Abstract: Use of a compound of the general formula I and/or a pharmaceutically acceptable salt thereof as active ingredient for the preparation of a pharmaceutical composition for the treatment of multiple sclerosis in humans: wherein X represents NCH3, O or S. A represents an unsubstituted C1-4 alkylene or a substituted C1-4 alkylene that is mono- or poly-substituted with substituents independently selected from CH3, CH2CH3, CH2CH2CH3 und CH(CH3)2, M represents H; benzoyl; unsubstituted C1-12 alkanoyl; substituted C1-12 alkanoyl that is mono- or poly-substituted with substituents independently selected from CH3, CH2CH3, F and Cl; unsubstituted C1-12 alkyl; or substituted C1-12 alkyl that is mono- or poly-substituted with substituents independently selected from CH3, CH2CH3, F and Cl; R represents CH3, CH2CH3 or NR1R2, wherein R1 and R2 independently represent H, CH3 or CH2CH3, and Y1, Y2 and Y3 are independently selected from H, CH3, CH2CH3, F and Cl.