An efficient regioselective synthesis of endocrocin and structural related natural anthraquinones starting from emodin

OSMAC Approach and Cocultivation for the Induction of Secondary Metabolism of the Fungus Pleotrichocladium opacum

The application of an OSMAC (One Strain-Many Compounds) approach on the fungus Pleotrichocladium opacum, isolated from a soil sample collected on the coast of Asturias (Spain), using different culture media, chemical elicitors, and cocultivation techniques resulted in the isolation and identification of nine new compounds (8, 9, 12, 15-18, 20, 21), along with 15 known ones (1-7, 10, 11, 14, 19, 22-25). Compounds 1-9 were detected in fungal extracts from JSA liquid fermentation, compounds 10-12 were isolated from a solid rice medium, whereas compounds 14 and 15 were isolated from a solid wheat medium. Addition of 5-azacytidine to the solid rice medium caused the accumulation of compounds 16-18, whereas adding N-acetyl-d-glucosamine triggered the production of two additional metabolites, 19 and 20. Finally, cocultivation of the fungus Pleotrichocladium opacum with Echinocatena sp. in a solid PDA medium led to the production of five additional natural products, 21-25. The structures of the new compounds were elucidated by HRESIMS and 1D and 2D NMR as well as by comparison with literature data. DP4+ and mix-J-DP4 computational methods were applied to determine the relative configurations of the novel compounds, and in some cases, the absolute configurations were assigned by a comparison of the optical rotations with those of related natural products.

Synthesis and Antioxidant Evaluation of O-Methylated Emodacidamides: Starting from Parietin, a Secondary Metabolite of Lichen Xanthoria parietina

Polyhydroxy-anthraquinones bearing amino acids are found rather seldom in nature. Emodacidamides, isolated from a marine-derived fungus, Penicillium sp. SCSIO sof101 by Luo et al. (2017) are the first natural example of amino acid conjugated anthraquinone. In this study, O-methylated emodacidamides and emodinic acid-anilides were synthesized starting from parietin, extracted from the lichen Xanthoria parietina (L.) Th. Fr. The structural elucidations of prepared compounds were confirmed by 1D and 2D NMR analyses including HSQC and HMBC techniques. In addition, all newly synthesized compounds were evaluated for the antioxidant activities with free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging. The synthesized compounds showed low to moderate antioxidant and DPPH scavenging activities. The antioxidant activities were supported within quantum chemical calculations using the DFT-B3LYP/6-311++G(d,p) level of theory. It is observed that the antioxidant activity of emodacidamides mostly depends on the phenolic groups on anthraquinone ring. The phenolic groups on other substituents help to improve antioxidant activity and also the position of hydroxy group is a decisive factor for antioxidant ability.

Four New Anthraquinones with Histone Deacetylase Inhibitory Activity from Ventilago denticulata Roots

Chromatographic separation of the crude extracts from the roots of Ventilago denticulata led to the isolation of four new anthraquinones, ventilanones L-O (1-4), together with eight known anthraquinones (5-12). Their structures were elucidated by spectroscopic methods (UV, IR, 1H NMR, 13C NMR, and 2D NMR) and mass spectrometry (MS), as well as comparison of their spectroscopic data with those reported in the literature. HDACs inhibitory activity evaluation resulted that compound 2 exhibited moderate antiproliferative activity against HeLa and A549 cell lines but nontoxic to normal cell. Molecular docking indicated the phenolic functionality of 2 plays crucial interactions with class II HDAC4 enzyme.

Intertwined Biosynthesis of Skyrin and Rugulosin A Underlies the Formation of Cage-Structured Bisanthraquinones

Skyrin and rugulosin A are bioactive bisanthraquinones found in many fungi, with the former suggested as a precursor of hypericin (a diversely bioactive phytochemical) and the latter characterized by its distinct cage-like structure. However, their biosynthetic pathways remain mysterious, although they have been characterized for over six decades. Here, we present the rug gene cluster that governs simultaneously the biosynthesis of skyrin and rugulosin A in Talaromyces sp. YE3016, a fungal endophyte residing in Aconitum carmichaeli. A combination of genome sequencing, gene inactivation, heterologous expression, and biotransformation tests allowed the identification of the gene function, biosynthetic precursor, and enzymatic sets involved in their molecular architecture constructions. In particular, skyrin was demonstrated to form from the 5,5'-dimerization of emodin radicals catalyzed by RugG, a cytochrome P450 monooxygenase evidenced to be potentially applicable for the (chemo)enzymatic synthesis of dimeric polyphenols. The fungal aldo-keto reductase RugH was shown to be capable of hijacking the closest skyrin precursor (CSP) immediately after the emodin radical coupling, catalyzing the ketone reduction of CSP to inactivate its tautomerization into skyrin and thus allowing for the spontaneous intramolecular Michael addition to cyclize the ketone-reduced form of CSP into rugulosin A, a representative of diverse cage-structured bisanthraquinones. Collectively, the work updates our understanding of bisanthraquinone biosynthesis and paves the way for synthetic biology accesses to skyrin, rugulosin A, and their siblings.

