Mechanistic analysis of carbon–carbon bond formation by deoxypodophyllotoxin synthase

Deoxypodophyllotoxin contains a core of four fused rings (A to D) with three consecutive chiral centers, the last being created by the attachment of a peripheral trimethoxyphenyl ring (E) to ring C. Previous studies have suggested that the iron(II)- and 2-oxoglutarate–dependent (Fe/2OG) oxygenase, deoxypodophyllotoxin synthase (DPS), catalyzes the oxidative coupling of ring B and ring E to form ring C and complete the tetracyclic core. Despite recent efforts to deploy DPS in the preparation of deoxypodophyllotoxin analogs, the mechanism underlying the regio- and stereoselectivity of this cyclization event has not been elucidated. Herein, we report 1) two structures of DPS in complex with 2OG and (±)-yatein, 2) in vitro analysis of enzymatic reactivity with substrate analogs, and 3) model reactions addressing DPS’s catalytic mechanism. The results disfavor a prior proposal of on-pathway benzylic hydroxylation. Rather, the DPS-catalyzed cyclization likely proceeds by hydrogen atom abstraction from C7', oxidation of the benzylic radical to a carbocation, Friedel–Crafts-like ring closure, and rearomatization of ring B by C6 deprotonation. This mechanism adds to the known pathways for transformation of the carbon-centered radical in Fe/2OG enzymes and suggests what types of substrate modification are likely tolerable in DPS-catalyzed production of deoxypodophyllotoxin analogs.

Terretonin as a New Protective Agent against Sepsis-Induced Acute Lung Injury: Impact on SIRT1/Nrf2/NF-κBp65/NLRP3 Signaling

Endophytic fungi are proving to be an excellent source of chemical entities with unique structures and varied bioactivities. Terretonin (TE) and its structurally related derivatives are a class of meroterpenoids, possessing the same unique tetracyclic core skeleton, which have been reported from the Aspergillus genus. This study was carried out to assess the potential protective effects of TE separated from the endophytic fungus A. terreus against LPS (lipopolysaccharide)-induced ALI (acute lung injury) in mice. The results revealed that TE alleviated pulmonary edema as it lowered both the W/D lung ratio and protein content. The inflammatory response represented by inflammatory cell infiltration into the lung tissues was greatly repressed by TE. That was supported by the improved histopathological results and also by the reduced level of myeloperoxidase in the lung. TE showed a potent antioxidant activity as it attenuated lipid peroxidative markers (malondialdehyde, 4-hydroxynonenal, and protein carbonyl) and enhanced endogenous antioxidants (reduced glutathione, superoxide dismutase, and catalase) in lung tissues. Similarly, TE increased the mRNA expression of SIRT1, Nrf2, and its genes (HO-1, NQO1, and GCLm). On the other hand, TE restrained the activation of NF-κB (nuclear factor-κB) in the lung. Consequently, TE depressed the pro-inflammatory cytokines: nitric oxide (NOx), TNF-α (tumor necrosis factor-α), and interleukins (IL-6 and -1β). Additionally, TE inhibited NLRP3 signaling and interrupted apoptosis by decreasing the levels of proapoptotic markers (Bax and caspase-3) and increasing the level of an anti-apoptotic marker (Bcl-2). In conclusion, TE had a remarkable protective potential on LPS-induced lung damage via antioxidant and anti-inflammatory mechanisms. This finding encourages further investigations on this promising candidate.

Unprecedented Monoterpenoid Polyprenylated Acylphloroglucinols with a Rare 6/6/5/4 Tetracyclic Core, Enhanced MCF-7 Cells’ Sensitivity to Camptothecin by Inhibiting the DNA Damage Response

(±)-Hypersines A–C (1–3), the three pairs of enantiomerically pure monoterpenoid polyprenylated acylphloroglucinols with an unprecedented 6/6/5/4 fused ring system, were isolated from Hypericum elodeoides. Their structures, including absolute configurations, were elucidated by comprehensive spectroscopic data, single-crystal X-ray diffraction, and quantum chemical calculations. The plausible, biosynthetic pathway of 1–3 was proposed. Moreover, the bioactivity evaluation indicated that 1a might be a novel DNA damage response inhibitor, and could enhance MCF-7 cell sensitivity to the anticancer agent, camptothecin.

