6UPJ:
reference: Use of medium-sized cycloalkyl rings to enhance secondary binding: discovery of a new class of human immunodeficiency virus (HIV) protease inhibitors., Romines KR, Watenpaugh KD, Tomich PK, Howe WJ, Morris JK, Lovasz KD, Mulichak AM, Finzel BC, Lynn JC, Horng MM, et al., J Med Chem 1995 May 26;38(11):1884-91. PMID: 7783120

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