The synthesis, chromatographic isolation, and structure elucidation of β,β-substituted isomers of dinitro-5,10,15,20-tetraphenylporphyrin complexes are described. meso-Tetraphenyl-porphyrin chelates (CuII, NiII, CoII) upon reaction wit e.g., itric acid (yellow HNO₃, d = 1.52, diluted to 25⁻50%) in CHCl₃ formed a mixture of nitro-derivatives with combined yields of ca 80%. This nitration (under optimized conditions: 25⁻30% HNO₃, 30⁻40 min, r.t.) can be carried out selectively to give mainly β,β-dinitro-compounds in yields of up to 73%. From the above mixtures of five possible regioisomers that can be formed, usually two or three of them were isolated, for which the structures were assigned on the basis of ¹H NMR spectra including COSY and NOESY measure-ments. These types of products are attractive starting materials for synthesis of potential anticancer PDT agents with unique structures, being practically unavailable by any other alternative method.
Keywords: 2D NMR.; complexes; electrophilic substitution; nitric acid; porphyrins; β-nitration.