Discovery of pyranonaphthoquinones and an eighteen-membered ring macrolide from the rhizospheric soil-derived fungus Phialocephala sp. YUD18001 by OSMAC strategy

Two new pyranonaphthoquinones, phialoyxinones A (1) and B (2), a new eighteen-membered ring lactone, phialoyxtone (3), and five known pyranonaphthoquinone derivatives were identified from the fungus Phialocephala sp. YUD18001, which was isolated from the rhizospheric soil associated with Gastrodia elata. Their structures were unequivocally established by a comprehensive interpretation of the spectroscopic data, with the stereochemistry for 1-3 was defined by a combination of TDDFT calculations, and the DP4+ probability analysis based on NMR chemical shift calculations. All of the new compounds 1-3 were evaluated for cytotoxicity and acetylcholinesterase inhibitory, compound 2 exhibited in vitro cytotoxic activities against five human cancer cell lines (HL-60, SMMC-7721, A549, MCF-7 and SW480) with IC50 values ranging from 11.80 to 19.32 μM. Compounds 2 and 3 exhibited moderate AChE inhibitory activities. A putative biosynthetic pathway for the pyranonaphthoquinones was proposed.

Actinorhodin Biosynthesis Terminates with an Unprecedented Biaryl Coupling Reaction

A plethora of dimeric natural products exist with diverse chemical structures and biological activities. A major strategy for dimerization is aryl coupling catalyzed by cytochrome P450 or laccase. Actinorhodin (ACT) from Streptomyces coelicolor A3(2) has a dimeric pyranonaphthoquinone structure connected by a C-C bond. In this study, we identified an NmrA-family dimerizing enzyme, ActVA-ORF4, and a cofactor-independent oxidase, ActVA-ORF3, both involved in the last step of ACT biosynthesis. ActVA-ORF4 is a unique NAD(P)H-dependent enzyme that catalyzes the intermolecular C-C bond formation using 8-hydroxydihydrokalafungin (DHK-OH) as the sole substrate. On the other hand, ActVA-ORF3 was found to be a quinone-forming enzyme that produces the coupling substrate, DHK-OH and the final product, ACT. Consequently, the functional assignment of all essential enzymes in the biosynthesis of ACT, one of the best-known model natural products, has been completed.

Base-induced isomerization of red uroleuconaphins revisited: characterization and absolute stereochemistry of the yellow aphid pigments uroleuconaphins A2 and B2

A base-induced isomerization of red uroleuconaphin A1 to yellow uroleuconaphin A2 having polycyclic acetal is described here.

Strong acid-promoted skeletal remodeling of the aphid pigment: red uroleuconaphin to green viridaphin

A strong acid-promoted single-step transformation of red uroleuconaphin A1 to green viridaphins A1 and A2 is described here.

Stereoselective Total Synthesis of the Dimeric Naphthoquinonopyrano-γ-lactone (-)-Crisamicin A: Introducing the Dimerization Site by a Late-Stage Hartwig Borylation

The first stereoselective total synthesis of the dimeric naphthoquinonopyrano-γ-lactone (-)-crisamicin A was realized (13 steps, 5% overall yield). 1,4,5-Trimethoxynaphthalene, reached in five known steps, was brominated at C-3 to install a but-3-enoic ester by an ensuing Heck coupling. An asymmetric Sharpless dihydroxylation followed and gave a β-hydroxy-γ-lactone with >99.9% ee. Its OH substituent and acetaldehyde established the dihydropyran ring in a completely diastereoselective oxa-Pictet-Spengler cyclization. The 2,3-fused anisole moiety allowed the C⁵-H bond under Hartwig's conditions to be borylated. This set the stage for engaging the resulting C⁵-B bond in an oxidative dimerization, which led to a binaphthohydroquinon-5-yl. The latter was advanced to synthetic crisamicin A by a double CAN oxidation (→ a binaphthoquinon-5-yl) and a double demethylation.

