Naphthoquinone Analogues Research Articles

ChemInform Abstract: Syntheses of 3,4-Bisaryl-3-cyclobutene-1,2-diones and Related Heterocycles.

Abstract 3,4-Dichloro-3-cyclobutene-1,2-dione was reacted with various aromatics to yield 3,4-bisaryl-3-cyclobutene-1,2-diones. Their naphthoquinone analogues were also synthesized.

Antiviral agents 2. Synthesis of trimeric naphthoquinone analogues of conocurvone and their antiviral evaluation against HIV

The synthesis of a new series of conocurvone analogues is presented that explores the importance of the pyran rings of conocurvone, their degree of unsaturation as well as the role of alkoxy functionalities as pyran ring replacements, for the inhibition of the HIV-1 integrase (IN) enzyme. Difficulties in synthesising a trimeric naphthoquinone where the central quinone bears a peri-dihydropyran ring was attributed to distortion of the electrophilic dihaloquinone successfully utilised in the past. Increased electron density could also be a factor in reducing reactivity. The desired central dihydropyran bearing trimeric naphthoquinone was successfully synthesised by using a more reactive bromo-tosyloxyquinone intermediate. A maleimide derivative, where the central quinone between the pendant hydroxyquinones was replaced, was successfully synthesised and although it exhibited comparable enzyme inhibitory activity it had negligible HIV inhibitory cellular activity. Compounds were assessed for activity in both in vitro assays using purified recombinant HIV-1 IN and demonstrated superior or comparable activity to conocurvone derivatives previously reported.

ChemInform Abstract: Naphthoquinone Analogues as Inactivators of cdc25 Phosphatase.

ChemInform Abstract: Naphthoquinone Analogues as Inactivators of cdc25 Phosphatase.

Synthesis and biological evaluation of naphthoquinone analogs as a novel class of proteasome inhibitors

Screening of the NCI Diversity Set-1 identified PI-083 (NSC-45382) a proteasome inhibitor selective for cancer over normal cells. Focused libraries of novel compounds based on PI-083 chloronaphthoquinone and sulfonamide moieties were synthesized to gain a better understanding of the structure–activity relationship responsible for chymotrypsin-like proteasome inhibitory activity. This led to the demonstration that the chloronaphthoquinone and the sulfonamide moieties are critical for inhibitory activity. The pyridyl group in PI-083 can be replaced with other heterocyclic groups without significant loss of activity. Molecular modeling studies were also performed to explore the detailed interactions of PI-083 and its derivatives with the β5 and β6 subunits of the 20S proteasome. The refined model showed an H-bond interaction between the Asp-114 and the sulfonamide moiety of the PI-083 in the β6 subunit.

Three antibacterial naphthoquinone analogues from cultured mycobiont of lichen Astrothelium sp

A new naphthoquinone compound named 7-hydroxyl-8-methoxyltrypethelone 3 together with two known compounds trypethelone 1 and trypethelone methyl ether 2 was isolated from cultured mycobiont of Astrothelium sp. The structures were elucidated by 1D and 2D NMR spectroscopic analysis as well as comparison with those reported in literatures. Compound 1 displayed significant antibacterial activity against Bacillus subtilis (ATCC 6633), and showed modest antibacterial activity against Staphylococcus aureus col (MRSA) (CGMCC 1.2465), while compounds 2 and 3 showed modest antibacterial activity against Enterococcus faecalis 850E (CGMCC 1.2135) and S. aureus col (MRSA) (CGMCC 1.2465).

Design and Synthesis of Novel Quinone Inhibitors Targeted to the Redox Function of Apurinic/Apyrimidinic Endonuclease 1/Redox Enhancing Factor-1 (Ape1/Ref-1)

The multifunctional enzyme apurinic endonuclease 1/redox enhancing factor 1 (Ape1/ref-1) maintains genetic fidelity through the repair of apurinic sites and regulates transcription through redox-dependent activation of transcription factors. Ape1 can therefore serve as a therapeutic target in either a DNA repair or transcriptional context. Inhibitors of the redox function can be used as either therapeutics or novel tools for separating the two functions for in vitro study. Presently there exist only a few compounds that have been reported to inhibit Ape1 redox activity; here we describe a series of quinones that exhibit micromolar inhibition of the redox function of Ape1. Benzoquinone and naphthoquinone analogues of the Ape1-inhibitor E3330 were designed and synthesized to explore structural effects on redox function and inhibition of cell growth. Most of the naphthoquinones were low micromolar inhibitors of Ape1 redox activity, and the most potent analogues inhibited tumor cell growth with IC(50) values in the 10-20 microM range.

