Ferrocene‐modified thiopyrimidines: synthesis,enantiomeric resolution,antitumor activity

Ferrocenylalkyl thiopyrimidines ( 6a–d to 9a–d ) were prepared via the reaction of the α‐(hydroxy)alkyl ferrocenes, FcCHR(OH) ( 1a–d ; Fc = ferrocenyl; R = H, Me, Et, Ph), with 2‐thiopyrimidines ( 2 – 5 ) in acetone at room temperature in the presence of TFA, yielding 50–95%. The resulting enantiomers were resolved using HPLC on modified cellulose as chiral selector. The antitumor activities of S‐ferrocenylethyl 2‐thiopyrimidine ( 6b ) against two murine solid tumor models, carcinoma 755 (Ca755) and Lewis lung carcinoma (LLC) were evaluated in vivo. The strong antitumor effect of compound 6b on Ca755 and LLC was demonstrated. The index of tumor growth inhibition on Ca755 equaled 95% in comparison with control. Copyright © 2010 John Wiley & Sons, Ltd.     

Vapour pressures and sublimation enthalpies of thymine and cytosine

The vapour pressures of cytosine and thymine were measured using the torsion-effusion technique. The sublimation processes of cytosine and thymine were investigated over the temperature ranges 480–553 K and 420–503 K, respectively. The following pressure—temperature equations were derived by least-squares treatment of the vapour pressure data

The standard sublimation enthalpies were obtained by second-and third-law treatment of the experimental data and the values ΔH⁰₂₉₈ = 167 ± 10 kJ mole^?1 and ΔH⁰₂₉₈ = 138 ± 10 kJ mole^?1 were derived for cytosine and thymine, respectively. IR and Raman spectra were recorded in the gas phase in order to evaluate the thermodynamic functions of gaseous cytosine and thymine.     

1,8-Dimercuri-6-Phenyl-1H-Carbazole as a Monofacial Dinuclear Organometallic Nucleobase

A C-nucleoside with 6-phenyl-1H-carbazole as the base moiety has been synthesized and incorporated in the middle of an oligonucleotide. Mercuration of this modified residue at positions 1 and 8 gave the first example of an oligonucleotide featuring a monofacial dinuclear organometallic nucleobase. The dimercurated oligonucleotide formed stable duplexes with unmodified oligonucleotides placing either cytosine, guanine, or thymine opposite to the organometallic nucleobase. A highly stabilizing (ΔT_m=7.3 °C) Hg^II-mediated base pair was formed with thymine. According to DFT calculations performed at the PBE0DH level of theory, this base pair is most likely dinuclear, with the two Hg^II ions coordinated to O2 and O4 of the thymine base.     

Antitumor activity of carboplatin in the composition of a copolymer of lactic and glycolic acids

Polymer particles containing carboplatin (CPt) were developed by the inclusion of this antitumor agent in a copolymer of lactic and glycolic acids (PLGA-COOH 50/50). The polymer particles were found to have a spherical form with an average diameter not exceeding 200 nm, the ζ-potential is equal to–32.2±1 mV. The CPt-loaded polymer particles possess a cytotoxic activity against human small cell and non-small cell lung carcinoma (lines H69 and A549), as well as against mouse mammary adenocarcinoma (line Ca755). The results of the in vivo studies carried out on female mice of line C₅₇Bl/6 with inoculated mouse melanoma of line B16 showed increasing of lifespan of the animals and inhibition of tumor growth for groups treated with the polymer particles, as compared to the animals treated with the drug substance CPt.     

PHOTOCHEMISTRY OF 4-THIOURIDINE AND THYMINE

Abstract— When thymine is irradiated in aqueous solution with monochromatic 334-nm UV radiation in the presence of 4-thiouridine a photoproduct of thymine is formed, as shown by thin-layer chromatography and autoradiography. The quantum yield for the formation of thymine photoproduct (θ=0.017) is greater than that for cytosine photoproduct formation (θ= 0.0015). The identity of the photoproduct is not known: one possibility is the formation of an adduct between the sensitizer and the base yielding a pyrimidine-pyrimidone type of photoproduct.     

