Structural and reactivity studies on the ternary system guanine/methionine/trans-[PtCl2(NH3)L] (L=NH3, quinoline): implications for the mechanism of action of nonclassical trans-platinum antitumor complexes

 The present model study explores the chemistry of methionine complexes and ternary methionine-guanine adducts formed by trans-[PtCl₂(NH₃)₂] (1) and antitumor trans-[PtCl₂(NH₃)quinoline] (2) using 1D (¹H, ¹⁹⁵Pt) and 2D NMR spectroscopy. Compound 2 was substitution inert in reactions with N-acetyl-lmethionine [AcMet(H)]. Reactions of trans-[PtCl(NO₃)(NH₃)quinoline] (5) ("monoactivated" 2) with AcMetH in water and acetone at various stoichiometries point to Pt(II)-S binding that requires prior activation of the Pt-Cl bond by labile oxygen donors. Trans-[PtCl{AcMet(H)-S}(NH₃)quinoline](NO₃) (6) and trans-[Pt{AcMet(H)-S}₂(NH₃)quinoline](NO₃)₂ (7) were isolated from these mixtures. At high [Cl^–], AcMet(H) is displaced from 7, giving 6. Frozen stereodynamics in 6 at the thioether-S and slow rotation about the Pt-N_quinoline bond result in four spectroscopically distinguishable diastereomers. ¹H NMR spectra of 7 show faster exchange dynamics due to mutual trans-labilization of the sulfur donors. Substitution of chloride in trans-[PtCl(9-EtGua)(NH₃)L]NO₃ (L=NH₃, 3; L=quinoline, 4; 9-EtGua=9-ethylguanine, which mimics the first DNA binding step of 1 and 2) by methionine-sulfur proceeded ca. 2.5 times slower for the quinoline compound. Both reactions, in turn, proved to be ca. 4 times faster than binding of a second nucleobase under analogous conditions. From the resulting mixtures the ternary adducts trans-[Pt(AcMet-S)(9-EtGua-N7)(NH₃)L](NO₃, Cl) (L=NH₃, 8; L=quinoline, 9) were isolated. A species analogous to 9 formed in a rapid reaction between 6 and 5′-guanosine monophosphate (5′-GMP). From NMR data an AMBER-based solution structure of the resulting adduct, trans-[Pt(AcMet-S)(5′-GMP-N7)(NH₃)quinoline] (10), was derived. The unusual reactivity along the N7-Pt-S axis in 8–10 resulted in partial release of both 9-EtGua and AcMet at high [Cl^–]. Possible consequences of the kinetic and structural effects (e.g., trans effect of sulfur, steric demand of quinoline) observed in these systems with respect to the (trans)formation of potential biological cross-links are discussed. Received: 25 May 1998 / Accepted: 6 August 1998     

Method for the Synthesis of Uric Acid Derivatives

Abstract

A general procedure to obtain tetra-substituted uric acid by stepwise N-alkylation is described. 2,6-Dichloropurine (1) was condensed with 1-propanol by Mitsunobu reaction to give 9-propyl congener (2). Treatment of 2 with ammonia gave adenine derivative (4a), which was converted to the 8-oxoadenine (5b) in 3 steps. Methylation of 5b proceeded site-specifically to give 6-amino-2-chloro-7,8-dihydro-7-methyl-9-propylpurin-8-one (6) as a sole product. Compound 6 was successively treated with NaNO₂ and iodomethane to give 2-chloro-1,6,7,8-tetrahydro-1,7-dimethyl-9-propylpurin-6,8-dione (9) accompanied by the O ⁶-methyl product (8) in 75% and 6.9%, respectively. After nucleophilic substitution of 9 with NaOAc, the product (11) was reacted with iodomethane to give the uric acid (12) and the 2-methoxy product (13) in 46% and 15.5%, respectively. However, the reaction of 11 with the benzylating agents gave only O-benzyl products (14a,b).     

