Metal-induced chiral folding of depsipeptide dendrimers.
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 Zn(2+) and Cu(2+) ions leading to diastereoselective folding. To elucidate the coordination motif in the resulting "foldamers" of 3-ZnCl(2), 7-ZnCl(2), 3-CuCl(2), and 7-CuCl(2), the coordination behavior of the tetramethyl ester of EDTA (8) has been investigated as a model case. The corresponding complexes 8-ZnCl(2) and 8-CuCl(2) have been structurally characterized by (1)H NMR spectroscopy and X-ray analysis. The complexes involve the inherently chiral octahedral cis-alpha coordination motif, in which 8 serves as a tetradentate ligand. In the case of the Zn(II) complex 8-ZnCl(2), both Deltacis-alpha(S,S,lambda) and Lambdacis-alpha(R,R,lambda) stereoisomers were found in the unit cell. For the Cu(II) complex 8-CuCl(2), only one stereoisomer, namely Deltacis-alpha(S,S,lambda) was found in the crystal under investigation. (1)H NMR spectroscopy has shown that the same coordination motif is diastereoselectively formed in the chiral Zn(2+) dendrimers 3-ZnCl(2) and 7-ZnCl(2). Likewise, the calculated CD spectrum of the Deltacis-alpha(S,S,lambda) stereoisomer of the model complex 8-CuCl(2) shows good agreement with the experimental spectrum of the Cu(II) dendrimers 3-CuCl(2) and 7-CuCl(2), allowing assignment of the absolute configurations of the preferred foldamers as Lambdacis-alpha(R,R,lambda) for 3-CuCl(2) and Deltacis-alpha(S,S,lambda) for 7-CuCl(2). This work represents the first example of metal-complexation-mediated diastereoselective folding of chiral dendrimers with known absolute configuration.
Buschhaus
Boris
B
Institut für Organische Chemie, Friedrich Alexander Universität Erlangen-Nürnberg, Germany.
Hampel
Frank
F
Grimme
Stefan
S
Hirsch
Andreas
A
D002942:Circular Dichroism; D003300:Copper / Q000737:chemistry; D018360:Crystallography, X-Ray; D004492:Edetic Acid / Q000737:chemistry*; D019216:Metals, Heavy / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D009842:Oligopeptides / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism; D015032:Zinc / Q000737:chemistry
D019216:Metals, Heavy; D009842:Oligopeptides; D009942:Organometallic Compounds; D003300:Copper; D004492:Edetic Acid; D015032:Zinc