Piperazine derivatives and application thereof

A compound of formula (III) or pharmaceutically acceptable salts thereof,

• wherein,
• each R1 is independently selected from the group consisting of halogen, C1-3 alkyl, C1-3 alkoxyl, —C(═O)NRaRb and —CH2C(═O)NRaRb, the C1-3 alkyl and the C1-3 alkoxyl are optionally substituted by 1, 2 or 3 halogens;
• each R2 is independently selected from the group consisting of C1-3 alkyl and C3-6 cycloalkyl;
• each R3 is independently selected from the group consisting of halogen, —C1-3 alkyl and C1-3 alkoxyl;
• R4 is selected from the group consisting of tert-butyl, phenyl, pyridyl, pyridazinyl, tetrahydropyranyl, cyclobutyl, cyclohexyl, tetrahydrofuranyl and oxabicyclooctyl, each of which is independently optionally substituted by 1, 2 or 3 Rc;
• Ra and Rb are each independently selected from the group consisting of H and C1-3 alkyl;
• each Rc is independently selected from the group consisting of halogen, —CN and C1-3 alkyl;
• m and t are each independently selected from the group consisting of 0, 1 and 2;
• n is 1 or 2;
• and
• T1 is selected from the group consisting of N and CH.