Synthesis, characterization and computational investigation of the phosphatase activity of a dinuclear Zinc(II) complex containing a new heptadentate asymmetric ligand.

We report the synthesis of a new asymmetric heptadentate ligand based on the 1,3-diaminopropan-2-ol backbone. The ligand 3-[[3-(bis-pyridin-2-ylmethyl-amino)-2-hydroxy-propyl]-(2-carbamoyl-ethyl)-amino]-propionamide (HL1) contains two amide and two pyridine groups attached to the 1,3-diaminopropan-2-ol core. Reaction between HL1 and Zn(ClO4)2.6H2O resulted in the formation of the dinuclear [Zn2(L1)(µ-OAc)](ClO4)2 complex, characterized by single crystal X-ray diffraction, 1H, 13C and 15N NMR, ESI-(+)-MS, CHN elemental analysis as well as infrared spectroscopy. The phosphatase activity of the complex was studied in the pH range 6-11 employing pyridinium bis(2,4-dinitrophenyl)phosphate (py(BDNPP)) as substrate. The complex exhibited activity dependent on the pH, presenting an asymmetric bell shape profile with the highest activity at pH 9; at high pH ligand exchange is rate-limiting. The hydrolysis of BDNPP- at pH 9 displayed behavior characteristic of Michaelis-Menten kinetics, with kcat = 5.06 × 10-3 min-1 and Km = 5.7 ± 1.0 mM. DFT calculations map out plausible reaction pathways and identify a terminal, Zn(II)-bound hydroxide as likely nucleophile.

Preparation, cytotoxic activity and DNA interaction studies of new platinum(II) complexes with 1,10-phenanthroline and 5-alkyl-1,3,4-oxadiazol-2(3H)-thione derivatives.

This work describes the synthesis, characterization and in vitro anticancer activity of two platinum(II) complexes of the type [Pt(L1)2(1,10-phen)] 1 and [Pt(L2)2(1,10-phen)] 2, where L1 = 5-heptyl-1,3,4-oxadiazole-2-(3H)-thione, L2 = 5-nonyl-1,3,4-oxadiazole-2-(3H)-thione and 1,10-phen = 1,10-phenanthroline. As to the structure of these complexes, the X-ray structural analysis of 1 indicates that the geometry around the platinum(II) ion is distorted square-planar, where two 5-alkyl-1,3,4-oxadiazol-2-thione derivatives coordinate a platinum(II) ion through the sulfur atom. A chelating bidentate phenanthroline molecule completes the coordination sphere. We tested these complexes in two breast cancer cell lines, namely, MCF-7 (a hormone responsive cancer cell) and MDA-MB-231 (triple negative breast cancer cell). In both cells, the most lipophilic platinum compound, complex 2, was more active than cisplatin, one of the most widely used anticancer drugs nowadays. DNA binding studies indicated that such complexes are able to bind to ct-DNA with Kb values of 104 M-1. According to data from dichroism circular and fluorescence spectroscopy, these complexes appear to bind to the DNA in a non-intercalative, probably via minor groove. Molecular docking followed by semiempirical simulations indicated that these complexes showed favorable interactions with the minor groove of the double helix of ct-DNA in an A-T rich region. Thereafter, flow cytometry analysis showed that complex 2 induced apoptosis and necrosis in MCF-7 cells.

Synthesis and in vitro and in silico studies of 1H- and 2H-1,2,3-triazoles as antichagasic agents.

1,2,3-triazole heterocycles stand out in medicinal chemistry for having great structural diversity and bioactivities. In this study, two series of triazoles were synthesized. One was obtained by the 1,3-dipolar cycloaddition reaction between ethyl cyanoacetate and several phenyl azides forming 1H-1,2,3-triazoles and the other by rearrangement of Dimroth forming and 2H-1,2,3-triazoles. Both series were shown to be active against the epimastigote form of Trypanosoma cruzi. The 1,2,3-triazoles 16d (S.I. between 100 and 200), 17d and 16f (S.I. > 200) were the most active compounds and capable of breaking the plasma membrane of trypomastigotes acting on CYP51 and inhibiting ergosterol synthesis. Candidate 16d exhibited the best and most favorable profile when interacting with CYP51.

Semisynthesis of Dolabellane Diterpenes: Oxygenated Analogues with Increased Activity against Zika and Chikungunya Viruses.

