9 Methyladenine

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Bruno Longato - One of the best experts on this subject based on the ideXlab platform.

  • metal promoted synthesis of amidines containing the model nucleobases 1 methylcytosine and 9 Methyladenine
    Dalton Transactions, 2011
    Co-Authors: Diego Montagner, Ennio Zangrando, Giuseppe Borsato, Vittorio Lucchini, Bruno Longato
    Abstract:

    The amidine complexes cis-[L2PtNHC(R){1-MeCy(-2H)}]NO3 (R = Me, 1a; Ph, 1b, Me3C, 1c; Ph2(H)C, 1d) and cis-[L2PtNHC(R){9-MeAd(-2H)}]NO3 (R = Me, 2a; Ph, 2b; Me3C, 2c; Ph2(H)C, 2d), are formed when cis-[L2Pt(μ-OH)]2(NO3)2 (L = PPh3) reacts with 1-methylcytosine (1-MeCy) and 9-Methyladenine (9-MeAd) in solution of MeCN, PhCN, Me3CCN and Ph2(H)CCN. Reaction of 1a,b and 2a,b with HCl affords the protonated amidines [NH2C(R){1-MeCy(-H)}]NO3 (R = Me, 3a; Ph, 3b) and [NH2C(R){9-MeAd(-H)}]NO3 (R = Me, 4a; Ph, 4b) and cis-(PPh3)2PtCl2 in quantitative yield. Treatment of 3b and 4b with NaOH allows the isolation of the neutral benzimidamides NH2-C(Ph){1-MeCy(-2H)} (5b) and NH2-C(Ph){9-MeAd(-2H)} (6b). In the solid state 3b shows a planar structure with the hydrogen atom on N(4) cytosine position involved in a strong H-bond with the NO3− ion. Intermolecular H-bonds between the oxygen of the cytosine ring and one of the H atoms of the amidine-NH2 group allow the dimerization of the molecule. A detailed analysis of the spectra of 3b in DMF-d7 at −55 °C indicates the presence of an equilibrium between the species [NH2C(R){1-MeCy(-H)}]NO3 and [NH2C(R){1-MeCy(-H)}]2(NO3)2, exchanging with trace amounts of water at 25 °C. [15N,1H]-HMBC experiments for 5b and 6b indicate that the amino tautomer H2N-C(Ph){nucleobase(-2H)}, is the only detectable in solution and such structure has been confirmed in the solid state. The reaction of 5b and 6b with cis-L2Pt(ONO2)2 (L = PPh3), in chlorinated solvents, determines the immediate appearance of a pale yellow colour due to the coordination of the neutral amidine, likely in its imino form HNC(Ph){nucleobase(-H)}, to give the adducts cis-[L2PtNHC(Ph){nucleobase(-H)}]2+. In fact, addition of “proton sponge” leads to the immediate deprotonation of the amidine ligand with formation of the starting complexes 1b and 2b.

  • platinum ii mediated coupling reactions of acetonitrile with the exocyclic nitrogen of 9 Methyladenine and 1 methylcytosine synthesis nmr characterization and x ray structures of new azametallacycle complexes
    Inorganic Chemistry, 2006
    Co-Authors: Bruno Longato, Diego Montagner, Giuliano Bandoli, Ennio Zangrando
    Abstract:

    The hydroxo complex cis-[L2Pt(μ-OH)]2(NO3)2, (L = PMePh2, 1a), in CH3CN solution, deprotonates the NH2 group of 9-Methyladenine (9-MeAd) to give the cyclic trinuclear species cis-[L2Pt{9-MeAd(−H)}]3(NO3)3, (L = PMePh2, 2a), in which the nucleobase binds the metal centers through the N(1), N(6) atoms. In solution at room temperature, 2a slowly reacts with the solvent to form quantitatively the mononuclear azametallacycle cis-[L2PtNHC(Me){9-MeAd(−2H)}]NO3 (L = PMePh2, 3a), containing as anionic ligand the deprotonated form of molecule N-(9-methyl-1,9-dihydro-purin-6-ylidene)-acetamidine. In the same experimental conditions, the hydroxo complex with PPh3 (1b) forms immediately the insertion product 3b. Single-crystal X-ray analyses of 3a and 3b show the coordination of the platinum cation at the N(1) site of the purine moiety and to the N atom of the inserted acetonitrile, whereas the exocyclic amino nitrogen binds the carbon atom of the same CN group. The resulting six-membered ring is slightly distorted fr...

