Tyrosine-derived stimuli responsive, fluorescent amino acids

Area of Science:

• Organic Chemistry
• Biochemistry
• Materials Science

Background:

• Fluorescent unnatural amino acids (UAAs) are valuable tools in chemical biology.
• Existing fluorescent UAAs often have limited emission ranges.
• Development of UAAs with tunable and broad emission properties is desirable.

Purpose of the Study:

• To synthesize novel fluorescent UAAs with stilbene and meta-phenylenevinylene backbones.
• To investigate the optical properties and stimuli-responsive behavior of these new UAAs.
• To demonstrate the utility of these UAAs in peptide synthesis and cellular imaging.

Main Methods:

• Synthesis of UAAs via palladium-catalyzed Heck coupling of protected diiodo-l-tyrosine with styrene analogs.
• Characterization of optical properties, including emission spectra and quantum yields.
• Incorporation of a UAA into a cell-penetrating peptide (CPP) using solid-phase peptide synthesis.
• Confocal fluorescence microscopy to monitor CPP internalization in cell lines.

Main Results:

• Successfully synthesized novel UAAs with broad emission wavelengths (400-800 nm), including near-infrared (NIR) emission with a quantum yield (QY) of 4%.
• Achieved distinct red, green, and blue (RGB) emission based on pH (basic, acidic, neutral states) due to pyridine and phenol groups.
• Demonstrated reversible pH and redox responsiveness, indicating potential as fluorescent probes.
• Incorporated UAA into a CPP and successfully visualized its internalization in cells via fluorescence microscopy.

Conclusions:

• Developed a new class of fluorescent unnatural amino acids with broad and tunable emission spectra.
• These UAAs exhibit promising stimuli-responsive behavior (pH, redox) for sensing applications.
• Demonstrated the feasibility of incorporating these UAAs into peptides for biological imaging and tracking.