Naphthazarin derivatives (VI): synthesis, inhibitory effect on DNA topoisomerase-I and antiproliferative activity of 2- or 6-(1-oxyiminoalkyl)-5,8-dimethoxy-1,4-naphthoquinones

How Substitution Combines with Non-Covalent Interactions to Modulate 1,4-Naphthoquinone and Its Derivatives Molecular Features-Multifactor Studies

Substitution is well-known to modulate the physico-chemical properties of molecules. In this study, a combined, multifactor approach was employed to determine a plethora of substitution patterns using –Br and –O-H in 1,4-naphthoquinone and its derivatives. On the basis of classical Density Functional Theory (DFT), 25 models divided into three groups were developed. The first group contains 1,4-naphthoquinone and its derivatives substituted only by –Br. The second group consists of compounds substituted by –Br and one –O-H group. As a result of the substitution, an intramolecular hydrogen bond was formed. The third group also contains –Br as a substituent, but two –O-H groups were introduced and two intramolecular hydrogen bonds were established. The simulations were performed at the ωB97XD/6-311++G(2d,2p) level of theory. The presence of substituents influenced the electronic structure of the parent compound and its derivatives by inductive effects, but it also affected the geometry of the 2 and 3 groups, due to the intramolecular hydrogen bonding and the formation of a quasi-ring/rings. The static DFT models were applied to investigate the aromaticity changes in the fused rings based on the Harmonic Oscillator Model of Aromaticity (HOMA). The OH stretching was detected for the compounds from groups 2 and 3 and further used to find correlations with energetic parameters. The evolution of the electronic structure was analyzed using Hirshfeld atomic charges and the Substituent Active Region (cSAR) parameter. The proton reaction path was investigated to provide information on the modulation of hydrogen bridge properties by diverse substitution positions on the donor and acceptor sides. Subsequently, Car–Parrinello Molecular Dynamics (CPMD) was carried out in the double-bridged systems (group 3) to assess the cooperative effects in double –O-H-substituted systems. It was determined that the –O-H influence on the core of the molecule is more significant than that of –Br, but the latter has a major impact on the bridge dynamics. The competitive or synergic effect of two –Br substituents was found to depend on the coupling between the intramolecular hydrogen bridges. Thus, the novel mechanism of a secondary (cooperative) substituent effect was established in the double-bridged systems via DFT and CPMD results comparison, consisting of a mediation of the bromine substitutions’ influence by the cooperative proton transfer events in the hydrogen bridges.

Naphthazarin Derivatives in the Light of Intra- and Intermolecular Forces

Our long-term investigations have been devoted the characterization of intramolecular hydrogen bonds in cyclic compounds. Our previous work covers naphthazarin, the parent compound of two systems discussed in the current work: 2,3-dimethylnaphthazarin (1) and 2,3-dimethoxy-6-methylnaphthazarin (2). Intramolecular hydrogen bonds and substituent effects in these compounds were analyzed on the basis of Density Functional Theory (DFT), Møller-Plesset second-order perturbation theory (MP2), Coupled Clusters with Singles and Doubles (CCSD) and Car-Parrinello Molecular Dynamics (CPMD). The simulations were carried out in the gas and crystalline phases. The nuclear quantum effects were incorporated a posteriori using the snapshots taken from ab initio trajectories. Further, they were used to solve a vibrational Schrödinger equation. The proton reaction path was studied using B3LYP, ωB97XD and PBE functionals with a 6-311++G(2d,2p) basis set. Two energy minima (deep and shallow) were found, indicating that the proton transfer phenomena could occur in the electronic ground state. Next, the electronic structure and topology were examined in the molecular and proton transferred (PT) forms. The Atoms In Molecules (AIM) theory was employed for this purpose. It was found that the hydrogen bond is stronger in the proton transferred (PT) forms. In order to estimate the dimers' stabilization and forces responsible for it, the Symmetry-Adapted Perturbation Theory (SAPT) was applied. The energy decomposition revealed that dispersion is the primary factor stabilizing the dimeric forms and crystal structure of both compounds. The CPMD results showed that the proton transfer phenomena occurred in both studied compounds, as well as in both phases. In the case of compound 2, the proton transfer events are more frequent in the solid state, indicating an influence of the environmental effects on the bridged proton dynamics. Finally, the vibrational signatures were computed for both compounds using the CPMD trajectories. The Fourier transformation of the autocorrelation function of atomic velocity was applied to obtain the power spectra. The IR spectra show very broad absorption regions between 700 cm-1-1700 cm-1 and 2300 cm-1-3400 cm-1 in the gas phase and 600 cm-1-1800 cm-1 and 2200 cm-1-3400 cm-1 in the solid state for compound 1. The absorption regions for compound 2 were found as follows: 700 cm-1-1700 cm-1 and 2300 cm-1-3300 cm-1 for the gas phase and one broad absorption region in the solid state between 700 cm-1 and 3100 cm-1. The obtained spectroscopic features confirmed a strong mobility of the bridged protons. The inclusion of nuclear quantum effects showed a stronger delocalization of the bridged protons.