  • complexes of platinum ii containing neutral and deprotonated 9 Methyladenine synthesis x ray structures and nmr studies on the cyclic trimer cis l2pt 9 mead bond h 3 no3 3 and the dinuclear cis l2pt ono2 9 mead bond h ptl2 no3 2 l pmeph2
    Inorganic Chemistry, 2003
    Co-Authors: Bruno Longato, Lucia Pasquato, Adele Mucci, Luisa Schenetti, Ennio Zangrando
    Abstract:

    The dinuclear hydroxo complex cis-[L 2 Pt(μ-OH)] 2 (NO 3 ) 2 (L = PMePh 2 , 1), in CH 2 Cl 2 , CH 3 CN, or DMF solution, deprotonates the NH 2 group of 9-Methyladenine (9-MeAd) to give the complex cis-[L 2 Pt{9-MeAd(-H)}] 3 (NO 3 ) 3 , 2, which was isolated in good yield. The X-ray structure shows that the nucleobase binds symmetrically the metal centers through the N(1),N(6) atoms forming a cyclic trimer with Pt...Pt distances in the range 5.202(1)-5.382(1) A. Dissolution of 2 in DMSO or DMF determines the partial (or total) dissociation of the cyclic structure to form several fragments. A multinuclear NMR analysis of the resulting mixture supports the presence of the mononuclear species cis-[L 2 Pt{9-MeAd(-H)}] + , 3, in which the deprotonated nucleobase chelates the metal center with the N(6),N(7) atoms. Addition of a stoichiometric amount of the nitrato complex cis-[L 2 Pt(ONO 2 ) 2 ] (L = PMePh 2 , 4) to a DMSO or DMF solution of 2 affords quantitatively the diplatinated compound cis-[L 2 Pt(ONO 2 ){9-MeAd(-H)}-PtL 2 ](NO 3 ) 2 , 5. The single-crystal X-ray analysis shows that the adenine behaves as a tridentate ligand bridging two cis-L 2 Pt units at the N(1) and N(6),N(7) sites, respectively [Pt(1)-N(1) = 2.109(5) A, Pt(2)-N(6) = 2.095(7) A, Pt(2)-N(7) = 2.126(7) A]. The N(1)-bonded metal center completes the coordination sphere through an oxygen atom of a nitrate group, and its coordination plane is arranged orthogonally with respect the second one. The Pt-O distance [2.109(5) A] is similar to those found in the nitrato complex 4 [2.110 A, average]. The related complex cis=[(L 2 Pt(ONO 2 )} 2 (9-MeAd)](NO 3 ) 2 , 6, containing the neutral adenine platinated at the N(1),N(7) atoms, was isolated and its stability in solution investigated by NMR spectroscopy. In DMSO, 6 undergoes decomposition forming a mixture of the species 4, 5, and the adenine mono- and bis-adducts cis-[L 2 Pt(9-MeAd)(DMSO)] 2 + , 7, and cis-[L 2 -Pt(9-MeAd) 2 ] 2 + , 8, respectively. This last complex, quantitatively formed upon addition of 9-MeAd (Pt/adenine = 1:2) to the mixture, was also isolated and characterized.

  • coordination modes of 9 Methyladenine in cis platinum ii complexes with dimethyl phenyl phosphanes as ancillary ligands synthesis and characterization of cis ptl2 9 mead 2 no3 2 cis ptl2 9 mead h 3 no3 3 and cis l2pt 9 mead h ptl2 no3 3
    European Journal of Inorganic Chemistry, 2003
    Co-Authors: Bruno Longato, Lucia Pasquato, Adele Mucci, Luisa Schenetti
    Abstract:

