Fused tricyclic derivative and pharmaceutical application thereof

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

• wherein,
• R1 is selected from the group consisting of H, halogen, C1-4 alkyl and phenyl;
• R2 is each independently selected from the group consisting of H, halogen and C1-4 alkyl;
• or two R2, together with the thiophene ring to which they are connected, form benzothiophene;
• n is selected from the group consisting of 1 and 2;
• T1 is selected from the group consisting of a single bond, —NH— and —N(CH3)—;
• L1 is selected from the group consisting of a single bond and —CH2—;
• the structural unit
• is selected from the group consisting of
• ring A is selected from the group consisting of the following groups optionally substituted with 1 or 2 Rb:
• C4-6 cycloalkenyl, 4- to 6-membered heterocycloalkenyl, 5- to 6-membered heteroaryl,
• and phenyl;
• Rb is each independently selected from the group consisting of —F, —Cl, —Br, —I, —CH3 and —CH2CH3;
• ring B is selected from the group consisting of cyclopentyl, cyclohexyl and 6- to 10-membered heterocycloalkyl, wherein the 6- to 10-membered heterocycloalkyl is optionally substituted with 1 Ra;
• Ra is selected from the group consisting of —F, —Cl, methyl, —OH and —CN;
• wherein “hetero” of the “6- to 10-membered heterocycloalkyl” comprises 1, 2 or 3 heteroatoms or heteroatom groups independently selected from the group consisting of O, S, NH and N, wherein the nitrogen atom is optionally quaternized with methyl halide.