Complexes of pyrimidine DNA bases with thallium(I)

The stability constants of complexes of a thallium(I) ion with cytosine and thymine were determined in aqueous solution at 25°C and 0.1 mol dm⁻³ ionic media, using a combination of potentiometric and spectrophotometric techniques. Sodium perchlorate was used to maintain the ionic strength. The composition of the formed complexes was determined and it was shown that thallium(I) forms two mononuclear 1:1 species with cytosine of the type TIHL⁺ and TIL, and a mononuclear 1:1 complex species with thymine in the form TIHL, in the pH range of study (1–11), where L represents the fully dissociated ligand. The cumulative stability constants, β _xyz, of the complexes, [(thallium)_x(H)_y(ligand)_z], were calculated by a nonlinear fitting method and their distributions were presented as a function of-log[H⁺]. This text was submitted by the authors in English.     

Cytotoxic alkaloids and a flavan from the bulbs of Crinum asiaticum var. japonicum

A new pyrrolophenanthridone alkaloid, criasiaticidine A (1), was isolated from the bulbs of Crinum asiaticum var. japonicum, together with pratorimine (2), lycorine (3) and 4'-hydroxy-7-methoxyflavan (4). The structure of the new alkaloid was determined to be 4,5-etheno-9,10-dihydroxy-6-phenanthridone by spectroscopic means. The cytotoxicity of the isolated compounds 1-4 was evaluated in vitro against Meth-A (mouse sarcoma) and Lewis lung carcinoma (mouse lung carcinoma) tumor cell lines. Furthermore, 3 was examined for in vivo antitumor activity with LLC tumor cells.     

Gas-phase thermochemical properties of pyrimidine nucleobases

The gas-phase acidity and proton affinity of thymine, cytosine, and 1-methyl cytosine have been examined using both theoretical (B3LYP/6-31+G*) and experimental (bracketing, Cooks kinetic) methods. This paper represents a comprehensive examination of multiple acidic sites of thymine and cytosine and of the acidity and proton affinity of thymine, cytosine, and 1-methyl cytosine. Thymine exists as the most stable "canonical" tautomer in the gas phase, with a DeltaH(acid) of 335 +/- 4 kcal mol(-1) (DeltaG(acid) = 328 +/- 4 kcal mol(-1)) for the more acidic N1-H. The acidity of the less acidic N3-H site has not, heretofore, been measured; we bracket a DeltaH(acid) value of 346 +/- 3 kcal mol(-1) (DeltaG(acid) = 339 +/- 3 kcal mol(-1)). The proton affinity (PA = DeltaH) of thymine is measured to be 211 +/- 3 kcal mol(-1) (GB = DeltaG = 203 +/- 3 kcal mol(-1)). Cytosine is known to have several stable tautomers in the gas phase in contrast to in solution, where the canonical tautomer predominates. Using bracketing methods in an FTMS, we measure a DeltaH(acid) for the more acidic site of 342 +/- 3 kcal mol(-1) (DeltaG(acid) = 335 +/- 3 kcal mol(-1)). The DeltaH(acid) of the less acidic site, previously unknown, is 352 +/- 4 kcal mol(-1) (345 +/- 4 kcal mol(-1)). The proton affinity is 228 +/- 3 kcal mol(-1) (GB = 220 +/- 3 kcal mol(-1)). Comparison of these values to calculations indicates that we most likely have a mixture of the canonical tautomer and two enol tautomers and possibly an imine tautomer under our conditions in the gas phase. We also measure the acidity and proton affinity of cytosine using the extended Cooks kinetic method. We form the proton-bound dimers via electrospray of an aqueous solution, which favors cytosine in the canonical form. The acidity of cytosine using this method is DeltaH(acid) = 343 +/- 3 kcal mol(-1), PA = 227 +/- 3 kcal mol(-1). We also examined 1-methyl cytosine, which has fewer accessible tautomers than cytosine. We measure a DeltaH(acid) of 349 +/- 3 kcal mol(-1) (DeltaG(acid) = 342 +/- 3 kcal mol(-1)) and a PA of 230 +/- 3 kcal mol(-1) (GB = 223 +/- 3 kcal mol(-1)). Our ultimate goal is to understand the intrinsic reactivity of nucleobases; gas-phase acidic and basic properties are of interest for chemical reasons and also possibly for biological purposes because biological media can be quite nonpolar.     

