The kinetic model showed that most EDC -between 60 and 80% -was used to produce anhydride. A small fraction of these anhydrides reacted further with inter-or intramolecular tyrosine to produce the products of the dynamic combinatorial library while the rest hydrolyzed to the peptide. Specifically, with 1 mM of peptide, only 6% of the anhydride is converted into linear esters, while 34% is converted through intramolecular ring closure. Increasing the peptide concentration to 3 mM increased the fraction of anhydride used to make linear esters to 19%, while cyclization was unaffected at 29%. The half-life of each of these esters is 3.5 hours for the cyclomonomer, 1.3 hours for the linear dimer, and 40 minutes for the cyclodimer, as calculated from the corresponding k-values of the ester hydrolysis.