Cyclopiazonic acid type indole alkaloids from Nicotiana tabacum-derived fungus Aspergillus versicolor and their anti-tobacco mosaic virus activities

Indole alkaloids isolated from the Nicotiana tabacum-derived Aspergillus fumigatus 0338 as potential inhibitors for tobacco powdery mildew and their mode of actions

To explore active natural products against tobacco powdery mildew caused by Golovinomyces cichoracearum, an extract from the fermentation of endophytic Aspergillus fumigatus 0338 was investigated. The mechanisms of action for active compounds were also studied in detail. As a result, 14 indole alkaloid derivatives were isolated, with seven being newly discovered (1-7) and the remaining seven previously described (8-14). Notably, compounds 1-3 are rare linearly fused 6/6/5 tricyclic prenylated indole alkaloids, with asperversiamide J being the only known natural product of this kind. The isopentenyl substitutions at the 5-position in compounds 4 and 5 are also rare, with only compounds 1-(5-prenyl-1H-indol-3-yl)-propan-2-one (8) and 1-(6-methoxy-5-prenyl-1H-indol3-yl)-propan-2-one currently available. In addition, compounds 6 and 7 are new framework indole alkaloid derivatives bearing a 6-methyl-1,7-dihydro-2H-azepin-2-one ring. The purified compounds were evaluated for their activity against G. cichoracearum, and the results revealed that compounds 7 and 9 demonstrated obvious anti-G. cichoracearum activities with an inhibition rate of 82.6% and 85.2%, respectively, at a concentration of 250 μg/mL, these rates were better than that of the positive control agent, carbendazim (78.6%). The protective and curative effects of compounds 7 and 9 were also better than that of positive control, at the same concentration. Moreover, the mechanistic study showed that treatment with compound 9 significantly increased the structural tightness of tobacco leaves and directly affect the conidiospores of G. cichoracearum, thereby enhancing resistance. Compounds 7 and 9 could also induce systemic acquired resistance (SAR), directly regulating the expression of defense enzymes, defense genes, and plant semaphorins, which may further contribute to increased plant resistance. Based on the activity experiments and molecular dockings, the indole core structure may be the foundation of these compounds' anti-G. cichoracearum activity. Among them, the indole derivative parent structures of compounds 6, 7, and 9 exhibit strong effects. Moreover, the methoxy substitution in compound 7 can enhance their activity. By isolating and structurally identifying the above indole alkaloids, new candidates for anti-powdery mildew chemical screening were discovered, which could enhance the utilization of N. tabacum-derived fungi in pesticide development.

Origin of the 6/5/6/5 Tetracyclic Cyclopiazonic Acids

The natural product α-cyclopiazonic acid (α-CPA) is a very potent Ca2+-ATPase inhibitor. The CPA family of compounds comprise over 80 chemical entities with at least five distinct skeletons. While α-CPA features a canonical 6/5/6/5/5 skeleton, the 6/5/6/5 skeleton is the most prevalent among the CPA family. However, the origin of the unique tetracyclic skeleton remains unknown. The 6/5/6/5-type CPAs may derive from a precursor of acetoacetyl-l-tryptophan (AATrp) generated from a hypothetic thioesterase-like pathway. Alternatively, cleavage of the tetramic acid ring would also result in the formation of the 6/5/6/5 scaffold. Aspergillus oryzae HMP-F28 is a marine sponge-associated filamentous fungus known to produce CPAs that act as primary neurotoxins. To elucidate the origin of this subfamily of CPAs, we performed homologous recombination and genetic engineering experiments on strain HMP-F28. Our results are supportive of the ring cleavage pathway through which the tetracyclic 6/5/6/5-type CPAs are generated from 6/5/6/5/5-type pentacyclic CPAs.