Ribosylation of the Base Residue of Inosine Derivatives by Phase-Transfer Catalysis

Abstract

Reaction of 2′,3′,5′-O-silylated inosine derivative 1 with 2, 3-O-isopropylidene-5-O-tritylribosyl chloride (3) in a two-phase (CH₂Cl₂-aq. NaOH) system in the presence of Bu₄NBr gave three products, i. e., 6-O-α-, 6-O-β-, and N ¹-β-isomers of glycosides 4, 5a, and 5b. A similar PTC reaction of 1 with 2, 3, 5-tri-O-benzylribosyl bromide (9) gave four regio- and stereo-isomers involving the N¹-β-glycoside 10. Reaction of 1 with 2, 3, 5-tri-O-benzoylribosyl bromide (11) afforded three products involving the desired N¹-β-glycoside 12b, which could be deprotected to give N ¹-ribosylinosine (15b) as a useful intermediate for the synthesis of cIDPR.

     

Synthesis of functionalized amino acid derivatives as new pharmacophores for designing anticancer agents

A new series of functionalized amino acid derivatives N-substituted 1-N-(tert-butoxycarbonyl)-2,2-dimethyl-4-phenyl-5-oxazolidine carboxamide (1-17) and 1-N-substituted-3-amino-2-hydroxy-3-phenylpropane-1-carboxamide (18-34) were synthesized and evaluated for their in vitro cytotoxicity against human cancer cell lines. Compound 6 has shown interesting cytotoxicity (IC₅₀ = 5.67 μm) in ovarian cancer, while compound 10 exhibited promising cytotoxicity in ovarian (IC₅₀ = 6.1 μm) and oral (IC₅₀ = 4.17 μm) cancers. These compounds could be of use in designing new anti-cancer agents.     

1,3-Cycloaddition of Cyclic Isothioureas to Heterocumulenes and Fungitoxicity of the Resulting l,2,4-Triazolo[3,4-c]-l,2,4-dithiazoles

Phenacylation of 5-aryl-3-mercapto-l,2,4-triazoles (I) furnished 5-aryl-3-phenacylthio-1,2,4-triazoles (II) which reacted with CS₂ and aryl isothiocyanates to give 5-aryl-l,2,4-triazolo[3,4-c]-1,2,4-dithiazole-3-thiones (III) and 5-aryl-3-arylimino-l,2,4-triazolo[3,4-c]-l,2,4-dithiazoles (IV), respectively. (IV) on refluxing with CS₂ yielded (III) which, when heated with aryl isothiocyanates, regenerated (IV). Compounds(II) ~ (IV) were compared with Dithane M-45 for their fungitoxicity against Helminthosporium oryzae and Fusarium oxysporium. The screening results have been correlated with the structural features of the tested compounds.     

Synthesis and biological evaluation of tricarbonyl Re(I) and Tc(I) complexes anchored by poly(azolyl)borates: application on the design of radiopharmaceuticals for the targeting of 5-HT<Subscript>1A</Subscript> receptors

The building blocks fac-[^99mTc{κ³-HB(tim^Me)₃}(CO)₃] and fac-[^99mTc{κ³-R(μ-H)B(tim^Me)₂}(CO)₃] [R is H (4a), Ph (5a); tim^Me is 2-mercapto-1-methylimidazolyl] were obtained almost quantitatively by reacting fac-[^99mTc(CO)₃(H₂O)₃]⁺ with the corresponding scorpionate. These compounds cross the intact blood–brain barrier in mice, with significant retention in the case of 4a and 5a. Using 4a as the lead structure, we have synthesized the functionalized complexes fac-[M{κ³-H(μ-H)B(tim^Bu-pip)₂}(CO)₃] [M is Re (8), ^99mTc (8a); tim^Bu-pip is methyl[4-((2-methoxyphenyl)-1-piperazinyl)butyl](2-mercapto-1-methylimidazol-5-yl)methanamide] and fac-[M{κ ³-H(μ-H)B(tim^Me)(tim^Bu-pip)}(CO)₃] [M is Re (9), ^99mTc (9a)] and evaluated their potential as radioactive probes for the targeting of brain 5-HT_1A serotonergic receptors. The Re complexes exhibit excellent affinity [IC₅₀=0.172 ± 0.003 nM (8); IC₅₀=0.65 ± 0.01 nM (9)] for the 5-HT_1A receptor. The radioactive congeners (^99mTc) have shown an initial brain uptake of 1.38 ± 0.46%ID g⁻¹ (8a) and 0.43 ± 0.12%ID g⁻¹ (9a), but suffer from a relatively fast washout.     

