Indium-mediated atom-transfer and reductive radical cyclizations of iodoalkynes: synthesis and biological evaluation of HIV-protease inhibitors |
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Authors: | Yanada Reiko Koh Yasuhiro Nishimori Nobuaki Matsumura Akira Obika Shingo Mitsuya Hiroaki Fujii Nobutaka Takemoto Yoshiji |
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Institution: | Graduate School of Pharmaceutical Sciences, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan. ryanada@pharm.kyoto-u.ac.jp |
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Abstract: | Novel indium-mediated radical cyclization reactions of aliphatic iodoalkynes have been studied. Treatment of iodoalkynes with a catalytic amount of In (0.1 equiv) and I(2) (0.05 equiv) promotes atom-transfer 5-exo cyclization to give five-membered alkenyl iodides. In contrast, reaction with In (2 equiv) and I(2) (1 equiv) yields reductive 5-exo cyclization products via the same 5-exo cyclization. Both processes are most likely initiated by low-valent indium species. To demonstrate versatility of these reactions, optically active HIV protease inhibitors were synthesized by this reductive cyclization method. Among them, several products, which contain a hydroxyethylamine dipeptide isostere as a transition state-mimicking substructure, proved to possess potent activity (IC(50) = 5-39 nM) against a wide spectrum of HIV strains, including multidrug-resistant variants. |
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