Photochemistry of the alkaloids eudistomin N (6-bromo-nor-harmane) and eudistomin O (8-bromo-nor-harmane) and other bromo-β-carbolines

• Autores: Tarzi, Olga Inés; Erra Balsells, Rosa
• Año de publicación: 2005
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: fotochemistry; fotofisica; carbolinas; bromo-carbolinas
• Institución: Consejo Nacional de Investigaciones Científicas y Técnicas

The UV-absorption, fluorescence excitation and emission spectra of the alkaloids eudistomin N (6-bromo-nor-harmane) and eudistomin O (8-bromo-nor-harmane) were described. In order to perform a comparative analysis, we also studied other bromob-carbolines and the corresponding non-substituted-carboline. Thus, 6-bromo-, 8-bromo-, 6,8-dibromo-, 3,6-dibromo- and 3,6,8- tribromo-derivatives of nor-harmane, harmane and harmine were studied. These studies were performed in EtOH and in EtOH + 1% perchloric acid solutions (pa). Furthermore, fluorescence quantum yields (/f) in acetonitrile and acetonitrile + 1% perchloric acid solutions at 298 K were measured. The HOMO and LUMO energy, the positions (kmax) and oscillator strength (f) of the 1 S1 1 S0 band for all the neutral and protonated b-carbolines studied was calculated and compared with the experimental data. The pKa values in aqueous solution for eudistomin N and O (6-bromo- and 8-bromo-nor-harmane), for 6-bromo-, 8-bromoand 6,8-dibromo-harmane, and for 6-bromo- and 8-bromo-harmine were spectrophotometrically measured ðpKaðH2OÞÞ. The change of the acid–base character of these compounds on going from the ground state (pKa) to the first electronic excited singlet state ðpK aÞ as DpKa ¼ pK a pKa ¼ 0:625D m=T , in ethanol solution at 298 K were calculated (DpKa(EtOH)). Proton affinities (PA) for all the compounds studied defined as minus the enthalpy change of the reaction M + H+ ! MH+ (gas state) were calculated. Basicity relative to pyridine (DHrPy) defined as the enthalpy change of the isodesmic reaction MH+ + Py ! M + PyH+ (gas state) was also calculated. The effect of bromine as substituent on the properties of the b-carboline moiety in nor-harmane, harmane and harmine is discussed.
Fil: Tarzi, Olga Inés. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones en Hidratos de Carbono. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones en Hidratos de Carbono; Argentina
Fil: Erra Balsells, Rosa. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones en Hidratos de Carbono. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones en Hidratos de Carbono; Argentina