- Conformational Study of Heteropentapeptides Containing an α-Ethylated α,α-Disubstituted Amino Acid: (S)-Butylethylglycine (=2-Amino-2-ethylhexanoic Acid) within a Sequence of Dimethylglycine (= 2-Aminoisobutyric Acid) Residues
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Heteropentapeptides containing the α-ethylated α,α-disubstituted amino acid (S)-butylethylglycine and four dimethylglycine residues, i.e., CF3CO-[(S)-Beg]-(Aib)4-OEt (4) and CF3CO-(Aib)2-[(S)-Beg]-(Aib)2OEt (7), were synthesized by conventional solution methods. In the solid state, the preferred conformation of 4 was shown to be both a right-handed (P) and a left-handed (M) 310-helical structure, and that of 7 was a right-handed (P) 310-helical structure. IR, CD, and 1H-NMR spectra revealed that the dominant conformation of both 4 and 7 in solution was the 310-helical structure. These conformations were also supported by molecular-mechanics calculations.
- Tanaka, Masakazu,Oba, Makoto,Imawaka, Naoto,Tanaka, Yoshitsugu,Kurihara, Masaaki,Suemune, Hiroshi
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