2R9C:
reference: Cocrystal structures of primed side-extending alpha-ketoamide inhibitors reveal novel calpain-inhibitor aromatic interactions., Qian J, Cuerrier D, Davies PL, Li Z, Powers JC, Campbell RL, J Med Chem. 2008 Sep 11;51(17):5264-70. Epub 2008 Aug 15. PMID: 18702462

This OCA Structure page
uses Jmol, developed by the Jmol Development Team (documentation).