Pyrrolic pigments

Christian. Brückner
Part 1 presents studies aimed at the synthesis of novel aromatic tetra- and pentapyrrolic pigments with meso-phenyl substituents and with long wavelengths of absorption. Such compounds are potential photosensitizers for use in photodynamic therapy (PDT). Several approaches are described: 1. The osmium tetroxide mediated dihydroxylation of variously substituted mesotetraphenylporphyrins (TPP) to provide novel stable chlorins such as 129 and bacteriochlorins such as 141 and 146 is reported. The
more » ... recting effect of the central metal zinc in the stereo- and regiochemical outcome of the dihydroxylation of meso-tetraphenylchlorins is outlined. The resulting 8,6'-dihydroxylated amphiphilic chlorins are characterized by spectroscopic and analytical techniques. Preliminary in vitro biological results of their potency as drugs in PDT have been encouraging. One side-product of the osmylation reaction, the 2-oxa-3-oxochlorin 163, was structurally characterized by X-ray crystallography. [Model not included] Some unique physical (observable rotation of the phenyl groups) and chemical properties of the 6,6'-diolchlorins are reported. For instance, me,«?-tetraphenyl-2,3-vjcdihydroxy- 2,3-chlorinato)nickel(II) can be converted oxidatively into the corresponding 2,3- secochlorin-2,3-dialdehyde 167. This compound can ring-close to the novel double ketal 175. This severely distorted pigment has been structurally characterized by X-ray crystallography and is without precedent. [Model not included] 2. A directed synthesis of N-confused porphyrin 104 was developed. The key step in the synthesis was a 2+2-type condensation of dipyrromethane 197 with the novel a,6-linked dipyrromethane 190. Although the goal of producing 104 in high yields could not be met, this study provided valuable insight into the chemistry of dipyrromethanes and provided through fortuitous circumstance tripyrrane 180. [Model not included] 3. Tripyrrane 180 is the key reagent in the directed high-yield synthesis of meso-phenylsapphyrins such as [...]
doi:10.14288/1.0059560 fatcat:amubvrkjfrdcdasxej5jz5a2jy