Synthesis and some spectroscopic properties of porphyrin derivatives connected with nucleobases (adenine, thymine, guanine and cytosine) by alkanamide chains

Several kinds of porphyrin derivatives covalently connected with adenine, thymine, guanine, cytosine or adenine-thymine pair in a stacking mode between the porphyrin and nucleobase moiety have been synthesized via amide formation reaction of (2-aminophenyl)porphyrin derivatives with nucleobase-alkanoic acids, and characterized by spectroscopic methods. In the H-1-NMR spectra of these nucleobase-porphyrins the proton signals of the nucleobase moieties appear at remarkably higher fields than those of the reference compounds (the corresponding nucleobase-alkanoates) which have no porphyrin moiety. The behaviors of the high field shifts, due to the diamagnetic ring current effect of the porphyrin ring, reflect the characteristic conformational features of these compounds in which the base moieties are located at the upper zone of the porphyrin ring. The Soret bands of the porphyrin in the electronic absorption spectra were markedly weaker in intensity compared with those of the reference compound which has no nucleobase moiety. Both the high-field shifts of the base protons and the hypochromic effects on the Soret band are larger in guanine and cytosine systems than those in adenine and thymine systems, respectively. Those results indicate greater affinity of guanine and cytosine for porphyrin in comparison with adenine and cytosine, respectively, and this conclusion is compatible with the reported electronic spectral properties of mixtures of polynucleotides and water-soluble porphyrin derivatives.