Plasmin inhibitor, preparation method therefor, and application thereof

A compound represented by the structure of formula I, or a pharmaceutically acceptable salt, isomer, or mixture thereof:

• wherein
• R1 is selected from the group consisting of hydrogen, hydroxy, amino, alkyl, alkoxy, —NH-alkyl, cycloalkyl, aryl, aliphatic heterocyclyl, and aromatic heterocyclyl;
• wherein said R1 is optionally substituted with 1-2 groups selected from hydroxy, alkyl, arylalkyl, halogen, aryl, and cycloalkyl;
• R2 is independently selected from the group consisting of hydrogen, carboxyl, amido, alkyl, —NH-alkyl, —CH2O-alkyl,—CH2NH-alkyl, —COO-alkyl,—CONH-alkyl, cycloalkyl, aryl, aliphatic heterocyclyl, aromatic heterocyclyl, arylalkyl, and cycloalkylalkyl;
• wherein said R2 is optionally substituted with 1-2 groups selected from hydroxy, alkyl, and alkoxy;
• or two R2 together with the carbon atom to which they are attached form a cycloalkyl or aliphatic heterocyclyl;
• R3 is selected from hydrogen and halogen;
• and
• at least one of R1, R2 and R3 is not hydrogen.