Oligoamides, aromatic

One type of oligoamide that can readily be prepared on supports without the need for any partially protected monomers (which are often tedious and expensive to synthesize) are N-substituted oligoglycines (Figure 16.21). These compounds are prepared by a sequence of acylation of a support-bound amine with bromoacetic acid, displacement of the bromide with a primary aliphatic or aromatic amine, and repeated acylation with bromoacetic acid. Because primary amines are cheap and available in large number, this approach enables the cost-efficient production of large, diverse compound libraries. Alternatively, protected N-substituted glycines can also be prepared in solution and then assembled on insoluble supports (Entry 5, Table 16.2). 

Keywords Aromatic oligoamides Foldamer Folding Helix Nanoporous... 

In addition to the aromatic oligoamides discussed above, we have also designed foldamers by enforcing folded conformations on other oligomers consisting of aromatic residues. 

Hue et al. reported aromatic oligoamides based on quinoline residues (Fig. 24a) [65]. It was found that the corresponding oligomers folded into stable helical conformations based on three-center intramolecular hydrogenbonding interactions involving the amide protons and their adjacent pyridine N atoms. This class of oligomers was found to be stably folded in both nonpolar and polar solvents. Their folded conformations were also revealed by their crystal structures. 

Except for the folding aromatic oligoamides developed by us, few other helical foldamers reported so far contain any meaningful interior cavities. Unnatural foldamers with interior cavities include those described by Lehn [29] and Moore [31]. A few examples of porous helical oligoamides have started to appear in recent years. 

Figure 3.25 Solid-phase synthesis of aromatic oligoamides. Source Reproduced with permission from Santiago-Garcia JL, Aguilar-Vega M. Ear Polym J 2009 45 3210 [79]. Copyright 2009 Elsevier Ltd.

The aromatic oligoamides are well-known oligomers with folding properties similar to the phenylacetylenes. These compounds have already been reviewed and most of them cannot be considered as nanotubes because they have only one helical turn (see Organic Foldamers and Helices, Self-Processes). From the nanotube point of view, foldamers of the type shown in Figure 4(a) are remarkable examples, for which molecular modeling... 

Figure 15 Formula of several aromatic oligoamides and their crystal structures, (a) Double heUx of an oligo-pyridinecaboxamide. (b) Triple heUx of an oligo-naphthyridinecarboxamide. (c) Quadruple heUx of an oUgo-quinolinecarboxamide. (d) Branched structure comprised of two single helical quinolinecaboxamide oligomCTs connected by an ethylene glycol bridge.

Fig. 8.3 Hydrogen bonded nanotube from aromatic oligoamides. a The structure of an aromatic oligoamide derived from 2,6-diaminopyridine and 2,6-pyridine dicarboxylic acids and the hydrogen bonding pattern in the formation of the helical structure, b Hydrogen bonding patterns that cause the oligoamide backbone to switch between the folded and unfolded cotrformations...

Aromatic oligoamide macrocycles from the bimolecular coupling of folded oligomeric precursors. New J Chem 33(4) 729-733... 

Jiang H, Leger J-M, Guionneau P, Hue I (2004) Strained aromatic oligoamide macrocycles as new molecular clips. Org Lett 6(17) 2985-2988... 

Helsel AJ, Brown AL, Yamato K, Feng W, Yuan LH, Clements AJ, Harding SV, Szabo G, Shao ZF, Gong B (2008) Highly conducting tiansmembrane pores formed by aromatic oligoamide macrocycles. J Am Chem Soc 130(47) 15784-15785... 

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