Cyclopeptide pcsk9 inhibitor and its medical use

A compound as shown in formula I or a pharmaceutically acceptable salt thereof:

• wherein,
• R1 is selected from —CH3, —C(O)—(CH2)n1-N+(CH3)3, or —C(O)—(CH2CH2O)n2-CH2CH2N+(CH3)3, where n1 is selected from an integer of 1 to 14, and n2 is selected from an integer of 1 to 5;
• R1′ and R1″ are each independently selected from absence, hydrogen or —CH3;
• R2 is selected from hydrogen, halogen, —SCH3, —SCH2X, —SCHX2, or —SCX3;
• R3 is selected from hydrogen, or halogen;
• A is selected from:
• wherein R4 and R5 are each independently selected from a bond, a linear C1-C5 alkyl, phenyl, provided that R4 and R5 are not a bond or phenyl at the same time;
• R41 and R42 are each independently selected from absence, hydrogen, deuterium, substituted or unsubstituted C1-C3 alkyl, halogen, or, R41 and R42 together with one carbon atom to which they are connected, form a C3-C5 cycloalkyl;
• R51 and R52 are each independently selected from absence, hydrogen, deuterium, substituted or unsubstituted C1-C3 alkyl, halogen, or, R51 and R52 together with one carbon atom to which they are connected, form a C3-C5 cycloalkyl;
• n3 is selected from an integer of 0 or 1-4;
• n4 is selected from 0 or 1;
• among the substituted C1-C3 alkyl, the substituent is selected from deuterium, or halogen.