Synthesis of a Tyr-Tyr Peptide Library and Fluorescence of the Stilbenyl Derivatives

An expeditious ultrasound–assisted synthesis of a tyrosine–tyrosine peptide library is presented. Dipeptide synthesis and functionalization, via Suzuki-Miyaura or Sonogashira cross-coupling reactions, was carried out and led to sixteen extended conjugation derivatives in moderate to good yields. Both o-hydroxy- and o-methoxy-trans-stilbenyl-Tyr-Tyr peptides emit blue fluorescence when irradiated with ultraviolet light. The fluorescence quantum yield of solutions of these peptides in methanol, acetonitrile or THF was 0.20 ± 0.05. Quantum chemical calculations at the Time-Dependent Density Functional Theory (TDDFT) level suggests that, for both peptides, emission originates from the stilbene core.