Polyketone metabolites isolated from Rhodiola tibetica endohytic fungus Alternaria sp. HJT-Y7 and their SARS-CoV-2 virus inhibitory activitives

3,5-Dimethyl-8-methoxy-3,4-dihydro-1H-isochromen-6-ol Attenuates Ulcerative Colitis via Targeting NLRP3 in Mice

3,5-Dimethyl-8-methoxy-3,4-dihydro-1H-isochromen-6-ol (DMD) is a polyketide compound obtained from the endophytic fungus Penicillium sp. HJT-A-10 of Rhodiola tibetica. R. tibetica is a nourishing food and also used in traditional Chinese medicine and Xizang medicine. In dextran sulfate sodium (DSS)-induced ulcerative colitis (UC) mice, DMD significantly alleviated the pathological symptom of UC. Network pharmacology studies have shown that nucleotide-binding domain-like receptor family pyrin domain containing (NLRP) 3 is the primary target protein of DMD associated with anti-UC. In molecular biology studies, DMD suppressed the activation of NLRP3 and decreased the expression of downstream inflammatory proteins and pro-inflammatory cytokines in UC. The finding was further verified in knockout mice. DMD lost the effect of attenuating DSS-induced UC in NLRP3-/- mice. In conclusion, this study demonstrates that DMD reduces inflammatory response and balances the barrier integrity to attenuate UC via targeting NLRP3, and DMD is a potential natural agent or dietary supplement for attenuating UC.

A New Quinazolinone Alkaloid along with Known Compounds with Seed-Germination-Promoting Activity from Rhodiola tibetica Endophytic Fungus Penicillium sp. HJT-A-6

A new quinazolinone alkaloid named peniquinazolinone A (1), as well as eleven known compounds, 2-(2-hydroxy-3-phenylpropionamido)-N-methylbenzamide (2), viridicatin (3), viridicatol (4), (±)-cyclopeptin (5a/5b), dehydrocyclopeptin (6), cyclopenin (7), cyclopenol (8), methyl-indole-3-carboxylate (9), 2,5-dihydroxyphenyl acetate (10), methyl m-hydroxyphenylacetate (11), and conidiogenone B (12), were isolated from the endophytic Penicillium sp. HJT-A-6. The chemical structures of all the compounds were elucidated by comprehensive spectroscopic analysis, including 1D and 2D NMR and HRESIMS. The absolute configuration at C-13 of peniquinazolinone A (1) was established by applying the modified Mosher's method. Compounds 2, 3, and 7 exhibited an optimal promoting effect on the seed germination of Rhodiola tibetica at a concentration of 0.01 mg/mL, while the optimal concentration for compounds 4 and 9 to promote Rhodiola tibetica seed germination was 0.001 mg/mL. Compound 12 showed optimal seed-germination-promoting activity at a concentration of 0.1 mg/mL. Compared with the positive drug 6-benzyladenine (6-BA), compounds 2, 3, 4, 7, 9, and 12 could extend the seed germination period of Rhodiola tibetica up to the 11th day.

Current status of research on endophytes of traditional Tibetan medicinal plant and their metabolites

The Qinghai-Tibet Plateau, known as the "Third Pole of the World," has a rich variety of medicinal plants that play an important role in the field of medicine due to its unique geographical environment. However, due to the limited resources of Tibetan medicinal plants and the fragility of the ecological environment of the Qinghai-Tibet Plateau, more and more Tibetan medicinal plants are on the verge of extinction. As a reservoir of biologically active metabolites, endophytes of medicinal plants produce a large number of compounds with potential applications in modern medicine (including antibacterial, immunosuppressive, antiviral, and anticancer) and are expected to be substitutes for Tibetan medicinal plants. This paper reviews 12 Tibetan medicinal plants from the Qinghai-Tibet Plateau, highlighting the diversity of their endophytes, the diversity of their metabolites and their applications. The results show that the endophytes of Tibetan medicinal plants are remarkably diverse, and the efficacy of their metabolites involves various aspects, such as antioxidant, anti-disease and anti-parasitic. In addition, conservation measures for the resources of Tibetan medicinal plants are summarised to provide a reference for an in-depth understanding of the endophytes of Tibetan medicinal plants and to stimulate the scientific community to bioprospect for the endophytes of Tibetan medicinal plants, as well as to provide ideas for their rational exploitation.

