From the initial discovery of the type 1 human immunodepressant virus (HIV-1), which is the causative agent of the acquired immunodepressed syndrome (AIDS) [1, 2], considerable attention has been directed to the study of the life cycle of the virus and the identification of potential targets for chemotherapeutic reactions [3, 4]. Among the many approaches to the discovery of new anti-HIV-1 agents, one of the most promising is inhibition of the reverse transcriptase which catalyzes the transcription of the single chain RNA of the virus into the double chain DNA. Two classes of HIV-1 reverse transcriptases have been identified: nucleoside and non-nucleoside.The nucleoside inhibitors of HIV-1 reverse transcriptases interfere with the preliminary phosphorylation of the cell enzyme to the corresponding 5'-triphosphates, which simultaneously inhibits the HIV-I reverse transcriptases and terminates the growth of the viral DNA chain. 3'-Azido-3'-desoxythymidine was the first of these to be used clinically for the alleviation of AIDS. Other 2',3'-didesoxynucleosides (2',3'--didesoxyinosine, 2',3'-didesoxycytidine, 2',3'-didesoxy-2',3'-didehydrothymidine) are currently in clinical use [5, 7]. However, despite the evident selectivity for inhibition of HIV-1 reverse transcriptases, the triphosphates of these nucleoside analogs also inhibit the cellular DNA polymerases and have considerable toxic side effects [8]. Moreover, resistant strains of HIV-1 have arisen with prolonged use of the nucleoside inhibitors [9].Non-nucleoside inhibitors of HIV-1 reverse transcriptases differ from the nucleoside inhibitors. They do not affect the preliminary phosphorylation, they have high selectivity towards HIV-1, they do not inhibit the activity of cellular DNApolymerase, and they show considerably smaller toxic effects. One of the basic classes of non-nucleoside inhibitors of HIV-1 reverse transcriptases includes derivatives of pyrimidine bases, in particular 1-[(2-hydroxyethoxy)methyl]-6-(phenylthio)thymine (HERT) (I, R 1 = CH 3, R 2 = CH2OH, R 3 = H, X = S) [10]. The selectivity index for this compound exceeds 100. Its analogs which lack a hydroxy group in the side chain, for example, 1-Coenzyloxymethyl)-6-(phenylthio)thymine (II, R 1 = CH 3, R 2 = C6H 5, R 3 = H, X = S) and 1-(benzyloxymethyl)-5-ethyl-6-(phenylthio)uracil (III, R l = C2H 5, R 2 = C6H 5, R 3 = H, X = S) are even more active with respect to HIV-1 reverse transcriptases. The inhibitory properties of HERT analogs increase with the presence of methyl substituents in the meta-position (R 3 = CH3) [11][12][13][14][15].The selenium analog of HERT, l-[(2-hydroxyethoxy)methyl]-6-(phenylseleno)thymine (IV, R 1 = CH 3, R 2 = CH2OH, R 3 = H, X = Se), is a highly active inhibitor of HIV-1 reverse transcriptases but its mechanism is different [16]. Similar in structure and inhibitory activity are the 2-alkoxy-and 2-cycloalkoxy-6-benzylpyrimidin-4(3H)-ones (V, R 1 and R 3 = H, CH3) [17, 18], but the inhibitory activity was greater in compounds containing a cyclic radical R 2, e.g., c...

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