# Development of a Novel, Easy-to-Prepare, and Potentially Valuable Peptide Coupling Technology Utilizing Amide Acid as a Linker

## TL;DR

This study introduces a new, simple method for coupling peptides with chelators using amide acid, which improves the efficiency of making radionuclide drugs.

## Contribution

A novel one-step peptide coupling method using tridentate amide acid as a linker is developed, simplifying the synthesis of radionuclide-coupled drugs.

## Key findings

- The maximum conversion of the peptide feedstock reached 87% using the new method.
- The first reactive site was identified as the terminal amino group, followed by lysine side chains.
- The tridentate amide acid framework effectively binds lanthanide ions, reducing synthesis time and cost.

## Abstract

The process of synthesizing radionuclide-coupled drugs, especially shutdown technology that links bipotent chelators with biomolecules, utilizes traditional coupling reactions, including emerging click chemistry; these reactions involve different drawbacks, such as complex and cumbersome reaction steps, long reaction times, and the use of catalysts at various pH values, which can negatively impact the effects of the chelating agent. To address the above problems in this study, This research designed a novel bipotent chelator coupled with peptides. In the present study, dichloromethane was used as a solvent, and the reaction was conducted at room temperature for 12 h. A one-step ring-opening method was employed to introduce the coupling functional group of tridentate amide acid. The coupling materials consisted of the amino active site of the peptide and diethylene glycol anhydride. In this paper, this study explored the reactions between different equivalents of acid anhydride coupled to the peptide (peptide sequence: HLRKLRKR) and determined that the maximum conversion of the peptide feedstock was 87%. To determine the selectivity of the reaction sites in this polypeptide, This study identified the peptide sequence at the reaction site using nuclear magnetic resonance (NMR) and liquid chromatography–mass spectrometry (LC-MS). For the selected peptide, the first reactive site was on the terminal amino group, followed by the amino group on the tetra- and hepta-lysine side chains. The tridentate amic acid framework functions as a chelating agent, capable of binding a range of lanthanide ions. This significantly reduces and optimizes the time and cost associated with synthesizing radionuclide-coupled drugs.