MC-Val-Cit-PAB

Synthesis of Compound 19 (Fmoc-VC-PABA):

1.5g of compound 18 (Fmoc-Val-Cit) was dissolved in a mixed solvent of 14ml dichloromethane and 7ml methanol. 4-Aminobenzyl alcohol (445.2mg, 3.62mmol) was added, followed by EEDQ (1.5g, 6mmol). The reaction mixture was stirred overnight at room temperature. After the solvent was concentrated and removed, isopropyl ether was added to the residue and the mixture was washed for 30min. The solid was filtered, and isopropyl ether was added again and the mixture was washed for 30min. After filtration, 1.5g of Fmoc-VC-PABA was obtained, with a yield of 82%.

M(+1)＝602.6.

Synthesis of Compound 20 (N-[6-(2,5-dihydro-2,5-dioxo-1H-pyrrolo-1-yl)-1-oxohexyl]-L-valine-N5-(carbamoyl)-N-[4-(hydroxymethyl)phenyl]-L-guanineamide):

2g of Fmoc-VC-PABA was dissolved in 10ml of DMF, and 2ml of piperidine was added. The mixture was stirred at room temperature for 30min. After the reaction was completed by TLC monitoring, it was concentrated under reduced pressure using a high-vacuum oil pump to obtain a yellow solid, which could be used directly in the next reaction without purification.

MC-Val-Cit-PAB-OH is a cleavable peptide linker. The Val-Cit was designed to be cleaved specifically by Cathepsin B. MC group is reactive with thiol moiety

N-[6-(2,5-Dihydro-2,5-dioxo-1H-pyrrol-1-yl)-1-oxohexyl]-L-valyl-N5-(aminocarbonyl)-N-[4-(hydroxymethyl)phenyl]-L-ornithinamide is used as a reagent to prepare antibody-drug conjugates, which are compounds that selectively deliver cytotoxic drugs to a tumour-associated antigen.

MC-Val-Cit-PAB is a peptide linker that can be used to prepare antibody-drug conjugates (ADCs) for cancer therapy research. For example, CBP-1018, a dual-ligand PDC, is conjugated to MMAE via a cleavable linker (MC-Val-Cit-PABC) that can be cleaved by proteinase B^[1]. MC-Val-Cit-PAB can also be used to prepare cetuximab-vc-DOX-NPs conjugates, which have good tumor targeting ability and low systemic toxicity, and are a promising drug delivery targeting system^[2].

[1] LC-MS/MS method for dual-ligand peptide-drug CBP-1018 and its deconjugated payload MMAE including sample stabilization strategy for its MC-Val-Cit-PABC linker[J]. Talanta, 2024. DOI:10.1016/j.talanta.2024.126596.
[2] ZIXUAN YE. EGFR Targeted Cetuximab-Valine-Citrulline (vc)-Doxorubicin Immunoconjugates- Loaded Bovine Serum Albumin (BSA) Nanoparticles for Colorectal Tumor Therapy.[J]. International Journal of Nanomedicine, 2021. DOI:10.2147/IJN.S289228.