Polyhydroxy-P-Terphenyls and Related P-Terphenylquinones From Fungi

A Review of the Chemistry and Biological Activities of Natural Colorants, Dyes, and Pigments: Challenges, and Opportunities for Food, Cosmetics, and Pharmaceutical Application

Natural pigments are important sources for the screening of bioactive lead compounds. This article reviewed the chemistry and therapeutic potentials of over 570 colored molecules from plants, fungi, bacteria, insects, algae, and marine sources. Moreover, related biological activities, advanced extraction, and identification approaches were reviewed. A variety of biological activities, including cytotoxicity against cancer cells, antioxidant, anti-inflammatory, wound healing, anti-microbial, antiviral, and anti-protozoal activities, have been reported for different pigments. Considering their structural backbone, they were classified as naphthoquinones, carotenoids, flavonoids, xanthones, anthocyanins, benzotropolones, alkaloids, terpenoids, isoprenoids, and non-isoprenoids. Alkaloid pigments were mostly isolated from bacteria and marine sources, while flavonoids were mostly found in plants and mushrooms. Colored quinones and xanthones were mostly extracted from plants and fungi, while colored polyketides and terpenoids are often found in marine sources and fungi. Carotenoids are mostly distributed among bacteria, followed by fungi and plants. The pigments isolated from insects have different structures, but among them, carotenoids and quinone/xanthone are the most important. Considering good manufacturing practices, the current permitted natural colorants are: Carotenoids (canthaxanthin, β-carotene, β-apo-8'-carotenal, annatto, astaxanthin) and their sources, lycopene, anthocyanins, betanin, chlorophyllins, spirulina extract, carmine and cochineal extract, henna, riboflavin, pyrogallol, logwood extract, guaiazulene, turmeric, and soy leghemoglobin.

Blue Light-Emitting Diode-Induced Direct C-H Functionalization of 1,4-Quinones with Aryl and Alkyl Boronic Acids

A direct functionalization of numerous 1,4-quinones with various aryl boronic acids is reported under blue light-emitting diodes (LEDs). This reaction occurs at room temperature in an open flask without any catalysts, base, and oxidants in acetonitrile (ACN) and is scalable in grams. With diverse 1,4-quinones like 1,4-benzo-, naphtho-, anthra-, and 4-bromonaphthoquinones as substrates, facile cross coupling reactions occur with aryl and alkyl boronic acids without assistance from any photocatalysts. 2-Alkylated cyclohexene-1,4-diones were obtained when the 1,4-quinones were reacted with alkyl boronic acids under standard reaction conditions. However, slight warming of the reaction mixture afforded the desired alkylated 1,4-quinones. The reaction is believed to proceed through the blue LED-induced radical formation of the aryl rings assisted by the 1,4-quinones.

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.

New Terpenoids from the Corticioid Fungus Punctularia atropurpurascens and their Antimycobacterial Evaluation

Chemical investigation of Punctularia atropurpurascens strain HM1 (Punctulariaceae), a corticioid isolated from a decorticated piece of Quercus bark collected in Bosque de Tlalpan, Mexico City, led to the isolation of a new drimane, 1-α-hydroxy-isodrimenine (1: ) and a new tetrahydroxy kauranol, 16-hydroxy-phlebia-nor-kauranol (2: ), together with the known N-phenylacetamide (3: ). Structures of all compounds were elucidated by spectroscopic and spectrometric methods, and the absolute configuration of 1: and 2: was confirmed via single-crystal X-ray crystallography. The isolated compounds showed modest antimycobacterial activity.

Bioactive Terphenyls Isolated from the Antarctic Lichen Stereocaulon alpinum

Three p-terphenyls (2–4)—2-hydroxy-3,5-dimethoxy-p-terphenyl (2), 2-hydroxy-3,6-dimethoxy-p-terphenyl (3), and 2,3,5,6-tetramethoxy-p-terphenyl (4)—were isolated for the first time as natural products along with seven known compounds (1, 5–10) from the Antarctic lichen Stereocaulon alpinum. Structures of the new compounds were elucidated by comprehensive analyses of 1D and 2D NMR and HREIMS experiments. Compound 3 exhibited cytotoxicity against HCT116 cells with the IC₅₀ value of 3.76 ± 0.03 μM and also inhibited NO production in LPS-induced RAW264.7 macrophages with the IC₅₀ value of 22.82 ± 0.015 μM.

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.