Effects of geometric isomerism in dinuclear antitumor platinum complexes on their interactions with N-acetyl-L-methionine

In this study, the reactions of N-acetyl-L-methionine (AcMet) with [{trans-PtCl(NH₃)₂}₂-μ-H₂N(CH₂)₆NH₂](NO₃)₂ (BBR3005: 1,1/t,t 1) and its cis analog [{cis-PtCl(NH₃)₂}₂-μ-{H₂N(CH₂)₆NH₂}]Cl₂ (1,1/c,c 2) were analyzed to determine the rate and reaction profile of chloride substitution by methionine sulfur. The reactions were studied in PBS buffer at 37°C by a combination of multinuclear (¹⁹⁵Pt, {¹H-¹⁵N} HSQC) magnetic resonance (NMR) spectroscopy and electrospray ionization time of flight mass spectrometry (ESITOFMS). The diamine linker of the 1,1/t,t trans complex was released as a result of the trans influence of the coordinated sulfur atom, producing trans-[PtCl(AcMet)(NH₃)₂]⁺ (III) and trans-[Pt(AcMet)₂(NH₃)₂]²⁺ (IV). In contrast the cis geometry of the dinuclear compound maintained the diamine bridge intact and a number of novel dinuclear platinum compounds obtained by stepwise substitution of sulfur on both platinum centers were identified. These include (charges omitted for clarity): [{cis-PtCl(NH₃)₂}-μ-NH₂(CH₂)₆NH₂-{cis-Pt(AcMet)(NH₃)₂}] (V); [{cis-Pt(AcMet)(NH₃)₂}₂-μ-NH₂(CH₂)₆NH₂] (VI); [{cis-PtCl(NH₃)₂}-μ-NH₂(CH₂)₆NH₂-{PtCl(AcMet)NH₃] (VII); [{PtCl(AcMet)(NH₃)}₂-μ-NH₂(CH₂)₆NH₂] (VIII); [{trans-Pt(AcMet)₂(NH₃)}-μ-NH₂(CH₂)₆NH₂-{PtCl(AcMet)(NH₃)] (IX) and the fully substituted [{trans-Pt(AcMet)₂(NH₃)}₂-μ-{NH₂(CH₂)₆NH₂] (X). For both compounds the reactions with methionine were slower than those with glutathione (Inorg Chem 2003, 42:5498–5506). Further, the 1,1/c,c geometry resulted in slower reaction than the trans isomer, because of steric hindrance of the bridge, as observed previously in reactions with DNA and model nucleotides.     

Phenoxyl-copper(II) complexes: models for the active site of galactose oxidase

 The reaction of the macrocycles 1,4,7-tris (3,5-di-tert-butyl-2-hydroxy-benzyl)-1,4,7-triazacyclononane, L¹H₃, or 1,4,7-tris(3-tert-butyl-5-methoxy-2-hydroxy-benzyl)-1,4,7-triazacyclononane, L²H₃, with Cu(ClO₄)₂·6H₂O in methanol (in the presence of Et₃N) affords the green complexes [Cu^II(L¹H)] (1), [Cu^II(L²H)]·CH₃OH (2) and (in the presence of HClO₄) [Cu^II(L¹H₂)](ClO₄) (3) and [Cu^II(L²H₂)] (ClO₄) (4). The Cu^II ions in these complexes are five-coordinate (square-base pyramidal), and each contains a dangling, uncoordinated pendent arm (phenol). Complexes 1 and 2 contain two equatorially coordinated phenolato ligands, whereas in 3 and 4 one of these is protonated, affording a coordinated phenol. Electrochemically, these complexes can be oxidized by one electron, generating the phenoxyl-copper(II) species [Cu^II(L¹H)]^+ ·, [Cu(L²H)]^+ ·, [Cu^II(L¹H₂)]^2+ ·, and [Cu^II(L²H₂)]^2+ ·, all of which are EPR-silent. These species are excellent models for the active form of the enzyme galactose oxidase (GO). Their spectroscopic features (UV-VIS, resonance Raman) are very similar to those reported for GO and unambiguously show that the complexes are phenoxyl-copper(II) rather than phenolato-copper(III) species. Received: 10 February 1997 / Accepted: 7 April 1997     

