1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

2 State of The Art & Aims
2.2 Aim of the Work
Within the course of this thesis, novel cycloketo-porphyrin systems shall be established and
thoroughly investigated. As they are related to pyropheophorbides, being active
photosensitizers suited for applications in photodynamic therapy, both substance classes
shall be compared and finally, trials are to be conducted to synergize both approaches to
photosensitization – the fully synthetic and the nature based one – to gain the ability of
developing novel photosensitizing systems with improved characteristics.
Concerning the porphyrin building blocks, which represent the basis for the development of
cycloketo-porphyrins, it seems worth to revisit the used synthetic protocols to rationalize
their formation to be able to access those systems in multi-gram quantities. Then novel
synthetic protocols shall be established leading to systems like M-53 (see Scheme 19) as
rational as possible and to free base systems. Furthermore, it is to be investigated, whether
those protocols are also applicable to obtain bis- or even higher annulated analogs of
specific symmetries. All obtained systems shall then be characterized and thoroughly
investigated concerning their general behavior and especially their photophysical and
electrochemical properties. Dependent on those findings, it is to be studied, if thereof arise
potential candidates for PDT applications and if those could be directly implemented into a
3 rd generation sensitizer concept or whether further structural modifications have to be
performed. Also, those adapted compounds are then to be subjected to detailed studies.
Additionally, the assumption that some of those compounds appear as mixtures of
atropisomers, and thus are considered to be inherently chiral, shall be further investigated
and, if possible, a pathway shall be figured out to finally be able to resolve the racemic
mixtures.
Meanwhile, also the isolation and transformation protocols to access pyropheophorbide a
derivatives shall be worked over, since the isolation from higher plants (e.g. spinach and
stinging nettles) or chlorella algae involves the very laborious separation of chlorophylls a
and b. The use of spirulina algae can offer a good alternative therefore, which is to be
verified. The obtained derivatives will furthermore serve as reference compounds for
investigations on the synthesized cycloketo-porphyrin systems being regarded as artificial
structural analogs.
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