RESUMO
The complete NMR signal assignment of title compounds were carried out by extensive use of 1D and 2D NMR techniques (1H, 13C, COSY, HSQC and HMBC).
Assuntos
Antineoplásicos/química , Antineoplásicos/classificação , Indóis/química , Quinolinas/química , Isótopos de Carbono , Espectroscopia de Ressonância Magnética/normas , Estrutura Molecular , Isótopos de Nitrogênio , Prótons , Padrões de ReferênciaRESUMO
Topotecan (TPT) is in clinical use as an antitumor agent. It acts by binding to the covalent complex formed between nicked DNA and topoisomerase I, and inserts itself into the single-strand nick, thereby inhibiting the religation of the nick and acting as a poison. A crystal structure analysis of the ternary complex has shown how the drug binds (B. L. Staker, K. Hjerrild, M. D. Feese, C. A. Behnke, A. B. Burgin, L. Stewart, Proc. Natl. Acad. Sci. U.S.A., 2002, 99, 15 387-15 392), but has left a number of unanswered questions. Herein, we use NMR spectroscopy and molecular modeling to show that the solution structure of a complex of TPT with nicked natural DNA is similar, but not identical to the crystal conformation, and that other geometries are of very low population. We also show that the lactone form of TPT binds approximately 40 times more strongly than the ring-opened carboxylate.
Assuntos
DNA/química , Oligonucleotídeos/química , Topotecan/química , Sítios de Ligação , Simulação por Computador , Modelos Químicos , Modelos Moleculares , Conformação Molecular , Oligonucleotídeos/síntese química , Oligonucleotídeos/isolamento & purificação , Soluções/químicaRESUMO
The complete NMR signal assignment of title compounds were carried out by extensive use of 1D and 2D NMR techniques (1H, 13C, GCOSY, GHSQC and GHMBC).
Assuntos
Aminoglicosídeos/análise , Antineoplásicos/análise , Isótopos de Carbono/química , Hidrogênio/química , Espectroscopia de Ressonância Magnética/métodos , Aminoglicosídeos/química , Antineoplásicos/química , Indóis/análise , Indóis/química , Estrutura Molecular , Prótons , Quinolinas/análise , Quinolinas/químicaRESUMO
The syntheses of 5-pyridyl-3(beta-D-galactopyranosyl)-1,3,4-oxadiazole-2-thiones 3a-3c and 5-pyridyl-2(beta-D-galactopyranosyl)-4-benzyl-1,2, 4-triazole-3-thiones 6a-6c are reported. The existence of N-galactosides--not S-galactosides--was proven by IR and 15N NMR spectroscopy. The structures of the final products and the intermediates were elucidated by IR, 1H, 13C and 15N NMR spectroscopy and mass spectrometry.
Assuntos
Galactosídeos/química , Galactosídeos/síntese química , Oxidiazóis/química , Tionas/química , Triazóis/química , Cromatografia em Camada Fina , Espectroscopia de Ressonância Magnética , Espectrometria de Massas , Oxidiazóis/síntese química , Espectrofotometria Infravermelho , Tionas/síntese química , Triazóis/síntese químicaRESUMO
A dumbbell double-stranded DNA decamer tethered with a hexaethylene glycol linker moiety (DDSDPEG), with a nick in the centre of one strand, has been synthesised. The standard NMR methods, E.COSY, TOCSY, NOESY and HMQC, were used to measure (1)H, (31)P and T:(1) spectral parameters. Molecular modelling using rMD-simulated annealing was used to compute the structure. Scalar couplings and dipolar contacts show that the molecule adopts a right-handed B-DNA helix in 38 mM phosphate buffer at pH 7. Its high melting temperature confirms the good base stacking and stability of the duplex. This is partly attributed to the presence of the PEG(6) linker at both ends of the duplex that restricts the dynamics of the stem pentamers and thus stabilises the oligonucleotide. The inspection of the global parameters shows that the linker does not distort the B-DNA geometry. The computed structure suggests that the presence of the nick is not disturbing the overall tertiary structure, base pair geometry or duplex base pairing to a substantial extent. The nick has, however, a noticeable impact on the local geometry at the nick site, indicated clearly by NMR analysis and reflected in the conformational parameters of the computed structure. The (1)H spectra also show much sharper resonances in the presence of K(+) indicating that conformational heterogeneity of DDSDPEG is reduced in the presence of potassium as compared to sodium or caesium ions. At the same time the (1)H resonances have longer T:(1) times. This parameter is suggested as a sensitive gauge of stabilisation.
Assuntos
Etilenoglicóis/química , Oligonucleotídeos/química , Cátions/farmacologia , Concentração de Íons de Hidrogênio , Espectroscopia de Ressonância Magnética/métodos , Estrutura Molecular , Conformação de Ácido Nucleico/efeitos dos fármacos , Desnaturação de Ácido Nucleico , Ácidos Nucleicos Heteroduplexes/química , Concentração Osmolar , TemperaturaRESUMO
The 15N results reveal a difference in the extent of intramolecular hydrogen bond formation exhibited by the Schiffs base, compound 2, in solution and the solid state. Comparison of the 15N shielding changes observed, with those arising from protonation, provides the basis for a quantitative estimate of the strength of the hydrogen bonds formed.