4ABJ:
reference: Braces for the Peptide backbone: insights into structure-activity relationships of protease inhibitor mimics with locked amide conformations., Tischler M, Nasu D, Empting M, Schmelz S, Heinz DW, Rottmann P, Kolmar H, Buntkowsky G, Tietze D, Avrutina O, Angew Chem Int Ed Engl. 2012 Apr 10;51(15):3708-12. doi: 10.1002/anie.201108983. , Epub 2012 Feb 28. PMID: 22374650

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