Harada and Kishi'isolated from Streptomyces novoguineensis a new antibiotic amipurimycin, which was active against Pyricularia oryzae, had a molecular formula C20H27_31N708* H20 and showed pKa'3.7 and 9.1 and the signals in the pmr and cmr spectra as well as the maxima of its uv spectra characteristic to those of 2-aminopurine moiety. We now report here structure determination of amipurimycin (&)[C26H29N708 ...