FAPI dimer compound, FAPI dimer-based positron emission tomography (PET) imaging agent for tumor diagnosis, and preparation method and use thereof

A preparation method of a fibroblast activation protein inhibitor (FAPI) dimer compound with a structure shown in formula I:

• the preparation method comprising the following steps:
• (1) mixing a compound 1, a compound 2, a first condensation reagent, and a first organic base to allow a first condensation reaction, and subjecting a resulting condensation product to a first Boc protecting group removal reaction to obtain a compound 3;
• (2) mixing the compound 3, a compound 4, a second condensation reagent, and a second organic base to allow a second condensation reaction, and subjecting a resulting condensation product to a second Boc protecting group removal reaction to obtain a compound 5;
• (3) mixing the compound 5, a compound 6, a third condensation reagent, and a third organic base to allow a third condensation reaction, and subjecting a resulting condensation product to an Fmoc protecting group removal reaction to obtain a compound 7;
• and
• (4) mixing the compound 7, a compound 8, a fourth condensation reagent, and a fourth organic base to allow a fourth condensation reaction, and subjecting a resulting condensation product to a carboxylic acid protecting group removal reaction to obtain the FAPI dimer compound with a structure shown in formula I;
• wherein in step (2), the compound 3, the compound 4, the second condensation reagent, and the second organic base are in a molar ratio of 1:(1-5):(1-5):(2-6);
• the second condensation reaction is conducted at 25° C. to 100° C. for 4 h to 16 h;
• and
• the second Boc protecting group removal reaction is conducted at 0° C. to 50° C. for 0.5 h to 3 h;
• and
• wherein in step (3), the compound 5, the compound 6, the third condensation reagent, and the third organic base are in a molar ratio of 1:(1-3):(2-6):(5-10);
• the third condensation reaction is conducted at 25° C. to 100° C. for 4 h to 16 h;
• and
• the Fmoc protecting group removal reaction is conducted at 0° C. to 50° C. for 0.5 h to 3 h.