Bioactive Alkaloids as Secondary Metabolites from Plant Endophytic Aspergillus Genus

Alkaloids represent a large family of natural products with diverse structures and bioactivities. These compounds and their derivatives have been widely used in clinics to treat various diseases. The endophytic Aspergillus is a filamentous fungus renowned for its extraordinary ability to produce active natural products of high therapeutic value and economic importance. This review is the first to focus on Aspergillus-derived alkaloids. Through an extensive literature review and data analysis, 263 alkaloids are categorized according to their structural features into those containing cytochalasans, diketopiperazine alkaloids, quinazoline alkaloids, quinoline alkaloids, indole alkaloids, pyrrolidine alkaloids, and others. These metabolites exhibited diverse biological activities, such as antibacterial activity, cytotoxicity, anti-inflammatory activity, and α-glucosidase, ACE, and DPPH inhibitory activities. The bioactivity, structural diversity, and occurrence of these alkaloids are reviewed in detail.

Antimicrobial activity of natural and semi-synthetic carbazole alkaloids

Since the first natural carbazole alkaloid, murrayanine, was isolated from Mwraya Spreng, carbazole alkaloid derivatives have been widely concerned for their anti-tumor, anti-viral and anti-bacterial activities. In recent decades, a growing body of data suggest that carbazole alkaloids and their derivatives have different biological activities. This is the first comprehensive description of the antifungal and antibacterial activities of carbazole alkaloids in the past decade (2012-2022), including natural and partially synthesized carbazole alkaloids in the past decade. Finally, the challenges and problems faced by this kind of alkaloids are summarized. This paper will be helpful for further exploration of this kind of alkaloids.

Extraction and characterization of anti-virus anthraquinones from Nicotiana tabacum-derived Aspergillus oryzae YNCA1220

In this study, seven novel anthraquinones (1-7) and four described anthraquinones (8-11) were purified from Nicotiana tabacum-derived Aspergillus oryzae YNCA1220. It is worth noting that only analogs of 4 and 5 have been reported as natural products to date, while the nuclei of compounds 1-3, 6 and 7 were isolated for the first time in nature. Among them, compounds 1-3 bear an unusual anthra[2,3-b]furan-9,10-dione nucleus, 4 and 5 possess a rare 3-methyl-1H-pyrrol-2-yl substituent, and 6 and 7 are new framework anthraquinones bearing a 6-methyl-1,7-dihydro-2H-azepin-2-one ring. Interestingly, the in vivo assays indicated that 1, 4 and 5 had inactivation effects against tobacco mosaic virus (TMV) with inhibition rates of 41.6%, 55.4% and 38.6%, respectively, at a concentration of 50 μg/mL, which were better than that of the positive control agent, ningnanmycin (33.8%). Compounds 1, 4 and 5 also had protective effects with inhibition rates of 48.7%, 60.2% and 43.5% at the same concentration, while 4 had a better curative effect than ningnanmycin at a concentration of 100 μg/mL. In addition, mechanistic studies also revealed that a potent direct effect on TMV, the induction of SAR in tobacco plants, and the effective regulation of defense enzymes, defense genes, and defense hormones may be the reasons for the significant effects of 4 against TMV. At the same time, downregulation of the expression of total NtHsp70 protein by inhibiting the related Hsp70 genes may also be involved in tobacco resistance to TMV. To evaluate whether compounds have broader antiviral activities, the antirotavirus activities of new isolates were also evaluated and found to be highly effective with a therapeutic index (TI) value ranging from 11.6 to 17.7. This study suggests that the above anthraquinone compounds, particularly 4, have broad spectrum antiviral activities. The successful isolation and structure identification of the above anthraquinones provide new materials for the screening of anti-TMV agents and contribute to the improved utilization of N. tabacum-derived fungi.

C-Alkylated flavonoids from the whole plants of Desmodium caudatum and their anti-TMV activity

BACKGROUND

Natural products are important sources of biopesticides to control plant virus, and flavonoids are identified as promising anti-tobacco mosaic virus (TMV) agents. Since Desmodium caudatum is a rich source of flavonoids, this study focuses on the discovery of the new anti-TMV active flavonoids from D. caudatum and their possible mode of action.

