The research on the functional modification of Fmoc-Arg(Pbf)-OH in the synthesis of vaccine adjuvants is of great significance. The relevant content is as follows:
I. Structural Characteristics and Advantages
Fmoc-Arg(Pbf)-OH is composed of N-fluorenylmethyloxycarbonyl (Fmoc), 2,2,4,6,7-pentamethyldihydrobenzofuran-3-sulfonyl (Pbf), and L-arginine. Fmoc can protect the amino group of the amino acid and increase the molecular stability; Pbf makes the amino acid stable under acidic conditions. The guanidino group and the side-chain amino group of arginine are active groups. However, due to the basic nature of arginine and the presence of multiple functional groups, the amino group and the side-chain guanidino group need to be protected during polypeptide synthesis. Pbf is sensitive to acid and can be removed at room temperature in the TFA/H₂O system, which is a commonly used protecting group for arginine.
II. Methods of Functional Modification in the Synthesis of Vaccine Adjuvants
Participation in the construction of polypeptide sequences: As a raw material for solid-phase polypeptide synthesis, arginine is accurately introduced into the polypeptide sequences related to adjuvants. Arginine may participate in the interaction between the adjuvant and the antigen, as well as the receptors on the surface of immune cells, or affect the spatial structure of the adjuvant, thereby regulating the immune activation effect. For example, through specific sequence design, the polypeptide adjuvant containing Fmoc-Arg(Pbf)-OH can specifically bind to the receptors on the surface of immune cells, enhancing the uptake of the adjuvant and the antigen by immune cells.
Regulation of adjuvant properties: Arginine can enhance the water solubility of the polypeptide, making the adjuvant more soluble and diffusible in the body, which is conducive to its transmission among immune tissues and cells. At the same time, the introduction of Fmoc-Arg(Pbf)-OH may also affect the charge properties of the adjuvant, change the interaction between the adjuvant and the charges on the surface of the antigen and immune cells, and influence the intensity and specificity of immune activation.
As a connection site: After the protecting groups Fmoc and Pbf are removed, the amino group and the guanidino group of arginine can serve as connection sites. Small molecules with immunomodulatory effects, polysaccharides, or other functional groups can be connected to the arginine residue to construct multifunctional adjuvants. For example, small molecules that can activate specific immune cell signaling pathways can be connected to enhance the immune activation ability of the adjuvant; or targeting groups can be connected to enable the adjuvant to specifically accumulate around immune organs or cells, improving the efficiency of the adjuvant.
III. Performance Research and Influence after Modification
Immune activation ability: The modified vaccine adjuvant may better activate antigen-presenting cells, promote their uptake, processing, and presentation of the antigen, thereby enhancing the immune response of T cells and B cells and increasing the antibody titer and the level of cellular immunity.
Safety: Reasonable functional modification can reduce the toxic and side effects of the adjuvant and improve its biocompatibility in the body. For example, through modification, the distribution of the adjuvant in non-immune tissues can be reduced, and the stimulation and damage to normal tissues can be decreased.
Stability: Modification may affect the stability of the adjuvant. For example, through chemical modification, the interaction between molecules can be increased, and the stability of the adjuvant in the storage and in vivo environment can be improved, prolonging its action time.
IV. Research Cases
The Li Zigang and Yin Feng research group from the Pingshan Biomedical R&D and Transformation Center of Shenzhen Bay Laboratory and the Shenzhen Graduate School of Peking University has developed a novel polypeptide delivery system based on the reversible "sulfonium salt" ring-closing reaction for the co-delivery of immune adjuvants and tumor neoantigen peptides. The research found that the Fmoc at the end of the polypeptide, Trp, three Arg in the sequence, and the side-chain ring-closing play a key role in inducing the assembly of the nanocomplex and maintaining the stability of the complex structure. By adjusting the ring-closing and sequence order, the polypeptide carrier M-CP, which can be used for the delivery of the nucleic acid adjuvant CpG-antigen peptide conjugate, has been screened. It can efficiently carry CpG-OVA into immune cells at the cellular level, and the released CpG further induces the activation of downstream immune pathways. Moreover, M-CP itself also shows the potential as a vaccine adjuvant. This indicates that the polypeptide constructed with the participation of Fmoc-Arg(Pbf)-OH plays an important role in the research related to vaccine adjuvants.
