Piperazine compounds

A compound of formula (I):

• or a stereoisomer, tautomer, pharmaceutically acceptable salt or solvate thereof,
• wherein,
• n is 0 or 1;
• X1 and X2 are different or identical, and are each independently CHR3;
• R1 and R2 are different or identical, and each independently selected from the group consisting of C1-4 alkyl and —C1-4 alkyl Y, wherein Y is —OR4, —SR4, or N(R4)2, and the C1-4 alkyl is optionally substituted with one or more selected from the group consisting of halogen and C1-4 alkyl;
• R3 is, independently at each occurrence, selected from the group consisting of hydrogen, alkyl, alkenyl, alkynyl, and cycloalkyl, wherein the alkyl, alkenyl, alkynyl, or cycloalkyl is optionally substituted with one or more selected from the group consisting of hydroxyl, —SH, alkoxyl, alkylthio, aryl, cycloalkyl, and heterocycle and said aryl or cycloalkyl or heterocycle is optionally substituted with one or more selected from the group consisting of halogen, hydroxyl, alkoxy, and amino;
• R4 is, independently at each occurrence, selected from the group consisting of alkyl and —C1-4 alkyl Z, wherein Z is —OR5, —SR5, or N(R5)2, and the alkyl is optionally substituted with one or more hydroxyl groups;
• R5 is, independently at each occurrence, selected from the group consisting of hydroxyl-substituted alkyl and (—C1-4 alkyl O)m—C1-4-alkyl-N(R6)2, wherein m is 0 or 1, R6 is hydroxyl-substituted alkyl;
• and
• with a proviso that at least one of R1 and R2 is not C1-4 alkyl.