Electrochemical detection of DNA methylation using a glassy carbon electrode modified with a composite made from carbon nanotubes and β-cyclodextrin

We describe a method for detecting DNA methylation. It is based on direct oxidation of DNA bases at a glassy carbon electrode (GCE) modified with film of a multiwalled carbon nanotube-β-cyclodextrin composite. This nano-structured film causes a strong enhancement on the oxidation current of DNA bases due to its large effective surface area and extraordinary electronic properties. Well-defined peaks were obtained as a result of electro-oxidation of guanine (at 0.67 V), adenine (at 0.92 V), thymine (at 1.11 V), cytosine (at 1.26 V), and 5-methylcytosine (at 1.13 V; all data vs. saturated calomel electrode (SCE)). The potential difference between 5-methylcytosine and cytosine (130 mV) is large enough to enable reliable simultaneous determination and analysis. The interference by thymine can be eliminated by following the principle of complementary pairing between purine and pyrimidine bases in DNA. The modified electrode was successfully applied to the evaluation of 5-methylcytosine in a fish sperm DNA, the methylation level of cytosine was found to be 7.47 %, and the analysis process took less than 1 h.     

Synthesis, structure and redox potentials of biologically active ferrocenylalkyl azoles

The syntheses, structures, electrochemical properties of the series of ferrocenylalkyl azoles, FcAlkAz, as well as the antitumor activity of ferrocenylmethyl benzimidazole (8) have been studied. Above mentioned compounds were investigated by the method of cyclic voltametry. All of them exhibited a reversible one-electron oxidation-reduction wave owing to the ferrocene-ferrocenium redox couple with a positive shift (0.50-0.65 V) compared with that of ferrocene (0.42 V). The X-ray determination of molecular structures of 1-(ferrocenylmethyl)imidazole (4), 1-(ferrocenylbenzyl)imidazole (7) and 1-(ferrocenylmethyl)bezimidazole (8) was carried out. Compound 4 with imidazolyl substituent was found to be present in N-protonated form. Antitumor activity of 1-(ferrocenylmethyl)benzimidazole (8) against some solid tumor models such as adenocarcinoma 755 (Ca755), melanoma B16 (B16) and Lewis lung carcinoma was studied. The antitumor activity of compound 8 was compared with cisplatin effectiveness against some experimental tumor systems.     

Guaiane Sesquiterpenoids Isolated from the Fruits of Torilis japonica and Their Cytotoxic Activity

Two new guaiane sesquiterpenoids, 11‐(acetyloxy)‐1,8‐dihydroxyguai‐4‐en‐3‐one ( 5 ) and (1α,6β)‐1,6‐dihydroxytorilin ( 6 ), were isolated from the fruits of Torilis japonica (Umbelliferae), along with four known sesquiterpenes, torilin ( 1 ), torilolone ( 2 ), (1β)‐1‐hydroxytorilin ( 3 ), and (1α)‐1‐hydroxytorilin ( 4 ). During the phytochemical investigation, daucosterol, friedelin, and epifriedelanol were also isolated from the plant for the first time. The structures of the new sesquiterpenoids 5 and 6 were determined by comprehensive analyses of MS and NMR spectroscopic data. These isolates were evaluated against human breast cancer cells (MCF‐7) and Lewis lung carcinoma (LLC) cells. Compounds 1, 3 , and 4 exhibited cytotoxic activity against the LLC cells with IC₅₀ values of 31.3, 32.5, and 34.0 μg/ml, respectively. However, no significant cytotoxicity was found against the MCF‐7 cells for any of the compounds tested.     