Brown algae and soft corals represent the main marine sources of dolabellane diterpenes. The antiviral activity of dolabellanes has been studied for those isolated from algae, whereas dolabellanes isolated from soft corals have been barely studied. In this work, a collection of dolabellane diterpenes consisting of five natural and 21 semisynthetic derivatives was constructed, and their antiviral activities against Zika (ZIKV) and Chikungunya (CHIKV) viruses were tested. Dolabellatrienone (1) and (1R,7R,8R,11S)-7,8-epoxy-13-keto-dolabella-3,12(18)-diene (2), isolated from Eunicea genus soft corals, were employed to obtain 21 dolabellane and dolastane diterpenes by reactions such as allylic oxidations, reductions, acid-catalyzed epoxide ring opening, and acetylations. All of the compounds were identified by a combination of one- and two-dimensional NMR, mass spectrometry, and X-ray diffraction experiments. The cytotoxicites against Vero cells and the antiviral activities against ZIKV and CHIKV was tested to calculate the half-maximal effective concentration (EC50) and selectivity indexes (SIs). In general, the addition of oxygen-containing functional groups improved the bioactivity of dolabellane and dolastane diterpenes against ZIKV and CHIKV replication. Compound 9 showed an EC50 = 0.92 ± 0.08 µM and SI = 820 against ZIKV.

Effect of the hydroxamate group in the antitumoral activity and toxicity toward normal cells of new copper(II) complexes.

The synthesis, physico-chemical characterization and cytotoxicity of four copper(II) coordination complexes, i.e. [Cu(HBPA)Cl2] (1), [Cu(BHA)2] (2), [Cu(HBPA)(BHA)Cl] CH3OH (3) and [Cu(HBPA)2]Cl2·4H2O (4), are reported. HBPA is the tridentate ligand N-(2-hydroxybenzyl)-N-(2-pyridylmethyl)amine and HBHA is the benzohydroxamic acid. The reaction between the HBHA and CuCl2.2H2O has resulted in the new complex (2) and the reaction between complex (1) and HBHA has resulted in the new complex (3). X-ray diffraction studies for complex (3) indicated the effective coordination of HBHA as BHA-. Their cytotoxicity was evaluated against three human tumoral cell lines (Colo-205, NCI-H460 and U937) and PBMC (peripheral blood mononuclear cells), using the MTT cytotoxic assay. The results toward PBMC reveal that the new copper(II) complex (2) presents lower toxicity toward normal cells. Furthermore, complex (2) presents IC50 values lower than cisplatin toward NCI-H460 and the best selectivity index obtained towards NCI-H460 (SI = 2.2) and U937 cell lines (SI = 2.0), as a result of the presence of two molecules of HBHA in its structure. Complex (3) presents IC50 values lower than cisplatin toward NCI-H460, Colo-205 and comparable to cisplatin toward U937. The evaluation of the cell death type promoted by complexes (2) and (4) was investigated toward NCI-H460 revealing better results than the standard drug cisplatin, according to the Annexin V and propidium iodide (PI) labeling experiment. Based on the studies here performed, HBHA seems to be related to lower toxicity toward PBMC and HBPA is improving directly the cytotoxity.

Chemistry and anti-herpes simplex virus type 1 evaluation of 4-substituted-1H-1,2,3-triazole-nitroxyl-linked hybrids.

HSV disease is distributed worldwide. Anti-herpesvirus drugs are a problem in clinical settings, particularly in immunocompromised individuals undergoing herpes simplex virus type 1 infection. In this work, 4-substituted-1,2,3-1H-1,2,3-triazole linked nitroxyl radical derived from TEMPOL were synthesized, and their ability to inhibit the in vitro replication of HSV-1 was evaluated. The nitroxide derivatives were characterized by infrared spectroscopy and elemental analysis, and three of them had their crystal structures determined by single-crystal X-ray diffraction. Four hybrid molecules showed important anti-HSV-1 activity with IC50 values ranged from 0.80 to 1.32 µM. In particular, one of the nitroxide derivatives was more active than Acyclovir (IC50 = 0.99 µM). All compounds tested were more selective inhibitors than the reference antiviral drug. Among them, two compounds were 4.5 (IC50 0.80 µM; selectivity index CC50/IC50 3886) and 7.7 times (IC50 1.10 µM; selectivity index CC50/IC50 6698) more selective than acyclovir (IC50 0.99 µM; selectivity index CC50/IC50: 869). These nitroxide derivatives may be elected as leading compounds due to their antiherpetic activities and good selectivity.

Crystal structure of 1-anilino-5-methyl-1H-1,2,3-triazole-4-carb-oxy-lic acid monohydrate.

