Ezomycins A, C26H38N8015S*H20 (I) and A2 C19H26N6012 2 l H 0 (II) are antifungal nucleoside antibiotics produced by a strain of Streptomyces. 132) Positive colorations to a e-dimethyl- aminobenzaldehyde test **,3) suggest the presence of a ureido group in both I and II. On acid hydrolysis, I liberated cytosine. 1) Hydrolysis of I with Dowex 50W (H+) afforded L-cystathionine and II as main products. II was further acid-hydrolyzed to give ezoaminuroic acid (III), 3- amino-3,4-dideoxy-D-xylohexopyranuroic acid. 4) Hydrolysis of I with 1.5N NaOH at 90" gave anhydronucleoside A (IV): C13H14N40gX; needles, mp >280" (dec.); [a]E5 +21.8' (~=1.2, N NH40H); $;5N HC1 nm (E) 211 (8400), 238 (7700), 257 (7700). , h0*05N NaoH 225 (sh max ., 10,700), 261 (5700); pKa' 3.8, 9.9; M+ m/e 714 for C13HgN408(TMS)5. -All of the signals in the pmr spectrum of IV were assigned by spin-decoupling experiments as shown in Table 1. The UV (Amax 261 nm) and p&' (9.9) data indicated that the cytosine moiety in I was converted to uracil in IV. IV was negative to ninhydrin but still positive to DMA. On esterification with methanolic HCl, IV gave monomethyl ester (V): C14H16N408#; needles, mp >300ยฐ; M+ m/e 656 for C14H12N408(TMS)4. Acetylation of V with acetic anhydride-pyridine afforded mainly monoacetate (VI): fine needles, mp >256" (dec.); A~~~" nm (E) 212.5 (21,200), 244 (23,200). Chemical shift of H-2' of VI (Table 1) shows that C-2' hydroxyl was acetylated. Spin-decoupling experiments showed that the broad multiplet (4.7, H-5', Wl,2 =18) is coupled with an amide proton (6.48, d., 9.0) as well as with H-4' and H-6'. This indicated that the ureido is attached to C-5'. Thus, four nitrogens of IV were attributed to a uracil moiety and a ureido group. Six of * This paper comprises part IV of the series, "Studies on Ewmycins, Antifungal Antibiotics." Preceding paper, see Reference 2. l * Abbreviated as DMA hereafter. # This formula was confirmed by elemental analysis.