    Treatment of 9-Methyladenine (9-MeAd) with cis-[PtL2(NO3)2] (1) (L = PMe2Ph) in a 2:1 molar ratio generated the bis(adduct) cis-[PtL2(9-MeAd)2](NO3)2 (2), which was isolated and fully characterized by multinuclear (1H, 31P, 13C, 195Pt and 15N) NMR analysis, which showed that the two nucleobases are selectively coordinated through the N1 atom. Small amounts of a mono(adduct) cis-[PtL2(S)(9-MeAd)]2+ (3) (S = solvent) and of a diplatinated species cis-[L2Pt(S){9-MeAd(−H)}PtL2]3+ (4) are formed in DMSO solution when 9-MeAd is present in smaller quantities than 1. Complex 3 is platinated at N1, with a solvent molecule representing the fourth ligand around the metal center. Complex 4 contains an adenine molecule deprotonated and platinated at N1,N6,N7, with two cis-L2Pt units bonded to nitrogen atom N1 and to nitrogen atoms N6 and N7, respectively. With increasing relative concentration of the nucleobase, both complexes 3 and 4 progressively convert into the bis(adduct) 2, the only species detectable in solution when the Ad/Pt molar ratio is 2:1. The trinuclear compound cis-[L2Pt{9-MeAd(−H)}]3(NO3)3 (5) (L = PMe2Ph), containing an NH2-deprotonated nucleobase bridging the metal centers through the N1 and N6 atoms, is quantitatively formed when the dinuclear hydroxo complex cis-[Pt(μ-OH)L2]2(NO3)2 (6) reacts with 9-MeAd in CH3CN solution. The isolated complex was fully characterized by multinuclear NMR spectroscopy and mass spectrometry. It appears to be stable in solution in CH3CN and chlorinated solvents, whereas in DMSO it partially converts into a new species, probably the dinuclear analog cis-[PtL2{9-MeAd(−H)}]2(NO3)2, in which the adenine maintains its coordination mode. At equilibrium the trinuclear/dinuclear species molar ratio is 20:1. Through the addition of a stoichiometric amount of nitrate 1 to a DMSO solution of 5 we were able to generate the diplatinated compound 4 in high yield. Complex 4 displays a new coordination mode for the adeninate ion, with N1 bonded to one platinum atom whereas N6 and N7 are chelated to a second one. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Bernhard Lippert - One of the best experts on this subject based on the ideXlab platform.

  • Multiple Metal Binding to the 9Methyladenine Model Nucleobase Involving N1, N6, and N7: Discrete Di- and Trinuclear Species with Different Combinations of Monofunctional PdII and PtII Entities
    2016
    Co-Authors: Tímea Mihály, Marta Garijo Añorbe, Francisca M. Albertí, Pablo Sanz J. Miguel, Bernhard Lippert
    Abstract:

    Several di- and trinuclear metal complexes consisting of the model nucleobase 9-Methyladenine (9-MeA) or its mono-deprotonated form (9-MeA–) and monofunctional (dien)­PdII, (dien)­PtII, (NH3)3PtII, or (trpy)­PdII in different combinations have been prepared and/or studied in solution by NMR spectroscopy: [{Pd­(dien)}3(9-MeA–-N1,N6,N7)]­Cl3.5(PF6)1.5·3H2O (1), [(dien)­Pd­(N1-9-MeA-N7)­Pt­(NH3)3]­(ClO4)4·9.33H2O (2), [(dien)­Pt­(N1-9-MeA-N7)­Pt­(NH3)3]­(ClO4)4·H2O (3), and [{(trpy)­Pd}2(N1,N6-9-MeA–-N7)­Pt­(NH3)3]­(ClO4)5·3H2O (4). A migration product of 3, [(dien)­Pt­(N6-9-MeA–-N7)­Pt­(NH3)3]3+ (3a), has been identified in solution. Unlike Pt-adenine bonds, Pd-adenine bonds are substantially labile, and consequently all Pd-containing complexes discussed here (1, 2, 4) exist in aqueous solution in equilibria of slowly interconverting species, which give rise to individual resonances in the 1H NMR spectra. For example, 1 exists in an equilibrium of five adenine-containing species when dissolved in D2O, 2 undergoes dissociation to [Pt­(NH3)3(9-MeA-N7)]2+ or forms the migration product [(dien)­Pd­(N6-9-MeA–-N7)­Pt­(NH3)3]3+ (2a), depending on pD, and 4 loses both (trpy)­PdII entities as the pD is increased. In no case is Pd binding to N3 of the adenine ring observed. A comparison of the solid-state structures of the two trinuclear complexes 1 and 4 reveals distinct differences between the Pd atoms bonded to N1 and N6 in that these are substantially out of the nucleobase plane in 1, by ca. 0.6 Å and −1.0 Å, respectively, whereas they are coplanar with the 9-MeA– plane in 4. These out-of-plane movements of the two (dien)­PdII units in 1 are not accompanied by changes in hybridization states of the N1 and N6 atoms

