Isolation and characterisation of a prenylated p-terphenyl metabolite of Aspergillus candidus possessing potent and selective cytotoxic activity; studies on mechanism of action

Isolation and biosynthesis of daturamycins from Streptomyces sp. KIB-H1544

Two novel diarylcyclopentenones daturamycin A and B (1 and 2), and one new p-terphenyl daturamycin C (3), along with three known congeners (4–6), were isolated from a rhizosphere soil-derived Streptomyces sp. KIB-H1544. The structures of new compounds were elucidated via a joint use of spectroscopic analyses and single-crystal X-ray diffractions. Compounds 1 and 2 belong to a rare class of tricyclic 6/5/6 diarylcyclopentenones, and compounds 3–6 possess a C-18 tricyclic aromatic skeleton. The biosynthetic gene cluster of daturamycins was identified through gene knockout and biochemical characterization experiments and the biosynthetic pathway of daturamycins was proposed.

Structural diversity and biological activity of natural p-terphenyls

p-Terphenyls are aromatic compounds consisting of a central benzene ring substituted with two phenyl groups, and they are mainly isolated from terrestrial and marine organisms. The central ring of p-Terphenyls is usually modified into more oxidized forms, e.g., para quinone and phenols. In some cases, additional ring systems were observed on the terphenyl-type core structure or between two benzene moieties. p-Terphenyls have been reported to have cytotoxic, antimicrobial, antioxidant and α-glucosidase inhibitory effects. In this review, we will mainly summarize the structural diversity and biological activity of naturally occurring p-Terphenyls referring to the research works published before.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-021-00117-8.

Polyhydroxy p-Terphenyls from a Mangrove Endophytic Fungus Aspergillus candidus LDJ-5

Six undescribed polyhydroxy p-terphenyls, namely asperterphenyllins A–F, were isolated from an endophytic fungus Aspergillus candidus LDJ-5. Their structures were determined by NMR and MS data. Differing from the previously reported p-terphenyls, asperterphenyllin A represents the first p-terphenyl dimer connected by a C-C bond. Asperterphenyllin A displayed anti-influenza virus A (H1N1) activity and protein tyrosine phosphatase 1B (PTP1B) inhibitory activity with IC₅₀ values of 53 μM and 21 μM, respectively. The anti-influenza virus A (H1N1) activity and protein tyrosine phosphatase 1B (PTP1B) inhibitory activity of p-terphenyls are reported for the first time. Asperterphenyllin G exhibited cytotoxicity against nine cell lines with IC₅₀ values ranging from 0.4 to 1.7 μM. Asperterphenyllin C showed antimicrobial activity against Proteus species with a MIC value of 19 μg/mL.

Prenylated p-Terphenyls from a Mangrove Endophytic Fungus, Aspergillus candidus LDJ-5

Nine previously undescribed prenylated p-terphenyls, prenylterphenyllins F-J (1, 2, 4-6) and prenylcandidusins D-G (3, 7-9), were isolated from an endophytic fungus, Aspergillus candidus LDJ-5. Their structures were determined from NMR and MS data. Differing from previously reported p-terphenyls, compound 3 represents a rare 6,5,6,6-fused ring system. Compounds 4-6 are antimicrobial, and compounds 1, 4, 6, and 9 are cytotoxic.

Design, semisynthesis, α-glucosidase inhibitory, cytotoxic, and antibacterial activities of p-terphenyl derivatives

Terphenyllin (1), a naturally abundant p-terphenyl metabolite, was isolated from the coral derived fungus Aspergillus candidus together with four natural analogues 2-5. To evaluate their potency and selectivity, a series of new derivatives of 1 were designed and semisynthesized. They were evaluated for their α-glucosidase inhibitory, cytotoxic, and antibacterial activities. Compounds 1, 3, 4, 7, 8, 10, 11, 14, 15, 21, 23, 24, 29, 39, and 40 showed significant α-glucosidase inhibitory activity with IC₅₀ values of 4.79-15 μM, which were stronger than that of the positive controls, 1-deoxynojirimycin (IC₅₀ = 192.0 μM) and acarbose (IC₅₀ = 707.9 μM). Compounds 7 and 10 have relatively higher therapeutic indices (CC₅₀/IC₅₀ = 17 and 10, respectively), representing potential promising leads. The enzyme kinetic studies of compounds 1 and 24 showed a non-competitive inhibition on α-glucosidase with Ki values of 1.50 and 3.45 μM, respectively. Additionally, compounds 14, 21, 26, 29, 32, 35, and 37 were found to exhibit strong cytotoxicity against three tumor cell lines A549 (lung adenocarcinoma epithelial), HeLa (cervical carcinoma), and HepG2 (hepatocellular liver carcinoma) with IC₅₀ values ranging from 0.15 to 5.26 μM. Further study indicated that 32 could induce S-phase arrest in the cell cycle progression.

Chemoselective synthesis of m-teraryls through ring transformation of 2H-pyran-2-ones by 2-(1-arylethylidene)-malononitriles

Base mediated chemoselective synthesis of m-teraryls was carried out by the reaction of 2H-pyran-2-ones and 2-(1-arylethylidene)malononitriles.