Non-Covalent Forces in Naphthazarin-Cooperativity or Competition in the Light of Theoretical Approaches

Non-covalent interactions responsible for molecular features and self-assembly in Naphthazarin C polymorph were investigated on the basis of diverse theoretical approaches: Density Functional Theory (DFT), Diffusion Quantum Monte Carlo (DQMC), Symmetry-Adapted Perturbation Theory (SAPT) and Car-Parrinello Molecular Dynamics (CPMD). The proton reaction paths in the intramolecular hydrogen bridges were studied. Two potential energy minima were found indicating that the proton transfer phenomena occur in the electronic ground state. Diffusion Quantum Monte Carlo (DQMC) and other levels of theory including Coupled Cluster (CC) employment enabled an accurate inspection of Potential Energy Surface (PES) and revealed the energy barrier for the proton transfer. The structure and reactivity evolution associated with the proton transfer were investigated using Harmonic Oscillator Model of Aromaticity - HOMA index, Fukui functions and Atoms In Molecules (AIM) theory. The energy partitioning in the studied dimers was carried out based on Symmetry-Adapted Perturbation Theory (SAPT) indicating that dispersive forces are dominant in the structure stabilization. The CPMD simulations were performed at 60 K and 300 K in vacuo and in the crystalline phase. The temperature influence on the bridged protons dynamics was studied and showed that the proton transfer phenomena were not observed at 60 K, but the frequent events were noticed at 300 K in both studied phases. The spectroscopic signatures derived from the CPMD were computed using Fourier transformation of autocorrelation function of atomic velocity for the whole molecule and bridged protons. The computed gas-phase IR spectra showed two regions with OH absorption that covers frequencies from 2500 cm−1 to 2800 cm−1 at 60 K and from 2350 cm−1 to 3250 cm−1 at 300 K for both bridged protons. In comparison, the solid state computed IR spectra revealed the environmental influence on the vibrational features. For each of them absorption regions were found between 2700–3100 cm−1 and 2400–2850 cm−1 at 60 K and 2300–3300 cm−1 and 2300–3200 cm−1 at 300 K respectively. Therefore, the CPMD study results indicated that there is a cooperation of intramolecular hydrogen bonds in Naphthazarin molecule.

Investigation of the antimicrobial and anticancer activity of aminonaphthoquinones

In this study, we report on the inhibitory activity of synthesized aminonaphthoquinones against two bacterial and one fungal species to determine their antimicrobial properties. A minimum inhibitory concentration (MIC) of 7.8 μg/mL was obtained against the fungus, Candida albicans, which was better than that of Amphotericin B (MIC = 31.25 μg/mL). Escherichia coli (Gram -), was inhibited at a MIC of 23.4 μg/mL and Staphylococcus aureus (Gram +) at a MIC of 31.3 μg/mL. The aminonaphthoquinones were also screened against HCT116 colon, PC3 prostate and HepG2 liver cancer cell lines to evaluate their cytostatic effects. They had potent activity (GI₅₀  = 5.87-9.90 μM) which was about three-6-fold better than that of parthenolide (GI₅₀  = 25.97 μM) against the prostate cancer cell line. These compounds were generally more selective for cancer cells than for normal human lung fetal fibroblasts (WI-38).

