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Synthesis of porphyrins with ABAB symmetry from dipyrromethanes as potential phototherapeutic agents
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1  IDAS-CONICET, Departamento de Química, Facultad de Ciencias Exactas, Físico-Químicas y Naturales, Universidad Nacional de Río Cuarto, Ruta Nacional 36 Km 601, X5804BYA Río Cuarto, Córdoba, Argentina.


Porphyrin derivatives have been used as photosensitizers in the photodynamic inactivation of microorganisms. However, depending on the substituents on the periphery of the tetrapyrrolic macrocycle, these molecules tend to aggregate, producing a loss of photodynamic activity. Thus, to achieve effective photoinactivation, these compounds can bind to different supports forming photoactive materials. In this sense, it is interesting to develop porphyrins asymmetrically substituted in the meso positions by two different structures (A and B). In these compounds, structure A has a functional group that allows covalent attachment to other molecules, while B is substituted by groups that allows changing the properties of the tetrapyrrolic macrocycle.

In this work, asymmetrically meso-substituted porphyrins were synthesized with ABAB symmetry patterns. The approach required the formation of dipyrromethanes, which were obtained from the condensation of an aldehyde (pentafluorobenzaldehyde or N,N-diphenylaminobenzaldehyde) with a large excess of pyrrole (1:47 aldehyde/pyrrole mol ratio), catalyzed by trifluoroacetic acid in 70-94% yields. Then, acid catalyzed condensation of these dipyrromethanes with an aldehyde (N,N-dimethylaminobenzaldehyde, N-ethyl-3-carbazolecarbaldehyde or 4-carboxymethylbenzaldehyde) (1:1 mol ratio) in dichloromethane, followed by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone affords the diseased porphyrins in 25-40% yields. These ABAB-porphyrins are interesting starting materials to obtain photoactive molecular structures as potential phototherapeutic agents.

Keywords: porphyrin; carbazoyl; pentafluorophenyl; dipyrromethane; photosensitizer