The coupled reaction catalyzed by EchB and EchC lead to the formation of the common 2',3',5'-trihydroxy-benzene core in echosides biosynthesis

p-Terphenyls represent a unique family of aromatic natural products generated by nonribosomal peptide synthetase-like (NRPS-like) enzyme. After formation of p-terphenyl skeleton, tailoring modifications will give rise to structural diversity and various biological activities. Here we demonstrated a two-enzyme (EchB, a short-chain dehydrogenase/reductase (SDR), and EchC, a nuclear transport factor 2 (NTF2)-like dehydratase) participated transformation from dihydroxybenzoquinone core to 2',3',5'-trihydroxy-benzene in the biosynthesis of echosides. Beginning with polyporic acid as substrate, successive steps of reduction-dehydration-reduction cascade catalyzed by EchB-EchC-EchB were concluded after in vivo gene disruption and in vitro bioassay experiments. These findings demonstrated a conserved synthesis pathway of 2',3',5'-trihydroxy-p-terphenyls in bacteria, such as Actinomycetes and Burkholderia. The parallel pathway in fungi has yet to be explored.

Structure-Activity Relationships and Potent Cytotoxic Activities of Terphenyllin Derivatives from a Small Compound Library

A small library of 120 compounds was established with seventy new alkylated derivatives of the natural product terphenyllin, together with 45 previous reported derivatives and four natural p-terphenyl analogs. The 70 new derivatives were semi-synthesized and evaluated for cytotoxic activities against four cancer cell lines. Interestingly, 2',4''-diethoxyterphenyllin, 2',4,4''-triisopropoxyterphenyllin, and 2',4''-bis(cyclopentyloxy)terphenyllin showed potent activities with IC₅₀ values in a range from 0.13 to 5.51 μM, which were similar to those of the positive control, adriamycin. The preliminary structure-activity relationships indicated that the introduction of alkyl substituents including ethyl, allyl, propargyl, isopropyl, bromopropyl, isopentenyl, cyclopropylmethyl, and cyclopentylmethyl are important for improving the cytotoxicity.

Hawaiienols A-D, Highly Oxygenated p-Terphenyls from an Insect-Associated Fungus, Paraconiothyrium hawaiiense

Four new highly oxygenated p-terphenyls, hawaiienols A-D (1-4), have been isolated from cultures of Paraconiothyrium hawaiiense, a fungus associated with the Septobasidium-infected insect Diaspidiotus sp.; their structures were elucidated primarily by NMR experiments. The absolute configurations of 1 and 2-4 were assigned by single-crystal X-ray diffraction analysis using Cu Kα radiation and via electronic circular dichroism calculations, respectively. Compound 1 incorporated the first naturally occurring 4,7-dioxatricyclo[3.2.1.0^3,6]octane unit in its p-terphenyl skeleton and showed cytotoxicity toward six human tumor cell lines.

Asperindoles A⁻D and a p-Terphenyl Derivative from the Ascidian-Derived Fungus Aspergillus sp. KMM 4676

Four new indole-diterpene alkaloids asperindoles A⁻D (1⁻4) and the known p-terphenyl derivative 3″-hydroxyterphenyllin (5) were isolated from the marine-derived strain of the fungus Aspergillus sp., associated with an unidentified colonial ascidian. The structures of 1⁻5 were established by 2D NMR and HRESIMS data. The absolute configurations of all stereocenters of 1⁻4 were determined by the combination of ROESY data, coupling constants analysis, and biogenetic considerations. Asperindoles C and D contain a 2-hydroxyisobutyric acid (2-HIBA) residue, rarely found in natural compounds. Asperindole A exhibits cytotoxic activity against hormone therapy-resistant PC-3 and 22Rv1, as well as hormone therapy-sensitive human prostate cancer cells, and induces apoptosis in these cells at low-micromolar concentrations.

Bioactivity-Guided Isolation of Antimicrobial and Antioxidant Metabolites from the Mushroom Tapinella atrotomentosa

Bioassay-guided fractionation of the chloroform extract of Tapinella atrotomentosa led to the isolation of four secondary metabolites 1⁻4. Two of the compounds are lactones—osmundalactone (1) and 5-hydroxy-hex-2-en-4-olide (2)—while 3 and 4 were identified as terphenyl quinones, spiromentins C and B, respectively. The structures of the compounds were established on the basis of NMR and MS spectroscopic analysis. The isolated fungal metabolites were evaluated for their antibacterial activities against several Gram-positive and negative bacteria. In addition, their synergistic effect with cefuroxime against methicillin-resistant Staphylococcus aureus (MRSA) was also evaluated. Compounds 1⁻3 proved to possess significant antibacterial activity against multiresistant Acinetobacter baumannii and extended-spectrum β-lactamase (ESBL)-producing Escherichia coli. The investigation of the antioxidant effect of the isolated compounds in DPPH and ORAC assays revealed that spiromentins C (3) and B (4) have remarkable antioxidant activity.

