AIDS-187906 AIDS187906 D-Ribitol, 1,4-anhydro-1-C-(4,7-dihydro-7-oxo-1H-pyrazolo[4,3-d]pyrimidin-3-yl)-, (1S)-, compd. with (1S)-1-C-(7-amino-1H-pyrazolo[4,3-d]pyrimidin-3-yl)-1,4-anhydro-D-ribitol (1:1) Formycins