Bis(diamino)-bridged basket resorcin[4]arenes as enantioselective receptors for amino acids and amines

On the research avenue opened by the rigidified doublespanned resorcin[4]arene 1, we have synthesized both enantiomers of the two chiral basket resorcin[4]arenes 3 and 4, each containing two 1,2-diaminocyclohexane and 1,2-diphenylethylenediamine bridges, respectively. In the new compounds, the aromatic rims assume the expected flattened cone arrangement, whereas two different conformations, tentatively designated as “open wings” and “folded wings”, were attributed to the bridge substituents according to molecular modeling studies. In MSn (ESI) experiments, the proton-bonded diastereomeric [4·H·A]+ complexes with amino acidic guests (A) exhibited a pronounced selectivity towards the enantiomers of tyrosine methyl ester (tyrOMe) and amphetamine (amph), whereas the chirality of tryptophan (trp) was ineffective. Moreover, a kinetic study on the base-induced displacement of the guest revealed that the L-tyrOMe (and L-amph) enantiomer is faster displaced from the heterochiral [4·H·L-tyrOMe]+ (or [ent-4·H·L-amph]+) complex than from the homochiral [ent-4·H·L-tyrOMe]+ (or [4·H·L-amph]+) one.