Asperfloketals A and B, the First Two Ergostanes with Rearranged A and D Rings: From the Sponge-Associated Aspergillus flocculosus 16D-1

Three new Furano-lactones from the endophytic fungus Aspergillus nidulans

Three new furano-lactones, asperilactones A-C (1-3), and two known compounds silvaticol (4) and violaceic acid (5) were isolated from an ethanol extract of Aspergillus nidulans, a fungus isolated from the Annelida Whitmania pigra Whitman (Haemopidae). Their structures were elucidated by a combination of spectroscopy, ECD calculations, comparing optical rotation values, and single-crystal X-ray diffraction analyses. Asperilactone A (1) represented the first example of furano-lactone with an unusual 2-thia-6-oxabicyclo[3.3.0]octane ring system. Asperilactones A and B showed weak toxicity against the HL-60 and RKO.

Controllable skeletal reorganizations in natural product synthesis

Covering: 2016 to 2023The synthetic chemistry community is always in pursuit of efficient routes to natural products. Among the many available general strategies, skeletal reorganization, which involves the formation, cleavage, and migration of C-C and C-heteroatom bonds, stands out as a particularly useful approach for the efficient assembly of molecular skeletons. In addition, it allows for late-stage modification of natural products for quick access to other family members or unnatural derivatives. This review summarizes efficient syntheses of steroid, terpenoid, and alkaloid natural products that have been achieved by means of this strategy in the past eight years. Our goal is to illustrate the strategy's potency and reveal the spectacular human ingenuity demonstrated in its use and development.

Isolation and total synthesis of dysidone A: a new piperidone alkaloid from the marine sponge Dysidea sp

A new piperidone alkaloid, dysidone A (1), was isolated from the marine sponge Dysidea sp. The structure of 1 was elucidated by the method of spectroscopic analysis. Compound 1 represented the first example of piperidone alkaloid isolated from the sponge of the genus Dysidea with the exocyclic double bond. Furthermore, the total synthesis of 1 was also carried out, which was started with piperidine proceeding a PIDA/I2-mediated α and β-C (sp3) -H bond dual oxygenation to achieve a 5-steps synthesis in a total yield of 10.6%. In addition, the anti-inflammatory activities of 1 and its derivative dysidone B (1d) were evaluated, which suggested that 1 showed weak anti-inflammatory activity.

Rubensteroid A, a new steroid with antibacterial activity from Penicillium rubens AS-130

A new steroid with strong antibacterial activity, rubensteroid A (1), along with its decarboxylic analogue, solitumergosterol A (2), were isolated and identified from the Magellan Seamount-derived fungus Penicillium rubens AS-130. The structure and absolute configuration of compound 1 were established by detailed interpretation of NMR spectroscopic analysis, mass spectrometry data, and TDDFT-ECD calculations. Compound 1 had a rare 6/6/6/6/5 pentacyclic system, which might be the [4 + 2] Diels-Alder adduct of 14,15-didehydroergosterol (14-DHE) cycloaddition with maleic acid or maleimide, followed by decarboxylation. Rubensteroid A (1) exhibited potent antibacterial activity against Escherichia coli and Vibrio parahaemolyticus, both with MIC value of 0.5 μg/mL.

Biological Activity and Structural Diversity of Steroids Containing Aromatic Rings, Phosphate Groups, or Halogen Atoms

This review delves into the investigation of the biological activity and structural diversity of steroids and related isoprenoid lipids. The study encompasses various natural compounds, such as steroids with aromatic ring(s), steroid phosphate esters derived from marine invertebrates, and steroids incorporating halogen atoms (I, Br, or Cl). These compounds are either produced by fungi or fungal endophytes or found in extracts of plants, algae, or marine invertebrates. To assess the biological activity of these natural compounds, an extensive examination of referenced literature sources was conducted. The evaluation encompassed in vivo and in vitro studies, as well as the utilization of the QSAR method. Numerous compounds exhibited notable properties such as strong anti-inflammatory, anti-neoplastic, anti-proliferative, anti-hypercholesterolemic, anti-Parkinsonian, diuretic, anti-eczematic, anti-psoriatic, and various other activities. Throughout the review, 3D graphs illustrating the activity of individual steroids are presented alongside images of selected terrestrial or marine organisms. Additionally, the review provides explanations for specific types of biological activity associated with these compounds. The data presented in this review hold scientific interest for academic science as well as practical implications in the fields of pharmacology and practical medicine. The analysis of the biological activity and structural diversity of steroids and related isoprenoid lipids provides valuable insights that can contribute to advancements in both theoretical understanding and applied research.