Metal-modified nucleobase pairs involving 7,9-dimethylguanine: trans-a2PtII analogues (a = NH3 or CH3NH2) of Watson-Crick GC and homo GG pairs

 The analogy between H-bonded nucleobase pairs and their metalated analogues is extended to the hemiprotonated pair of 7,9-dimethylguanine (7,9-DimeG) and the Watson-Crick and reversed Watson-Crick pair between 7,9-dimethylguaninium (7,9-DimeGH⁺) and 1-methylcytosine (1-MeC). The crystal structure analyses of two model compounds, trans–[Pt(CH₃NH₂)₂(7,9-DimeG-N1)₂](NO₃)₂ (1) and trans–[Pt(NH₃)₂(1-MeC-N3)(7, 9-DimeG-N1)](PF₆)₂· 2.5 H₂O (3a) are reported. Pt binding is through N1 of 7,9-DimeG and N3 of 1-MeC. In solution, 3a exists in a mixture with Watson-Crick and reversed Watson-Crick arrangements of the two bases, depending on solvent, concentration and anions. Received: 16 October 1996 / Accepted: 27 January 1997     

Complete basis set,hybrid-DFT study and NBO interpretation of conformational analysis of 2-methoxytetrahydropyran and its thiopyran and selenopyran analogues in relation to the anomeric effect

2-Methoxytetrahydropyran (1), -thiopyran (2) and -selenopyran (3) have been chosen as model compounds to investigate the origin of the anomeric effect (AE). The impacts of the hyperconjugation, electrostatic and steric interactions on the conformational preferences of compounds 1–3 have been analysed by means of complete basis set-4, hybrid-density functional theory (B3LYP/6-311+G**) based methods and natural bond orbital (NBO) interpretation. Both levels of theory showed that the axial conformations of compounds 1–3 are more stable than their equatorial conformations. The Gibbs free energy difference (G _eq–G _ax) values (i.e. ΔG _eq–ax) between the axial and equatorial conformations increase from compound 1 to compound 2 but decrease from compound 2 to compound 3. Based on the NBO results obtained, the AE associated with the electron delocalisation [i.e. Σ(endo-AE_eq + exo-AE_eq) ? Σ(endo-AE_ax + exo-AE_ax)] increase slightly from compound 1 to compound 2 but decrease from compound 2 to compound 3. Similar trend is also observed for the differences between the calculated total steric exchange energy values [i.e. Δ(TSEE)_eq–ax]. On the other hand, the calculated differences between the dipole moment values of the axial and equatorial conformations [i.e. Δ(μ_eq–μ_ax)] decrease from compound 1 to compound 3. These findings led to the proposal that the AE associated with the electron delocalisation (the hyperconjugation effect) is more significant for the explanation of the conformational preferences of compounds 1–3 than the electrostatic model. The correlations between the AE associated with the electron delocalisation, bond orders, TSEE, ΔG _eq–ax, dipole–dipole interactions, structural parameters and conformational behaviours of compounds 1–3 have been investigated.     

