Abstract: The present invention relates to novel semisynthetic cyclosporin analogs of Formula (I): X is absent, —C1-C6 alkyl-, or —C3-C6 cycloalkyl- Y is selected from the group consisting of: (i) C(O)—O—R1, where R1 is hydrogen, C1-C6 alkyl, optionally substituted with halogen, heterocyclic, aryl, C1-C6 alkoxy, C1-C6 alkylthio, halogen-substituted C1-C6 alkoxy, or halogen-substituted C1-C6 alkylthio; (ii) C(O)—S—R1, where R1 is as previously defined; (iii) C(O)—OCH2—OC(O)R2, where R2 is C1-C6 alkyl, optionally substituted with halogen, C1-C6 alkoxy; C1-C6 alkylthio, heterocyclic or aryl; (iv) C(S)—O—R1, where R1 is as previously defined, and (v) C(S)—S—R1, where R1 is as previously defined; B is -&agr;Abu-, -Val-, -Thr- or -Nva-; and U is -(D)Ala-, -(D)Ser-, —[O-(2-hydroxyethyl)(D)Ser]-, —[O-acyl(D)Ser]- or —[O-(2-acyloxyethyl)(D)Ser]-.

Abstract: There are described novel 5-O-mycaminosyltylonide derivatives and pharmaceutically acceptable compositions comprising a therapeutically effective amount of a compound of the invention in combination with a pharmaceutically acceptable carrier. Also described are a method for treating bacterial infections by administering to an animal a pharmaceutical composition containing a therapeutically-effective amount of a compound of the invention, and processes for the preparation of such compounds.