114781-15-6Relevant articles and documents
The first fully planar C5-conformation of homooligopeptides prepared from a chiral α-ethylated α,α-disubstituted amino acid: (S)-butylethylglycine (=(2S)-2-amino-2-ethylhexanoic acid)
Imawaka, Naoto,Tanaka, Masakazu,Suemune, Hiroshi
, p. 2823 - 2835 (2007/10/03)
An optically active α-ethylated α,α-disubstituted amino acid, (S)-butylethylglycine (=(2S)-2-amino-2-ethylhexanoic acid; (S)-Beg; (S)-2), was prepared starting from butyl ethyl ketone (1) by the Strecker method and enzymatic kinetic resolution of the racemic amino acid. Homooligopeptides containing (S)-Beg (up to hexapeptide) were synthesized by conventional solution methods. An ethyl ester was used for the protection at the C-terminus, and a trifluoroacetyl group was used for the N-terminus of the peptides. The structures of tri-and tetrapeptides 5 and 6 in the solid state were solved by X-ray crystallographic analysis, and were shown to have a bent planar C5-conformation (tripeptide) and a fully planar C5-conformation (tetrapeptide) (see Figs. 1 and 2, resp.). The IR and 1H-NMR spectra of hexapeptide 8 revealed that the dominant conformation in CDCl3 solution was also a fully planar C5-conformation. These results show for the first time that the preferred conformation of homopeptides containing a chiral α-ethylated α,α-disubstituted amino acid is a planar C5-conformation.