Binding investigation and preliminary optimisation of the 3-amino-1,2,4-triazin-5(2H)-one core for the development of new Fyn inhibitors

Fyn tyrosine kinase inhibitors are considered potential therapeutic agents for a variety of human cancers. Furthermore, the involvement of Fyn kinase in signalling pathways that lead to severe pathologies, such as Alzheimer’s and Parkinson’s diseases, has also been demonstrated. In this study, starting from 3-(benzo[d][1,3]dioxol-5-ylamino)-6-methyl-1,2,4-triazin-5(2H)-one (VS6), a hit compound that showed a micromolar inhibition of Fyn (IC₅₀?=?4.8?μM), we computationally investigated the binding interactions of the 3-amino-1,2,4-triazin-5(2H)-one scaffold and started a preliminary hit to lead optimisation. This analysis led us to confirm the hypothesised binding mode of VS6 and to identify a new derivative that is about 6-fold more active than VS6 (compound 3, IC₅₀?=?0.76?μM).     

An Investigation of the Structural Diversities of Lithiated HMPA Complexes of o-Mercaptopyridine and Trithiocyanuric Acid: Syntheses, Crystal structures and Model Molecular Orbital Calculations

Reaction of o-mercaptopyridine (o-MPH) and trithiocyanuric acid (TTCyH₃) with one equivalent of BuⁿLi in the presence of HMPA yields the mono-lithiated salts MPLi.HMPA (1) and TTCyH₂Li.2HMPA (2) respectively, which have been characterised by NMR spectroscopy and X-ray crystallography. Reaction of three equivalents of BuⁿLi with anhydrous TTCyH₃ in THF yields the tri-lithiated species TTCyLi₃.4THF (3). In all three compounds the lithium centres have N,S-bridged coordination modes. Whereas 1 is dimeric in the solid state, 2 has an unusual monomeric structure and 3, which is a very rare example of a structurally characterised tri-lithiated compound, has an unprecedented polymeric structure incorporating (NCSLi) _n (n = 1, 2) rings. The structural diversities displayed by 1 and 2 have been probed, and thereby in part rationalised, by ab initio (6-31G*/RHF, 6-31G**/RHF and 6-31G*/MP2 levels) MO calculations on both their thio-keto and thiol isomers and on their uncomplexed and complexed lithiated derivatives. In particular, the optimised structures predict and reproduce the N,S-bridging coordination modes found for lithium and explain why structure 1 is dimeric whereas 2 is monomeric.Electronic Supplementary Material available.     

Synthesis,inhibitory activity and molecular docking studies of two Cu(II) complexes against Helicobacter pylori urease

Two mononuclear copper(II) complexes, [Cu(C₁₅H₁₆NO₂)₂] (1) and [Cu(C₆H₉N₂O₄)₂·3H₂O] (2·3H₂O), were synthesised and structurally characterised by single-crystal X-ray analysis. The copper(II) atom adopts a square-planar environment in complex 1, while the geometry in 2·3H₂O could be described as the distorted square pyramidal. Complexes 1 and 2·3H₂O were evaluated for their inhibitory activities against Helicobacter pylori (H. pylori) urease in vitro. They both were found to have strong inhibitory activities against H. pylori urease comparable to that of acetohydroxamic acid (AHA). A docking simulation was performed to position 2 into the H. pylori urease active site to determine the probable binding conformation.     

Ruthenium(III) dimethyl sulfoxide pyridinehydroxamic acid complexes as potential antimetastatic agents: synthesis,characterisation and in vitro pharmacological evaluation

