A self-assembled, cylindrical capsule was used to bind N-alpha-protected amino acid esters. The reversible encapsulation was studied using NMR spectroscopy in deuterated mesitylene solution and by computer-aided molecular modeling. BOC-L-alanine alkyl esters and BOC-beta-alanine alkyl esters were tested as guests, and the relative binding affinities were established by direct competition experiments. A good correlation was found between the experimental and calculated relative binding affinities in these two series. Guests that were slightly longer than the internal dimensions of the cavity were accommodated by adopting compacted conformations.