Cytotoxicity of Synthesized 1,4-Naphthoquinone Oxime Derivatives on Selected Human Cancer Cell Lines

In an effort to develop potent and selective antitumor agents, a series of 1,4-naphthoquinone oxime derivatives were designed and synthesized. The cytotoxicity of these compounds were evaluated against five human cancer cell lines (colorectal cancer cell: HCT-15, breast cancer cell: MDA-MB-231, liver cancer cell: BEL-7402, colorectal cancer cell: HCT-116 and ovarian cancer cell: A2780) in vitro. Among them, compound 14 was found to be the most potent cytotoxic compound against three cell lines (MDA-MB-231, BEL-7402 and A2780) with IC₅₀ values of 0.66±0.05, 5.11±0.12 and 8.26±0.22 µM, respectively. Additionally, the length of the side chains and the position of the substituent may also affect the cytotoxic activity of the naphthoquinone oxime derivatives. In general, compound 14 effectively inhibited breast cancer cell proliferation and may become a promising anticancer agent.

Synthesis of Selenium-Quinone Hybrid Compounds with Potential Antitumor Activity via Rh-Catalyzed C-H Bond Activation and Click Reactions

In continuation of our quest for new redox-modulating catalytic antitumor molecules, selenium-containing quinone-based 1,2,3-triazoles were synthesized using rhodium-catalyzed C-H bond activation and click reactions. All compounds were evaluated against five types of cancer cell lines: HL-60 (human promyelocytic leukemia cells), HCT-116 (human colon carcinoma cells), SF295 (human glioblastoma cells), NCIH-460 (human lung cells) and PC3 (human prostate cancer cells). Some compounds showed good activity with IC50 values below 1 µM. The cytotoxic potential of the naphthoquinoidal derivatives was also evaluated in non-tumor cells, exemplified by L929 cells. Overall, these compounds represent promising new lead derivatives and stand for a new class of chalcogenium-containing derivatives with potential antitumor activity.

Regioselective semi-synthesis of 6-isomers of 5,8-O-dimethyl ether of shikonin derivatives via an 'intramolecular ring-closing/ring-opening' strategy as potent anticancer agents

Synthesis of 6-isomer of 5,8-O-dimethyl ether of shikonin (13), a promising anticancer scaffold, always remains a huge challenge. Herein a key intermediate for 13, 2-(1-hydroxyl-4-methyl-3-pentenyl)-1,4,5,8-tetramethoxynaphthalene (10), was obtained on the large-scale synthesis. A ring-closing/ring-opening strategy was applied to avoid the undesired reactivity posed by the side chain and racemization of the chiral centre. Incorporation of bulky substituent 4-((tertbutoxycarbonyl)amino)phenyl to hydroxyl group in the side chain redistributed electron density of naphthalene core (10), overwhelmingly favoring the generation of 13 when oxidized by cerium(IV) ammonium nitrate followed by hydrolysis. As a result, three 6-isomers (14a-14c) with very potent antitumor activity were easily synthesized. This study opened an novel avenue to selectively prepare 6-isomers of 5,8-dimethoxy1-1,4-naphthaquinones, bearing the synthetically challenging side chain such as 2-hydroxyl-5-methylpentenyl group. Graphical abstract A novel semi-synthesis of 6-isomer of 5,8-O-dimethyl ether of shikonin (13) was developed in a threestep rounte using a ring-closing/ring-opening strategy and a bulky substituent-mediated oxidative demethylation one.

Aromatase inhibitory activity of 1,4-naphthoquinone derivatives and QSAR study

A series of 2-amino(chloro)-3-chloro-1,4-naphthoquinone derivatives (1-11) were investigated for their aromatase inhibitory activities. 1,4-Naphthoquinones 1 and 4 were found to be the most potent compounds affording IC₅₀ values 5.2 times lower than the reference drug, ketoconazole. A quantitative structure-activity relationship (QSAR) model provided good predictive performance (R²_CV = 0.9783 and RMSE_CV = 0.0748) and indicated mass (Mor04m and H8m), electronegativity (Mor08e), van der Waals volume (G1v) and structural information content index (SIC2) descriptors as key descriptors governing the activity. To investigate the effects of structural modifications on aromatase inhibitory activity, the model was employed to predict the activities of an additional set of 39 structurally modified compounds constructed in silico. The prediction suggested that the 2,3-disubstitution of 1,4-naphthoquinone ring with halogen atoms (i.e., Br, I and F) is the most effective modification for potent activity (1a, 1b and 1c). Importantly, compound 1b was predicted to be more potent than its parent compound 1 (11.90-fold) and the reference drug, letrozole (1.03-fold). The study suggests the 1,4-naphthoquinone derivatives as promising compounds to be further developed as a novel class of aromatase inhibitors.

