Cyclopiane-type diterpenes from the deep-sea-derived fungus Penicillium commune MCCC 3A00940

Synthesis of Polycyclic n/5/8 and n/5/5/5 Skeletons Using Rhodium-Catalyzed [5 + 2 + 1] Cycloaddition of Exocyclic-ene-vinylcyclopropanes and Carbon Monoxide

A rhodium-catalyzed [5 + 2 + 1] reaction of exocyclic-ene-vinylcyclopropanes (exo-ene-VCPs) and CO has been realized to access challenging tricyclic n/5/8 skeletons (n = 5, 6, 7), some of which are found in natural products. This reaction can be used to build tetracyclic n/5/5/5 skeletons (n = 5, 6), which are also found in natural products. In addition, 0.2 atm CO can be replaced by (CH₂O)_n as the CO surrogate to achieve the [5 + 2 + 1] reaction with similar efficiency.

A Review of Diterpenes from Marine-Derived Fungi: 2009-2021

Marine-derived fungi are important sources of novel compounds and pharmacologically active metabolites. As an important class of natural products, diterpenes show various biological activities, such as antiviral, antibacterial, anti-inflammatory, antimalarial, and cytotoxic activities. Developments of equipment for the deep-sea sample collection allow discoveries of more marine-derived fungi with increasing diversity, and much progress has been made in the identification of diterpenes with novel structures and bioactivities from marine fungi in the past decade. The present review article summarized the chemical structures, producing organisms and biological activities of 237 diterpenes which were isolated from various marine-derived fungi over the period from 2009 to 2021. This review is beneficial for the exploration of marine-derived fungi as promising sources of bioactive diterpenes.

Enantioselective Total Synthesis of (+)-Aberrarone

We disclose the first total synthesis of (+)-aberrarone, a diterpenoid natural product featuring a 5-5-5-6-fused tetracyclic skeleton. Key to the approach is a Au-catalyzed-Sn-mediated Meyer-Schuster-Nazarov-cyclopropanation-aldol cascade, which closes four rings in high yield. The convergent approach furnishes the natural product (+)-aberrarone stereoselectively in 15 steps. We highlight the benefits of using a Sn-alkoxide to considerably expand the opportunities of Au-catalysis for the synthesis of complex molecules.

Diterpenes Specially Produced by Fungi: Structures, Biological Activities, and Biosynthesis (2010–2020)

Fungi have traditionally been a very rewarding source of biologically active natural products, while diterpenoids from fungi, such as the cyathane-type diterpenoids from Cyathus and Hericium sp., the fusicoccane-type diterpenoids from Fusicoccum and Alternaria sp., the guanacastane-type diterpenoids from Coprinus and Cercospora sp., and the harziene-type diterpenoids from Trichoderma sp., often represent unique carbon skeletons as well as diverse biological functions. The abundances of novel skeletons, biological activities, and biosynthetic pathways present new opportunities for drug discovery, genome mining, and enzymology. In addition, diterpenoids peculiar to fungi also reveal the possibility of differing biological evolution, although they have similar biosynthetic pathways. In this review, we provide an overview about the structures, biological activities, evolution, organic synthesis, and biosynthesis of diterpenoids that have been specially produced by fungi from 2010 to 2020. We hope this review provides timely illumination and beneficial guidance for future research works of scholars who are interested in this area.

Revision of the Cyclisation Mechanism for the Diterpene Spiroviolene and Investigations of Its Mass Spectrometric Fragmentation

The diterpene spiroviolene, its diterpene synthase from Streptomyces violens and the experimentally determined terpene cyclisation mechanism were reported in 2017. Recently, the structure of spiroviolene was revised based on a total synthesis, with consequences for the cyclisation mechanism. Herein, a reinvestigation of the terpene cyclisation to spiroviolene and the mass spectrometric fragmentation mechanism investigated by 13 C-labelling experiments are presented.

Marine natural products

This review covers the literature published between January and December in 2018 for marine natural products (MNPs), with 717 citations (706 for the period January to December 2018) 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 (1554 in 469 papers for 2018), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. The proportion of MNPs assigned absolute configuration over the last decade is also surveyed.

Bioassay-Directed Isolation of Antibacterial Metabolites from an Arthropod-Derived Penicillium chrysogenum

Bioassay-directed isolation of secondary metabolites from an extract of Penicillium chrysogenum TJ403-CA4 isolated from the medicinally valuable arthropod Cryptotympana atrata afforded five new and 10 known compounds (1-15). All the compounds (except 14) belong to a minor class of highly rigid 6-5-5-5-fused tetracyclic cyclopiane-type diterpenes known to be exclusively produced by members of the Penicillium genus. The structures and absolute configurations of the new compounds (1-5) were elucidated by extensive spectroscopic analyses, including HRESIMS and 1D and 2D NMR, single-crystal X-ray diffraction, and comparison of the experimental electronic circular dichroism data. Compounds 1 and 2 represent the first examples of cyclopianes bearing a C-20 carboxyl group; compound 3 represents the first example of a cyclopiane with a gem-hydroxymethyl group; compound 4 represents the second example of a cyclopiane bearing a hydroxy group at C-7; compound 5 represents the first example of a cyclopiane bearing a hydroxy group at C-8. Compounds 2 and 3 exhibited activity against MRSA, with MIC values of 4.0 and 2.0 μg/mL, respectively. In addition, the structure-antibacterial activity relationship (SAR) of compounds 1-15 is discussed.

