1. A method of treating and / or preventing mucositis in a mammal, comprising administering to a mammal in need thereof a therapeutically effective amount of a compound of formula III: or a pharmaceutically acceptable salt thereof, wherein: each A independently is —C = O, —C = S or CH； each D independently represents O or S； each R independently represents hydrogen, C 1-6 alkyl, Calkoxy, halogen or halogen C 1 alkyl； each R independently represents hydrogen, C 1-6 alkyl, C 1 alkoxy, halogen or halogen C 1 alkyl； each R independently represents Orod, alkyl, alkoxy, halogen or galogenCalkil； each R independently is hydrogen, C1-6alkyl, C1-6 alkoxy, halogen or halogenoalkyl. 2. The method of claim 1, wherein the compound of formula III is a pharmaceutically acceptable salt thereof. A method for treating and / or preventing mucositis in a mammal, comprising administering to a mammal in need thereof a therapeutically effective amount of a compound of formula I: or a pharmaceutically acceptable salt thereof, wherein: X is O or S； R is a straight or branched chain C 1-6 alkyl optionally substituted one or more groups —NH or —NH — C (═NH) NH； Y represents a bond or carbonyl； Z represents a bond or carbonyl； R represents hydrogen or a straight or branched chain C — C alkyl, optionally substituted by one or more groups —NH or —NH — C (═NH) NH； or R is —XR； R is methylene or, where methylene is substituted by straight or branched C — C alkyl, where straight or branched C — C alkyl is optional substituted by one or more groups -NH or -NH-C (= NH) NH； n is 2-101. Способ лечения и/или профилактики мукозита у млекопитающего, включающий введение нуждающемуся в этом млекопитающему терапевтически эффективного количества соединения формулы III:или его фармацевтически приемлемой соли,где:каждый A независимо представляет собой -C=O, -C=S или CH；каждый D независимо представляет собой О или S；каждый Rнезависимо представляет собой водород, Cалкил, Cалкокси, галоген или галогенCалкил；каждый