Synthesis and biological evaluation of naphthoquinone-coumarin conjugates as topoisomerase II inhibitors

Based on previous Topoisomerase II docking studies of naphthoquinone derivatives, a series of naphthoquinone-coumarin conjugates was synthesized through a multicomponent reaction from aromatic aldehydes, 4-hydroxycoumarin and 2-hydroxynaphthoquinone. The hybrid structures were evaluated against the α isoform of human topoisomerase II (hTopoIIα), Escherichia coli DNA Gyrase and E. coli Topoisomerase I. All tested compounds inhibited the hTopoIIα-mediated relaxation of negatively supercoiled circular DNA in the low micromolar range. This inhibition was specific since neither DNA Gyrase nor Topoisomerase I were affected. Cleavage assays pointed out that naphthoquinone-coumarins act by catalytically inhibiting hTopoIIα. ATPase assays and molecular docking studies further pointed out that the mode of action is related to the hTopoIIα ATP-binding site.

Naphthazarin enhances ionizing radiation-induced cell cycle arrest and apoptosis in human breast cancer cells

Naphthazarin (Naph, DHNQ, 5,8-dihydroxy-l,4-naphthoquinone) is one of the naturally available 1,4-naphthoquinone derivatives that are well-known for their anti-inflammatory, antioxidant, antibacterial and antitumor cytotoxic effects in cancer cells. Herein, we investigated whether Naph has effects on cell cycle arrest and apoptosis in MCF-7 human breast cancer cells exposed to ionizing radiation (IR). Naph reduced the MCF-7 cell viability in a dose-dependent manner. We also found that Naph and/or IR increased the p53-dependent p21 (CIP/WAF1) promoter activity. Noteworthy, our ChIP assay results showed that Naph and IR combined treatment activated the p21 promoter via inhibition of binding of multi-domain proteins, DNMT1, UHRF1 and HDAC1. Apoptosis and cell cycle analyses demonstrated that Naph and IR combined treatment induced cell cycle arrest and apoptosis in MCF-7 cells. Herein, we showed that Naph treatment enhances IR-induced cell cycle arrest and death in MCF-7 human breast cancer cells through the p53-dependent p21 activation mechanism. These results suggest that Naph might sensitize breast cancer cells to radiotherapy by enhancing the p53-p21 mechanism activity.

Understanding cancer and the anticancer activities of naphthoquinones – a review

Naphthoquinone moieties are present in drugs such as doxorubicin which are used clinically to treat solid cancers.

l-Proline catalyzed three-component synthesis of para-naphthoquinone–4-aza-podophyllotoxin hybrids as potent antitumor agents

A series of novelpara-naphthoquinone embodied 4-aza-podophyllotoxin hybrids were synthesized and some of the compounds exhibited excellent antitumor activities.

Cytotoxicity of synthesized 1,4-naphthoquinone analogues on selected human cancer cell lines

In an effort to establish new candidates with enhanced anticancer activity of 5-hydroxy-7-methyl-1,4-naphthoquinone scaffold (7-methyljuglone) previously isolated from the root extract of Euclea natalensis, a series of 7-methyljuglone derivatives have been synthesized and assessed for cytotoxicity on selected human cancer lines. These compounds were screened in vitro for anticancer activity on MCF-7, HeLa, SNO and DU145 human cancer cell lines by MTT assay. Most of them exhibited significant toxicity on cancer cell lines with lower IC50 values. The most potent derivative (19) exhibited the toxicity on HeLa and DU145 cell lines with IC50 value of 5.3 and 6.8μM followed by compound (5) with IC50 value of 10.1 and 9.3μM, respectively. Structure-activity relationship reveals that the fluoro substituents at position C-8 while hydroxyl substituents at C-2 and C-5 positions played an important role in toxicity.