  • synthesis and x ray crystal structure analysis of 1 1 and 1 2 complexes of cisplatin with the model nucleobase 9 Methyladenine in its protonated form and a unique hno3 adduct of cis nh3 2pt 9 meah n7 2 4
    Inorganica Chimica Acta, 2005
    Co-Authors: Egla Yareth Biviancastro, Michael Roitzsch, Deepali Gupta, Bernhard Lippert
    Abstract:

    Abstract The 1:1 and 1:2 complexes of cis-(NH3)2PtII with 9-methyladeninium cations, 9-MeAH+, have been prepared and characterized by X-ray crystallography: cis-[(NH3)2Pt(9-MeAH-N7)Cl](NO3)2 (1) and cis-[(NH3)2Pt(9-MeAH-N7)2](NO3)4 · 2HNO3 · 2H2O (2). The pKa values for 9-MeAH+ in H2O are 1.7 in 1 as well as 0.4 (pKa1) and 1.3 (pKa2) for 2, as determined by pD dependent 1H NMR spectroscopy. Compound 2 is special in that it crystallizes with two equivalents of HNO3 per Pt entity. The HNO3 molecules are stacked in rectangular channels provided by cis-(NH3)2PtII units, 9-methyladeninium ligands and nitrate anions, which form a porous network of hydrogen bonds.

  • metal stabilized rare tautomers of nucleobases 6 imino tautomer of adenine in a mixed nucleobase complex of mercury ii
    Inorganic Chemistry, 1997
    Co-Authors: Felix Zamora, Michal Sabat, Michele Kunsman, Bernhard Lippert
    Abstract:

    (1,3-Dimethyluracil-5-yl)mercury(II), (1,3-DimeU-C5)HgII, reacts with the model nucleobase 9-Methyladenine (9-MeA) to give the mixed-nucleobase complex [Hg(1,3-DimeU-C5)(9-MeA-N6)]NO3·H2O. Hg(II) binds to the adenine via the N6 position with N1 being protonated. The neutral adenine nucleobase is therefore present in its imino form, which represents the rare tautomer form of this nucleobase. The X-ray crystal structure analysis reveals an anti orientation of the (1,3-DimeU-C5)HgII entity with respect to N1 of 9-MeA and substantial differences in nucleobase geometry as compared to the amino tautomer form of 9-MeA. These differences refer to both the pyrimidine and the imidazole rings of the purine base. The possible relevance of this compound with regard to nucleobase cross-linking in DNA and nucleobase mispairing is discussed. Attempts to demonstrate mispairing between the metalated rare tautomer and “the wrong” bases 1-methylcytosine (1-MeC) and 9-ethylguanine (9-EtGH) in DMSO-d6 proved unsuccessful due t...

  • cis pt nh3 2 9 mea n7 9 etgh n7 pf6 2 1 5h2o 9 mea 9 Methyladenine 9 etgh 9 ethylguanine a right handed helicoidal model compound for the intrastrand a g cross link in duplex dna
    Inorganic Chemistry, 1997
    Co-Authors: Guy Schroder, Michal Sabat, Ivan Baxter, Jiri Kozelka, Bernhard Lippert
    Abstract:

    The counterions X in cis-[Pt(NH3)2(9-MeA-N7)(9-EtGH-N7)]X2 (1) determine, in the solid state, which of the possible orientations the two purine nucleobases display. With X = PF6-, the right-handed helicoidal head−head conformation R2 encountered in double-stranded oligonucleotide adducts of cis-Pt(NH3)22+ is realized, together with its enantiomeric counterpart L2. 1 therefore provides a model of the d(ApG) intrastrand adduct of cisplatin with double-stranded DNA. H-bond formation between the platinated guanine in 1 and 1-methylcytosine in DMSO-d6 is not strictly analogous to that between the Watson−Crick pair of free 9-EtGH and 1-MeC.

Ennio Zangrando - One of the best experts on this subject based on the ideXlab platform.

