To control the formation of the library members, we substituted the flexible glycine for a non-nucleophilic, cationic amino acid. We hypothesized that this amino acid can form a salt bridge with the C-terminal aspartic acid, facilitating peptide cyclization. Indeed, when comparing the chromatograms of Ac-YGGD-OH and Ac-YRGD-OH 45 minutes after adding EDC, two main products were favored in the case of Ac-YRGD-OH, namely the cyclic monomer and a smaller fraction of linear dimer. To substantiate the idea of pre-organization, we also analyzed the evolution of products from Ac-YRGD-OH in the presence of 1.9 M guanidinium chloride, which is known to disrupt salt bridges. In the experiment, the yield of cyclic monomer and dimer products decreased by 42%. we substituted the remaining glycine for phenylalanine or tryptophan (Ac-YRFD-OH or Ac-YRWD-OH). Moreover, we also made a peptide with an acetyl-protected alanine at the N-terminus (Ac-AYRGD-OH). In line with the literature, we hypothesized that the increased bulkiness diminishes cyclic monomer formation, favoring dimerization and cyclic dimer formation. After the fuel was applied, we observed that the ratio of cyclic monomer to linear dimer and cyclic dimer had decreased. Consequently, there were now only three main products in the chromatograms -cyclic monomer, dimer, and cyclic dimer. Moreover, in the case of Ac-YRWD-OH, hardly any cyclic monomer was formed. Comparing the total amount of products to the starting material showed that the arginine-containing peptides, compared to Ac-YGGD-OH, form up to 50% more ester products, further showing the preorganization effect. When we further modified the N-termini with peptides, we found that the general trend still held, i.e., the main products were dimer and cyclic dimer. These modifications allowed us, in later stages of the work, to control the self-assembly of the products of this combinatorial library. In conclusion, we observed that the outcome of the dynamic combinatorial library is very sensitive to the peptide structure Ac-XYRXD-OH.