Given that the N-acylurea side product formation decreased with increasing concentration, we tested the effect of local concentration effects on the reaction cycle-we used dicarboxylate catalysts that can form intramolecular anhydride in a ring-closing reaction. We evaluated the ring-size effect in aspartate-like (Figure ) and succinate-like derivatives (Figure ) and varied the side chain length from 1 carbon to 4 carbons. We fueled 100 mM dicarboxylate catalysts with 50 mM EDC and determined the lost catalyst concentration to measure the N-acylurea concentration formed after 24 hours. No catalyst was lost for N-acetyl-L-aspartate (n=1, 5membered anhydride, Figure ), and HPLC showed no new N-acylurea peak. As the neighboring carboxylates were spaced farther from one another by increasing the number of carbons, an increasing concentration of Nacylurea was formed. For example, when the side chain has two carbons (n = 2, N-acetyl-L-glutamate, corresponding to a 6-membered ring anhydride), 9% of the catalyst is lost. This value rises to 32% when the side chain has four carbons (n=4). Similar effects were observed for the succinic acid series (n = 1, 2, and 3, Figure ). Taken together, as the distance between the O-acylurea and the second carboxylate as a nucleophile increases, the local concentration effect is suppressed, leading to more unwanted side product. Next, we tested the role of additives in suppressing the unwanted N-acylurea. We focused on trapping agents, i.e., reagents like pyridine, that react rapidly with the Oacylurea to form intermediates that cannot rearrange to the N-acylurea (Figure ). Besides pyridine, we tested the performance of 1,2,4-triazole, and DMAP (4dimethylaminopyridine), by fueling 100 mM C3 with 50 mM EDC with 10 mM of the additives. Compared to the reaction cycle without additives, 1,2,4-triazole and DMAP showed a very limited ability to increase the efficiency and selectivity of the reaction cycle with similar yields of Nacylurea (40%) and anhydride (60%) (Figure ). In contrast, pyridine significantly suppressed N-acylurea formation to 5% of the EDC added, while 92% of EDC was used to form anhydride (Figure ).