4DFG:
reference: Substituent effects on P2-cyclopentyltetrahydrofuranyl urethanes: Design, synthesis, and X-ray studies of potent HIV-1 protease inhibitors., Ghosh AK, Chapsal BD, Steffey M, Agniswamy J, Wang YF, Amano M, Weber IT, Mitsuya H, Bioorg Med Chem Lett. 2012 Mar 15;22(6):2308-11. Epub 2012 Feb 2. PMID: 22364812

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