抄録
A new nucleoside antibiotic, mildiomycin, was isolated from the culture filtrate of Streptoverticillium rimofaciens B-98891 in our laboratories. It is effective on powdery mildews and has remarkably low toxicity in mammalian animals and fishes. This antibiotic has a novel structure which was determined by chemical degradations and spectral studies. Mildiomycin (1) is a water-soluble, basic substance; mp>300℃, [α]_D+100°, C_<19>H_<30>N_8O_9・H_2O. On acidic and basic hydrolyses, mildiomycin afforded 5-hydroxymethyl cytosine (5), L-serine (6) and urea. On periodate oxidation in 2N-HCl, 1 also gave optically active γ-guanidino-β-hydroxy butyric acid (8). The pyran-3-en ring moiety was elucidated on the basis of ^1H- and ^<13>C-NMR data of mildiomycin and its degradation products as well as those of blasticidin S. PtO_2 hydrogenation of 1 afforded a decytosinyl compound (9, C_<14>H_<27>N_5O_7); subsequent acidic hydrolysis yielded a deseryl lactone (12, C_<11>H_<20>N_4O_4・2HCl). A ureido compound (15, C_<11>H_<21>N_3O6) derived from the lactone was cleaved by Pb(OAc)_4 oxidation to afford CO_2 and a ketone (18, C_<10>H_<19>N_3O_4). These degradation studies and spectral analyses, especially ^<13>C-NMR study, have revealed the structure of mildiomycin (1). Absolute configuration of 1 was determined by ^1H-NMR and CD spectra to be 1'R, 4'R, 5'S and 2"S within 6 asymmetric carbons.