RESULTS

Three new (compounds 1-3) and nine known (compounds 4-12) C-alkylated flavonoids were isolated from D. caudatum. To the best of our knowledge, the framework of 1-3 was reported in natural products for the first time. In addition, 1-3, 5, and 6 showed notable anti-TMV activity with inhibition rates in the range of 35.8-64.3% at a concentration of 50 μg/mL, and these rates are higher than that of positive control (with inhibition rates of 34.6% ± 2.8). In addition, the structure-activity relationship study revealed that the (pyrrol-2-yl)methyl moiety on flavone can significantly increases the activity. This result is helpful to find new anti-TMV inhibitors.

CONCLUSION

C-Alkylated flavonoids showed potent activities against TMV with multiple modes of actions. The increase of defense-related enzyme activities, up-regulate the expression of defense related genes, down-regulate the expression of Hsp70 protein by inhibiting the related Hsp genes that are involved in tobacco resistance to TMV. By the actions mentioned earlier, the infection of TMV was influenced, thereby achieving the effects of control of TMV. The successful isolation of the earlier-mentioned flavonoids provide the new source of biopesticides to TMV proliferation, and also contribute to the utilization of D. caudatum. © 2023 Society of Chemical Industry.

Pegriseofamines A-E: Five cyclopiazonic acid related indole alkaloids from the fungus Penicillium griseofulvum

Five new cyclopiazonic acid related indole alkaloids, pegriseofamines A-E (1-5), were isolated from the fungus Penicillium griseofulvum. Their structures and absolute configurations were determined by NMR, HRESIMS, quantum-chemical calculation, and X-ray diffraction experiments. Among them, pegriseofamine A (1) possesses an undescribed 6/5/6/7 tetracyclic ring system generated by the fusion of an azepine and an indole unit via a cyclohexane, and the postulated biosynthetic origin of 1 was discussed. Compound 4 could relieve liver injury and prevent hepatocyte apoptosis in ConA-induced autoimmune liver disease.

Three new chromones from the whole plants of Chamaecrista rotundifolia and their anti-rotavirus activities

Chamaecrista rotundifolia (C. rotundifolia) is a perennial herb of leguminosae, which increasingly being grown as a forage in China. In our search for original bioactive metabolites from Cassia plants, the phytochemical reinvestigation of the C. rotundifolia was carried out, which led to the isolation of three new (1-3) and six known (4-9) chromones. Their structures were confirmed by spectroscopic methods, including extensive 1D and 2D NMR techniques. Compounds 1-9 were evaluated for their anti-rotavirus activities, and the results revealed that compounds 1-9 exhibited potential anti-rotavirus activities with therapeutic index (TI) valves in the range of 12.0 ∼ 20.2, respectively.

The anti-TMV potency of the tobacco-derived fungus Aspergillus versicolor and its active alkaloids, as anti-TMV activity inhibitors

Nicotiana tabacum (tobacco) has attracted interest as one of the most economically important industrial crops widely cultivated in China, whose dried leaves are popularly consumed medicinally and recreationally by human societies. In this study, five undescribed alkaloids derivatives, isoaspergillines A-E, together with eight known alkaloids, notoamide D, (1R,4S)-4-benzyl-1-isopropyl-2,4-dihydro-1H-pyrazino-[2,1-b]quinazoline-3,6-dione, protuboxepin K, notoamide C, notoamide M, deoxybrevianamide E, cyclo (D-Pro-L-Trp), and versicolamide B, were obtained from the culture of the Nicotiana tabacum-derived fungus Aspergillus versicolor. Their structures were mainly elucidated through comprehensive analyses of spectroscopic data. Bioactivity evaluation of all isolated compounds revealed that isoaspergilline A and notoamide M exhibited anti-TMV activities with IC₅₀ values of 20.0 and 22.8 μM, respectively. Molecular docking suggested that isoaspergilline A and notoamide M were well located into the active site of anti-TMV by interacting with SER138, SER143, and ASN73 residues. This study enlightens the therapeutic potential of the endophytic fungus A. versicolor and it is helpful to find undescribed anti-TMV activity inhibitors, as well as searching for new anti-TMV candidates from natural sources.