled the recognition of two new phylogenetic species. One of the new phylogenetic species showed morphological and chemical distinguishable features in comparison to the known species A. welwitschiae and A. niger. This species is illustrated and described as Aspergillus vinaceus sp. nov. In contrast to A. niger and A. welwitschiae, A. vinaceus strains produced Asperazine, but none of them were found to produce ochratoxin A and/or fumonisins. Sclerotium production on laboratory media, which does not occur in strains of A. niger and A. welwitschiae, and strictly sclerotium-associated secondary metabolites (14-Epi-hydroxy-10,23-dihydro-24,25-dehydroaflavinine; 10,23-Dihydro-24,25-dehydroaflavinine; 10,23-Dihydro-24,25-dehydro-21-oxo-aflavinine) were found in A. vinaceus. The strain type of A. vinaceus sp. nov. is ITAL 47,456 (T) (=IBT 35556).

Teratopyrones A-C, Dimeric Naphtho-gamma-Pyrones and Other Metabolites from Teratosphaeria sp. AK1128, a Fungal Endophyte of Equisetum arvense.[Pubmed:33143346]

Molecules. 2020 Oct 30;25(21):5058.

Bioassay-guided fractionation of a cytotoxic extract derived from a solid potato dextrose agar (PDA) culture of Teratosphaeria sp. AK1128, a fungal endophyte of Equisetum arvense, afforded three new naphtho-gamma-pyrone dimers, teratopyrones A-C (1-3), together with five known naphtho-gamma-pyrones, aurasperone B (4), aurasperone C (5), aurasperone F (6), nigerasperone A (7), and fonsecin B (8), and two known diketopiperazines, Asperazine (9) and isorugulosuvine (10). The structures of 1-3 were determined on the basis of their spectroscopic data. Cytotoxicity assay revealed that nigerasperone A (7) was moderately active against the cancer cell lines PC-3M (human metastatic prostate cancer), NCI-H460 (human non-small cell lung cancer), SF-268 (human CNS glioma), and MCF-7 (human breast cancer), with IC(50)s ranging from 2.37 to 4.12 muM while other metabolites exhibited no cytotoxic activity up to a concentration of 5.0 muM.

Characterization of diketopiperazine heterodimers as potential chemical markers for discrimination of two dominant black aspergilli, Aspergillus niger and Aspergillus tubingensis.[Pubmed:32408190]

Phytochemistry. 2020 Aug;176:112399.

Black aspergilli are distributed worldwide and represent one of the most prolific sources of metabolites with biomedical and agrochemical interests. However, due to their similar morphological characteristics and insufficient molecular identification, the taxonomic classification of black aspergilli remains ill-defined. The production of specialised metabolites is often unique for species among black aspergilli and could be used as diagnostic chemical markers for species identification. In this study, chemical investigation of Aspergillus tubingensis OUCMBIII 143291 led to the discovery of the diagnostic chemical marker Asperazine, a complex diketopiperazine heterodimer, as well as two previously undescribed analogues, Asperazine B and C. In addition, an undescribed 2-benzylpyridin-4(1H)-one-containing amide, pestalamide D, along with four known related metabolites were isolated. Their chemical structures, including their absolute configurations, were established on the basis of comprehensive spectral analysis and chiral HPLC analysis of the acidic hydrolysates. Asperazines B and C can serve as potential chemical markers for distinguishing A. tubingensis from A. niger, two representative species of black aspergilli that are usually incorrectly identified. Moreover, the isolated compounds were evaluated for their antifungal activity against eight phytopathogenic fungi including Alternaria alternata, A. brassicae, Botrytis cinerea, Colletotrichum lagenarium, Fusarium oxysporum, Gaeumannomyces graminis, Penicillium digitatum, and Valsa mali. Pestalamide D exhibited significant activities against B. cinerea, C. lagenarium, and V. mali, with MIC values of 4, 8, and 8 mug/mL, respectively, compared with the positive controls carbendazim (MICs = 8, 4, and 4 mug/mL) and prochloraz (MICs = 8, 8, and 4 mug/mL). The results of this study reveal two additional chemical markers and provide a powerful tool for the rapid identification of black aspergilli.

Antifungal activity of compounds isolated from Aspergillus niger and their molecular docking studies with tomatinase.[Pubmed:30582365]

Nat Prod Res. 2020 Sep;34(18):2642-2646.

Using a dual culture antagonism assay, Aspergillus niger exhibited 51.5 +/- 1.1% growth inhibition against Fusarium oxysporum f.sp. lycopersici, the wilt pathogen of tomato. For enhanced production of antifungal metabolites, nutrient optimization was performed and in vitro well-diffusion antifungal assays demonstrated that crude extract obtained from GPYB culture showed a maximum zone of inhibition (8.8 +/- 0.4 mm) against the wilt pathogen, which is corroborated by the comparative LCMS profiles of the extracts from all three media i.e. GPYB, YEB and PDB. Two known compounds, Asperazine (m/z 665 [M + H](+)) and Nigerone (m/z 571 [M + H](+)), were isolated from A. niger and their antifungal activity is reported here for the first time. In MIC experiments, Asperazine and Nigerone inhibited the pathogen at 60 and 80 microg.mL(-1) respectively. Molecular docking studies of Nigerone and Asperazine with F. oxysporum tomatinase showed five and six binding interactions respectively.

