1NPA:
reference: An orally bioavailable pyrrolinone inhibitor of HIV-1 protease: computational analysis and X-ray crystal structure of the enzyme complex., Smith AB 3rd, Hirschmann R, Pasternak A, Yao W, Sprengeler PA, Holloway MK, Kuo LC, Chen Z, Darke PL, Schleif WA, J Med Chem 1997 Aug 1;40(16):2440-4. PMID: 9258349

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