Quadristerols A-G: Seven undescribed ergosterols from Aspergillus quadrilineata

Quadristerols A-G, seven undescribed ergosterols, were obtained from Aspergillus quadrilineata. Their structures and absolute configurations were determined based on HRESIMS, NMR, quantum-chemical calculations, and single-crystal X-ray diffraction analyses. Quadristerols A-G featured ergosterol skeletons with different attachments; quadristerols A-C were three diastereoisomers possessing a 2-hydroxy-propionyloxy group at C-6, and quadristerols D-G were two pairs of epimers with a 2,3-butanediol group at C-6. All of these compounds were evaluated for their immunosuppressive activities in vitro. Quadristerols B and C showed excellent inhibitory effects against concanavalin A-induced T lymphocyte proliferation with IC₅₀ values of 7.43 and 3.95 μM, respectively, and quadristerols D and E strongly inhibited lipopolysaccharide-induced B lymphocyte proliferation with IC₅₀ values of 10.96 and 7.47 μM, respectively.

Spectasterols, Aromatic Ergosterols with 6/6/6/5/5, 6/6/6/6, and 6/6/6/5 Ring Systems from Aspergillus spectabilis

Spectasterols A-E (1-5), aromatic ergosterols with unique ring systems, were isolated from Aspergillus spectabilis. Compounds 1 and 2 possess a 6/6/6/5/5 ring system with an additional cyclopentene, while 3 and 4 have an uncommon 6/6/6/6 ring system generated by the D-ring expansion via 1,2-alkyl shifts. Compound 3 exhibited cytotoxic activity (IC50 6.9 μM) and induced cell cycle arrest and apoptosis in HL60 cells. Compound 3 was anti-inflammatory; it decreased COX-2 levels at the transcription and protein levels and inhibited the nuclear translocation of NF-κB p65.

Biogenetic space-guided synthesis of rearranged terpenoids

Natural product chemistry is constantly challenged by newly discovered, complex molecules. Elements of complexity arise from unprecedented frameworks, with a large amount of densely packed stereogenic centres and different functional groups along with a generally high oxidation state. As a prime example, rearranged triterpenoids possess all these elements. For their total synthesis, a limit of what is considered sensible in terms of steps and yield is frequently reached. As an alternative, semisynthetic approaches have gained a great amount of attention in recent years. In this featured article, we present our and others' contributions towards the development of efficient and economic syntheses of complex terpenoid natural products and elaborate on the underlying rationale of biogenetic space-guided synthetic analysis.

Marine natural products

Covering: January to December 2021This review covers the literature published in 2021 for marine natural products (MNPs), with 736 citations (724 for the period January to December 2021) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1425 in 416 papers for 2021), together with the relevant biological activities, source organisms and country of origin. Pertinent reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. An analysis of the number of authors, their affiliations, domestic and international collection locations, focus of MNP studies, citation metrics and journal choices is discussed.

Chemical Emulation of the Biosynthetic Route to Anthrasteroids: Synthesis of Asperfloketal A

The anthrasteroid rearrangement has been discussed for the formation of the eponymous substance class since its discovery. We here report its chemical emulation from a plausible biogenetic precursor and show how it accounts for the formation of asperfloketals A and B through a mechanistic bifurcation event. As a result, these natural products arise from double Wagner-Meerwein rearrangements and, thus, are 1(10→5),1(5→6)- and 1(10→5),4(5→6)diabeo-14,15-secosteroids, respectively. To establish an efficient route to a bioinspired precursor, we devised a sequence of orchestrated oxidative activation and rearrangement from ergosterol.

Survey of natural products reported by Asian research groups in 2021

The new natural products reported in 2021 in peer-reviewed articles in journals with good reputations were reviewed and analyzed. The advances made by Asian research groups in the field of natural products chemistry in 2021 were summarized. Compounds with unique structural features and/or promising bioactivities originating from Asian natural sources were discussed based on their structural classification.