Terretonins from Aspergillus Genus: Structures, Biosynthesis, Bioactivities, and Structural Elucidation

: Fungi are considered as a prosperous pool of microbial bio-metabolites. Terretonins are meroterpenoids that are reported mainly from Aspergillus genus. They exhibited unique tetracyclic core skeletons and various bioactivities. The current review summarizes the published researches on the source, biosynthesis, isolation, structural characterization, and bioactivities of terretonins that have been reported from Aspergillus species, as well as from synthetic sources. A literature search on the published studies was conducted over different databases: Web of Science, MedLine (PubMed), Scopus, SpringerLink, Google Scholar, SciFinder, Wiley, and ACS Publications up to 2020. In this work, 18 compounds from Aspergillus species and synthetic sources are depicted. They have unrivaled and diversified skeletons as well as various bioactivities. Moreover, 37 references are included. Terretonins form a class of fungal bio-metabolites that attain all the characters for becoming lead compounds in their particular therapeutic category.

Construction of the Tetracyclic Core of the Lycopodium Alkaloid Annotinolide C

A concise method of synthesizing the tetracyclic core of annotinolide C has been developed. The key steps feature a tandem epoxidation/semipinacol rearrangement step to construct an aza quaternary aza [6.5]...

ESTRATÉGIAS PARA A SÍNTESE DO ÁCIDO LISÉRGICO

STRATEGIES FOR THE SYNTHESIS OF LYSERGIC ACID. (+)-Lysergic acid [(+)-1] is a precursor of several substances with well-established pharmacological properties, including some drugs approved and commercialized around the world. Thus, the importance of (+)-1 as a synthetic target becomes undoubted and various strategies for the synthesis of its tetracyclic core have been reported in the literature. Therefore, in this review article we will address in chronological order the total and formal syntheses of lysergic acid (1), separating them into racemic and chiral/asymmetric syntheses. Until now, there are 24 syntheses described in the literature, namely, 11 total and 13 formal syntheses. Considering all the syntheses accomplished, 15 were planned to produce (±)-lysergic acid [(±)-1] and 9 presented routes to eventually provide (+)-lysergic acid [(+)-1]. A significant evolution regarding approaches and efficiency may be observed since the first synthesis of (±)-1 until the last asymmetric synthesis of (+)-1.

Copper-catalyzed radical cascade cyclization for synthesis of CF3-containing tetracyclic benzimidazo[2,1-a]iso-quinolin-6(5H)-ones

A practical copper-catalyzed radical cascade carbocyclization reaction was developed for the preparation of a variety of structurally diverse CF3-containing tetracyclic core benzimidazo[2,1-a]isoquinoline-6(5H)-ones.

An Efficient Synthesis Towards the Core of Crinipellin and Alliacol-B Along With Their Docking Studies

In this present work, we are reporting a novel route for the synthesis of the tetracyclic ring systems, which is a common core of crinipellin via oxidative dearomatization, cycloaddition and oxa- di-pi-methane rearrangement. We considered to exploring a route to tetracyclic core (1e) of Crinipellin and tricyclic core (1g) of Allicaol B through intermolecular diels alder reaction and photochemically 1,2 acyl shift. Moreover, docking study of compound 13 and 16has been investigated against AcrB multidrug efflux pump of Escherichia coli (PDB ID: 1T9U), main protease of SARS COV-2 (PDB ID: 6W63), DNA gyrase of Streptococcus pneumonia (PDB ID: 4Z2C), human estrogen receptor alpha (PDB ID: 3ERT), human lanosterol 14-alpha-demethylase (CYP51)(PDB ID: 3JUS) and cyclooxygenase-2 (Prostaglandin Synthase-2) (PDB ID: 1CX2). The obtained results herein are important for the exploitation of the therapeutic potential of these derivatives as antimicrobial, antiviral, anticancer, antifungal or anti-inflammatory agents.