Genome-Inspired Chemical Exploration of Marine Fungus Aspergillus fumigatus MF071

The marine-derived fungus Aspergillus fumigatus MF071, isolated from sediment collected from the Bohai Sea, China, yielded two new compounds 19S,20-epoxy-18-oxotryprostatin A (1) and 20-hydroxy-18-oxotryprostatin A (2), in addition to 28 known compounds (3-30). The chemical structures were established on the basis of 1D, 2D NMR and HRESIMS spectroscopic data. This is the first report on NMR data of monomethylsulochrin-4-sulphate (4) and pseurotin H (10) as naturally occurring compounds. Compounds 15, 16, 20, 23, and 30 displayed weak antibacterial activity (minimum inhibitory concentration: 100 μg/mL). Compounds 18 and 19 exhibited strong activity against S. aureus (minimum inhibitory concentration: 6.25 and 3.13 μg/mL, respectively) and E. coli (minimum inhibitory concentration: 6.25 and 3.13 μg/mL, respectively). A genomic data analysis revealed the putative biosynthetic gene clusters ftm for fumitremorgins, pso for pseurotins, fga for fumigaclavines, and hel for helvolinic acid. These putative biosynthetic gene clusters fundamentally underpinned the enzymatic and mechanistic function study for the biosynthesis of these compounds. The current study reported two new compounds and biosynthetic gene clusters of fumitremorgins, pseurotins, fumigaclavines and helvolinic acid from Aspergillus fumigatus MF071.

A New Xanthone Glycoside from the Endolichenic Fungus Sporormiella irregularis

A new xanthone glycoside, sporormielloside (1), was isolated from an EtOAc extract of an endolichenic fungal strain Sporormiella irregularis (No. 71-11-4-1), along with two known xanthones (2, 3). Their structures were determined by detailed spectroscopic analysis (IR, MS, and 1D- and 2D-NMR), a chemical method, and a comparison of NMR data with closely related compounds previously reported. According to the structures of isolated compounds, their plausible biosynthetic pathway was deduced.

Anthraquinone-steroids, evanthrasterol A and B, and a meroterpenoid, emericellic acid, from endophytic fungus, Emericella variecolor

Two new anthraquinone-steroids, evanthrasterol A and B (1 and 2), and a new meroterpenoid, emericellic acid (3), together with six known compounds (4-9) were isolated from an endophytic fungus, Emericella variecolor. Their structures were determined by spectroscopic analysis (1D and 2D NMR, HRESIMS and FTIR). Herein emericellic acid (3) is a new skeleton of meroterpenoid with carboxylic functional group at C-9' and this is the first report on isolation of anthraquinone-steroids from E. variecolor.

Physically discrete beta-lactamase-type thioesterase catalyzes product release in atrochrysone synthesis by iterative type I polyketide synthase

ATEG_08451 in Aspergillus terreus, here named atrochrysone carboxylic acid synthase (ACAS), is a nonreducing, iterative type I polyketide synthase that contains no thioesterase domain. In vitro, reactions of ACAS with malonyl-CoA yielded a polyketide intermediate, probably attached to its acyl carrier protein (ACP). The addition of ATEG_08450, here named atrochrysone carboxyl ACP thioesterase (ACTE), to the reaction resulted in the release of products derived from atrochrysone carboxylic acid, such as atrochrysone and endocrocin. ACTE, belonging to the beta-lactamase superfamily, thus appears to be a novel type of thioesterase responsible for product release in polyketide biosynthesis. These findings show that ACAS synthesizes the scaffold of atrochrysone carboxylic acid from malonyl-CoA, and that ACTE hydrolyzes the thioester bond between the ACP of ACAS and the intermediate to release atrochrysone carboxylic acid as the reaction product.