Reaction of 3-pyridinehydroxamic acid and 4-pyridinehydroxamic acid (3-pyha and 4-pyha) with either [NBu₄][RuCl₄(dmso-S)₂] or [(dmso)₂H][RuCl₄(dmso-S)₂] (dmso is dimethyl sulfoxide) in acetone afforded three new ruthenium(III) dimethyl sulfoxide pyridinehydroxamic acid complexes: [NBu₄][trans-RuCl₄(dmso-S)(4-pyha)]·CH₃COCH₃ (1), [3-pyhaH][trans-RuCl₄(dmso-S)(3-pyha)] (2) and [4-pyhaH][trans-RuCl₄(dmso-S)(4-pyha)] (3). The solid-state structure of [NBu₄][trans-RuCl₄(dmso-S)(4-pyha)]·CH₃COCH₃ (1) was determined by X-ray crystallography. 2 and 3 were pharmacologically evaluated for their in vitro cytotoxicity, their ability to inhibit cell invasion and their gelatinase activity. 2 and 3 were devoid of cytotoxicity against the cell lines tested. 2 inhibited invasion of the highly invasive MDA-MB-231 cells to a much greater extent than 3. Contrary to expectations, neither 2 nor 3 had any inhibitory effect on matrix metalloproteinase (MMP) production and/or activity and in fact 3 was found to enhance the production and/or activity of both MMP-2 and MMP-9.     

Preparation of 6-azafulleroid-6-deoxy-2,3-di-O-myristoylcellulose

6-Azafulleroid-6-deoxy-2,3-di-O-myristoylcellulose (3) was synthesized from 6-azido-6-deoxycellulose (1) by two reaction steps. The myristoylation of compound 1 with myristoyl chloride/pyridine proceeded smoothly to give 6-azido-6-deoxy-2,3-di-O-myristoylcellulose (2) in 97.0% yield. The reaction of compound 2 with fullerene (C₆₀) was carried out by microwave heating to afford compound 3 in high yield. It was found from FT-IR, ¹³C NMR, UV–vis, differential pulse voltammetry (DPV), SEC analyses that compound 3 was the expected C₆₀-containing polymer. Consequently, maximum degree of substitution of C₆₀ (DS_C60) of compound 3 was 0.33.     

Aliphatic pincer-type POCOP ligands and their complexation behaviour with iridium: Crystal structure of an iridium(III) phosphinite complex

Reaction of 2 equivalents of 1,3-bis-(di-tert-butylphosphinito)-2-methyl-propane (1a) with [Ir(COD)Cl]₂ affords the first aliphatic diphosphinite PCP pincer complex with iridium, Ir(H){(t-Bu₂POCH₂)₂C(Me)}Cl (2). The poor yield of 2 is partly explained by the formation of a di-nuclear byproduct [IrCl(COD)]₂(μ₂-{(t-Bu₂POCH₂)₂CH(Me)}) (3). Reaction of 1,3-bis-(di-iso-propylphosphinito)-2-methyl-propane (1b) under the same condition does not give any cyclometallation, and reaction with IrCl₃·H₂O in DMF leads to complete decomposition of the pincer ligand under the formation of Ir(H)(i-Pr₂P(OH))₃(CO) (4), underpinning the comparatively low thermal stability of aliphatic phosphinite pincer systems.     

Phytochemical and Bioactivity Studies on Constituents of the Leaves of Vitex Quinata

A phytochemical investigation of the leaves of Vitex quinata (Lour.) F.N. Williams (Verbenaceae), guided by a cytotoxicity assay against the MCF-7 human breast cancer cell line, led to the isolation of a new δ-truxinate derivative (1) and a new phytonoic acid derivative (2), together with 12 known compounds. The structures of the new compounds were determined by spectroscopic methods as dimethyl 3,4,3′,4′-tetrahydroxy-δ-truxinate (1) and methyl 10R-methoxy-12-oxo-9(13),16E-phytodienoate (2), respectively. In a cytotoxicity assay, (S)-5-hydroxy-7,4′-dimethoxyflavanone (3) was found to be the sole active principle, with ED₅₀ values of 1.1–6.7 μM, respectively, when tested against a panel of three human cancer cells. Methyl 3,4,5-O-tricaffeoyl quinate (4) showed activity in an enzyme-based ELISA NF-κB p65 assay, with an ED₅₀ value of 10.3 μM.     