In the mol-ecular structure of the title compound, C10H10N4O2·H2O, the angle between the triazole and arene rings is 87.39 (5)°. The water of crystallization connects the mol-ecules in the crystal packing. The crystal structure exhibits N-H⋯O, O-H⋯O and O-H⋯N inter-actions, resulting in the formation of a three-dimensional framework. The inter-molecular inter-actions were identified and qu-anti-fied using Hirshfeld surface analysis.

Modulating the antitumoral activity by the design of new platinum(II) compounds: Synthesis, characterization, DFT, ultrastructure and mechanistic studies.

The synthesis, physico-chemical characterization, Density functional theory (DFT) calculation and cytotoxicity against five human tumoral cell lines (THP-1, U937, Molt-4, Colo205 and H460) of four new platinum(II) coordination compounds are reported, i.e. [Pt(HL1)Cl]·H2O (1), [Pt(HL2)Cl]·H2O (2), [Pt(HL3)Cl]·H2O (3) and [Pt(HL4)Cl]·H2O (4). The ligands contain N2O donor sets. Furthermore, H2L3 and H2L4 present α and ß-naphthyl groups respectively, which are absent in HL1 and H2L2. X-ray diffraction studies were performed for complex (3), indicating the formation of a mononuclear platinum(II) complex. Complexes (3) and (4), which contain α and ß-naphthyl groups respectively, have presented lower IC50 (inhibitory concentration) values than those exhibited by complexes (1) and (2). The mechanism of cell death promoted by complexes (3) and (4) was investigated, suggesting that, toward U937 cell line, the α isomer promotes death by apoptosis and the ß isomer by necrosis. Transmission and scanning electron microscopy investigations are in agreement with the loss of mitochondrial membrane potential (ΔΨm) observed by JC-1 mitochondrial potential sensor and indicate that the activity of complex (3) against U937 cell line is mediated by an apoptotic mechanism associated with mitochondrial dysfunction. A quantification of caspases 3, 6, 8 and 9 indicated that both the intrinsic and extrinsic pathways are involved in the apoptotic stimuli. Based on DFT calculations all the Pt(II) complexes present the same coordination environment for the metal centre, indicating that the higher cytotoxic activities exhibited by complexes (3) and (4) are related to the presence of the α and ß-naphthyl groups in the ligand structure.

Screening of acetylcholinesterase inhibitors in marine organisms from the Caribbean Sea.

The acetylcholinesterase inhibitory activity of 89 organic extracts from marine organisms was evaluated through a TLC bioautography methodology. Extracts from soft corals (Eunicea and Plexaura) were the most active compared with extracts from sponges. The bioguided chemical study of the most active extract, obtained from Pseudoplexaura porosa, led to the isolation of a diterpene with spectroscopic properties consistent to those published to the cembrane Steylolide. However, further analysis by X-ray diffraction indicated that the compound was the 14-acetoxycrassine (1), correcting the structure reported to the Styelolide. Additionally, the acetylcholinesterase inhibitory activity of fourteen cembranoids (2-15) isolated from soft corals Eunicea knighti and Pseudoplexaura flagellosa was evaluated. Cembranoids 2, 3 and 4 were the most active compounds in the TLC bioassay. Then, the most promising cembranoids, 14-acetoxycrassine (1) and asperdiol (2), were tested quantitatively and they exhibited IC50 values of 1.40 ± 0.113 and 0.358 ± 0.130 µM, respectively.

A New Mixed-Valence Mn(II)Mn(III) Compound With Catalase and Superoxide Dismutase Activities.

