The isolation of maridomycins (I, II, III, IV, V, VI) and the structure of maridomycin II have been reported in the preceding paper 1. All of these components show similar physicochemical, chemical and biological properties. Each component gave the same color reactions with erythromycin test and Dragendorff reagent, and showed the same ultraviolet end absorption. The following functional groups were observed in the NMR-and IR-spectra of these compounds (Table I). Alkali hydrolysis of maridomycin I (I), C4sH71NO16, lII (III), C41HevNOl~, IV (IV), C40H65NO~6, V (V), Ca0H65NO16, VI (VI) C30H~aNO16 gave 1 mole each of propionic acid and isovaleric acid, 2 moles of propionic acid, 1 mole each of acetic acid and propionic acid, 1 mole each of acetic acid and propionic acid, and 2 moles of acetic acid, respectively. Methanolysis of I afforded ~- and B-methyl isovaleryl mycaroside. By the same treatment both III and IV gave s-methyl propionyl mycaroside (XXVIII)2, [~]~2--145.2 (c = 0.5 in CHCla), and its B-anomer (XXIX), [~]~1 4- 18.2 (c = 1.5, in CHCI3), while V and VI yielded m and B-methyl acetyl mycaroside (XXX) 2 (Table II). On mild acid hydrolysis of 9-dehydromaridomycins, 2 kinds of demycarosyl derivatives were obtained; one from 9-dehydro compounds of I, III, V and the other from those of II, IV, VI. The difference between the 2 demycarosyl derivatives is assumed to come from the fatty acid moieties at carbon 3. And the differences among 9-dehydromaridomycin I, III, V and among 9-dehydromaridomycin II, IV, VI, all come from the fatty acid moieties at carbon 4. On the basis of these findings, the structures of maridomycins were proposed as shown in the Figure. To confirm the proposed structures, the mass fragmentation patterns 4 of each component and their derivatives were inspected (Table III). Comparison of Maridomycin I and II; Maridomycin I shows molecular peak at 857, which is 14 mass unit greater than that of II. The fragments (1), (2), (3), (4), (9) and (10) correspond to aglycone moieties and show 1 methylene (m/e 14) difference between I and II. The fragments (11), (12), (13) and (14) indicate that they have the same acylsugar moiety. These mass patterns and the liberation of propionic acid from I with alkali hydrolysis suggest that the propionyl group is located at carbon 3 or 9. The NMR spin decoupling study excludes the possibility of carbon 9. The elimination mechanism of the propionic acid accounts for the fragments (5), (6), (7) and (8). Thus it was concluded that I has propionyl group at carbon 3 instead of acetyl group at carbon 3 in II. The structures of other maridomycin components were established analogously as shown in the figure 5.