Molecules derived from the extremes of life: a decade later

Covering: Early 2008 until the end of 2019Microorganisms which survive (extreme-tolerant) or even prefer (extremophilic) living at the limits of pH, temperature, salinity and pressure found on earth have proven to be a rich source of novel structures. In this update we summarise the wide variety of new molecules which have been isolated from extremophilic and extreme-tolerant microorganisms since our original 2009 review, highlighting the range of bioactivities these molecules have been reported to possess.

Total Syntheses of (-)-Conidiogenone B, (-)-Conidiogenone, and (-)-Conidiogenol

Cyclopianes are novel diterpenes featuring a highly strained 6/5/5/5 tetracyclic core embedded with 6-8 consecutive stereocenters. The concise total syntheses of (-)-conidiogenone B, (-)-conidiogenone, and (-)-conidiogenol have been accomplished in 14-17 steps. The present work features a HAT-mediated alkene-nitrile cyclization to access the cis-biquinane, a Nicholas/Pauson-Khand reaction to construct the linear triquinane, and a Danheiser annulation to afford the congested angular triquinane skeleton.

A Review of Terpenes from Marine-Derived Fungi: 2015-2019

Marine-derived fungi are a significant source of pharmacologically active metabolites with interesting structural properties, especially terpenoids with biological and chemical diversity. In the past five years, there has been a tremendous increase in the rate of new terpenoids from marine-derived fungi being discovered. In this updated review, we examine the chemical structures and bioactive properties of new terpenes from marine-derived fungi, and the biodiversity of these fungi from 2015 to 2019. A total of 140 research papers describing 471 new terpenoids of six groups (monoterpenes, sesquiterpenes, diterpenes, sesterterpenes, triterpenes, and meroterpenes) from 133 marine fungal strains belonging to 34 genera were included. Among them, sesquiterpenes, meroterpenes, and diterpenes comprise the largest proportions of terpenes, and the fungi genera of Penicillium, Aspergillus, and Trichoderma are the dominant producers of terpenoids. The majority of the marine-derived fungi are isolated from live marine matter: marine animals and aquatic plants (including mangrove plants and algae). Moreover, many terpenoids display various bioactivities, including cytotoxicity, antibacterial activity, lethal toxicity, anti-inflammatory activity, enzyme inhibitor activity, etc. In our opinion, the chemical diversity and biological activities of these novel terpenoids will provide medical and chemical researchers with a plenty variety of promising lead compounds for the development of marine drugs.

Unraveling Plant Natural Chemical Diversity for Drug Discovery Purposes

The screening and testing of extracts against a variety of pharmacological targets in order to benefit from the immense natural chemical diversity is a concern in many laboratories worldwide. And several successes have been recorded in finding new actives in natural products, some of which have become new drugs or new sources of inspiration for drugs. But in view of the vast amount of research on the subject, it is surprising that not more drug candidates were found. In our view, it is fundamental to reflect upon the approaches of such drug discovery programs and the technical processes that are used, along with their inherent difficulties and biases. Based on an extensive survey of recent publications, we discuss the origin and the variety of natural chemical diversity as well as the strategies to having the potential to embrace this diversity. It seemed to us that some of the difficulties of the area could be related with the technical approaches that are used, so the present review begins with synthetizing some of the more used discovery strategies, exemplifying some key points, in order to address some of their limitations. It appears that one of the challenges of natural product-based drug discovery programs should be an easier access to renewable sources of plant-derived products. Maximizing the use of the data together with the exploration of chemical diversity while working on reasonable supply of natural product-based entities could be a way to answer this challenge. We suggested alternative ways to access and explore part of this chemical diversity with in vitro cultures. We also reinforced how important it was organizing and making available this worldwide knowledge in an "inventory" of natural products and their sources. And finally, we focused on strategies based on synthetic biology and syntheses that allow reaching industrial scale supply. Approaches based on the opportunities lying in untapped natural plant chemical diversity are also considered.

Cytotoxic Polyketides Isolated from the Deep-Sea-Derived Fungus Penicillium chrysogenum MCCC 3A00292

