| Abstract
| - Four cone resorc[4]arene octamethyl ethers (10, 11, ent-10, and ent-11) tetrafunctionalized at the feetwith valyl-leucine [ll- (6); dd- (ent-6)] and leucyl-valine [ll- (9); dd- (ent-9)] methyl esters have beensynthesized. These compounds, obtained by conjugation of macrocycle tetracarboxylic acid chlorideswith the appropriate terminal amino groups of the above dipeptides, are N-linked peptidoresorc[4]arenes.We found that these macrocycles (M) are capable of recognizing the homologue dipeptides as guests(G), both in solution and in the gas phase, by forming relatively stable host−guest complexes ([M·G]),resistant to chromatographic purification but not to heating. Complexation phenomena between M andG in solution were investigated by NMR methods, including NMR DOSY experiments, for the detectionof translational diffusion. Heteroassociation constants of 2030 and 186 M-1 were obtained by the Foster−Fyfe method for the complexes [10·6] and [10·ent-6], respectively, the latter being comparable to theself-association constant of dipeptide itself. Conversely, the structural features of the proton-boundcomplexes [M·H·Gn]+ (n = 1, 2), generated in the gas phase by electrospray ionization mass spectrometry(ESI-MS), were investigated by collision-induced dissociation (CID) experiments. In both cases, the fourN-linked peptidoresorc[4]arenes were shown to act as synthetic receptors and to recognize the homologuedipeptide by means of hydrogen bonds.
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