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Biological glycosidation of platenolide I (I), a biosynthetic intermediate of 16-membered macrolide antibiotic platenomycin aglycones, with desosamine by Streptomycetes producing 14-membered macrolide antibiotics was attempted. Streptomyces narbonensis producing narbomycin gave a new product designated as 5-O-desosaminyl-platenolide I (III), and Streptomyces venezuelae producing narbomycin and picromycin gave III together with a second new product, 5-O-desosaminyl-14-hydroxyplatenolide I (IV). A nonantibiotic-producing blocked mutant of Streptomyces platensis subsp. malvinus, a producer of platenomycins, converted III to an antibiotically active compound identified as 3-O-propionyl-5-O-desosaminyl-9-dihydro-18-oxo-platenolide I (V).

Glycosidation of narbonolide with mycaminose was attempted by feeding narbonolide during the fermentation of a parent or a mutant strain of Streptomyces platensis, a producer of 16-membered macrolide antibiotics, platenomycins. As a result, two new compounds I and II were isolated from the fermentation broth and identified as 5-O-mycaminosyl narbonolide (I) and 9-dihydro-5-O-mycaminosyl narbonolide (II), respectively. Physicochemical and antimicrobial properties of I and II are also referred to.

A series of basic 16-membered macrolide antibiotics, M-4365 A1, A2, A3, G1, G2 and G3, were isolated from the culture broth of strain MCRL 0940 which is assigned to be a new species of Micromonospora and for which the name Micromonospora capillata sp. nov. is proposed. Among these antibiotics, M-4365 A2 and G2 showed strong inhibitory activity against Gram-positive and Gram-negative bacteria.

In vitro activities of M-4365 G2, a new basic 16-membered macrolide antibiotic, against a total 19 strains including human, bovine, porcine, rodent, avian and saprophytic mycoplasmas were compared with those of three other macrolide antibiotics, josamycin, erythromycin and tylosin. M-4365 G2 exhibited stronger activities than the other macrolide antibiotics against 11 strains of mycoplasma tested. Especially, its higher activities against M. pneumoniae Mac and FU, U. urealyticum T-960, M. mycoides PG-1 and M. gallisepticum Kp-13, PG-31 and 9-49A were to be noticed (final minimum inhibitory concentrations: 0.0001 approximately 0.049 microgram/ml). Higher antimycoplasmal activity of M-4365 G2 than that of tylosin was also proved in experimental treatment of chickens intranasally inoculated with M. gallisepticum Kp-13 by feeding a diet containing the drug. M. gallisepticum Kp-13 was not isolated from the infected chickens fed a diet containing 0.0063% or more of M-4365 G2.