[60]Fullerene l‑Amino Acids and Peptides: Synthesis under Phase-Transfer Catalysis Using a Phosphine–Borane Linker. Electrochemical Behavior

A new method to link amino acid and peptide derivatives to [60]­fullerene is described. It uses hydrophosphination with a secondary phosphine borane. First, the stereoselective synthesis of secondary phosphine borane amino acid derivatives was achieved by alkylation of phenylphosphine borane with γ-iodo-α-amino ester reagents under phase-transfer catalysis (PTC). Second, a sec-phosphine borane amino ester was saponified and coupled with α,γ-diamino esters to afford the corresponding dipeptide derivatives in good yields. Finally, the hydrophosphination reaction of [60]­fullerene by the sec-phosphine borane compounds was performed under PTC to obtain C60-amino acid or dipeptide derivatives in yields up to 80% by P–C bond formation. This addition reaction which proceeds in mild and moderate dilute conditions (0.03 M) leads to [60]­fullerene derivatives as epimeric mixtures (∼1:1) due to the P-chirogenic center but without racemization of the amino acid or peptide moiety. In addition, the electrochemical behavior of a C60-phosphine borane amino ester was investigated by cyclic voltammetry and spectroelectrochemistry after controlled-potential electrolysis. It showed evidence for the retro-hydrophosphination reaction into free [60]­fullerene and sec-phosphine borane amino ester compound. Consequently, the synthesis of sec-phosphine borane amino acids followed by their use in hydrophosphination reactions of [60]­fullerene under phase-transfer catalysis has demonstrated a great utility for the preparation of C60-derivatives. Indeed, the hydrophosphination and the retro-hydrophosphination reactions of [60]­fullerene/phosphine borane compounds offer a promising new strategy for the reversible immobilization of amino acid or peptide derivatives on carbon nanomaterials such as [60]­fullerene.