An idea to use 4′-C-substituted-2′-deoxynucleoside derivatives was proposed based on a working hypothesis to solve the problems of existing acquired immune deficiency syndrome chemotherapy (highly active antiretroviral therapy). Subsequent studies have successfully proved the validity of the idea and resulted in the development of 2′-deoxy-4′-C-ethynyl-2-fluoroadenosine and 2′-deoxy-4′-C-ethynyl-2-chloroadenosine, nucleoside reverse transcriptase inhibitors, which have supremely high activity against all human immunodeficiency viruses including multidrug-resistant HIV and low toxicity.

(Communicated by Takao SEKIYA, M.J.A.)