We also employed biotin capture to test the intramolecular reaction of KYL modified phage libraries with exogenous amines. We treated the aldehyde-monocyclic libraries with 10 mM NaCNBH3 and different concentrations of three biotin containing amines (Figure ) in NH4OAc buffer (pH 4.6, 5.6) overnight. Modified libraries were then captured by streptavidin-coated magnetic beads (Figure ). The capture results (Figure ) showed trend similar to the reactions on a synthetic peptide (Figure -25): The aniline derivative exhibited 40 times greater reactivity than the aliphatic amine and glycine derivative, and the reaction can be driven forward by increasing the amine concentration. 2 mM concentration of aniline derivative converted all KYL modified phage library to monocyclic product, whereas for aliphatic amine and glycine derivative, same results were achieved by 10 mM concentration.