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.

Azobenzene Container Showing a Definite Folding – Synthesis and Structural Investigation

“…This effect is already known for this kind of switches. [49][50] The trans,trans / cis,trans / cis,cis ratio of the solution after synthesis amounts to 63:35:2 and resemble the 1 H NMR data (68:31:<1).…”

“…[43][44][45][46][47][48] Up to now two artificial Lissoclinum cyclopeptides, which feature azobenzene to change the distance between the amino acid side chains, are described in the literature. [49][50] One example is the platform 4, which consists of two imidazole building blocks connected by two azobenzene units ( Figure 2). 50 Irradiation of the platform 4 with UV light results in a trans→cis isomerization accompanied by a reduction of the distance between the two isopropyl groups.…”

“…[49][50] One example is the platform 4, which consists of two imidazole building blocks connected by two azobenzene units ( Figure 2). 50 Irradiation of the platform 4 with UV light results in a trans→cis isomerization accompanied by a reduction of the distance between the two isopropyl groups. As further example the chiral foldable container 5 should be mentioned.…”

An azobenzene container showing a definite folding – synthesis and structural investigation

“…Up to now two artificial Lissoclinum cyclopeptides, which feature an azobenzene moiety to change the distance between the amino acid side chains, are described in the literature [49–50]. One example is the platform 4 , which consists of two imidazole building blocks connected by two azobenzene units (Fig.…”

“…One example is the platform 4 , which consists of two imidazole building blocks connected by two azobenzene units (Fig. 2) [50]. Irradiation of the platform 4 with UV light results in a trans → cis isomerization accompanied by a reduction of the distance between the two isopropyl groups.…”