New α-glucosidase inhibitors with p-terphenyl skeleton from the mushroom Hydnellum concrescens

The purpose of this study is to elucidate the bioactive components responsible for the the α-glucosidase inhibitory activity detected in the EtOAc extract of the mushroom Hydnellum concrescens. Two new p-terphenyl derivatives, concrescenins A (1) and B (2), in along with six known compounds thelephantins L (3), I (4), J (5), K (6), dihydroauran-tiacin dibenzoate (7), and curtisian A (8) were isolated from the fruiting bodies of H. concrescens. Their chemical structures were elucidated by NMR experiments. Compounds 1-4 and 6-8 showed the inhibitory activity against α-glucosidase with the IC50 of 0.99, 3.11, 4.53, 18.77, 2.98, 5.16, and 8.34 μM, respectively. Kinetic analysis of α-glucosidase indicated that compounds 1 and 2 inhibited the activity of α-glucosidase in a noncompetitive fashion with a Ki value of 0.02 and 0.21 μM, respectively. In antioxidant evaluation, compounds 1 and 4 showed weak DPPH scavenging activity (EC50=82.50 and 161.75 μM) and weak reducing ability (EC50=193.57 and 152.94 μM). The current research supports the potential use of mushroom-derived p-terphenyl derivatives for the treatment of diabetes.

Two New p-Terphenyl Derivatives from the Marine Fungal Strain Aspergillus sp. AF119

Two new p-terphenyl derivatives (1, 2), together with six known ones (3 - 8), have been isolated from the marine fungal strain Aspergillus sp. AF119. The structures for terphyl acid (1) and terphyl diacid (2) were determined on the basis of HR Q-TOF-MS, and 1D- and 2D-NMR spectroscopic data. The in vitro cytotoxic activities of compounds 1 – 8 were tested against human tumor cell lines HeLa, HepG-2 and MDA-MB-435; only compounds 5 – 8 exhibited inhibitory activity against the tested cell lines with IC50 values < 20 μM. Moreover, compound 5 showed a mechanism of inducing cell cycle arrest and apoptosis mediated by the generation of ROS and subsequent DNA double-strand break.

Synthesis of terphenyl benzimidazoles as tubulin polymerization inhibitors

A series of new terphenyl benzimidazoles (3a-z and 3aa-ad) were synthesized and evaluated for their anticancer activity. All the 30 compounds have shown moderate to good anticancer potency, however some of the compounds (3j, 3m-t and 3aa-ad) exhibited prominent anticancer potency with GI(50) values ranging from <0.1 to 9.72 μM. These compounds exhibit G2/M phase arrest and the analysis of tubulin by Western blot experiments in case of 3t and 3ad shows the disturbances that are caused in the ratio of soluble versus polymerized tubulin in cells. Compounds 3t and 3ad are the most promising candidates amongst the series and has the potential to be taken up for further detailed studies either alone or in combination with the existing therapies.

Traceless Liquid-Phase Synthesis of Biphenyls and Terphenyls Using Pentaerythritol as a Tetrapodal Soluble Support

Application of a novel sulfonate-based traceless multifunctional linker system using pentaerythritol as a tetrapodal soluble support was demonstrated using liquid-phase parallel and combinatorial preparation of biphenyl and terphenyl compounds. Nickel-catalyzed reactions of pentaerythritol tetrakis(arenesulfonate)s with arylmagnesium bromides generated the desired products in sufficient yields through reductive cleavage/cross-coupling of the C-S bond. Homogeneous pentaerythritol-supported reactions could be accomplished using less nucleophile with shorter reaction periods than could the corresponding heterogeneous polymer-supported reactions. This liquid-phase approach using a small polyfunctionalized support combines advantages of solution-phase and solid-phase syntheses by allowing high reactivity, high atom economy, simple isolation, and real-time monitoring of the reaction progress.

Highly Efficient Non-Palladium-Catalyzed Controlled Synthesis and X-ray Analysis of Functionalized 1,2-Diaryl-, 1,2,3-Triaryl-, and 1,2,3,4-Tetraarylbenzenes

A general, two-step, highly efficient synthesis of 1,2-diaryl-, 1,2,3-triaryl-, and 1,2,3,4-tetraarylbenzenes from simple stitching of alpha-oxo-ketene-S,S-acetals and active methylene compounds via a lactone intermediate is described. This procedure offers easy access to highly functionalized arylated benzenes that contain sterically demanding groups in good to excellent yields. The novelty of the procedure lies in the construction of aromatic compounds with the desired conformational flexibility along the molecular axis in a transition-metal-free environment through easily accessible precursors. Crystal analysis of these arylated benzene scaffolds showed that the peripheral aryl rings are arranged in a propeller-like fashion with respect to the central benzene ring. Examination of the crystal packing in the structure of a 1,2,3,4-tetraarylbenzene revealed an N...pi interaction between molecules related by a two-fold screw axis running in the direction of the a axis. Interestingly, the repeating array of N...pi interactions around the axis of this 1,2,3,4-tetraarylbenzene forces the molecules into a helical pattern.

Hydnellins A and B, Nitrogen-Containing Terphenyls from the Mushrooms Hydnellum suaveolens and Hydnellum geogerirum

Fractionation of methanol extracts of the fruit bodies of two inedible mushrooms Hydnellum suaveolens and Hydnellum geogerirum (Thelephoraceae) resulted in isolation of two new p-terphenyl derivatives named hydnellins A and B and sarcodonin delta possessing N-oxide. Their structures were determined by 2D NMR, IR, UV spectroscopy, and chemical reaction. These terphenyls showed moderate antioxidant activity.