  • metal promoted synthesis of amidines containing the model nucleobases 1 methylcytosine and 9 Methyladenine
    Dalton Transactions, 2011
    Co-Authors: Diego Montagner, Ennio Zangrando, Giuseppe Borsato, Vittorio Lucchini, Bruno Longato
    Abstract:

    The amidine complexes cis-[L2PtNHC(R){1-MeCy(-2H)}]NO3 (R = Me, 1a; Ph, 1b, Me3C, 1c; Ph2(H)C, 1d) and cis-[L2PtNHC(R){9-MeAd(-2H)}]NO3 (R = Me, 2a; Ph, 2b; Me3C, 2c; Ph2(H)C, 2d), are formed when cis-[L2Pt(μ-OH)]2(NO3)2 (L = PPh3) reacts with 1-methylcytosine (1-MeCy) and 9-Methyladenine (9-MeAd) in solution of MeCN, PhCN, Me3CCN and Ph2(H)CCN. Reaction of 1a,b and 2a,b with HCl affords the protonated amidines [NH2C(R){1-MeCy(-H)}]NO3 (R = Me, 3a; Ph, 3b) and [NH2C(R){9-MeAd(-H)}]NO3 (R = Me, 4a; Ph, 4b) and cis-(PPh3)2PtCl2 in quantitative yield. Treatment of 3b and 4b with NaOH allows the isolation of the neutral benzimidamides NH2-C(Ph){1-MeCy(-2H)} (5b) and NH2-C(Ph){9-MeAd(-2H)} (6b). In the solid state 3b shows a planar structure with the hydrogen atom on N(4) cytosine position involved in a strong H-bond with the NO3− ion. Intermolecular H-bonds between the oxygen of the cytosine ring and one of the H atoms of the amidine-NH2 group allow the dimerization of the molecule. A detailed analysis of the spectra of 3b in DMF-d7 at −55 °C indicates the presence of an equilibrium between the species [NH2C(R){1-MeCy(-H)}]NO3 and [NH2C(R){1-MeCy(-H)}]2(NO3)2, exchanging with trace amounts of water at 25 °C. [15N,1H]-HMBC experiments for 5b and 6b indicate that the amino tautomer H2N-C(Ph){nucleobase(-2H)}, is the only detectable in solution and such structure has been confirmed in the solid state. The reaction of 5b and 6b with cis-L2Pt(ONO2)2 (L = PPh3), in chlorinated solvents, determines the immediate appearance of a pale yellow colour due to the coordination of the neutral amidine, likely in its imino form HNC(Ph){nucleobase(-H)}, to give the adducts cis-[L2PtNHC(Ph){nucleobase(-H)}]2+. In fact, addition of “proton sponge” leads to the immediate deprotonation of the amidine ligand with formation of the starting complexes 1b and 2b.

  • platinum ii mediated coupling reactions of acetonitrile with the exocyclic nitrogen of 9 Methyladenine and 1 methylcytosine synthesis nmr characterization and x ray structures of new azametallacycle complexes
    Inorganic Chemistry, 2006
    Co-Authors: Bruno Longato, Diego Montagner, Giuliano Bandoli, Ennio Zangrando
    Abstract:

    The hydroxo complex cis-[L2Pt(μ-OH)]2(NO3)2, (L = PMePh2, 1a), in CH3CN solution, deprotonates the NH2 group of 9-Methyladenine (9-MeAd) to give the cyclic trinuclear species cis-[L2Pt{9-MeAd(−H)}]3(NO3)3, (L = PMePh2, 2a), in which the nucleobase binds the metal centers through the N(1), N(6) atoms. In solution at room temperature, 2a slowly reacts with the solvent to form quantitatively the mononuclear azametallacycle cis-[L2PtNHC(Me){9-MeAd(−2H)}]NO3 (L = PMePh2, 3a), containing as anionic ligand the deprotonated form of molecule N-(9-methyl-1,9-dihydro-purin-6-ylidene)-acetamidine. In the same experimental conditions, the hydroxo complex with PPh3 (1b) forms immediately the insertion product 3b. Single-crystal X-ray analyses of 3a and 3b show the coordination of the platinum cation at the N(1) site of the purine moiety and to the N atom of the inserted acetonitrile, whereas the exocyclic amino nitrogen binds the carbon atom of the same CN group. The resulting six-membered ring is slightly distorted fr...