Structural and electronic property changes of the nucleic acid bases upon base pair formation

A systematic study of structures and electronic properties has been carried out for the nucleic acid bases adenine, guanine, thymine, and cytosine and for the base pairs adenine–thymine and guanine–cytosine. We focus our attention on these properties, which experience significant changes when single nucleic bases join to form base pairs. Such properties are expected to play an important role during the formation of the DNA molecule in its B conformation. All-electron calculations with inclusion of correlation effects were performed according to the local and nonlocal density functional approaches. We compare our results with previous ab initio and semiempirical values and with available experimental data. Advantages and disadvantages for these density functional-based methods are discussed. We conclude that applications of such models to investigate larger compounds of a similar nature are promising. © 1994 by John Wiley & Sons, Inc.     

Reactivities of hydroxyl and perhydroxyl radicals toward cytosine and thymine: A comparative study

As the hydroxyl (OH) and perhydroxyl (OOH) radicals are known to play important roles in biological systems, their reactions with cytosine and thymine were studied. Addition reactions of these radicals at different sites of cytosine and thymine, and hydrogen abstraction reactions by each of the two radicals from the different sites of the two molecules were studied at the B3LYP/6‐31G(d,p), B3LYP/AUG‐cc‐pVDZ and BHandHLYP/AUG‐cc‐pVDZ levels of density functional theory. Effect of solvation in aqueous media on the reactions was studied at all these levels of theory using single point energy calculations using the polarizable continuum model. The present study shows that whereas the OH radical would abstract H atoms from the various sites of cytosine and thymine efficiently, the OOH radical would have poor reactivity in this regard. The OH radical is also predicted to be much more reactive than the OOH radical with regard to addition reactions at the C5 and C6 sites of both thymine and cytosine, though the OOH radical is also predicted to have significant reactivity in this respect. © 2012 Wiley Periodicals, Inc.     

Antitumor activity of Pulsatilla koreana saponins and their structure-activity relationship

Seventeen saponins isolated from the root of Pulsatilla koreana were examined for their in vitro cytotoxic activity against the human solid cancer cell lines, A-549, SK-OV-3, SK-MEL-2, and HCT15, using the SRB assay method, and their in vivo antitumor activity using BDF1 mice bearing Lewis lung carcinoma (LLC). The saponins 5-17, with a free acidic functional group at C-28 of aglycon, exhibited moderate to considerable cytotoxic activity, however, the saponins 1-4, esterified with a trisaccharide at C-28 of aglycon, did not exhibit cytotoxic activity (ED50; >300 microM). Among them, oleanolic acid 3-O-alpha-L-rhamnopyranosyl-(1-->2)-[beta-D-glucopyranosyl-(1-->4)]-alpha-L-arabinopyranoside (10) exhibited the most potent cytotoxic activity (ED50; 2.56, 2.31, 1.57, 8.36 microM, respectively). In vivo test, hederagenin 3-O-alpha-L-rhamnopyranosyl-(1-->2)-[beta-D-glucopyranosyl-(1-->4)]-alpha-L-arabinopyranoside (6, Inhibition Ratio, IR; 66.9%) exhibited more potent antitumor activity than taxol (IR; 35.8%) and doxorubicin (IR; 62.1%). Also, hedragenin 3-O-beta-D-glucopyranosyl-(1-->4)-O-beta-D-glucopyranosyl-(1-->3)-O-alpha-L-rhamnopyranosyl-(1-->2)-alpha-L-arabinopyranoside (17, IR; 50.3%) exhibited potent antitumor activity. These two saponins were identically comprised of a hederagenin aglycon moiety and a sugar sequence O-alpha-L-rhamnopyranosyl-(1-->2)-alpha-L-arabinopyranoside at C-3 of the hederagenin, suggesting that the two elements are essential factors for the antitumor activity.     