Antiviral Agents. I. Synthesis and Antiviral Evaluation of Trimeric Naphthoquinone Analogues of Conocurvone

Conocurvone, a novel natural product isolated from the endemic Australian shrub Conosperum sp. (Proteaceae), exhibits anti-HIV activity but is a highly lipophilic compound, which suggests that there may be problems with its aqueous solubility and bioavailability. A general and convenient synthesis of trimeric naphthoquinones using the condensation of 2-hydroxynaphthoquinones and 2,3-dihaloquinones is described. The application of this method to the synthesis of a series of simpler and less lipophilic trimeric naphthoquinone simple analogues of conocurvone is also reported together with their anti-HIV activity.

Naphthoquinone analog‐induced g1 arrest is mediated by cdc25A inhibition and p53‐independent p21 induction in human hepatocarcinoma cells

Abstract The naphthoquinone analog (2,3‐dichloro‐6,9‐dihydroxy‐1,4‐naphtoquinone, NA) has an inhibitory effect on cdc25A protein phosphatase in vitro, which is responsible for G1/S transition during cell cycle. However, the exact mechanism inducing the growth inhibition is not understood. In this study, we investigated the regulatory mechanisms of growth arrest induced by NA, as a new potent inhibitor of cdc25A phosphatase, in human hepatocarcinoma SK‐hep‐1 cells. We found that NA induced the G1 arrest by perturbation of protein tyrosine dephosphorylation of Cdk2, which may be resulting from inhibition of cdc25A phosphatase. In addition, p21 was expressed in a p53‐independent manner and participated in the NA‐induced G1 arrest by inhibiting Cdk2 activity. Although the exact mechanism is not known, the p21 expression might be related to MAPK activation. From these results, we suggest that NA induces G1 arrest via inhibition of cdc25A and induction of p53‐independent p21 expression in SK‐Hep‐1 cells.

Naphthazarin and methylnaphthazarin cause vascular dysfunction by impairment of endothelium-derived nitric oxide and increased superoxide anion generation

The effects of the naphthoquinone analogue, naphthazarin (Nap), and its derivative, methylnaphthazarin (MetNap), on vascular reactivity were studied using isolated rat aortic rings and human umbilical vein endothelial cells (HUVECs). In this study, we determined vessel tension, nitric oxide (NO) formation, endothelial nitric oxide synthase (eNOS) activity, eNOS protein expression, and superoxide anion (O2-) generation in an effort to evaluate the effect of Nap and MetNap on the impairment of the NO-mediated pathway. Lower concentrations of Nap (0.01–1μM) and MetNap (1–10μM) concentration-dependently enhanced phenylephrine (PE)-induced vasocontraction and abrogated acetylcholine (ACh)-induced vasorelaxation in an endothelium-dependent manner. On HUVECs, both Nap and MetNap concentration-dependently inhibited NO formation induced by A23187, and also partially inhibited nitric oxide synthase (NOS) activity. eNOS protein expression by HUVECs was not affected by treatment with Nap or MetNap, even within 24h. These data suggest that Nap and MetNap might act as inhibitors of nitric oxide synthesis in the endothelium. In addition, Nap and MetNap were also shown to generate O2- on HUVECs with short-term treatment. We concluded that Nap and MetNap inhibited agonist-induced relaxation and induced vasocontraction in an endothelium-dependent manner, and these effects might have been due to modification of the NO content by inhibition of NOS activity and bioinactivation through O2- generation.