  • complexes of platinum ii containing neutral and deprotonated 9 Methyladenine synthesis x ray structures and nmr studies on the cyclic trimer cis l2pt 9 mead bond h 3 no3 3 and the dinuclear cis l2pt ono2 9 mead bond h ptl2 no3 2 l pmeph2
    Inorganic Chemistry, 2003
    Co-Authors: Bruno Longato, Lucia Pasquato, Adele Mucci, Luisa Schenetti, Ennio Zangrando
    Abstract:

    The dinuclear hydroxo complex cis-[L 2 Pt(μ-OH)] 2 (NO 3 ) 2 (L = PMePh 2 , 1), in CH 2 Cl 2 , CH 3 CN, or DMF solution, deprotonates the NH 2 group of 9-Methyladenine (9-MeAd) to give the complex cis-[L 2 Pt{9-MeAd(-H)}] 3 (NO 3 ) 3 , 2, which was isolated in good yield. The X-ray structure shows that the nucleobase binds symmetrically the metal centers through the N(1),N(6) atoms forming a cyclic trimer with Pt...Pt distances in the range 5.202(1)-5.382(1) A. Dissolution of 2 in DMSO or DMF determines the partial (or total) dissociation of the cyclic structure to form several fragments. A multinuclear NMR analysis of the resulting mixture supports the presence of the mononuclear species cis-[L 2 Pt{9-MeAd(-H)}] + , 3, in which the deprotonated nucleobase chelates the metal center with the N(6),N(7) atoms. Addition of a stoichiometric amount of the nitrato complex cis-[L 2 Pt(ONO 2 ) 2 ] (L = PMePh 2 , 4) to a DMSO or DMF solution of 2 affords quantitatively the diplatinated compound cis-[L 2 Pt(ONO 2 ){9-MeAd(-H)}-PtL 2 ](NO 3 ) 2 , 5. The single-crystal X-ray analysis shows that the adenine behaves as a tridentate ligand bridging two cis-L 2 Pt units at the N(1) and N(6),N(7) sites, respectively [Pt(1)-N(1) = 2.109(5) A, Pt(2)-N(6) = 2.095(7) A, Pt(2)-N(7) = 2.126(7) A]. The N(1)-bonded metal center completes the coordination sphere through an oxygen atom of a nitrate group, and its coordination plane is arranged orthogonally with respect the second one. The Pt-O distance [2.109(5) A] is similar to those found in the nitrato complex 4 [2.110 A, average]. The related complex cis=[(L 2 Pt(ONO 2 )} 2 (9-MeAd)](NO 3 ) 2 , 6, containing the neutral adenine platinated at the N(1),N(7) atoms, was isolated and its stability in solution investigated by NMR spectroscopy. In DMSO, 6 undergoes decomposition forming a mixture of the species 4, 5, and the adenine mono- and bis-adducts cis-[L 2 Pt(9-MeAd)(DMSO)] 2 + , 7, and cis-[L 2 -Pt(9-MeAd) 2 ] 2 + , 8, respectively. This last complex, quantitatively formed upon addition of 9-MeAd (Pt/adenine = 1:2) to the mixture, was also isolated and characterized.

Helmut Sigel - One of the best experts on this subject based on the ideXlab platform.

  • Steric Guiding of Metal Ion Binding to a Purine Residue by a Non-Coordinating Amino Group: Examplified by 9-[(2-Phosphonomethoxy)ethyl]-2-aminopurine (PME2AP), an Isomer of the Antiviral Nucleotide Analogue 9-[(2-Phosphonomethoxy)ethyl]adenine (PMEA)
    Coordination Chemistry Reviews, 2011
    Co-Authors: Astrid Sigel, Bert P. Operschall, Helmut Sigel
    Abstract:

    Abstract The role that the amino group plays in the metal ion (M2+) binding properties of the adenine residue is of great relevance because this residue occurs widely in nature. It is the aim of this review to evaluate this role. We consider first several 9-methylpurine derivatives with amino and methyl substituents at various positions: the data indicate that substituents at C6 inhibit M2+ binding at both, the N1 and N7 sites. To separate these effects we use (i) o-amino(methyl)pyridines as models for the pyrimidine part of the adenine residue, i.e., for N1, and (ii) benzimidazole derivatives regarding the properties of N7. The inhibiting effects of ortho-amino and ortho-methyl groups on N1 of pyridines are identical, which agrees with the fact that such an amino group has no basic properties at all. This is different with 1-methyl-4-aminobenzimidazole (MABI) ( 9-methyl-1,3-dideazaadenine) and 1,4-dimethylbenzimidazole (DMBI) ( 6,9-dimethyl-1,3-dideazapurine) because the amino group in MABI still has some basic properties and thus, its steric inhibition is somewhat smaller than that of the methyl group in DMBI. It is suggested that the methyl group in DMBI mimics the steric effects of (C6)NH2 upon (N7)-M2+ coordination in the adenine residue. The evaluation of the N1 versus N7 dichotomy for 2,9-dimethylpurine, 2-amino-9-methylpurine, and 6-amino-9-methylpurine ( 9-Methyladenine) reveals that the (N7)-M2+ isomer dominates. It is further suggested that the (C6)NH2 adenine group may act as a proton donor and the O atom of a coordinated water molecule as acceptor. The metal ion-binding properties of the two acyclic nucleotide analogues 9-[(2-phosphonomethoxy)ethyl]adenine (PMEA) and 9-[(2-phosphonomethoxy)ethyl]-2-aminopurine (PME2AP), which are structural isomers due to the shift of the (C6)NH2 group in PMEA to the C2 site in PME2AP, fit into the indicated coordination patterns. In the monoprotonated species M(H;PMEA)+ and M(H;PME2AP)+ the proton is located at the phosphonate group and M2+ at N7. However, the M(H;PME2AP)+ complexes are considerably more stable than the M(H;PMEA)+ ones: indeed, the steric effect on N1 is the same in both types of complexes, but the one on N7 has disappeared in M(H;PME2AP)+. Furthermore, there is evidence that the (N7)-coordinated M2+ interacts with the P(O)2(OH)− group in an outersphere manner leading to practically identical formation degrees of the macrochelates formed with Mn2+, Co2+, Ni2+, Cu2+ or Zn2+ [on average 65 ± 15% (3σ)]. The coordination chemistry of PMEA2− and PME2AP2− differs for the 3d ions as well, whereas for the alkaline earth ions, which are primarily coordinated (like all other M2+) to the phosphonate group, 5-membered chelates form involving the ether O of the – CH 2 CH 2 – O – CH 2 – P O 3 2 − residue. In contrast, Co2+, Ni2+, and Cu2+ form with PMEA2− a further isomer, which involves next to the ether O also N3; macrochelates involving N7 and the phosphonate-coordinated M2+ are minority species, but for Ni2+ and Cu2+ they occur and formation degrees of all four isomers could be determined. In the M(PME2AP) complexes a N3 interaction practically does not occur; macrochelate formation of the phosphonate-coordinated M2+ with N7, which is the dominating species for Co2+, Ni2+, Cu2+ or Zn2+ is important here. The possible interrelations between M2+ coordination and the antiviral activity of the two acyclic nucleotide analogues, PMEA being especially active, are discussed shortly.

Luisa Schenetti - One of the best experts on this subject based on the ideXlab platform.

  • complexes of platinum ii containing neutral and deprotonated 9 Methyladenine synthesis x ray structures and nmr studies on the cyclic trimer cis l2pt 9 mead bond h 3 no3 3 and the dinuclear cis l2pt ono2 9 mead bond h ptl2 no3 2 l pmeph2
    Inorganic Chemistry, 2003
    Co-Authors: Bruno Longato, Lucia Pasquato, Adele Mucci, Luisa Schenetti, Ennio Zangrando
    Abstract:

    The dinuclear hydroxo complex cis-[L 2 Pt(μ-OH)] 2 (NO 3 ) 2 (L = PMePh 2 , 1), in CH 2 Cl 2 , CH 3 CN, or DMF solution, deprotonates the NH 2 group of 9-Methyladenine (9-MeAd) to give the complex cis-[L 2 Pt{9-MeAd(-H)}] 3 (NO 3 ) 3 , 2, which was isolated in good yield. The X-ray structure shows that the nucleobase binds symmetrically the metal centers through the N(1),N(6) atoms forming a cyclic trimer with Pt...Pt distances in the range 5.202(1)-5.382(1) A. Dissolution of 2 in DMSO or DMF determines the partial (or total) dissociation of the cyclic structure to form several fragments. A multinuclear NMR analysis of the resulting mixture supports the presence of the mononuclear species cis-[L 2 Pt{9-MeAd(-H)}] + , 3, in which the deprotonated nucleobase chelates the metal center with the N(6),N(7) atoms. Addition of a stoichiometric amount of the nitrato complex cis-[L 2 Pt(ONO 2 ) 2 ] (L = PMePh 2 , 4) to a DMSO or DMF solution of 2 affords quantitatively the diplatinated compound cis-[L 2 Pt(ONO 2 ){9-MeAd(-H)}-PtL 2 ](NO 3 ) 2 , 5. The single-crystal X-ray analysis shows that the adenine behaves as a tridentate ligand bridging two cis-L 2 Pt units at the N(1) and N(6),N(7) sites, respectively [Pt(1)-N(1) = 2.109(5) A, Pt(2)-N(6) = 2.095(7) A, Pt(2)-N(7) = 2.126(7) A]. The N(1)-bonded metal center completes the coordination sphere through an oxygen atom of a nitrate group, and its coordination plane is arranged orthogonally with respect the second one. The Pt-O distance [2.109(5) A] is similar to those found in the nitrato complex 4 [2.110 A, average]. The related complex cis=[(L 2 Pt(ONO 2 )} 2 (9-MeAd)](NO 3 ) 2 , 6, containing the neutral adenine platinated at the N(1),N(7) atoms, was isolated and its stability in solution investigated by NMR spectroscopy. In DMSO, 6 undergoes decomposition forming a mixture of the species 4, 5, and the adenine mono- and bis-adducts cis-[L 2 Pt(9-MeAd)(DMSO)] 2 + , 7, and cis-[L 2 -Pt(9-MeAd) 2 ] 2 + , 8, respectively. This last complex, quantitatively formed upon addition of 9-MeAd (Pt/adenine = 1:2) to the mixture, was also isolated and characterized.

  • coordination modes of 9 Methyladenine in cis platinum ii complexes with dimethyl phenyl phosphanes as ancillary ligands synthesis and characterization of cis ptl2 9 mead 2 no3 2 cis ptl2 9 mead h 3 no3 3 and cis l2pt 9 mead h ptl2 no3 3
    European Journal of Inorganic Chemistry, 2003
    Co-Authors: Bruno Longato, Lucia Pasquato, Adele Mucci, Luisa Schenetti
    Abstract:

    Treatment of 9-Methyladenine (9-MeAd) with cis-[PtL2(NO3)2] (1) (L = PMe2Ph) in a 2:1 molar ratio generated the bis(adduct) cis-[PtL2(9-MeAd)2](NO3)2 (2), which was isolated and fully characterized by multinuclear (1H, 31P, 13C, 195Pt and 15N) NMR analysis, which showed that the two nucleobases are selectively coordinated through the N1 atom. Small amounts of a mono(adduct) cis-[PtL2(S)(9-MeAd)]2+ (3) (S = solvent) and of a diplatinated species cis-[L2Pt(S){9-MeAd(−H)}PtL2]3+ (4) are formed in DMSO solution when 9-MeAd is present in smaller quantities than 1. Complex 3 is platinated at N1, with a solvent molecule representing the fourth ligand around the metal center. Complex 4 contains an adenine molecule deprotonated and platinated at N1,N6,N7, with two cis-L2Pt units bonded to nitrogen atom N1 and to nitrogen atoms N6 and N7, respectively. With increasing relative concentration of the nucleobase, both complexes 3 and 4 progressively convert into the bis(adduct) 2, the only species detectable in solution when the Ad/Pt molar ratio is 2:1. The trinuclear compound cis-[L2Pt{9-MeAd(−H)}]3(NO3)3 (5) (L = PMe2Ph), containing an NH2-deprotonated nucleobase bridging the metal centers through the N1 and N6 atoms, is quantitatively formed when the dinuclear hydroxo complex cis-[Pt(μ-OH)L2]2(NO3)2 (6) reacts with 9-MeAd in CH3CN solution. The isolated complex was fully characterized by multinuclear NMR spectroscopy and mass spectrometry. It appears to be stable in solution in CH3CN and chlorinated solvents, whereas in DMSO it partially converts into a new species, probably the dinuclear analog cis-[PtL2{9-MeAd(−H)}]2(NO3)2, in which the adenine maintains its coordination mode. At equilibrium the trinuclear/dinuclear species molar ratio is 20:1. Through the addition of a stoichiometric amount of nitrate 1 to a DMSO solution of 5 we were able to generate the diplatinated compound 4 in high yield. Complex 4 displays a new coordination mode for the adeninate ion, with N1 bonded to one platinum atom whereas N6 and N7 are chelated to a second one. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)