Secondary metabolites of Alternaria: A comprehensive review of chemical diversity and pharmacological properties

Fungi are considered to be one of the wealthiest sources of bio-metabolites that can be employed for yielding novel biomedical agents. Alternaria, including parasitic, saprophytic, and endophytic species, is a kind of dark fungi that can produce a broad array of secondary metabolites (SMs) widely distributed in many ecosystems. These are categorized into polyketides, nitrogen-containing compounds, quinones, terpenes, and others based on the unique structural features of the metabolites. New natural products derived from Alternaria exhibit excellent bioactivities characterized by antibacterial, antitumor, antioxidative, phytotoxic, and enzyme inhibitory properties. Thus, the bio-metabolites of Alternaria species are significantly meaningful for pharmaceutical, industrial, biotechnological, and medicinal applications. To update the catalog of secondary metabolites synthesized by Alternaria fungi, 216 newly described metabolites isolated from Alternaria fungi were summarized with their diverse chemical structures, pharmacological activity, and possible biosynthetic pathway. In addition, possible insights, avenues, and challenges for future research and development of Alternaria are discussed.

Polyketides with anti-inflammatory activity from Rhodiola tibetica endophytic fungus Alternaria sp. HJT-Y7

Seven undescribed polyketides with particular ortho-trisubstituted benzo[c]furan and benzo[c]oxepin spiro structures were isolated from Rhodiola tibetica endophytic fungus Alternaria sp. HJT-Y7. Structural elucidations of these compounds were determined mainly by NMR and HR-ESI-MS analysis. An assumed polyketide biosynthetic pathway of these isolates was proposed. Two undescribed compounds and four known compounds showed significant inhibitory effects on LPS-induced NO production in RAW 264.7 cells without cytotoxicity at their effective concentrations.

Polyketides with IDH1 R132h and PTP1B inhibitory activities from the desert-plant-derived fungus Alternaria sp. HM 134

Five new polyketides named alternafurones A (1) and B (2), alternapyrones M-O (3–5), together with fourteen known ones (6–19), were isolated from the desert-plant-derived fungus Alternaria sp. HM 134. The structures of the new compounds were elucidated from spectroscopic data and ECD spectroscopic analyses. Alternafurones A and B represent polyketides with an unprecedented 6/5/6 skeleton core. Compounds 1, 2 and 4 showed definite inhibitory activities against isocitrate dehydrogenase 1 gene (IDH1 R132h) with IC₅₀ values of 29.38, 19.41 and 14.14 μg/ml, respectively. Seven compounds (6, 7, 9–12, 14) showed potent protein tyrosine phosphatase 1B (PTP1B) inhibitory activity with IC₅₀ values ranging from 0.97 μg/ml to 89.80 μg/ml.

Altereporenes A-E, five epoxy octa-hydronaphthalene polyketides produced by an endophytic fungus Alternaria sp. YUD20002

Five previously undescribed epoxy octa-hydronaphthalene polyketides, altereporenes A-E (1-5) were isolated from rice culture of the endophytic fungus Alternaria sp. YUD20002 derived from the tubers of Solanum tuberosum. Their structures were determined on the basis of comprehensive spectroscopic analyses, while the absolute configurations were elucidated by the comparison of experimental and calculated specific rotations. Meanwhile, the antimicrobial, cytotoxic, anti-inflammatory and acetylcholinesterase inhibitory activities of compounds 1-5 were also investigated.