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

✍ Scribed by Masakazu Tanaka; Makoto Oba; Naoto Imawaka; Yoshitsugu Tanaka; Masaaki Kurihara; Hiroshi Suemune

• Publisher: John Wiley and Sons
• Year: 2001
• Tongue: German
• Weight: 206 KB
• Volume: 84
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/1522-2675(20010131)84:1<32::aid-hlca32>3.0.co;2-4

✦ Synopsis

Heteropentapeptides containing the a-ethylated a,a-disubstituted amino acid (S)-butylethylglycine and four dimethylglycine residues, i.e., CF 3 CO-[(S)-Beg]-(Aib) 4 -OEt (4) and CF 3 CO-(Aib) 2 -[(S)-Beg]-(Aib) 2 -OEt (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) 3 10 -helical structure, and that of 7 was a righthanded (P) 3 10 -helical structure. IR, CD, and 1 H-NMR spectra revealed that the dominant conformation of both 4 and 7 in solution was the 3 10 -helical structure. These conformations were also supported by molecularmechanics calculations.