Anticancer enzyme L-lysine α-oxidase

Fungal L-lysine α-oxidase (1.4.3.14) (LO) from Trichodermaharzianum Rifai presents an oxidoreductase with a firmly attached coenzyme—FAD. This stable enzyme catalyzes an oxidative deamination of L-lysine yielding hydrogen peroxide, ammonia, and α-ketoacid. LO exhibits antitumor activity toward 5 of 12 tested transplantable tumors. The sensitive tumors were ascitichepatoma 22 (T/C=201%, CR=66%); mammary adenocarcinoma Ca-755 (TGI=96%); melanoma B-16 (TGI=81%); AKATOL (TGI=75%); RSHM 5 (TGI=79%). LO therapeutic activity was observed within a wide range of doses, 35–350 U/kg, by intraperitoneal daily injections for 5 d. Contrary to Escherichia coli L-asparaginase, LO demonstrates its antitumor activity by the low therapeutic doses in vivo within a wide range of optimal doses and through an other antitumor spectrum. Fisher lymphadenosis L-5178y highly sensitive toward L-asparaginase appeared to be LO resistant. The possible mechanisms of LO antitumor activity through the key biochemical processes are discussed.     

5‐Methyl‐2‐thiouracil

The molecular structure of the title compound, also known as 2‐thio­thymine [systematic name: 2,3‐di­hydro‐5‐methyl‐2‐thioxopyrimidin‐4(1H)‐one], C₅H₆N₂OS, is similar to that of thymine, with only small changes in the ring structure, apart from a significant difference at the substitution site [S=C = 1.674 (1) Å]. The mol­ecules are connected by hydrogen bonds, with N—H?O = 2.755 (2) Å and N—H?S = 3.352 (1) Å. The hydrogen‐bond network is different from that in thymine, since it involves all the donor and acceptor atoms.     

Metal‐based antitumor,cytotoxic and antimicrobial activity: pharmacological evaluation of Knoevenagel condensate β‐diketone Schiff base thiosemicarbazone Cu(II) and Zn(II) complexes

Knoevenagel condensate Schiff base ligands [L = 3‐cinnamalideneacetylacetone‐thiosemicarbazone (CAT)/3‐cinnama‐ lideneacetylacetoneethylthiosemicarbazone (CAET)/3‐cinnamalideneacetylacetonephenylthiosemicarbazone (CAPT)] and their copper/zinc complexes were synthesized. They were characterized by analytical and spectral techniques. From these data it was found that the ligands adopt square‐planar geometry on metalation with Cu²⁺ and Zn²⁺. To evaluate the antitumor and cytotoxic activity of the synthesized complexes in mice and human cancer cell lines, the antitumor activity of the complexes was evaluated against an Ehrlich ascites carcinoma (EAC) tumor model. The activity was assessed using survival time and short‐term in vitro cytotoxic activity. Oral administration of complexes (100 mg/kg) increased the survival time. The cytotoxic activity of complexes was evaluated using human breast cancer (MDA‐MB‐231), colon cancer (HCT‐116) and nonsmall lung cancer (NCI‐H‐23) cell lines. Both the complexes possessed significant antitumor and cytotoxic activity on EAC and human cancer cell lines. The in vitro antimicrobial screening effect of the investigated compounds was also tested against the various organisms by well diffusion method. Copyright © 2009 John Wiley & Sons, Ltd.     

