LINEAR OLIGOPEPTIDES - PART 406 - HELICAL SCREW SENSE OF PEPTIDE MOLECULES - THE PENTAPEPTIDE SYSTEM (AIB)(4) L-VAL[L-(ALPHA-ME)VAL] IN SOLUTION/

A variety of N-alpha-blocked pentapeptide esters, each containing four helicogenic, achiral alpha-aminoisobutyric acid residues and one chir al L-valine or C-alpha-methyl-L-valine residue in the N-terminal, inte rnal or C-terminal position of the sequence, have been synthesized by solution methods and fully characterized. The results of a solution co nformational analysis, performed by using FTIR absorption and H-1 NMR techniques, favour the conclusion that all of the pentapeptides examin ed fold into a 3(10)-helical structure. In addition, a CD study of the N-alpha-para-bromobenzoylated peptides strongly supports the view tha t the prevailing screw sense of the 3(10)-helical structure that is fo rmed is strongly dependent upon the position in the sequence of the si ngle chiral C-alpha-tri- or C-alpha-tetrasubstituted alpha-amino acid.