Pre-organized dinucleosides with pendant porphyrins for the formation of sandwich type complexes with DABCO with high association constants
Abstract
We report herein the synthesis of a dinucleotide bearing pendant porphyrins dedicated to adopt a pre-organized coformation with face-to-face porphyrins, and capable to self-organize in a stable sandwich type complexe with bidentate base such as DABCO. Earlier studies demonstrated that a peptidic linker does not provide sufficient pre-organization to enhance significantly the association constant with bidentate bases such as DABCO on the contrary of some other flexible linkers such as uridine or 2′-deoxyuridine. We document herein that the gain in stability for the formation of sandwich type host–guest complex with DABCO can be even greater when a dinucleotide linker is used. Such pre-organization increases the association constants by one to two orders of magnitude when compared to the association constants of the same bidentate ligands with a reference Zn(II) porphyrin. Comparison of these results with those obtained for rigid tweezers shows a better efficiency of the flexible nucleosidic dimers. We thus document the fact that the choice of rigid spacers is not the only way to pre-organize bis-porphyrins, and that some well-chosen nucleosidic linkers offer an interesting option for the synthesis of such devices. Furthermore, the chirality and enantio-purity of the nucleosidic linkers paves the way toward the selective complexation of enantio-pure bidentate guests and the resolution of racemates.
Dedicated to Professor Shunichi Fukuzumi on the occasion of his retirement
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