Metal‐Induced Chiral Folding of Depsipeptide Dendrimers

Abstract

The synthesis and metal complexation of chiral depsipeptide dendrimers 3 and 7 containing an ethylenediaminetetraacetic acid (EDTA) ester‐derived core is reported. The EDTA ester cavity of these dendrimers selectively complexes Zn2+ and Cu2+ ions leading to diastereoselective folding. To elucidate the coordination motif in the resulting “foldamers” of 3‐ZnCl2, 7‐ZnCl2, 3‐CuCl2, and 7‐CuCl2, the coordination behavior of the tetramethyl ester of EDTA (8) has been investigated as a model case. The corresponding complexes 8‐ZnCl2 and 8‐CuCl2 have been structurally characterized by 1H NMR spectroscopy and X‐ray analysis. The complexes involve the inherently chiral octahedral cis‐α coordination motif, in which 8 serves as a tetradentate ligand. In the case of the ZnII complex 8‐ZnCl2, both Δcis‐α(S,S,λ) and Λcis‐α(R,R,λ) stereoisomers were found in the unit cell. For the CuII complex 8‐CuCl2, only one stereoisomer, namely Δcis‐α(S,S,λ) was found in the crystal under investigation. 1H NMR spectroscopy has shown that the same coordination motif is diastereoselectively formed in the chiral Zn2+ dendrimers 3‐ZnCl2 and 7‐ZnCl2. Likewise, the calculated CD spectrum of the Δcis‐α(S,S,λ) stereoisomer of the model complex 8‐CuCl2 shows good agreement with the experimental spectrum of the CuII dendrimers 3‐CuCl2 and 7‐CuCl2, allowing assignment of the absolute configurations of the preferred foldamers as Λcis‐α(R,R,λ) for 3‐CuCl2 and Δcis‐α(S,S,λ) for 7‐CuCl2. This work represents the first example of metal‐complexation‐mediated diastereoselective folding of chiral dendrimers with known absolute configuration.

Supramolecular Dendrimers Self‐Assembled from Dendritic Fullerene Ligands and a Homotritopic Hamilton Receptor

“…General Remarks: All chemicals were obtained from Sigma–Aldrich and Acros Organics or were prepared according to known literature procedures. The preparation of the depsipeptide dendrons 14 – 18 was described previously 6. All reactions were performed using standard glassware under nitrogen.…”

Self‐Assembly of Supramolecular Architectures and Polymers by Orthogonal Metal Complexation and Hydrogen‐Bonding Motifs

“…Among the most common binding motifs for generating supramolecular structures are hydrogen-bonding interactions [4][5][6] and metal-ligand coordination. [7][8][9] A well-established hydrogenbonding building block is the Hamilton receptor [5,10] (see Scheme 2 below), which forms stable complexes with cyanuric acid derivatives with association constants ranging from 10 3 to 10 6 m À1 in apolar solvents. [11] We recently [12] reported on supramolecular dendrimers bearing two orthogonal noncovalent binding sites, namely, the Hamilton receptor and metal-ligand complexation of Ru and bipyridine.…”

Binding ability of first and second generation/carbazolylphenyl dendrimers with Zn(ii) tetraphenylporphyrin core towards small heterocyclic substrates

“…Porphyrin-based dendrimers are oen using as photofunctional articial receptors, in which the strong photoabsorption and intense uorescence signals of the porphyrin can respond sensitively to substrate binding. [12][13][14][15][16][17] ZnD2-G1, ZnD3-G1, ZnD4-G1, ZnD5-G1, ZnD6-G1) and the second (ZnD7-G2, ZnD8-G2, ZnD9-G2)] of carbazolylphenyl branches towards 1,4-diazabicyclo-[2.2.2]octane (L1), pyridine (L2), imidazole (L3), N-methylimidazole (L4) and 1,2,3-triazole (L5) in toluene. The dendrimers also differ by the nature of bridging spacers [oxygen (ZnD1-G1, ZnD2-G1, ZnD3-G1) and 1,2,3-triazole (ZnD4-G1, ZnD5-G1, ZnD6-G1, ZnD7-G2, ZnD8-G2, ZnD9-G2)] connecting the tetraarylporphyrin core and carbazolylphenyl fragments.…”