Pyranonaphthoquinone and anthraquinone derivatives from Ventilago harmandiana and their potent anti-inflammatory activity

The chemical study on the heartwoods extract of Ventilago harmandiana (Rhamnaceae) resulted in the isolation of ten previously undescribed pyranonaphthoquinones (ventilanones A-J), an undescribed anthraquinone (ventilanone K), together with eight known anthraquinone derivatives. Their structures were elucidated by extensive analysis of their spectroscopic data. The absolute configuration of ventilanone A was established from single crystal X-ray crystallographic analysis of its p-bromobenzenesulfonate ester derivative using Cu Kα radiation. The absolute configurations of the other related compounds were identified by comparison of their ECD data with those of ventilanone A and related known compounds. Cytotoxic and anti-inflammatory activities of some of the isolated compounds were evaluated. Ventilanone A and ventilanone C exhibited moderate cytotoxicity against P-388 cell line. Ventilanone D exhibited significant anti-inflammatory activity while ventilanone A and ventilanone C showed moderate activity.

Unified synthesis and cytotoxic activity of 8-O-methylfusarubin and its analogues

A simple and unified synthesis of four related pyranonaphthoquinone natural products, e.g. 8-O-methylfusarubin, 8-O-methylanhydrofusarubin, fusarubin and anhydrofusarubin, is reported. The key synthetic features include the precedented Diels-Alder cycloaddition to assemble the naphthalene skeleton, selective formylation and acetonylation and intramolecular acetalization to construct the pyran ring. Manipulation of the oxidation state of the naphthoquinone core was performed to construct the two analogues, fusarubin and anhydrofusarubin. This work also highlights an unprecedented directing effect of the hydroxymethylene group in the selective hypervalent iodine-mediated quinone oxidation. The four synthetic compounds were evaluated for their in vitro cytotoxic activities against six human cancer cells. 8-O-Methylfusarubin was the most potent analogue and displayed excellent cytotoxic activity against MCF-7 breast cancer cells with an IC₅₀ value of 1.01 μM with no cytotoxic effect on noncancerous Vero cells, which could potentially be a promising lead compound for anti-breast cancer drug discovery.

Dimeric Pyranonaphthoquinone Glycosides with Anti-HIV and Cytotoxic Activities from a Soil-Derived Streptomyces

Eight new sulfur-bridged pyranonaphthoquinone (PNQ) dimers, naquihexcins C-J (1-8), a new PNQ monomer, naquihexcin K (10), and three known analogues (9, 11, and 12) were isolated from Streptomyces sp. KIB3133. The new structures were elucidated by interpretation of spectroscopic data. Dimer 4 was synthesized via a cascade S_N2 reactions between two monomers and sodium sulfide, an approach motivated by the proposed biosynthetic pathway of dimeric pyranonaphthoquinones. Naquihexcin E (3) exhibited moderate HIV-1 inhibitory activity. Naquihexcins C (1), E (3), and I (7) showed inhibitory effects against two tumor cell lines (HL-60 and MCF-7) with IC₅₀ values ranging from 1.4 to 16.1 μM.

Total synthesis of griseusins and elucidation of the griseusin mechanism of action

An efficient divergent synthesis of griseusins enabled SAR studies, mechanistic elucidation and evaluation in an axolotl tail regeneration model.

A divergent modular strategy for the enantioselective total synthesis of 12 naturally-occurring griseusin type pyranonaphthoquinones and 8 structurally-similar analogues is described. Key synthetic highlights include Cu-catalyzed enantioselective boration–hydroxylation and hydroxyl-directed C–H olefination to afford the central pharmacophore followed by epoxidation–cyclization and maturation via diastereoselective reduction and regioselective acetylation. Structural revision of griseusin D and absolute structural assignment of 2a,8a-epoxy-epi-4′-deacetyl griseusin B are also reported. Subsequent mechanistic studies establish, for the first time, griseusins as potent inhibitors of peroxiredoxin 1 (Prx1) and glutaredoxin 3 (Grx3). Biological evaluation, including comparative cancer cell line cytotoxicity and axolotl embryo tail inhibition studies, highlights the potential of griseusins as potent molecular probes and/or early stage leads in cancer and regenerative biology.