Chemical-Enzymatic Synthesis of 3′-Amino-2′, 3′-dideoxy-β-D-ribofuranosides of Natural Heterocyclic Bases and Their 5′-Monophosphates

Abstract

Treatment of O², 3′-anhydro-5′-O-trityl derivatives of thymidine (1) and 2′-deoxyuridine (2) with lithium azide in dimethylformamide at 150 °C resulted in the formation of the corresponding isomeric 3′-azido-2′, 3′-dideoxy-5′-O-trityl-β-D-ribofuranosyl N¹- (the major products) and N³-nucleosides (3/4 and 5/6). 3′-Amino-2′, 3′-dideoxy-β-D-ribofuranosides of thymidine [Thd(3′NH₂)], uridine [dUrd(3′NH₂)], and cytidine [dCyd(3′NH₂)] were synthesized from the corresponding 3′-azido derivatives. The Thd(3′NH₂) and dUrd(3′NH₂) were used as donors of carbohydrate moiety in the reaction of enzymatic transglycosylation of adenine and guanine to afford dAdo(3′NH₂) and dGuo(3′NH₂). The substrate activity of dN(3′NH₂) vs. nucleoside phosphotransferase of the whole cells of Erwinia herbicola was studied.     

Metal-stabilized rare tautomers of nucleobases

 A Pt^II complex containing N4 bound neutral 1-methylcytosine (1-MeC), trans–[Pt(NH₃)₂(1-MeC-N4)₂](ClO₄)₂ (5), has been prepared and characterized by X-ray analysis. The complex contains the rare iminooxo tautomer form of the cytosine nucleobase. Pt^II binding is through the exocyclic N4 position of the nucleobases, with Pt and the N3 positions in a syn orientation. As a consequence, the proton at N3 is pointing toward the heavy metal, thereby allowing an agostic Pt···HN interaction. Formation of 5 is achieved via oxidation of the linkage isomer trans–[Pt(NH₃)₂(1-MeC-N3)₂]²⁺ (1) to a Pt^IV species (2), followed by metal migration to N4, and subsequent reduction to Pt^II. This process is a text-book example for a redox-assisted metal migration at a heterocyclic ligand. The existence of various rotamers of 5 in aqueous solution is evident from ¹H NMR spectroscopy. The possible role of these rotamers of the metalated rare tautomer, and in particular of those having Pt and the N3 position in an anti arrangement, with regard to base mispairing is discussed. Received: 27 February 1996 / Accepted: 10 June 1996     

Synthesis and anticonvulsant activity of new N-mannich bases derived from benzhydryl- and isopropyl-pyrrolidine-2,5-dione

Synthesis and anticonvulsant properties of 26 new N-Mannich bases of 3-benzhydryl-(5–17) and 3-isopropyl-pyrrolidine-2,5-diones (18–30) have been described. Initial anticonvulsant screening for these compounds was evaluated in mice after intraperitoneal administration in the maximal electroshock (MES) and subcutaneous pentylenetetrazole (scPTZ) seizures tests. The acute neurological toxicity was determined by applying the rotorod test. The in vivo results in mice showed that the majority of 3-benzhydryl-pyrrolidine-2,5-dione derivatives revealed effectiveness, while 3-isopropyl-pyrrolidine-2,5-dione derivatives were practically devoid of activity. The quantitative evaluation in both tests revealed that the most active were N-[{4-(3-chlorophenyl)-piperazin-1-yl}-methyl]-3-benzhydryl-pyrrolidine-2,5-dione (9) with ED_{5 0} value?=42.71?mg/kg (MES), ED_{5 0} value?>150?mg/kg (scPTZ), and N-[{4-(3-trifluoromethylphenyl)-piperazin-1-yl}-methyl]-3-benzhydryl-pyrrolidine-2,5-dione (13) with ED_{5 0} value?=101.46?mg/kg (MES) and ED_{5 0} value?=72.59?mg/kg (scPTZ). These molecules showed higher potency and lower neurotoxicity than the reference antiepileptic drugs (ethosuximide and valproic acid). To explain the probable mechanism of action of selected active derivatives (9 and 13), their influence on Na_v1.2 and l-type calcium channel was evaluated in vitro.