6-(1-Oxobutyl)-5,8-dimethoxy-1,4-naphthoquinone inhibits lewis lung cancer by antiangiogenesis and apoptosis

Lung cancer is a leading cause of cancer mortality worldwide. Novel and nontoxic agents targeting angiogenesis and tumor cell proliferation and survival are desirable for lung cancer chemoprevention and treatment. Previously we have reported that 6-(1-oxobutyl)-5,8-dimethoxy-1,4-naphthoquinone (OXO) exhibits anti-tumor activity against S-180 sarcoma in vitro and in vivo. Here we studied the anti-angiogenic and apoptogenic attributes of OXO in vitro and in vivo targeting lung cancer. In human umbilical vein endothelial cells (HUVECs), we show that OXO more potently inhibited VEGF-stimulated than basic bFGF-stimulated HUVEC proliferation and capillary differentiation. In Lewis lung carcinoma (LLC) cells, OXO not only induces S-phase arrest and mitochondria/caspase-9 pathway mediated apoptosis, but also effectively down-regulated the hypoxia-induced expression of HIF-1alpha and VEGF at mRNA and protein levels in LLC and decreased VEGF secretion into conditioned culture media. OXO significantly reduced in vivo functional angiogenesis in the mouse Matrigel plug assay. Furthermore, OXO potently inhibited the growth of LLC cells inoculated on the flank of syngenic mice at dosages that did not affect their body weight. The in vivo anti-cancer effect was associated with decreased HIF-1alpha and VEGF expression, decreased microvessel density as well as a reduction of tumor cell proliferation and increased tumor cell apoptosis. Taken together, these results demonstrate that OXO exerts anti-cancer activity through anti-angiogenesis and tumor cell cycle arrest and apoptosis. These findings warrant additional studies of OXO as a novel agent for the chemoprevention and treatment of lung cancer.

MAPK regulation and caspase activation are required in DMNQ S-52 induced apoptosis in Lewis lung carcinoma cells

6-(1-Hydroxyimino-4-methylpentyl)5,8-dimethyoxy 1,4-naphthoquinone S-52 (DMNQ S-52) was reported to have cytotoxic activity against L1210 leukemia cells. In the present study, we investigated the apoptotic mechanism of DMNQ S-52 in vitro and in vivo in murine solid cancer cells. DMNQ S-52 exerted cytotoxicity against Lewis lung carcinoma (LLC) cells (IC50=12.3 microM). DMNQ S-52 increased Annexin V positive cell population in a concentration-dependent manner. DMNQ S-52 also induced apoptosis through caspase-mediated pathway, including activation of caspase-3, cleavage of Poly(ADP-ribose) polymerase (PARP) and decreased expression of Bcl-2 in LLC cells in a time and concentration-dependent fashion. DMNQ S-52 activated the phosphorylation of c-Jun N-terminal kinase (JNK) and p38 as well as abrogated the expression of extracellular signal-regulated kinase (ERK) in a time-dependent manner at 10 microM. Similarly, cell proliferation inhibition by DMNQ S-52 was masked by caspase inhibitor Z-Asp-Glu-Val-Asp-fluoromethylketone (Z-VAD-FMK), JNK inhibitor SP600125 and p38 inhibitor SB203580, but not by MEK inhibitor U0126. Furthermore, i.p. administration of DMNQ S-52 at 5 mg/kg resulted in a potent inhibition of the growth of LLC cells implanted on the right flank of C57BL/6 mice compared to untreated control. Immunohistochemical analysis revealed the decreased tumor cell proliferation and increased tumor cell apoptosis in DMNQ S-52 treated tumor sections using terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) and proliferation cell nuclear antigen (PCNA). Taken together, these findings demonstrate that DMNQ S-52 may exhibit anti-tumor activity by inducing apoptosis via caspases and mitogen activated protein (MAP) kinase-dependent pathways.

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 (0.01-1 microM) and MetNap (1-10 microM) 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.

