Synthesis, NMR and ultraviolet spectroscopy of [10] (N6,9)-6-aminopurinophane; calculation of the chemical shifts in the [n](N6,9)-6-aminopurinophane series

Abstract

Abstract:[10](N6,9)-6-Aminopurinophane was prepared via a Mitsunobu reaction involving 6-chloropurine and 10-azido-1-decanol. Reduction of the azido moiety to an amine allowed for subsequent cyclization to the cyclophane. N6-Nonyladenine, 9-nonyladenine, and N6,9-dinonyladenine were also prepared using the established chemistry. Heating the [10](N6,9)-6-aminopurinophane to 90°C allowed for a complete assignment of the proton and carbon spectra, while cooling the sample to -77°C revealed additional isomers likely due to the anti-syn isomerization about the N6-C6 bond. A variable temperature proton NMR study revealed a AG,' of 59.4 2 5.5 kJ mol-' associated with the interchange between the two major conformers. The ultraviolet spectra of the [n](N6,9)-6-aminopurinophane series show a bathochromic shift and a hypochromic effect in the transitions as the methylene chain length decreases (i.e., n = 10 to 9 to 8). The aminopurinophanes are used to assess the relative merits of a semi-empirical model that allows for the calculation of the chemical shifts of the methylene bridge protons.Key words: synthesis of heterocyclophanes, variable temperature NMR, cyclophane conformational analysis, ultraviolet spectroscopy, calculation of chemical shift.Resume : On a prepare le [10](N6,9)-6-aminopurinophane via une reaction de Mitsunobu impliquant la 6-chloropurine et le 10-azidodkcan-1-01. La rCduction de la portion azido en amine a permis de rCaliser la cyclisation subsCquente en cyclophane. On a aussi prCparC les N6-nonyladCnine, 9-nonyladCnine et N6,9-dinonyladenine utilisant des mCthodes chimiques bien Ctablies. Par chauffage du [10](N6,9)-6-aminopurinophane B 90°C, on a pu faire une attribution complbte des spectres RMN du proton et du carbone alors que son refroidissement B -77°C a rCvClC la presence d'isombres additionnels qui sont probablement dus B une isomCrisation anti-syn autour de la liaison N G C 6 . Une ttude des spectres RMN du proton B temperature variable a permis d'Ctablir qu'un AG,' de 39,4 ? 5,5 kJ mol-' est associC B l'interconversion entre les deux conformkres principaux. Les spectres ultraviolets de la sCrie des [tz](N6,9)-6-aminopurinophanes montrent qu'une diminution de la chaine mCthylCnique (lorsque n passe de 10, B 9 et B 8) est associCe B un dCplacement bathochrome et L un effet hypochrome dans les transitions. On a utilisC les aminopurinophanes pour Cvaluer les mCrites relatifs d'un modble semi-empirique qui permet de calculer les deplacements chimiques des protons des ponts mCthylbnes. ..Mots elks : synthkse d'hCterocyclophanes, RMN B temperature variable, analyse conformationnelle des cyclophanes, spectroscopie ultraviolette, calcul des dCplacements chimiques.[Traduit par la rCdaction] Introductionanisotropy about these purine and pyrimidine systems could aid in thegssignment of ;he heterobase protons ii the 'H NMRThe shift to lower frequency of the heterobase protons in cerspectra of large oligomers. Furthermore, this information tain oligonucleotides is a well-documented phenomenon (1 1.could ...

UV/Vis Spectra of Cyclophanes

“…Capretta and Bell [75] have studied the influence of conformational distortion and deformation on the electronic excitation in [n](N 6,9)-6-aminopurinophanes (n = 8: 81, n = 9: 82, n = 10: 83), in which the nitrogen atom N-9 and the amino group on C-6 of the adenine core are linked by a polymethylene bridge. The UV spectra of these compounds were found to be markedly different from that of N 6,9-dinonyladenine [nonyl-(9-nonyl-9H-purin-6-yl)amine, 84] that was used as the undistorted standard.…”