Mechanism of antifeedant activity of plumbagin, a compound concerning the chemical defense in carnivorous plant

Dionaea muscipula Ellis accumulates a large amount of plumbagin ( 1 ), which operates as an antifeedant against predators. Content of 1 reached 0.5% weight of the fresh trap lobes. It was found that other carnivorous plants also accumulated similar naphthoquinone-type strong antifeedant. Thus, naphthoquinone analogs are widely used as an antifeedant among the carnivorous plants. By using several analogs of 1 , we clarified that both the high volatility and high redox potential of 1 are important for its strong antifeedant activity. It was known that plumbagin stimulates the mitochondrial electron transport system as a result of intercepting electrons. These results suggested that the Droseraceae family possesses a universal defensive mechanism against predators, that is, accumulation of volatile naphthoquinone with high redox potential as defensive substance. Thus, it is estimated that highly volatile naphthoquinone of moderately high redox potential would be used as an antifeedant of weak toxicity.

Alternative quinone substrates and inhibitors of human electron-transfer flavoprotein-ubiquinone oxidoreductase.

Electron-transfer flavoprotein (ETF)-ubiquinone (2,3-dimethoxy-5-methyl-1,4-benzoquinone) oxidoreductase (ETF-QO) is a membrane-bound iron-sulphur flavoprotein that participates in an electron-transport pathway between eleven mitochondrial flavoprotein dehydrogenases and the ubiquinone pool. ETF is the intermediate electron carrier between the dehydrogenases and ETF-QO. The steady-state kinetic constants of human ETF-QO were determined with ubiquinone homologues and analogues that contained saturated n-alkyl substituents at the 6 position. These experiments show that optimal substrates contain a ten-carbon-atom side chain, consistent with a preliminary crystal structure that shows that only the first two of ten isoprene units of co-enzyme Q10 (CoQ10) interact with the protein. Derivatives with saturated alkyl side chains are very good substrates, indicating that, unlike other ubiquinone oxidoreductases, there is little preference for the methyl branches or rigidity of the CoQ side chain. Few of the compounds that inhibit ubiquinone oxidoreductases inhibit ETF-QO. Compounds found to act as inhibitors of ETF-QO include 2-n-heptyl-4-hydroxyquinoline N-oxide, a naphthoquinone analogue, 2-(3-methylpentyl)-4,6-dinitrophenol and pentachlorophenol. 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB), which inhibits the mitochondrial bc1 complex and the chloroplast b6 f complex in redox-dependent fashion, can serve as an electron acceptor for human ETF-QO. The observation of simple Michaelis-Menten kinetic patterns and a single type of quinone-binding site, determined by fluorescence titrations of the protein with DBMIB and 6-(10-bromodecyl)ubiquinone, are consistent with one ubiquinone-binding site per ETF-QO monomer.

Impairment of vascular function of rat thoracic aorta in an endothelium-dependent manner by shikonin/alkannin and derivatives isolated from roots of Macrotomia euchroma.

The effects of a naphthoquinone analogue, shikonin/alkannin (SA) and derivatives (acetylshikonin and beta,beta-dimethylacrylshikonin), on vascular reactivity were studied with isolated rat aortic rings. At lower concentrations, SA and its derivatives concentration-dependently inhibit the agonist-induced (acetylcholine and histamine) relaxation in PE precontracted aorta in an endothelium-dependent manner with IC (50) values ranging from 0.2 to 1.5 microM. In addition to the effect on agonist-induced vasorelaxation, the Ca (2+) ionophore A23187-induced vasorelaxation was also inhibited or reversed by SA. However, SA had no effect on sodium nitroprusside-induced (guanylate cyclase activator) vasorelaxation. These data suggested that SA and its derivatives might be acting as inhibitors of nitric oxide synthesis in endothelium. At a concentration greater than 10 microM, SA induced contraction of intact but not denuded aorta which could be inhibited by prior treatment with indomethacin, a cyclooxygenase inhibitor. In summary, the results from this study showed that SA and its derivatives inhibited agonist-induced relaxation at lower concentrations and induced vasocontraction at higher concentrations. All the effects seen with SA were endothelium-dependent, however, through different mechanisms. Abbreviations. SA:shikonin/alkannin PE:phenylephrine Ach:acetylcholine SNP:sodium nitroprusside eNOS:endothelial nitric oxide synthase L-NAME: Nw-nitro- L-arginine methyl ester

Involvement of Akt in mitochondria-dependent apoptosis induced by a cdc25 phosphatase inhibitor naphthoquinone analog