Divergent Total Syntheses of C3 a-C7' Linked Diketopiperazine Alkaloids (+)-Asperazine and (+)-Pestalazine A Enabled by a Ni-Catalyzed Reductive Coupling of Tertiary Alkyl Chloride.[Pubmed:30447110]

Chemistry. 2019 Jan 18;25(4):989-992.

Short gram-scale asymmetric syntheses of Asperazine, pestalazine A, and their unnatural congeners thereof, have been achieved in approximately 10 steps by using readily accessible starting materials. The nickel-catalyzed reductive coupling protocol was utilized as a key step for the direct construction of C3a(sp3) -C7'(sp2) bond furnishing the diaryl-substituted quaternary carbon centers with remarkable steric hindrance. The streamlined access to this core structure of heterodimeric tryptophans under the mild reaction conditions, makes this strategy hold a great promise in the concise synthesis of other relevant oligomeric pyrroloindoline alkaloids with unique C3a-C7' linkages.

Whole-genome sequencing of Aspergillus tubingensis G131 and overview of its secondary metabolism potential.[Pubmed:29703136]

BMC Genomics. 2018 Mar 15;19(1):200.

BACKGROUND: Black Aspergilli represent one of the most important fungal resources of primary and secondary metabolites for biotechnological industry. Having several black Aspergilli sequenced genomes should allow targeting the production of certain metabolites with bioactive properties. RESULTS: In this study, we report the draft genome of a black Aspergilli, A. tubingensis G131, isolated from a French Mediterranean vineyard. This 35 Mb genome includes 10,994 predicted genes. A genomic-based discovery identifies 80 secondary metabolites biosynthetic gene clusters. Genomic sequences of these clusters were blasted on 3 chosen black Aspergilli genomes: A. tubingensis CBS 134.48, A. niger CBS 513.88 and A. kawachii IFO 4308. This comparison highlights different levels of clusters conservation between the four strains. It also allows identifying seven unique clusters in A. tubingensis G131. Moreover, the putative secondary metabolites clusters for Asperazine and naphtho-gamma-pyrones production were proposed based on this genomic analysis. Key biosynthetic genes required for the production of 2 mycotoxins, ochratoxin A and fumonisin, are absent from this draft genome. Even if intergenic sequences of these mycotoxins biosynthetic pathways are present, this could not lead to the production of those mycotoxins by A. tubingensis G131. CONCLUSIONS: Functional and bioinformatics analyses of A. tubingensis G131 genome highlight its potential for metabolites production in particular for TAN-1612, Asperazine and naphtho-gamma-pyrones presenting antioxidant, anticancer or antibiotic properties.

Concise total synthesis of (+)-asperazine A and (+)-pestalazine B.[Pubmed:29243756]

Org Biomol Chem. 2018 Jan 3;16(2):202-207.

The highly convergent total synthesis of dimeric diketopiperazine alkaloids (+)-Asperazine A and (+)-pestalazine B is described. A critical aspect of our expedient route was the development of a directed regio- and diastereoselective C3-N1' coupling of complex tetracyclic diketopiperazine components. This late-stage heterodimerization reaction was made possible by design of tetracyclic diketopiperazines that allow C3-carbocation coupling of the electrophilic component to the N1' locus of the nucleophilic fragment. The application of this new coupling reaction to the first total synthesis of (+)-Asperazine A led to our revision of the sign and magnitude of the optical rotation for the reported structure.

Concise Total Synthesis of (+)-Asperazine, (+)-Pestalazine A, and (+)-iso-Pestalazine A. Structure Revision of (+)-Pestalazine A.[Pubmed:26726924]

J Am Chem Soc. 2016 Jan 27;138(3):1057-64.

The concise, enantioselective total syntheses of (+)-Asperazine (1), (+)-iso-pestalazine A (2), and (+)-pestalazine A (3) have been achieved by the development of a late-stage C3-C8' Friedel-Crafts union of polycyclic diketopiperazines. Our modular strategy enables the union of complex polycyclic diketopiperazines in virtually their final forms, thus providing rapid and highly convergent assembly at the challenging quaternary stereocenter of these dimeric alkaloids. The significance of this carbon-carbon bond formation can be gauged by the manifold constraints that were efficiently overcome, namely the substantial steric crowding at both reactive sites, the nucleophilic addition of C8' over N1' to the C3 carbocation, and the multitude of reactivity posed by the use of complex diketopiperazine fragments in the coupling event. The success of the indoline pi-nucleophile that evolved through our studies is notable given the paucity of competing reaction pathways observed in the presence of the highly reactive C3 carbocation generated. This first total synthesis of (+)-pestalazine A also allowed us to revise the molecular structure for this natural alkaloid.

A new diketopiperazine heterodimer from an endophytic fungus Aspergillus niger.[Pubmed:25401948]

J Asian Nat Prod Res. 2015;17(2):182-7.

One new diketopiperazine heterodimer, Asperazine A (1), and eight known compounds, Asperazine (2), cyclo(d-Phe-l-Trp) (3), cyclo(l-Trp-l-Trp) (4), 4-(hydroxymethyl)-5,6-dihydro-pyran-2-one (5), walterolactone A (6), and campyrones A-C (7-9), were isolated from an endophytic fungus Aspergillus niger. Their structures were determined unequivocally on the basis of extensive spectroscopic data analysis. This is the first report of the presence of compound 3 as a natural product. Cytotoxicity test against human cancer cell lines PC3, A2780, K562, MBA-MD-231, and NCI-H1688 revealed that compounds 1 and 2 had weak activities.