International Scholarly Research Network ISRN Pharmaceutics Volume 2011, Article ID 137637, 9 pages doi:10.5402/2011/137637 Research Article Synthesis and Inhibiting Activity of Some 4-Hydroxycoumarin Derivatives on HIV-1 Protease Stancho Stanchev, 1 Frank Jensen, 2 Anton Hinkov, 3 Vasil Atanasov, 4 Petia Genova-Kalou, 5 Radka Argirova, 6 and Ilia Manolov 7 1 Department of Chemistry, Faculty of Pharmacy, 2 Dunav Street, 1000 Soﬁa, Bulgaria 2 Department of Chemistry, Faculty of Science, University of Aarhus, Langelandsgade 140, 8000 Aarhus C, Denmark 3 Laboratory of Virology, Faculty of Biology, Soﬁa University “St. Kliment Ohridski”, 8 Dragan Zankov, 1164 Soﬁa, Bulgaria 4 Laboratory of Biocoordination and Bioanalytical Chemistry, Faculty of Chemistry, Soﬁa University “St. Kliment Ohridski”, 1 J. Bourchier, 1164 Soﬁa, Bulgaria 5 Laboratory of Cell Cultures, National Center of Infectious and Parasitic Diseases, 44 A Stoletov Street, 1233 Soﬁa, Bulgaria 6 Laboratory of Retroviruses, National Center of Infectious and Parasitic Diseases, 44 A Stoletov Street, 1233 Soﬁa, Bulgaria 7 Department of Pharmaceutical Chemistry, Faculty of Pharmacy, 2 Dunav Street, 1000 Soﬁa, Bulgaria Correspondence should be addressed to Ilia Manolov, imanolov@gmx.net Received 11 April 2011; Accepted 14 May 2011 Academic Editors: R. Cao, F. Fullas, P.-W. Hsieh, and S. Raic-Malic Copyright © 2011 Stancho Stanchev et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Six novel 4-hydroxycoumarin derivatives were rationally synthesized, veriﬁed, and characterized by molecular docking using crystal HIV-1 protease. Molecular docking studies predicted antiprotease activity of (7) and (10). The most signiﬁcant functional groups, responsible for the interaction with HIV-1 protease by hydrogen bonds formation are pyran oxygen, atom, lactone carbonyl oxygen and one of the hydroxyl groups. The newly synthesized compounds were biologically tested in MT-4 cells for inhibiting HIV-1 replication, exploring the protection of cells from the cytopathic eﬀect of HIV measured by cell survival in MTT test. One derivative −7 showed 76–78% inhibition of virus infectivity with IC 50 = 0.01 nM, much less than the maximal nontoxic concentration (1 mM). Antiprotease activity of 7 in two diﬀerent concentrations was detected to be 25%. Nevertheless, the results of study of (7) encourage using it as a pharmacophore for further synthesis and evaluation of anti-HIV activity. 1. Introduction The retroviral protease (PR) of human immunodeﬁciency virus type 1 (HIV-1) is one of the key enzymes for virus repli- cation. It cleaves protein and glycoprotein precursors to yield active viral enzymes and structural proteins. The inactive HIV-1 PR leads to noninfectious virions. This fact stimulated search of potent substances with antiprotease activity inhibit- ing HIV-1 replication. During the past 12 years, a number of peptidomimetic analogs—inhibitors of HIV-1 PR (PIs)— have been clinically introduced, but the largest part of them show poor pharmacological characteristics such as bad oral bioavailability, rapid clearance, and tolerability problems— often associated with lypodystrophy and dyslipidemia [1]. Also, because of being peptidomimetics, viral isolates quickly demonstrate a high degree of resistance and cross-resistance even when using the members of the group before PIs were put on the market [2]. Development of new nonpeptidic PIs, such as Tipranavir and Darunavir, showed an impressive potency against PI- resistant mutants, so remaining an important option for patients harboring such resistance [3]. This is the rea- son to search for novel nonpeptidic substances—inhibitors of HIV-1 protease. Experimental data on some nonpep- tidic substances—4-hydroxycoumarins (Figure 1) and 4- hydroxypyran derivatives inhibiting HIV-1 PR, support this idea [4]. Being for long years interested in synthesis and eval- uation of a range of nonpeptidic substances such as 4- hydroxycoumarin derivatives [5–9], we were encouraged to