Issue 8, 2010
From the journal:

Organic & Biomolecular Chemistry

Locked chromophores as CD and NMRprobes for the helical conformation of tetraamidic macrocycles†

Carmine Coluccini,a   Andrea Mazzantib  and  Dario Pasini*a  

* Corresponding authors

a Department of Organic Chemistry, University of Pavia, Viale Taramelli, Pavia, Italy
E-mail: dario.pasini@unipv.it
Web: www.unipv.it/labt
Fax: (+39) 0382 987323
Tel: (+39) 0382 987835

b Department of Organic Chemistry “A. Mangini”, University of Bologna, Viale Risorgimento, Italy

Abstract

A series of tetraamidic homochiral macrocycles have been built convergently upon the introduction in the covalent scaffold of two 1,1′-binaphthyl-2,2′-diol derivatives, joined by aromatic spacers of differing shapes and rigidity (p-phenyl, 4,4′-biphenyl, 3,3′-biphenyl) through aromatic amide functionalities, perfectly positioned to intramolecularly hydrogen bond the naphtholic oxygen acceptors of the binaphthyl units, in order to effectively lock the central chromophores in spatial proximity. The combination of several techniques, namely NMR and CD spectroscopies, and computational modeling, allows for a clear depiction of the structure and conformation of the macrocycles in solution. In the case of the shape “unstable” 3,3′-biphenyl spacer, the preferred conformation of a “wrapped” form in a relatively polar (EtOH) solvent is clearly signalled by CD spectroscopy by analyzing the changes in the shape of the induced CD signal deriving from the central, achiral chromophore absorption band. The rigid, covalent scaffold in which the two central 3,3′-biphenyl spacers are embedded raises the energetic barrier for the rotation around the aryl–aryl bonds of the spacers to a value (8.0 kcal mol−1) much higher than the value calculated in the case of unlocked biphenyls.

Graphical abstract: Locked chromophores as CD and NMR probes for the helical conformation of tetraamidic macrocycles

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Article information

DOI
https://doi.org/10.1039/B924400J
Article type
Paper
Submitted
20 Nov 2009
Accepted
15 Jan 2010
First published
11 Feb 2010

Org. Biomol. Chem., 2010,8, 1807-1815

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Locked chromophores as CD and NMR probes for the helical conformation of tetraamidic macrocycles

C. Coluccini, A. Mazzanti and D. Pasini, Org. Biomol. Chem., 2010, 8, 1807 DOI: 10.1039/B924400J

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