Aspersterols A-D, Ergostane-Type Sterols with an Unusual Unsaturated Side Chain from the Deep-Sea-Derived Fungus Aspergillus unguis

Four previously undescribed ergostane-type sterols, aspersterols A-D (1-4), were isolated from a deep-sea-derived fungus, Aspergillus unguis IV17-109. The structures of the new compounds were determined by extensive analyses of their spectroscopic data, pyridine-induced deshielding effect, Mosher's method, and electronic circular dichroism calculations. The key feature of these sterols is the presence of a rare unsaturated side chain with conjugated double bonds at Δ¹⁷ and Δ²². The absolute configuration of C-24 in the side chain was determined by hydrogenation and comparing ¹³C NMR chemical shifts of the hydrogenated products with literature values. In addition, aspersterol A (1) is the second representative of anthrasteroids with a hydroxy group at the C-2 position. Compound 1 showed cytotoxicity against six cancer cell lines, with GI₅₀ values of 3.4 ± 0.3 to 4.5 ± 0.7 μM, while 2-4 showed anti-inflammatory activity, with IC₅₀ values ranging from 11.6 ± 1.6 to 19.5 ± 1.2 μM.

Structure and Biological Activity of Ergostane-Type Steroids from Fungi

Mushrooms are known not only for their taste but also for beneficial effects on health attributed to plethora of constituents. All mushrooms belong to the kingdom of fungi, which also includes yeasts and molds. Each year, hundreds of new metabolites of the main fungal sterol, ergosterol, are isolated from fungal sources. As a rule, further testing is carried out for their biological effects, and many of the isolated compounds exhibit one or another activity. This study aims to review recent literature (mainly over the past 10 years, selected older works are discussed for consistency purposes) on the structures and bioactivities of fungal metabolites of ergosterol. The review is not exhaustive in its coverage of structures found in fungi. Rather, it focuses solely on discussing compounds that have shown some biological activity with potential pharmacological utility.

Probing Indole Diketopiperazine-Based Hybrids as Environmental-Induced Products from Aspergillus sp. EGF 15-0-3

Comprehensive analyses of the metabolite spectra of Aspergillus sp. EGF 15-0-3 under different culture conditions revealed the presence of unique environmental-induced metabolites exclusively from the rice medium. Subsequent target isolation afforded four unprecedented indole diketopiperazine-based hybrids with a pyrano[3',2':7,8]isochromeno[4,3-b]pyrazino[2,1-i]indole core (1 and 2) or a spiro[piperazine-2,2'-pyrano[3,4,5-de]chromene] scaffold (3 and 4). Putative biosynthetic pathways for 1-4, with Diels-Alder cycloadditions as key steps, were proposed. 1-4 exhibited selective cytotoxicities among several human cancer cells.

A critical review on the use of DP4+ in the structural elucidation of natural products: the good, the bad and the ugly. A practical guide

Covering: 2015 up to the end of 2020Even in the golden age of NMR, the number of natural products being incorrectly assigned is becoming larger every day. The use of quantum NMR calculations coupled with sophisticated data analysis provides ideal complementary tools to facilitate the elucidation process in challenging cases. Among the current computational methodologies to perform this task, the DP4+ probability is a popular and widely used method. This updated version of Goodman's DP4 synergistically combines NMR calculations at higher levels of theory with the Bayesian analysis of both scaled and unscaled data. Since its publication in late 2015, the use of DP4+ to solve controversial natural products has substantially grown, with several predictions being confirmed by total synthesis. To date, the structures of more than 200 natural products were determined with the aid of DP4+. However, all that glitters is not gold. Besides its intrinsic limitations, on many occasions it has been improperly used with potentially important consequences on the quality of the assignment. Herein we present a critical revision on how the scientific community has been using DP4+, exploring the strengths of the method and how to obtain optimal results from it. We also analyze the weaknesses of DP4+, and the paths to by-pass them to maximize the confidence in the structural elucidation.

Hot off the press

A personal selection of 32 recent papers is presented covering various aspects of current developments in bioorganic chemistry and novel natural products such as chlorahupetone A from Chloranthus henryi var. hupehensis.