Amide catenanes

Each catenane consists of two identical, interlocked 26-membered rings with a relatively small internal cavity (with dimensions of 4x6 A). This interlocked species was the first amide-catenane to be structurally characterised (although Hunter s and Vogtle s catenanes were reported earlier). The structure supported the proposal that the driving force for catenane formation is hydrogen bonding between the newly formed 1,3-diamine units and carbonyl groups of the acid... 

Construction of Assemblies of Amide Catenanes, Rotaxanes and Knots... 

Other types of rotary motors can be constructed using catenanes, that is, species minimally composed of two mechanically interlocked macrocycles. In appropriately designed systems, the rotation of one ring around the other can be achieved by external stimulation. If suitable control elements are introduced in the structure, such a rotation can be performed unidirectionally. This concept was cleverly realized with benzylic amide catenanes by exploiting the isomerization of fumaramide to maleamide caused by UV light. Chiral C=N compounds such as imines also fulfill the criteria of two-step light-driven unidirectional molecular... 

Nonionic template synthesis of amide-linked catenanes and rotaxanes with macroheterocyclic fragments 97AG(E)930. 

R. Jager, F. Vogtle, A New Synthetic Strategy towards Molecules with Mechanical Bonds Nonionic Template Synthesis of Amide-Linked Catenanes and Rotaxanes , Angew. Chem Int. Ed. Engl. 1997,36,930-944. 

In the early 1990s Hunter [49] and Vogtle [50,51] discovered independently the possibility of using hydrogen bonding interactions displayed by amide groups to template the formation of [2 ] catenanes. While studying the reaction between the... 

Finally, chemical-shift variations originating in van der Waals compression are noteworthy, although very few reports have come to our attention discussing signal shifts of sp3 carbon atoms in terms of van der Waals interactions. Schill and co-workers (89) found downfield shifts of up to 1 ppm in the [2]-catenane 5 when its 13C resonances are compared with those of the two isolated subunits. From the increase of these chemical-shift differences with increasing distance from the nitrogen atom, these authors concluded that the strongest van der Waals interactions occur in that part of the heterocycle which is opposite to the amide moiety in space (cf. Scheme 4). 

Catenanes and Rotaxanes Incorporating Amide Recognition Sites in Their Components... 

The spectroscopic data of the amide-linked catenanes revealed that the cir-cumrotation [6 a] of the two interlocked cycles is hindered, i.e. the steric demand... 

A second experiment should prove that macromonocycles are actually the intermediate supramolecular templates in the course of catenane formation. Therefore macromonocycle 17 was reacted with 5 and 3, and the first [2]catenane 18 of the amide type consisting of two different macromonocycles was isolated (Figure 8). Unsymmetric catenanes like 18 can be identified unambiguously by mass spectrometry, because the corresponding tetrameric macromonocycle can not be formed in this reaction sequence. This confirms the presumption that catenation here proceeds via a macrocycle rather than via intertwining open chain units. 

Figure 7. Mechanism of catenane formation (amide type) the guest is orthogonally embedded in an intermediate macrocycle, the concave template. Depending on the substitution pattern of the reactants (pathways A and B) isomeric catenanes are obtained. For the sake of clarity the diacid dichloride is drawn here to be the nesting guest even though there is clear indication that the effective interactions take place between the corresponding monoamide and the macrocycle.

Figure 8. Synthesis of the first amide-linked [2]catenane consisting of two different macrocycles.

The tetramer exhibits an interesting folded conformation (in contrast to the open conformation of 6) which enables the binding of two p-benzoquinone molecules. Intramolecular hydrogen bonds between the nitrogen lone pair and the amide protons force the 2,6-pyridyl moiety into a NH cis conformation which consequently leads to the observed folded structure (Figure 10). In contrast to this, the open conformation of 6 enables the isophthaloyl unit to adopt the usually energetically favored NH trans conformation to optimize the amide-amide interactions. Because of the folded structure of tetramer 21 a tetramer-dimer catenane 22 could be isolated in 29% yield and even traces of the corresponding [3]cate-nane were detected. 

Recently Vogtle et al. in cooperation with Sessler et al. synthesized a Leigh-type amide-linked catenane 29 which coordinates anions (Figure 14) [26]. 

NMR studies showed that in polar solvents (DMSO, DMF) catenane 45 adopts a supramolecular conformation (II) that allows the amide protons to interact via multiple hydrogen bonds with solvent molecules and at the same time buries the lipophilic chains in the center of the molecule (Figure 18). In contrast, NMR spectra in nonpolar solvents indicate that the aliphatic chains are situated on the outer sphere of the catenane, whereas the isophthaloyl units are arranged in a way that ensures optimal intramolecular hydrogen-bonding (I). 

This conformation resembles that determined by X-ray single-crystal structure analysis. Apart from a close interaction of the -system of the amide groups with the para-substituted aryl moieties, no further n-n interactions are observed. The template-assisted catenane formation is on this account mainly driven by hydrogen-bonding, and n-n interactions are of minor importance only. 

While the above mentioned clipping method with larger wheels than the rather narrow 51 was not successful, die amide systems that had been developed by Vogtle et al. for catenane synthesis seemed ideal for submission to the threading... 

After the synthesis of the first amide-linked [2]rotaxanes, Vogtle et al. set out to study the limits of molecular recognition, which in terms of Emil Fischer means to discover if the lock (macrocycle) is specific to a certain key, or if several keys (monoamide threads) fit. It turned out that - in contrast to catenane formation - rotaxane synthesis is very tolerant towards the variation of the building... 

The sulfonamide macrocycle proved to be a hospitable template, and at the same time the sulfonamide functionality bears the possibility of farther derivatiza-tion of [2]rotaxanes (see Section 8.4 Chemistry with Amide-Based Catenanes and Rotaxanes). Furthermore the expansion of the cavity did not afford a change of the blocking group - no disassembly of wheel and axle was detected. 

Chemistry with Amide-Based Catenanes and Rotaxanes... 

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