Adaptive Encapsulation of ω‑Amino Acids and Their Guanidinium–Amide Congeners

The binding and the
encapsulation of the 6-aminohexanoic acid (1) and 11-aminoundecanoic
acid (2) are achieved in aqueous solution and in crystalline
Pyrene-box cages. Unexpectedly, the amino-guanidinium AG+ and the amino acids 1 or 2 are reacting in aqueous solution in the absence and in the
presence of Pyrene-box cages. The formation of an amide bond between
a carboxylic acid and the amino-guanidine unit under mild acidic conditions
in water without the use a coupling reagent is extremely interesting
and unexpected. The resulted adducts AG1 and AG2 show adaptive binding behaviors and compressions.