Scheme 5. Synthesis and affinity selection of an 8-million-membered library of tetrameric peptide macrocycles on DEL. (A) Design of library of tetrameric cyclic peptides with three cycles at AA1, AA2, acyl cap positions. (B) The selected library population is viewed in a cubic scatter plot generated by TIBCO Spotfire Analyst. In the cubic space, axis represents the bbs used in a given cycle of library synthesis and each dot represents an encoded compound above certain enrichment cut-off value (>500). Enrichment value is calculated by comparing the results from pre and post-selection counts. (C) Validation of two selected compounds 32-C and 33-C by off-DNA resynthesis and IC₅₀ assays (see ESI† for details).