Diketopiperazine and isoindolinone alkaloids from the endophytic fungus Aspergillus sp. HAB10R12

Four previously undescribed alkaloids, aspergillinine A-D, and four known diterpene pyrones were isolated from the potato dextrose agar (PDA) culture of Aspergillus sp. HAB10R12. The chemical structures of the isolated compounds were elucidated based on a detailed analysis of their NMR and MS data. The absolute configuration of the isolated compounds was determined by Electronic Circular Dichroism analysis coupled with computational methods. Aspergillinine A represents the first example of a diketopiperazine dipeptide containing the unnatural amino acid N-methyl kynurenine. Its absolute configuration revealed that it adopts a rather unusual conformation. Aspergillinine B represents a previously unencountered skeleton containing an isoindolinone ring. Aspergillinine C and D were similar to previously isolated diketopiperazine alkaloids, namely, lumpidin and brevianamide F, respectively. The diterpene pyrones were isolated twice previously, once from a soil-derived Aspergillus species, and once from the liquid culture of Aspergillus sp. HAB10R12. The alkaloids isolated in this study showed no antiproliferative activity when tested against HepG2 and A549 cancer cell lines.

Ethnomedicine, phytochemistry, and bioactivities of Hibiscus sabdariffa L. (Malvaceae)

Hibiscus sabdariffa L., belonging to the Malvaceae family, has been long used as herbal medicine, food, beverage, flavouring, and colouring agents. This study aims to review and document the evidence regarding the potential use of H. sabdariffa as ethnomedicine in some countries and its bioactive constituents and therapeutic properties. The electronic databases were used to search for the relevant information to the aims of this review up to March 2022. The high usage of H. sabdariffa as traditional medicine is due to its easy accessibility and low price. The plant is often used to treat intestinal problems, stomach disorders, and blood or liver toxicities. The plant contains phenolic compounds, including anthocyanins, flavonoids, and phenolic acids. The in vivo, in vitro, and clinical studies provide evidence that H. sabdariffa possesses therapeutic effects such as antihypertensive, antihyperlipidemic, antioxidants, antimicrobial, and antitumor activities. The studies provided scientific evidence for the statement of H. sabdariffa and its bioactive constituents in treating various diseases.

Ethnobotanical importance, phytochemical constituents, and pharmacological properties of Withania somnifera

Withania somnifera belongs to the family of Solanaceae. It is widely used by the locals, especially in India, as a medicinal plant. W. somnifera is rich in alkaloid and steroidal lactone that account for various pharmacological activities. The present study aimed to review all the evidence on the ethnobotanical perspective of W. somnifera in some countries. This review also analyses the bioactive compounds that account for the pharmacological activities. The online medical literature databases such as ScienceDirect, PubMed, and Google Scholar were used to search articles up to March 2022. W. somnifera is widely used in Asian and African countries like India and South Africa, Pakistan, Egypt, Jordan, and Lesotho. In India, W. somnifera is prepared by boiling and crushing the leaves and roots to make a tonic poultice, juice, and paste to treat bacterial infections and bruises. Numerous in vivo and in vitro studies have demonstrated that W. somnifera exerts pharmacological effects such as anti-Parkinson’s, anti-Alzheimer’s, cardioprotective, antidiabetic, antiarthritic, and antibacterial properties. Withaferin A and withanolide are the major bioactive compounds contributing to the pharmacological effects. W. somnifera is a valuable plant that has been used in traditional medicine systems for a long time and is supported by its wide range of pharmacological activities. The extensive medicinal uses of W. somnifera are a sign of its great potential.

Asperginols A and B, Diterpene Pyrones, from an Aspergillus sp. and the Structure Revision of Previously Reported Analogues

Two new diterpene pyrones, asperginols A (1) and B (2), and four known analogues (3-6) were isolated from the endophytic fungus Aspergillus sp. HAB10R12. The structures and absolute configurations of these compounds were elucidated based on the analysis of their NMR, MS, and X-ray diffraction data. The revision of the absolute configurations at C-10, C-11, and C-14 of the known diterpene pyrones (3-6) and the determination of the configuration at the polyene side chain for compounds (4-6) were made using chemical methods and vibrational circular dichroism analysis. This group of diterpene pyrone compounds showed unique structural features including a 7/6/6 tricyclic diterpene moiety with an unusual trans-syn-trans stereochemical arrangement. Compound 6 showed moderate activity against the HT-29 colon cancer cell line.

Structure Elucidation of the spiro-Polyketide Svalbardine B from the Arctic Fungal Endophyte Poaceicola sp. E1PB with Support from Extensive ESI-MSn Interpretation

Svalbardines A and B (1 and 2) and annularin K (3) were isolated from cultures of Poaceicola sp. E1PB, an endophyte isolated from the petals of Papaver dahlianum from Svalbard, Norway. Svalbardine A (1) is a pyrano[3,2-c]chromen-4-one, a new analogue of citromycetin. Svalbardine B (2) displays an unprecedented carbon skeleton based on a 5'-benzyl-spiro[chroman-3,7'-isochromene]-4,8'-dione core. Annularin K (3) is a hydroxylated derivative of annularin D. The structure of these new polyketides, along with those of known compounds 4-6, was established by spectrometric analysis, including extensive ESI-CID-MSⁿ processing in the case of svalbardine B (2).

Oligostilbenoids from the heartwood of N. Heimii: role of non-covalent association in their biogenesis

Four new oligostilbenes, including one dimer and three tetramers of resveratrol, that is, heimiols B-E (1-4) were isolated from the heartwood of Neobalanocarpus heimii (Dipterocarpaceae), together with thirteen known resveratrol oligomers (5-17). Examination of the structural diversity of the isolated oligostilbenes led to hypothesis of their biogenetic origin through a small number of versatile chemical pathways. These hypotheses are strongly supported by computational calculations (based on the density functional theory, DFT) that were performed to rationalize conformational re-arrangements and thus provide insights into the mechanism of oligostilbenoid biosynthesis. Non-covalent complexes are believed to drive the regio- and stereoselectivity of the oligomerization reactions.