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.

Structural and biological diversity of natural p-terphenyls

p-Terphenyls consisting of a C-18 tricyclic or polycyclic C-18 aromatic skeleton, have diverse structures because of the variation of the middle ring and the connections between the rings, and to the main skeleton. p-Terphenyls have recently been found to exhibit various biological activities such as cytotoxic, α-glucosidase inhibitory, antioxidant, and antimicrobial activity. In this review, we briefly summarized the structural varieties, biosyntheses, and bioactivities of natural p-terphenyl derivatives referring to the recent 10 years' publications.

Synthetic Method to Form 2,2'-Bis(naphthoquinone) Compounds

We have discovered a transition-metal-free approach to the synthesis of 2,2'-bis(naphthoquinones) using a Diels-Alder reaction of conjugated ketene silyl acetals with benzoquinone. Its monomer analogue can also be synthesized by simply increasing the equivalents of benzoquinone.

Cytotoxic Terphenyl Neolignans from Fungus Terana coerulea: New Natural Corticins D and E, and Revised Structure for Corticin A

The cobalt crust fungus Terana coerulea ( Phanerochaetaceae family) was selected for a bio-guided study after an ethnobotanical survey at the Irati's Forest (Navarra, Spain) for its local use as antibiotic. Six extracts of increasing polarity, from hexane to hot water, were obtained from powdered dry fungi and tested for cytotoxicity against four human tumour cell lines and one non-tumour primary cell culture. From the most cytotoxic, EtOAc extract, we isolated and identified three terphenyl neolignans: two of them new natural products, named corticins D and E, and one previously described as corticin A, whose earlier structure has been revised. Their structural elucidation and biological evaluation as cytotoxic agents are described.

Synthesis of functionalized alkyl substituted benzoquinones by Rh-catalyzed additions of boronic acids

An efficient, group tolerant one-pot process has been developed for the synthesis of functionalized-quinones, using a Rh-catalyzed addition as a key step.

Mild base-promoted benzannulation for the construction of polyfunctionalized m-terphenyl derivatives and their application as potent UV-filters

An efficient and facile transition-metal-free benzannulation was developed for the construction of polyfunctionalized m-terphenyl derivatives.

Bioactive natural products derived from mangrove-associated microbes

This review summarizes new findings concerning the sources and characteristics of various natural products that can be extracted from mangrove-associated microbes over the past three years (January 2011–December 2013).

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.

Prenylated Polyhydroxy-p-terphenyls from Aspergillus taichungensis ZHN-7-07

Six new prenylated polyhydroxy-p-terphenyl metabolites, named prenylterphenyllins A-C (1-3) and prenylcandidusins A-C (5-7), and one new polyhydroxy-p-terphenyl with a simple tricyclic C-18 skeleton, named 4''-dehydro-3-hydroxyterphenyllin (4), were obtained together with eight known analogues (8-15) from Aspergillus taichungensis ZHN-7-07, a root soil fungus isolated from the mangrove plant Acrostichum aureum. Their structures were determined by spectroscopic methods, and their cytotoxicity was evaluated using HL-60, A-549, and P-388 cell lines. Compounds 1 and 8 exhibited moderate activities against all three cell lines (IC50 1.53-10.90 μM), whereas compounds 4 and 6 displayed moderate activities only against the P-388 cell line (IC50 of 2.70 and 1.57 μM, respectively).

Practical C-H functionalization of quinones with boronic acids

A direct functionalization of a variety of quinones with several boronic acids has been developed. This scalable reaction proceeds readily at room temperature in an open flask using inexpensive reagents: catalytic silver(I) nitrate in the presence of a persulfate co-oxidant. The scope with respect to quinones is broad, with a variety of alkyl- and arylboronic acids undergoing efficient cross-coupling. The mechanism is presumed to proceed through a nucleophilic radical addition to the quinone with in situ reoxidation of the resulting dihydroquinone. This method has been applied to complex substrates, including a steroid derivative and a farnesyl natural product.

Terrestrins A-G: p-terphenyl derivatives from the inedible mushroom Thelephora terrestris

Seven p-terphenyl derivatives named terrestrins A-G together with three known ganbajunin B, thelephantins F and H, were isolated from the methanol extract of fruiting bodies of the Japanese inedible mushroom Thelephora terrestris (Thelephoraceae). Their structures were elucidated by means of high-resolution MS, 2D NMR, IR and UV spectroscopy, and X-ray crystallographic analysis.