Understanding topoisomerase I and II in terms of QSAR

A variety of antitumor agents currently used in chemotherapy or evaluated in clinical trials are known to inhibit DNA topoisomerase I or II. We have developed sixteen quantitative structure-activity relationships (QSAR) for different sets of compounds that are camptothecin analogs, 1,4-naphthoquinones, unsaturated acids, benzimidazoles, quinolones, and miscellaneous fused heterocycles to understand chemical-biological interactions governing their inhibitory activities toward topoisomerase I and II.

Elucidation of structure–activity relationships for 2- or 6-substituted-5,8-dimethoxy-1,4-naphthoquinones

1,4-Naphthoquinones have already been recognized to possess a wide range of biological activities. We have developed quantitative structure activity relationships (QSAR) for different series of 2- or 6-substituted-5,8-dimethoxy-1,4-naphthoquinones to understand the chemical-biological interaction governing antiproliferative/cytotoxic activities against L1210 cells. QSAR results have shown that these activities of 2- or 6-substituted-5,8-dimethoxy-1,4-naphthoquinones depend largely on their hydrophobicity.

Antitumor activities of a newly synthesized shikonin derivative, 2-hyim-DMNQ-S-33

2- or 6-(1-hydroxyiminoalkyl)-5,8-dimethoxy-1, 4-naphthoquinone(2- or 6-hyim-DMNQ) derived from the roots of Lithospermum erythrorhizon was synthesized for the evaluation of antitumor activities. Among those derivatives, 2-hyim-DMNQ-S33 was found to be a potent anticancer agent. This compound suppressed the proliferation of Radiation Induced Fibrosarcoma (RIF) cells in a dose-dependent manner. 2-hyim-DMNQ-S33 significantly prolonged the survival time by 239% as compared with Sarcoma 180 tumor-bearing control mice in vivo. We found that the compound significantly suppressed phosphorylation of extracellular signal-regulated kinase (pERK) and activated c-jun-N-terminal kinase (JNK) and protein kinase C (PKC)-alpha following 4 h-treatment. These findings indicate that 2-hyim-DMSQ-S33 exerts antitumor activities by regulating pERK, JNK and PKC-alpha.

Naphthazarin derivatives (VIII): Synthesis, inhibitory effect on DNA topoisomerase-I, and antiproliferative activity of 6-(1-acyloxyalkyl)-5,8-dimethoxy-1,4-naphthoquinones

6-(1-Acyloxyalkyl)-5,8-dimethoxy-1,4-naphthoquinone (DMNQ; 5,8-dimethoxy-1,4-naphthoquinone) derivatives were synthesized and examined for their inhibitory effect on DNA topoisomerase-I (Topo I) and their antiproliferative activity against L1210 cells. The Topo-I inhibitory effect of 6-(1-hydroxyalkyl)-DMNQ derivatives was found to be dependent on the size of the alkyl chains, suggesting that lipophilicity might be one important factor influencing the inhibitory effect. It was found that acylation of 6-(1-hydroxyalkyl)-DMNQ derivatives possessing alkyl chains of C2-C5 enhanced both bioactivities, suggesting that an increase of electrophilicity in the quinoid moiety makes the electrophilic arylation of bionucleophiles more favorable. It is noteworthy that 6-(1-heptanoyloxyethyl)-DMNQ exhibited both the most potent Topo I inhibitory activity (IC50, 11.5 microM) and the greatest antiproliferative activity (ED50, 0.05 microM) upon L1210 cells.

Naphthazarin derivatives (VII): antitumor action against ICR mice bearing ascitic S-180 cells

Various analogues of 5,8-dimethoxy-1,4-naphthoquinone (DMNQ) such as 2- or 6-(1-hydroxyiminoalkyl)-DMNQs were prepared and evaluated for the antitumor action. (1-Hydroxyiminoalkyl)-DMNQ derivatives expressed greater antitumor action than (1-hydroxyalkyl)- or acyl-DMNQ derivatives. Moreover, 6-(1-hydroxyiminoalkyl)-DMNQ derivatives expressed higher antitumor action than 2-sudstituted ones, suggestive of a steric effect. Some of 6-(1-propyloxyalkyl)-DMNQ derivatives with an alkyl group of butyl to octyl moiety showed T/C values of >400%.

