Synthesis of 3′′-Substituted TSAO Derivatives with Anti-HIV-1 and Anti-HIV-2 Activity through an Efficient Palladium-Catalyzed Cross-Coupling Approach Esther Lobato ´n, † Fa ´ tima Rodrı ´guez-Barrios, ‡ Federico Gago, ‡ Marı ´a-Jesu ´ s Pe ´rez-Pe ´rez, † Erik De Clercq, § Jan Balzarini, § Marı ´a-Jose ´ Camarasa, † and Sonsoles Vela ´ zquez* ,† Instituto de Quı ´mica Me ´ dica (C.S.I.C.), Juan de la Cierva 3, E-28006 Madrid, Spain, Departamento de Farmacologı ´a, Universidad de Alcala ´ , E-28871 Alcala ´ de Henares, Madrid, Spain, and Rega Institute for Medical Research, K. U. Leuven, Minderbroedersstraat 10, B-3000 Leuven, Belgium Received January 15, 2002 Various synthetic studies for the introduction of several functional groups at position 3′′ of the spiro moiety of TSAO derivatives have been explored. Among them, Stille cross-coupling of 3′′-iodo-TSAO derivatives with different stannanes provided an efficient and straightforward route for the direct and selective functionalization of the 3′′-position of the sultone spiro moiety via carbon-carbon bond formation. The compounds synthesized were evaluated for their inhibitory effect on HIV-1 and HIV-2 replication in cell culture. The introduction of a bromine and particularly an iodine at the 3′′-position conferred the highest anti-HIV-1 activity. In contrast, the presence at this position of (un)substituted vinyl, alkynyl, phenyl, or thienyl groups markedly diminished the anti-HIV-1 activity. Surprisingly, several of the 3′′-alkenyl-substituted TSAO derivatives also gained anti-HIV-2 activity at subtoxic concentrations, an observation that is very unusual for NNRTIs and never observed before for TSAO derivatives. Finally, the anti-HIV-1 activity of some of the 3′′-substituted TSAO derivatives is discussed in light of our recently proposed molecular model of interaction of TSAO derivatives with the interphase between the two subunits of HIV-1 reverse transcriptase. Introduction Among the different families of specific nonnucleoside reverse transcriptase inhibitors (NNRTIs) described so far, [2′,5′-bis-O-(tert-butyldimethylsilyl)--D-ribofuran- osyl]-3′-spiro-5′′-(4′′-amino-1′′,2′′-oxathiole-2′′,2′′-diox- ide) nucleosides (TSAO) represent a rather unique class of nucleoside analogues that have been identified as highly specific noncompetitive inhibitors of the RNA- dependent DNA polymerase function of reverse tran- scriptase. 1,2 The prototype compound is the thymine derivative designated as TSAO-T (1). The most selective compound is the 3-N-methyl-substituted derivative TSAO-m 3 T(2) (Figure 1). There are several features of the “unique” character of the TSAO family of com- pounds. Despite their nucleosidic structure, TSAO analogues, like the other NNRTIs, are targeted at a non- substrate-binding site of the human inmunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT). 1,2b,3 TSAO derivatives are, so far, the only HIV-1 RT inhibitors that seem to interfere at the interface be- tween the p51 and the p66 subunits of the RT het- erodimer. 4 Well-defined amino acids at both the p51 and the p66 RT subunits are needed for optimum interaction of TSAO compounds with the HIV-1 RT. 5,6 Our experi- mental data strongly suggest a specific interaction of the 3′-spiro moiety of TSAO molecules with the glutamic acid residue at position 138 (Glu-138) of the p51 subunit of HIV-1 RT. 5a,6b,7,8 Recent biochemical studies have revealed that both TSAO-T and its 3-N-ethyl derivative are able to destabilize the p66/p51 RT heterodimer in a concentration-dependent manner, leading to a loss in its ability to bind DNA. 4,9 This suggests a completely new and different mechanism of inhibition of HIV-1 RT with regard to the other known NNRTIs. Structure-activity relationship (SAR) studies within the TSAO family have revealed that the sugar part plays a crucial role in the interaction of the TSAO compounds with their target enzyme. 1-3 In particular, the presence of the unique 3′-spiro ring of 4-amino-1,2- oxathiole-2,2-dioxide in nucleosides having a ribo con- figuration is crucial for antiviral activity, and replace- ment of this amino sultone spiro ring by closely related analogues results in a 100-fold decrease of the anti- HIV-1 activity. 7 Moreover, the presence of bulky tert- butyldimethylsilyl (TBDMS) groups at both C-2′ and C-5′ positions is also a prerequisite for antiviral activ- ity. 1,3,10 As part of our program to further explore the impor- tance of substituent effects on the anti-HIV-1 activity/ toxicity of TSAO derivatives, we focused our attention * To whom correspondence should be addressed. Telephone: +34- 91 5622900. Fax: +34-91 5644853. E-mail: iqmsv29@iqm.csic.es. † Instituto de Quı ´mica Me ´dica (C.S.I.C.). ‡ Universidad de Alcala ´. § K. U. Leuven. Figure 1. Chemical structures of TSAO-T and TSAO-m 3 T. 3934 J. Med. Chem. 2002, 45, 3934-3945 10.1021/jm020820h CCC: $22.00 © 2002 American Chemical Society Published on Web 07/31/2002