Synthesis and Characterization of Porphyrin-Sugar Carbon Conjugates

Abstract

The synthesis, structures, and spectroscopic properties of some 5,15-di-C-glycosyl-10,20-diarylporphyrins, representatives of a novel class of meso-C-glycoconjugated porphyrins, have been investigated. Porphyrins 9-14 were prepared in 6-16% yield by condensation of suitable dipyrrylglycosides with aryl aldehydes in the presence of either trifluoroacetic acid or BF 3 promoters. In all instances, α,β-configured porphyrins were preferentially formed, α,α isomers being only marginal products. The UV-vis spectra in CHCl 3 solution showed Soret bands which are red-shifted by about 20 nm as compared to the corresponding absorption maximum of the planar reference compound meso-5,15-bis(p-fluorophenyl)-10,20-diethylporphyrin (15).This suggested that the porphyrin macrocycles of 9-14 are inherently distorted to a significant extent. Detailed 1D and 2D 1 H NMR spectroscopic studies, including variable-temperature experiments in deuterated chloroform or tetrachloroethane, were carried out using the trans-disposed porphyrins 9 and 10. It was found that, at ambient temperature, these porphyrins adopted distorted saddle conformations in solution. Molecular mechanics techniques were used to analyze the distortion of porphyrin 9 as determined by the orientation of carbohydrate legs on the porphyrin periphery