Abstract: Deformyltylosin derivatives of the formula ##STR1## wherein A is ##STR2## --CH.dbd.CH-- or --CH.sub.2 --CH.sub.2 --, R.sub.1 is hydrogen, lower alkanoyl or aryl-lower alkanoyl, X.sub.1 and X.sub.2 are hydrogen or are connected to form a valence bond, Y.sub.1 and Y.sub.2 are hydrogen or are connected to form a valence bond, Q.sub.1 is hydrogen or methyl, Q.sub.2 is hydrogen or ##STR3## R.sub.2 is hydrogen or lower alkanoyl, R is hydrogen or ##STR4## R.sub.3 is hydrogen or C.sub.2-5 alkanoyl, and R.sub.4 is hydrogen or C.sub.2-6 alkanoyl, and when R.sub.3 is not hydrogen, then R.sub.4 is not hydrogen, or a pharmaceutically acceptable salt thereof, have strong antibacterial activities as compared to the known antibiotic tylosin, and also have enhanced antibacterial activities against all macrolide antibiotic-resistant strains such as A, B and C group strains, and have higher blood levels as compared with tylosin.

Abstract: Derivatives of antibiotic tylosin of the formula ##STR1## wherein R.sub.1 is hydrogen or lower alkanoyl, A.sub.1 and A.sub.2 are groups of which one is R.sub.2 and the other is R.sub.3, and R.sub.2 and R.sub.3 are C.sub.2-6 alkanoyl, or a physiologically acceptable salt thereof, have enhanced antibacterial activity against macrolide antibiotic-resistant strains.

Abstract: 3"-acylated macrolide antibiotics of the formula ##STR1## wherein R.sub.1 is hydrogen or C.sub.2-3 alkanoyl, R.sub.2 is hydrogen or C.sub.2-4 alkanoyl, at least one of R.sub.1 and R.sub.2 being hydrogen, and one of R' and R" being R.sub.3 and the other R.sub.4, R.sub.3 being C.sub.2-6 alkanoyl and R.sub.4 being C.sub.2-5 alkanoyl, or a pharmaceutically acceptable salt thereof.