Vitamin K-related analogs induce growth inhibition via a cell cycle arrest through cdc25A phosphatase inhibition in various cancer cell lines. We report that 2,3-dichloro-5,8-dihydroxy-1,4-naphthoquinone (DDN), a naphthoquinone analog, induces mitochondria-dependent apoptosis in human promyelocytic leukemia HL-60 cells. DDN induced cytochrome c release, Bax translocation, cleavage of Bid and Bad, and activation of caspase-3, -8, -9 upon the induction of apoptosis. Cleavage of Bid, the caspase-8 substrate, was inhibited by the broad caspase inhibitor z-Val-Ala-Asp(OMe)-fluoromethylketone (zVAD-fmk), whereas cytochrome c release was not affected, suggesting that activation of caspase-8 and subsequent Bid cleavage occur downstream of cytochrome c release. DDN inhibited the activation of Akt detected by decreasing level of phosphorylation. Overexpression of constitutively active Akt protected cells from DDN-induced apoptosis, while dominant negative Akt moderately enhanced cell death. Furthermore, Akt prevented release of cytochrome c and cleavage of Bad in DDN-treated HL-60 cells. Taken together, DDN-induced apoptosis is associated with mitochondrial signaling which involves cytochrome c release via a mechanism inhibited by Akt.

Effects of a naphthoquinone analog on tumor growth and apoptosis induction.

Vitamin K-related analogs induce growth inhibition in various cancer cell lines. A naphthoquinone analog, termed 2,3-dichloro-5, 8-dihydroxy-1,4-naphthoquinone (DDN), induces apoptosis in human promyeloid leukemic HL-60 cells, and shows antitumor activity in vivo. Following treatment with DDN, evidence of apoptosis, including DNA fragmentation and cleavage of poly ADP ribose polymerase (PARP), was observed. DDN induced an upregulation of proapoptotic Bax protein, and Bid cleavage. Antiapoptotic Bcl-2 protein levels were not changed by DDN, but the expression of Bcl-xL was decreased. In addition, DDN reduced the mass of solid tumor in the Sarcoma 180 tumor-bearing mouse model. These results indicate that DDN exerts antitumor activity, which appears to be related to the induction of apoptosis by regulating Bcl-2 family proteins.

Induction of p73β by a naphthoquinone analog is mediated by E2F-1 and triggers apoptosis in HeLa cells

Recently, p73 was identified as a structural and functional homolog of p53. The p73 protein activates the transcription of genes downstream of p53 and induces apoptosis when overexpressed in several cell lines, similar to the tumor suppressor p53. However, the extracellular stimuli and molecular mechanisms regulating p73 activity remain to be elucidated. In this paper, we present evidence that the naphthoquinone analog, 2,3-dichloro-5,8-dihydroxy-1,4-naphthoquinone (NA), is a novel apoptotic stimulus that induces p73β expression. Treatment with NA induced the expression of p73β mRNA and protein and its downstream genes, p21 and bax, in HeLa cells. Similar results were obtained in MCF7 cells (p53 +/+, p73 +/+). In the MCF7 cells, p53 protein level was rather decreased by NA treatment. Overexpression of p73β led to the apoptosis of HeLa cells and enhancement of NA-induced cell death. Expression of p73β was mediated by E2F-1, which was activated via release from pRB after exposure of cells to NA. We additionally observed that overexpression of pRB inhibited NA-induced apoptosis. These results imply that p53-independent p73β-dependent p21 expression is involved in NA-induced apoptosis of HeLa cells.

Synthesis and biological studies of novel nucleoside phosphoramidate prodrugs.