The synthesis, X-ray molecular structure, physico-chemical characterization and dual antioxidant activity (catalase and superoxide dismutase) of a new polymeric mixed valence Mn(III)Mn(II) complex, containing the ligand H2BPClNOL (N-(2-hydroxybenzyl)-N-(2-pyridylmethyl)[(3-chloro)(2-hydroxy)] propylamine) is described. The monomeric unit is composed of a dinuclear Mn(II)Mn(III) moiety, [Mn(III)(µ-HBPClNOL)(µ-BPClNOL)Mn(II)(Cl)](ClO4)·2H2O, 1, in which the Mn ions are connected by two different bridging groups provided by two molecules of the ligand H2BPClNOL, a phenoxide and an alkoxide group. In the solid state, this mixed valence dinuclear unit is connected to its neighbors through chloro bridges. Magnetic measurements indicated the presence of ferromagnetic [J = +0.076(13) cm-1] and antiferromagnetic [J = -5.224(13) cm-1] interactions. The compound promotes O 2 • - dismutation in aqueous solution (IC50 = 0.370 µmol dm-3, k cat = 3.6x106 M-1 s-1). EPR studies revealed that a high-valent Mn(III)-O-Mn(IV) species is involved in the superoxide dismutation catalytic cycle. Complex 1 shows catalase activity only in the presence of a base, e.g., piperazine or triethylamine. Kinetic studies were carried out in the presence of piperazine and employing two different methods, resulting in k cat values of 0.58 ± 0.03 s-1 (detection of O2 production employing a Clark electrode) and 2.59 ± 0.12 s-1 (H2O2 consuption recorded via UV-Vis). EPR and ESI-(+)-MS studies indicate that piperazine induces the oxidation of 1, resulting in the formation of the catalytically active Mn(III)-O-Mn(IV) species.

Vibrational spectroscopic and Hirshfeld surface analysis of carvedilol crystal forms.

The drug carvedilol, used to treat cardiovascular conditions, is known to exist in distinct crystalline forms. Polymorphs II and III and the hydrate are characterized by variations in their molecular packing and conformation. This study deals with the spectroscopic (supported by quantum chemistry calculations) characterization of carvedilol structures. Band assignments were performed considering the isolated molecules and periodic calculations. We discuss the correlation between the vibrational modes and the intermolecular forces in the crystalline structures. Towards a better understanding of the intermolecular interactions, Hirshfeld surface was used. Besides band shifts related to stretching vibrations of N-H and O-H groups, differences between other modes have shown the possibility of using infrared spectroscopy to distinguish the crystal forms; technique routinely used in quality control of pharmaceutics. According to the spectroscopic analysis, the N-H groups participate in stronger bonds in the polymorph III, which contributes to its greater stability. With Hirshfeld surface we concluded that the bond with the nitrogen of the aliphatic chain participating as hydrogen acceptor in polymorph II is responsible for the pointy peaks in the fingerprint plot. This can explain why polymorph II shows lower dissolution in acid medium, as described in a previous work of our group.

Synthesis and Evaluation of the Anticancer and Trypanocidal Activities of Boronic Tyrphostins.

Molecules containing an (cyanovinyl)arene moiety are known as tyrphostins because of their ability to inhibit proteins from the tyrosine kinase family, an interesting target for the development of anticancer and trypanocidal drugs. In the present work, (E)-(cyanovinyl)benzeneboronic acids were synthesized by Knoevenagel condensations without the use of any catalysts in water through a simple protocol that completely avoided the use of organic solvents in the synthesis and workup process. The in vitro anticancer and trypanocidal activities of the synthesized boronic acids were also evaluated, and it was discovered that the introduction of the boronic acid functionality improved the activity of the boronic tyrphostins. In silico target fishing with the use of a chemogenomic approach suggested that tyrosine-phosphorylation-regulated kinase 1a (DYRK1A) was a potential target for some of the designed compounds.

Synthesis and evaluation of copper(II) complexes with isoniazid-derived hydrazones as anticancer and antitubercular agents.

In this study, the N,N,O metal chelator 2-pyridinecarboxaldehydeisonicotinoyl hydrazone (HPCIH, 1) and its derivatives 2-acetylpyridine-(HAPIH 2), 2-pyridineformamide-(HPAmIH, 3) and pyrazineformamide-(HPzAmIH, 4) were employed in the synthesis of four copper(II) complexes, [Cu(HPCIH)Cl2]·0.4H2O (5), [Cu(HAPIH)Cl2]·1.25H2O (6), [Cu(HPAmIH)Cl2]·H2O (7) and [Cu(HPzAmIH)Cl2]·1.25H2O (8). The compounds were assayed for their action toward Mycobacterium tuberculosis H37Rv ATCC 27294 strain and the human tumor cell lines OVCAR-8 (ovarian cancer), SF-295 (glioblastoma multiforme) and HCT-116 (colon adenocarcinoma). All copper(II) complexes were more effective in reducing growth of HCT-116 and SF-295 cells than the respective free hydrazones at 5 µg/mL, whereas only complex 7 was more cytotoxic toward OVCAR-8 lines than its ligand HPAmIH. 6 proved to be cytotoxic at submicromolar doses, whose IC50 values (0.39-0.86 µM) are similar to those ones found for doxorubicin (0.23-0.43 µM). Complexes 5 and 6 displayed high activity against M. tuberculosis (MIC = 0.85 and 1.58 µM, respectively), as compared with isoniazid (MIC = 2.27 µM), which suggests the compounds are attractive candidates as antitubercular drugs.