Pseudonectrins A–D, heptaketides from an endophytic fungus Nectria pseudotrichia

The new heptaketides, pseudonectrins A–D (1–4), were isolated from a plant endophyte Nectria pseudotrichia. Compounds 1–3 showed moderate cytotoxicity towards human tumor cells.

Pyranonaphthoquinones - isolation, biology and synthesis: an update

Covering: 2008 to 2015. A review on the isolation, biological activity and synthesis of pyranonaphthoquinone natural products from 2008-2015 is providedThis review discusses the isolation, biological activity and synthesis of pyranonaphthoquinone natural products, covering the years 2008-2015. The pyranonaphthoquinones are a group of metabolites sharing a common naphtho[2,3-c]pyran-5,10-dione ring system that have been isolated from a wide range of microorganisms, plants and insects. In addition to their synthetically challenging molecular structures, pyranonaphthoquinones exhibit a wide array of biological activity, including anti-bacterial, anti-fungal and anti-cancer properties. The therapeutic potential of these compounds has led to a dynamic interplay between total synthesis and biological evaluation.

Synthesis of dihydroindeno[1,2-c]isochromene via cascade cyclization and Friedel–Crafts reaction

Dihydroindeno[1,2-c]isochromene can be efficiently prepared from alkynol and aldehydesviacascade cyclization and Friedel–Crafts reaction. The reaction is highly regioselective.

DABCO catalyzed domino Michael/hydroalkoxylation reaction involving α-alkynyl-β-aryl nitroolefins: excellent stereoselective access to dihydropyrano[3,2-c]chromenes, pyranonaphthoquinones and related heterocycles

The stereoselective (up to ≤96 : 4 Z/E ratio) access to pyrano[3,2-c]chromenes and related scaffolds has been achieved in 72–89% yields via a domino reaction of enolizable cyclic 1,3-dicarbonyls and β-alkynyl nitroolefins.

New 1,4-anthracenedione derivatives with fused heterocyclic rings: synthesis and biological evaluation

New 1,4-anthracenediones bearing fused-heterocycle rings were synthesized and evaluated as cytotoxics, antifungals and antivirals. Some of them showed GI₅₀ at the μM level.

Design, synthesis, and anticancer activities of new compounds bearing the quinone–pyran–lactone tricyclic pharmacophore

A simple and effective synthesis of the tricyclic quinone–pyran–lactone skeleton was developed and subsequent structural modification was conducted.

Synthesis and cytotoxicity of pyranonaphthoquinone natural product analogues under bioreductive conditions

We have synthesised a focused library of derivatives of natural products containing the pyranonaphthoquinone moiety including the first report of such a scaffold with an appended tetrazole functionality. Examples include kalafungin derivatives as well as analogues of nanaomycin and eleutherin. These compounds were assessed for cytotoxic activation by breast cancer cell lines engineered to express the prototypic human one- and two-electron quinone bioreductive enzymes, NADPH: cytochrome P450 oxidoreductase (POR) and

NAD(P)H

quinoneoxidoreductase 1 (NQO1; DT-diaphorase), respectively. Several compounds were observed to be cytotoxic at sub-micromolar level and a pattern of increased aerobic potency was observed in cells over expressing POR. A subset of analogues was assessed under anoxic conditions, where cytotoxicity was reduced, implicating redox cycling as a major mechanism of toxicity. The substrate specificity for reductive enzymes is relevant to the future design of bioreductive prodrugs to treat cancer.

Convenient synthesis of Bioactive Pyranonaphthoquinones (±)9-Demethoxyeleutherin and (±)9-Demethoxyisoeleutherin

A convenient synthesis of (±)9-demethoxyeleutherin and (±)9-demethoxyisoeleutherin, the analogues of naturally occurring pyranonaphthoquinone antibiotics eleutherin and isoeleutherin, is described. The synthesis was achieved from 4-methoxy-1-napthol in four simple steps including Claisen rearrangement and oxymercuration–demercuration reactions.