Synthesis, Chiroptical Properties, and Configurational Assignment of Fulleroproline Derivatives and Peptides

1,3-Dipolar cycloaddition of azomethine ylides to
C60 leads to fulleroproline derivatives, in which a
proline
ring is fused on a 6,6-ring junction of the fullerene spheroid.
This unnatural amino acid can be manipulated under
standard coupling conditions to afford fulleroproline-containing
peptides. All optically active fulleroproline
derivatives
and peptides display a characteristic maximum at 428 nm in CD spectra,
which is diagnostic for the assignment of
the absolute configuration of the Cα atom of the proline
ring. Calculation of the CD spectra confirm the
configurational
assignment.