In vitro and in vivo studies of the antineoplastic activity of copper (II) compounds against human leukemia THP-1 and murine melanoma B16-F10 cell lines.

We investigated the antineoplastic activities of a previously reported copper (II) coordination compound, [Cu(BMPA)Cl2]CH3OH (1), and a new compound, [Cu(HBPA)Cl2]H2O (2), where BMPA is bis(pyridin-2-ylmethyl)amine and HBPA is (2-hydroxybenzyl)(2-pyridylmethyl)amine, using various cellular models of human leukemia (THP-1, U937, HL60, Molt-4, JURKAT) and human colon cancer (COLO 205), as well as a murine highly metastatic melanoma (B16-F10) cell line. Compound (2) was characterized using several physical and chemical techniques, including X-ray diffraction studies. The IC50 values of the copper coordination complexes in the human leukemia cell lines ranged from 87.63 ± 1.02 to ≥400 µM at high cell concentrations and from 19.17 ± 1.06 to 97.67 ± 1.23 µM at low cell concentrations. Both compounds induced cell death, which was determined by cell cycle analyses and phosphatidylserine exposure studies. THP-1 cells released cytochrome c to the cytoplasm 12 h after treatment with 400 µM of compound (2). To evaluate the apoptosis pathway induced by compound (2), we measured the activities of initiator caspases 8 and 9 and executioner caspases 3 and 6. The results were suggestive of the activation of both intrinsic and extrinsic apoptosis pathways. To investigate the activities of the compounds in vivo, we selected two sensitive cell lines from leukemia (THP-1) and solid tumor (B16-F10) lineages. BALB/c nude bearing THP-1 tumors treated with 12 mg·kg(-1) of compound (2) showed a 92.4% inhibition of tumor growth compared with the control group.

Synthesis and antimalarial activity of quinones and structurally-related oxirane derivatives.

A series of eighteen quinones and structurally-related oxiranes were synthesized and evaluated for in vitro inhibitory activity against the chloroquine-sensitive 3D7 clone of the human malaria parasite Plasmodium falciparum. 2-amino and 2-allyloxynaphthoquinones exhibited important antiplasmodial activity (median inhibitory concentrations (IC50) < 10 µM). Oxiranes 6 and 25, prepared respectively by reaction of α-lapachone and tetrachloro-p-quinone with diazomethane in a mixture of ether and ethanol, exhibited the highest antiplasmodial activity and low cytotoxicity against human fibroblasts (MCR-5 cell line). The active compounds could represent a good prototype for an antimalarial lead molecule.

Combining Nuclear Magnetic Resonance Spectroscopy and Density Functional Theory Calculations to Characterize Carvedilol Polymorphs.

The experiments of carvedilol form II, form III, and hydrate by (13)C and (15)N cross-polarization magic-angle spinning (CP MAS) are reported. The GIPAW (gauge-including projector-augmented wave) method from DFT (density functional theory) calculations was used to simulate (13)C and (15)N chemical shifts. A very good agreement was found for the comparison between the global results of experimental and calculated nuclear magnetic resonance (NMR) chemical shifts for carvedilol polymorphs. This work aims a comprehensive understanding of carvedilol crystalline forms employing solution and solid-state NMR as well as DFT calculations.

Induction of apoptosis in leukemia cell lines by new copper(II) complexes containing naphthyl groups via interaction with death receptors.

