Proximal and distalN,C-linked tetra-peptidocalix[4]arenes as bifunctional receptors: synthesis, conformation and preliminary binding studies

Abstract

New 1,2-proximal N,N,C,C-linked and 1,3-distal N,C,N,C-linked tetra-peptidocalix[4]arenes have been synthesised by functionalisation of the corresponding calixarene bis-amino acids. Their conformational properties in solution, which have been studied by ¹H NMR, are determined by the presence of an extensive network of intramolecular hydrogen bonds. Electrospray ionisation mass spectrometry studies show that the 1,2-proximal peptidocalix[4]arene 19 is a more efficient receptor than the 1,3-distal isomer 8 in the gas phase and that it is able to recognise aromatic amino acids both as methyl esters and N-acetyl derivatives. Interestingly, these observations indicate that 19 is a bifunctional receptor since it displays both the selectivity of N-linked peptidocalixarenes for ammonium groups and that of C-linked peptidocalixarenes for carboxylates.

Keywords:

• peptidocalixarenes
• calixarene amino acid
• ESI-MS binding studies
• amino acid receptors
• chiral host

Acknowledgements

We thank the Ministero dell'Istruzione, dell'Università e della Ricerca (MIUR, PRIN 2008 project nos. 2008HZJW2L and 200858SA98) for the financial support. The Centro Interfacoltà di Misure (CIM) of the University of Parma is also acknowledged for the use of NMR and mass spectrometers.

Notes

^†Dedicated to the memory of Dmitry (Prof. Dmitry M. Rudkevich, 1963–2007).