Naphthazarin derivatives (VII): antitumor action against ICR mice bearing ascitic S-180 cells

Various analogues of 5,8-dimethoxy-1,4-naphthoquinone (DMNQ) such as 2- or 6-(1-hydroxyiminoalkyl)-DMNQs were prepared and evaluated for the antitumor action. (1-Hydroxyiminoalkyl)-DMNQ derivatives expressed greater antitumor action than (1-hydroxyalkyl)- or acyl-DMNQ derivatives. Moreover, 6-(1-hydroxyiminoalkyl)-DMNQ derivatives expressed higher antitumor action than 2-sudstituted ones, suggestive of a steric effect. Some of 6-(1-propyloxyalkyl)-DMNQ derivatives with an alkyl group of butyl to octyl moiety showed T/C values of >400%

(E) -6-(1-alkyloxyiminoalkyl)-5,8-dimethoxy-1,4-naphthoquinones: synthesis, cytotoxic activity and antitumor activity

All of 13 (E)-6-(1-alkyloxyiminomethyl)-5,8-dimethoxy-1,4-naphthoquinone derivatives synthesized showed high ED50 values, ranging from 0.1 to 0.3 microg/mL against L1210 cells. However, they were inactive on A549 cells. Nine compounds exhibited higher T/C (%) values (318-388%) than Adriamycin (T/C, 315%).

2-(1 -hydroxyiminoalkyl)-1 ,4-dimethoxy-9,10-anthraquinones: synthesis and evaluation of cytotoxicity

A series of 2-(1-hydroxyiminoalkyl)-1,4-dimethoxy-9,10-anthraquinones (oximes) was synthesized and evaluated for cytotoxicity against L1210 cells and A549 cells. These oximes showed a greater cytotoxic activity compared to those of 2-(1-hydroxyalkyl)-1,4-dimethoxy-9,10-anthraquinones as the hydroxyalkyl bioisosteres. The enhanced cytotoxicity assumed to be due to the improved water solubility of the hydroxyimino group. Moreover, it was found that the cytotoxicity of the oximes decreased with elongation of alkyl groups at the side chain. All of the synthesized compounds showed higher cytotoxicity against L1210 cells than A549 cells.

Synthesis and evaluation of the antitumor activity of 2-substituted 1,4-dihydroxy-9,10-anthraquinones

2-(1-Hydroxyiminoalkyl)-1,4-dimethoxy-9,10-anthraquinones were demethylated to produce 2-(1-hydroxyiminoalkyl)-1,4-dihydroxy-9,10-anthraquinones (1,4-dihydroxy-9,10-anthraquinone, DHAQ), oxime hydroxyl groups were in turn acylated to give the corresponding 2-(1-acyloxyiminoalkyl)-DHAQ derivatives. The anti-proliferative activity of 2-(1-hydroxyiminoalkyl)-DHAQ derivatives was found to be dependent on the size of an alkyl chain. Thus, DHAQ analogues with alkyl chains longer than heptyl had negligible anti-proliferative activity, whilst those compounds possessing shorter chains demonstrated moderate anti-proliferative activity (ED50, 2.73-19.21 microM). However, the antitumor activity as expressed by T/C values did not correlate with the anti-proliferative activity; 2-(1-hydroxyiminononyl)-DHAQ with an ED50 value of more than 20 microM exhibited potent antitumor activity (T/C, 166%). Only four of the 2-(1-hydroxyiminoalkyl)-DHAQ analogues showed good antitumor activity (T/C, > 150%); 2-(1-hydroxyiminobutyl)-DHAQ (T/C, 163%), 2-(1-hydroxyiminopentyl)-DHAQ (T/C, 180%) and 2-(1-hydroxyiminononyl)-DHAQ (T/C, 166%). Acylation of the hydroxyl group of these oximes enhanced the anti-proliferative activity and antitumor effects; 2-(1-propanoyloxyiminopropyl)-DHAQ (ED50, 4.41 microM; T/C, 221%) vs. 2-(1-hydroxyiminopropyl)-DHAQ (ED50, 14.64 microM; T/C, 100%) and 2-(1-propanoyloxyiminobutyl)-DHAQ (ED50, 2.65 microM; T/C, 202%) vs. 2-(1-hydroxyiminobutyl)-DHAQ (ED50, 16.43 microM; T/C, 163%).