The chemical examination of the solid cultures of the deep-sea-derived fungus Penicillium chrysogenum MCCC 3A00292 resulted in the isolation of three new versiol-type analogues, namely peniciversiols A–C (1–3), and two novel lactone derivatives, namely penicilactones A and B (6 and 7), along with 11 known polyketides. The planar structures of the new compounds were determined by the comprehensive analyses of the high-resolution electrospray ionization mass spectroscopy (HRESIMS) and nuclear magnetic resonance (NMR) data, while their absolute configurations were resolved on the basis of comparisons of the experimental electronic circular dichroism (ECD) spectra with the calculated ECD data. Compound 1 is the second example of versiols featuring a 2,3-dihydropyran-4-one ring. Additionally, compounds 6 and 7 are the first representatives of γ-lactone derivatives constructed by a 1,3-dihydroxy-5-methylbenzene unit esterifying with the α-methyl-γ-hydroxy-γ-acetic acid α,β-unsaturated-γ-lactone moiety and α-hydroxy-γ-methyl-γ-acetic acid α,β-unsaturated-γ-lactone unit, respectively. All of the isolated compounds were evaluated for their cytotoxic activities against five human cancer cell lines of BIU-87, ECA109, BEL-7402, PANC-1, and Hela-S3. Compound 1 exhibited a selective inhibitory effect against the BIU-87 cell line (IC₅₀ = 10.21 μM), while compounds 4, 5, 8, and 12–16 showed inhibitory activities against the ECA109, BIU-87, and BEL-7402 cell lines with the IC₅₀ values ranging from 7.70 to > 20 μM.

Three new cyclopiane-type diterpenes from a deep-sea derived fungus Penicillium sp. YPGA11 and their effects against human esophageal carcinoma cells

Cyclopianes, featuring a highly rigid 6/5/5/5-fused tetracyclic framework, are structurally unique and biologically significant and belong to a rarely reported diterpenoid family. Chemical investigation of an EtOAc extract of a deep-sea-derived Penicillium sp. led to the isolation of three new cyclopiane diterpenes, namely, conidiogenols C-D (1-2) and conidiogenone L (3). The structures were determined by extensive analyses of the spectroscopic data in association with ECD calculations and chemical conversion for configurational assignments. Compound 1 represents the second example of cyclopianes bearing a hydroxyl group at C-13. Compound 2, the third example of conidiogenols, possesses a distinct α-oriented 1-hydroxy group relative to other analogues. The bioassay study demonstrated that compounds 2 and 4-6 exhibited moderate inhibitory effects against five esophageal cancer cell lines with IC₅₀ values ranging from 25 to 55 μM. The cytotoxicities of all compounds toward esophageal cancer cell lines were evaluated for the first time.

Biosynthetic study of conidiation-inducing factor conidiogenone: heterologous production and cyclization mechanism of a key bifunctional diterpene synthase

Conidiogenone, a diterpene with a unique structure, is known to induce the conidiation of Penicillium cyclopium. The biosynthetic pathway of (-)-conidiogenone has been fully elucidated by the heterologous expression of biosynthetic genes in Aspergillus oryzae and by in vitro enzyme assay with ¹³C-labeled substrates. After construction of deoxyconidiogenol by the action of bifunctional terpene synthase, one cytochrome P450 catalyzes two rounds of oxidation to furnish conidiogenone. Notably, similar biosynthetic genes are conserved among more than 10 Penicillium sp., suggesting that conidiogenone is a common conidiation inducer in this genus. The cyclization mechanism catalyzed by terpene synthase, which involves successive 1,2-alkyl shifts, was fully elucidated using ¹³C-labeled geranylgeranyl pyrophosphate (GGPP) as substrate. During the structural analysis of deoxyconidiogenol, we observed broadening of some of the ¹³C signals measured at room temperature, which has not been observed with other structurally related compounds. Careful examination using techniques including ¹³C NMR studies at -80 °C, conformational analysis and prediction of the ¹³C chemical shifts using density functional theory gave insights into this intriguing phenomenon.

Crystalline Sponge Method Enabled the Investigation of a Prenyltransferase-terpene Synthase Chimeric Enzyme, Whose Product Exhibits Broadened NMR Signals

By the genome-mining approach, a chimeric enzyme of prenyltransferase-diterpene synthase was discovered from Penicillium chrysogenum MT-12. Since its product exhibited broadened NMR signals, the structural determination by only the NMR analysis was difficult, but the crystalline sponge method successfully revealed the structure with a 6-5-5-5 fused ring system. This demonstrated that the collaboration between the genome-mining and crystalline sponge method has the potential to facilitate rapid inquiries into the unexplored chemical space of small molecules.

Deep-Sea-Derived Butyrolactone I Suppresses Ovalbumin-Induced Anaphylaxis by Regulating Mast Cell Function in a Murine Model

Deep-sea-derived butyrolactone I (BTL-I), which was identified as a type of butanolide, was isolated from Aspergillus sp. Ovalbumin (OVA)-induced BALB/c anaphylaxis was established to explore the antifood allergic activity of BTL-I. As a result, BTL-I was able to alleviate OVA-induced allergy symptoms, reduce the levels of histamine and mouse mast cell proteinases, inhibit OVA-specific IgE, and decrease the population of mast cells in the spleen and mesenteric lymph nodes. BTL-I also significantly suppressed mast-dependent passive cutaneous anaphylaxis. Additionally, the maturation of bone marrow-derived mast cells (BMMCs) declined as BTL-I caused down-regulation of c-KIT receptors. Furthermore, molecular docking analyses revealed that BTL-I interacted with the inhibitory receptor, FcγRIIB. In conclusion, the reduction of mast cell function by deep-sea-derived BTL-I as well as its interactions with the inhibitory receptor, FcγRIIB, may contribute to BTL-I-related protection against food anaphylaxis.