Ring-modified proline short peptide compound and use thereof

A compound represented by formula (I″) or a pharmaceutically acceptable salt thereof,

• wherein,
• R5 is selected from C1-3 haloalkyl;
• the structural moiety
• and the
• is optionally and independently substituted by 1, 2 or 3 Ra′;
• ring D is selected from C4-8 cycloalkyl, C5-8 cycloalkenyl and 5- to 8-membered heterocycloalkyl, and the C4-8 cycloalkyl is optionally substituted by 1 or 2 Ra′;
• Ra′ is each independently selected from F and methyl;
• the heterocycloalkyl contains 1, 2 or 3 heteroatoms or heteroatom groups independently selected from O, S, N and NH.