Porphyrin-substituted dinucleotides: Synthesis and spectroscopy

Deoxyuridine, which is substituted with either 5,15-diphenyl porphyrin (DPP) or 5,10,15,20-tetraphenyl porphyrin (TPP) at the 5-position via an alkynyl linker, was dimerised to the homo- and hetero-porphyrin dinucleotide. The synthesis was performed either in solution or on solid phase in order to compare the reactivity of the phosphoramidite building blocks under both conditions. The absorbance properties reveal electronic interactions in the dimers that are strongly dependent On the nature of the porphyrin. The DPP-containing dimers show significant differences between the calculated and the measured UV-Vis spectra, whereas in the TPP dimer hardly any difference is observed. Formation of the duplex with the corresponding diadenosine changes the electronic interactions between the chromophores; in the heteroporphyrin dimer, as shown by a blue shift of the absorbance. The low solubility of the DPP dimer in pure chloroform prevented formation of the duplex due to the necessity to add about 10% of methanol. The dimerisation is detectable using MALDI-TOF mass spectrometry for all dinucleotides.