The synthesis, physico-chemical characterization and cytotoxicity of four new ligands and their respective copper(II) complexes toward two human leukemia cell lines (THP-1 and U937) are reported (i.e. [(HL1)Cu(µ-Cl)2Cu(HL1)]Cl2·H2O (1), [(H2L2)Cu(µ-Cl)2Cu(H2L2)]Cl2·5H2O (2), [(HL3)Cu(µ-Cl)2Cu(HL3)]Cl2·4H2O (3), [(H2L4)Cu(µ-Cl)2Cu(H2L4)]Cl2·6H2O (4)). Ligands HL1 and HL3 contain two pyridines, amine and alcohol moieties with a naphthyl pendant unit yielding a N3O coordination metal environment. Ligands H2L2 and H2L4 have pyridine, phenol, amine and alcohol groups with a naphthyl pendant unit providing a N2O2 coordination metal environment. These compounds are likely to be dinuclear in the solid state but form mononuclear species in solution. The complexes have an antiproliferative effect against both leukemia cell lines; complex (2) exhibits higher activity than cisplatin against U937 (8.20 vs 16.25µmoldm(-3)) and a comparable one against THP-1. These human neoplastic cells are also more susceptible than peripheral blood mononuclear cells (PBMCs) toward the tested compounds. Using C57BL/6 mice an LD50 of 55mgkg(-1) was determined for complex (2), suggesting that this compound is almost four times less toxic than cisplatin (LD50=14.5mgkg(-1)). The mechanism of cell death promoted by ligand H2L2 and by complexes (2) and (4) was investigated by a range of techniques demonstrating that the apoptosis signal triggered at least by complex (2) starts from an extrinsic pathway involving the activation of caspases 4 and 8. This signal is amplified by mitochondria with the concomitant release of cytochrome c and the activation of caspase 9.

A new and efficient procedure for the synthesis of hexahydropyrimidine-fused 1,4-naphthoquinones.

A new and efficient method for the synthesis of hexahydropyrimidine-fused 1,4-naphthoquinones in one step with high yields from the reaction of lawsone with 1,3,5-triazinanes was developed.

A study on the properties and reactivity of naphthoquinone-cobalt(III) prototypes for bioreductive prodrugs.

Our group has recently initiated a study on the development of new prototypes for bioreductive prodrugs, based on Co(III) complexes with the ligand 2,2'-bis(3-hydroxy-1,4-naphthoquinone), H2bhnq. The focus of this work is to investigate the dissociation of bhnq(-2) from the complex upon reduction, and the effects of pH, redox potential, oxygen concentration and nature of the auxiliary ligands on this reaction. The bhnq(2-) ligand is a "non-cytotoxic" agent that was chosen as a probe for the reactivity studies due to its suitable chromophoric properties, at the same time that it resembles more cytotoxic naphthoquinones relevant for cancer therapy. In this way, two Co(III) complexes [Co(bhnq)(L1)]BF4·H2O (1) and [Co(bhnq)(L2)]BF4·H2O (2) (L1=N,N'-bis(pyridin-2-ylmethyl)ethylenediamine and L2=N,N'-dimethyl-N,N'-bis(pyridin-2-ylmethyl)ethylenediamine) were synthesized and fully characterized. The gallium analogs [Ga(bhnq)(L1)]NO3·3H2O (3) and [Ga(bhnq)(L2)]NO3·3H2O (4) were also prepared for helping with the assignments of the redox properties of the cobalt complexes and the structure of 2. Cyclic voltammetry analysis revealed a pH-independent quasi-reversible Co(III)/Co(II) process at -0.22 and -0.08V vs NHE for 1 and 2, respectively. An O2-dependent dissociation of bhnq(2-) was observed for the reaction of 1 with ascorbic acid. For 2, the dissociation of bhnq(2-) was found to be independent on the concentration of O2 and faster than in 1, with little influence of the pH on both complexes. The difference in reactivity between 1 and 2 and their redox properties, among other factors, suggests that 1 undergoes redox cycling, pointed out as a key feature for a prodrug to achieve hypoxic selectivity.

Cobalt lawsone complexes: searching for new valence tautomers.

Bi-stable molecular systems presenting valence tautomerism are associated with the development of new functional materials, which can be used for applications in organic electric conductors, optoelectronic and molecular magnetic devices. The properties of these materials can be adjusted with slight chemical changes and can be induced by external stimuli. Typical examples of valence tautomer compounds are coordination complexes of Co and o-dioxolene ligands, notably quinone like ones. In the search for a new class of cobalt complexes presenting valence tautomerism we report herein the synthesis and characterization of five new coordination compounds of cobalt and 2-hydroxy-1,4-naphthoquinone (lawsone or shortly Law). Complexes [Co(Law)2(im)2]·C6H5CH3 (1), [Co(Law)2(py)2]·CH3OH (2), [Co(Law)2(phen)]·(C4H8O)2 (3), [Co(Law)2(2,2-bpy)]·C6H5CH3 (4) and [Co(Law)2(2,2-bpy)] (5) were synthesized and fully characterized by X-ray diffraction and EPR techniques in a wide range of temperatures and under illumination. Despite presenting similar molecular and geometry packing of the valence tautomer complexes of cobalt and o-dioxolenes, neither structural nor electronic evidence of valence tautomerism could be found in the Co and lawsone complexes.