Both-faces hindered porphyrins. Part 5. Synthesis and characterization of iron(III) basket handle porphyrins having multiple secondary amide groups inserted in the superstructures

Abstract

The synthesis of basket handle porphyrins in a cross-trans configuration (27) and (28) derived from 5,10,15,20-tetrakis(o-aminophenyl)porphyrin, and their hydroxy-iron(III) complexes, in which one of the faces is hindered by a bridge substituted by one or two amino-acids (L-phenylalanine or L-valine) and with the other face protected by a hanging-imidazole chain is described. The synthetic methodology for these compounds allows the preparation of other superstructured porphyrins containing several amino acids in the handles; this gives an increasing number of secondary amide groups in the vicinity of the metallic centre. Structural assignments for the various compounds were made on the basis of the ¹H n.m.r. spectra of the free bases. The optical purity of the compounds was established by g.i.c. on a chiral phase. Absorption spectra of hydroxy-iron(III) derivatives of hanging imidazole basket handle porphyrins display an unusual pattern consistent with the presence of water partially co-ordinated to the metallic ion and stabilized in the distal cavity by a hydrogen bond formed between water proton(s) and the carbonyl group of the ‘peptide’ bond.