The synthesis and cytotoxic evaluation of a series of benzodioxole substituted titanocenes

Using 6‐benzo[1,3]dioxolefulvene ( 1a ), a series of benzodioxole substituted titanocenes was synthesized. The benzyl‐substituted titanocene bis[(benzo[1,3]dioxole)‐5‐methylcyclopentadienyl] titanium (IV) dichloride ( 2a ) was synthesized from the reaction of Super Hydride with 1a . An X‐ray determined crystal structure was obtained for 2a . The ansa‐titanocene {1,2‐di(cyclopentadienyl)‐1,2‐di‐(benzo[1,3]dioxole)‐ethanediyl} titanium(IV) dichloride ( 2b ) was synthesized by reductive dimerisation of 1a with titanium dichloride. The diarylmethyl substituted titanocene bis(di‐(benzo[1,3]dioxole)‐5‐methylcyclopentadienyl) titanium(IV) dichloride ( 2c ) was synthesized by reacting 1a with the para‐lithiated benzodioxole followed by transmetallation with titanium tetrachloride. When titanocenes 2a–c were tested against pig kidney (LLC‐PK) cells inhibitory concentrations (IC₅₀) of 2.8 × 10^?4, 1.6 × 10^?4 and 7.6 × 10^?5 M , respectively, were observed. These values represent improved cytotoxicity against LLC‐PK, when compared with unsubstituted titanocene dichloride, but are not as impressive as values obtained for titanocenes previously synthesized using the above methods. Copyright © 2006 John Wiley & Sons, Ltd.     

Copolymers containing alternating sequences of nucleic acid base pairs. III. Spectroscopic studies

A study was conducted of the complementary base pair interactions between various pairs of electron-donor monomers, electron-acceptor monomers, homopolymers and alternating copolymers selected from the following group: ( 1 ) 9-(2-vinyloxyethyl)adenine; ( 2 ) 1-(2-vinyloxyethyl)thymine; ( 3 ) 1-(2-vinyloxyethyl)cytosine; ( 4 ) 9-(2-maleimidoethyl)adenine; ( 5 ) 6-chloro-9-(2-maleimidoethyl)purine; ( 6 ) 1-(2-maleimidoethyl)thymine; ( 7 ) 1-(2-maleimidoethyl)cytosine; ( 8 ) homopolymer of ( 4 ); ( 9 ) homopolymer of ( 6 ); ( 10 ) alternating copolymer of ( 2 ) and maleic anhydride; ( 11 ) alternating copolymer of ( 2 ) and ( 5 ); and ( 12 ) alternating copolymer of ( 2 ) and ( 4 ). By ¹H-NMR, in CDCL₃, the base pair interactions between ( 1 ) and ( 2 ) were shown to be hydrogen bonding, the extent of which was shown by a calculated binding constant, K = 61.81 L/mol. The nature of this interaction was conformed by IR. Neither monomer pairs ( 1 )/( 2 ) nor ( 4 )/( 6 ) exhibited hydrogen bonding in DMSO-d₆. However, hydrogen bonding interaction was observed for DMSO-d₆ solutions of homopolymers ( 8 ) and ( 9 ) and for alternating copolymer ( 12 ). On the basis of an upfield chemical shift of the 2- and 8-aromatic protons of ademine of ( 1 ) in D₂O, a partial overlap stacking interaction is proposed. No charge-transfer interactions could be observed by UV between donor-acceptor monomer pairs.     

Synthesis and 15N NMR characterization of 4‐vinylbenzyl substituted bases of nucleic acids

The following substances have been synthesized and characterized as monomers or intermediates for syntheses of new polymers: 1‐(4‐vinylbenzyl)uracil ( 1a ), 1‐(4‐vinylbenzyl)thymine ( 1b ), N‐4‐acetyl‐1‐(4‐vinylbenzyl)cytosine ( 1c ), 1‐(4‐vinylbenzyl)cytosine ( 1d ), 9‐(4‐vinylbenzyl)adenine ( 2a ), 2‐amino‐9‐(4‐vinylbenzyl)‐6‐chloro‐9H‐purine ( 2b ), and 9‐(4‐vinylbenzyl)‐guanine ( 2c ). The alkylation reactions with 4‐vinylbenzyl chloride were catalyzed with anhydrous sodium iodide. The substitution at position 9 in substances 2a‐c was confirmed by ¹⁵N NMR.