1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

Discussion and Results 3
porphyrin. So it was tried to obtain 84 from 83 by treatment with HBr in glacial acetic acid.
Also this approach turned out to be unsuccessful as the initially formed traces of product
reacted further to give a mixture of educt 83 and presumably partially hydrolyzed
derivatives. That product mixture was not purified as the full hydrolysis was targeted
anyway.
Subsequently, both 83 and the mixture obtained from its tried bromination were subjected
to the set up conditions for nitrile hydrolysis. Unfortunately, this led to an immediate
rupture of the applied porphyrin systems as the initially green acidic solutions turned black
within a couple of minutes. Due to that, the reactions were immediately quenched and the
residing materials were analyzed. But there was no porphyrinoid material left which was
very surprising and not at all expected. Although side reactions have been taken into
consideration before, e.g. the formation of hydroxymethyl or acetoxymethyl derivatives
from 83, up to now, no plausible reasons for that drastic failures were found since the other
porphyrin systems under investigation endured these conditions without any considerable
decomposition and also since systems 83 has been formed under acidic conditions.
Thus, that kind of approach was rejected and it was turned to the set up of AB2C-type
porphyrin systems. Therefore, the characterization data for compounds 82 and 83 will not
be discussed here but is summarized in the experimental section.
3.2.8.2 Approaching a Modified Form of 53 via AB2C Type Porphyrin Precursors
To access a suitable system of the principle architecture displayed in Scheme 50, a
corresponding functionality –X had to be chosen fulfilling the following requirements:
• X, being already present in the parental aldehyde, should be (strongly) electron
withdrawing to allow the formation of a stable dipyrromethane not scrambling under
the conditions of porphyrin synthesis
• X (or at least a protected form thereof) should be able to endure the conditions of
the subsequent modifications necessary for the formation of the exocycle
• X should represent (or be convertible into) a functionality easily coupleable to groups
present in polypeptides or on functional surfaces like e.g. amines or carboxylic acids,
if possible without needing to utilize special linkers
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