MRF (also known as Methyltetrazine-PEG4-VHL Ligand) is a chemical compound designed for use in targeted protein degradation research, specifically within the PROTAC (Proteolysis Targeting Chimera) and molecular glue fields. Its structure consists of a VHL (von Hippel-Lindau) E3 ligase recruiting ligand, a flexible tetraethylene glycol (PEG4) linker, and a methyltetrazine group. The methyltetrazine moiety serves as a bioorthogonal reaction handle, enabling rapid and specific conjugation to molecules bearing a trans-cyclooctene (TCO) group via an inverse electron-demand Diels-Alder (IEDDA) reaction. The primary application of MRF is as a modular building block for constructing PROTACs and other bifunctional degraders. Researchers can easily conjugate the TCO-modified target protein ligand to the methyltetrazine group of MRF, creating a complete PROTAC molecule that simultaneously binds to the protein of interest and the VHL E3 ubiquitin ligase. This proximity induces ubiquitination and subsequent proteasomal degradation of the target protein. It is a critical tool for chemical biology, drug discovery, and the study of protein function. This compound exemplifies the "click chemistry" approach in degrader synthesis, offering advantages in speed, efficiency, and modularity over traditional synthetic routes. It is supplied as a stable solid and requires storage at low temperatures (e.g., -20°C) under desiccated conditions to maintain its reactivity. Handling should follow standard laboratory safety protocols for research chemicals.