Switchable Imidazole Platform – Synthesis and Structural Investigation

Abstract

Cyclic oligomers of azole peptides can be isolated from marine organisms and are used for a multitude of applications in supramolecular chemistry. They are used in particular as receptors, since the recognition units attached to these azole cyclopeptides show a predefined orientation to each other. Here we present the synthesis of an imidazole cyclopeptide showing a switchable behavior due to the incorporation of two azobenzene moieties into the macrocycle. The synthesis, in particular the cyclization to the macrocycle proved to be difficult. However, by using an optimized route the platform could be isolated in a rather good yield (32 %). Quantum chemical calculations, UV and NMR spectra showed that the platform can be light‐inducedly switched between the elongated trans,trans isomer and the compact cis,cis isomer. This switching process leads to a drastic change in the distance between the methyl groups attached to the imidazole rings.