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

Abstract

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 C-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 C-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 C-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.

Asymmetric electrophilic reactions in phosphorus chemistry

“…The hydrophosphination reaction of C60-fullerene with phosphine-borane was carried out under PTC conditions, with the formation of P-C derivatives of C60-dipeptides in yield up to 80%. The addition reactions of fullerene C60 were carried out under mild conditions without racemization of the amino acid or peptide moiety (Equation ( 24)) [44]. (24) Halogenphosphine-boranes possessing unique chemical properties are very valuable chiral reagents for the preparation of P-chiral phosphine ligands as shown in Equations ( 25) and (26).…”

Phosphorus-containing amino acids with a P–C bond in the side chain or a P–O, P–S or P–N bond: from synthesis to applications

“…In the following examples, phosphine boranes are used as the precursors for graing [60]fullerene to an amino acid side chain. 66 Fullerene derivatives have been studied for their biological activities and for medical diagnosis, as they are without known toxicity. Phenylphosphine borane 191 was linked to the side chain of the g-iodoamino ester 186 under solid-liquid phase transfer conditions, leading to the corresponding phosphine borane amino ester 192 with 98% yield.…”

Asymmetric Electrophilic Reactions in Phosphorus Chemistry

“…The hydrophosphination reaction of C60-fullerene with phosphine-borane was carried out under PTC conditions, with the formation of P-C derivatives of C60-dipeptides in yield up to 80%. The addition reactions of fullerene C60 were carried out under mild conditions without racemization of the amino acid or peptide moiety (Equation (24)) [44]. (24) Halogenphosphine-boranes possessing unique chemical properties are very valuable chiral reagents for the preparation of P-chiral phosphine ligands as shown in Equations (25) and (26).…”

“…The hydrophosphination reaction of C 60 -fullerene with phosphine-borane was carried out under PTC conditions, with the formation of P-C derivatives of C 60 -dipeptides in yield up to 80%. The addition reactions of fullerene C 60 were carried out under mild conditions without racemization of the amino acid or peptide moiety (Equation (24)) [44].…”

“…Examples of the stereospecific Michaelis-Becker reaction with alkyl halides and aryl halides are shown in Equations (46) and (47) [60][61][62]. Sodium ethylate, sodium in THF, sodium hydride, butyllithium, sodium naphthalide, Ca(OH)2 in DMF, KOH in acetonitrile and others were used as bases in the Michaelis- (44) Buono et al…”