A novel approach to the intracellular delivery of nucleotides using phosphoramidate-based prodrugs is described. Specifically, we have developed phosphoramidate prodrugs of the anticancer nucleotide 5-fluoro-2'-deoxyuridine-5'monophosphate (FdUMP). These phosphoramidate prodrugs contain an ester group that undergoes intracellular activation liberating phosphoramidate anion, which undergoes spontaneous cyclization and P-N bond cleavage to yield the nucleoside monophosphate quantitatively. In vitro evaluation of 5-fluoro-2'-deoxyuridine phosphoramidate prodrugs 2a and 3b against L1210 mouse leukemia cells show potent inhibition of cell growth (IC(50) 0.5-3 nM). Cell-based thymidylate synthase inhibition studies show that, in contrast to FUdR, the nitrofuran compound 2a is of comparable potency in wild type vs thymidine kinase deficient LM cells. This result indicates that the activation of this novel prodrug occurs via the proposed mechanism of intracellular delivery. However, naphthoquinone 3b has an IC(50) value for thymidylate synthase inhibition that is comparable to FUdR in thymidine kinase deficient cells. Further studies revealed that 3b rapidly decomposes to the nucleotide in cell culture medium, suggesting that the naphthoquinone analogue is not sufficiently stable to function as a nucleotide prodrug.

Development of Novel Quinone Phosphorodiamidate Prodrugs Targeted to DT-Diaphorase

A series of naphthoquinone and benzimidazolequinone phosphorodiamidates has been synthesized and studied as potential cytotoxic prodrugs activated by DT-diaphorase. Reduction of the quinone moiety in the target compounds was expected to provide a pathway for expulsion of the phosphoramide mustard alkylating agent. All of the compounds synthesized were excellent substrates for purified human DT-diaphorase (k(cat)/K(m) = 3 x 10(7) - 3 x 10(8) M(-1) s(-1)). The naphthoquinones were toxic to both HT-29 and BE human colon cancer cell lines in a clonogenic assay; however, cytotoxicity did not correlate with DT-diaphorase activity in these cell lines. The benzimidazolequinone analogues were 1-2 orders of magnitude less cytotoxic than the naphthoquinone analogues. Chemical reduction of the naphthoquinone led to rapid expulsion of the phosphorodiamidate anion; in contrast, the benzimidazole reduction product was stable. Michael addition of glutathione and other sulfur nucleophiles provides an alternate mechanism for activation of the naphthoquinone phosphorodiamidates, and this mechanism may contribute to the cytotoxicity of these compounds.

Naphthoquinone analogs as inactivators of cdc25 phosphatase

cdc25A and cdc25B were significantly overexpressed in certain types of cancers, and they represent potential therapeutic targets for anticancer drug. In this study, naphthoquinone analogs as cdc25A phosphatase inactivators were investigated.

The redox-controlled light-harvesting chlorophyll a/b protein kinase. Deactivation by substituted quinones.

The deactivation of the redox-controlled light-harvesting chlorophyll a/b protein kinase of Acetabularia acetabulum and pea thylakoids was studied. Substituted benzoquinone, naphthoquinone, and anthraquinone analogs including mono-, di-, and trihalogenated and/or alkylated quinones, which are known to inhibit the cytochrome b6/f activity, deactivate the kinase in the dark, and prevent its activation in the light. Analogs halogenated at positions 2- or 3- are the most effective deactivators. Increasing the size of the alkyl side chain and/or the number of rings lowers the deactivation effect. The activated state of the pea kinase decays with a t1/2 of 15 min, while the Acetabularia enzyme retains its active state for at least 2 h. The midpoint potential for Acetabularia kinase activity in the dark is 120 +/- 10 mV and is compatible with the involvement of plastoquinone in the kinase activation via reduction of the cytochrome complex. Deactivation of kinase by the analogs inhibiting cytochrome b6/f complex activity and the kinase copurification with the cytochrome b6/f fraction obtained from the Acetabularia thylakoid further support this conclusion. These results indicate that the process of kinase activation/deactivation includes the binding of plastoquinol or quinone analogs by the cytochrome complex and its interaction with the kinase. We propose that the latter process may constitute the rate-limiting step controlling the kinase activation/deactivation kinetics.

Benzoquinone derived 1,3-dithiole-2-ones and thiones

The syntheses and structures of 1,3-dithiole and tetrathiafulvalene derivatives of benzoquinone have been investigated. This work extends earlier investigations of naphthoquinone analogues. The X-ray structures, NMR, IR, UV, mass spectra, and E0 1/2 values from cyclic voltammetry measurements are reported.Ab initio STO-6-31G calculations are used to correlate the cyclic voltammetry and UV data for selected compounds.