Conformational analysis of helical aminoisobutyric acid (Aib) oligomers bearing C-terminal ester Schellman motifs.
The effect of Schellman motifs on the adoption of stable 310 helical conformations in a series of aminoisobutyric (Aib) oligomers has been studied in the solid state and solution. The destabilising effect of the Schellman motif (a local inversion of helical screw-sense due to a C-terminal ester residue) was quantified in the solid state using X-ray crystallography through analysis of the torsion angles and their deviation from those observed in an ideal 310 helix. Investigation of the intramolecular hydrogen-bonding interactions in the solid state led to the identification of a fully extended C5 conformation in one oligomer, which is a novel folding motif for Aib oligomers. The effect of ester groups with differing steric demands on intermolecular hydrogen-bonding contacts in the solid state was also ascertained. In solution, the adoption of a 310 conformation in Aib oligomers appeared to be more finely tuned, depending on a number of factors, including chain length and the steric demands of the C-terminal destabilising Schellman motif.
School of Chemistry, University of Manchester, Oxford Road, Manchester, M13 9PL, UK. sarah.pike@manchester.ac.uk S.Webb@manchester.ac.uk clayden@man.ac.uk.
Sarah J
SJ
Pike
James
J
Raftery
Simon J
SJ
Webb
Jonathan
J
Clayden
D000621:Aminoisobutyric Acids / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004121:Dimethyl Sulfoxide / Q000737:chemistry; D004952:Esters / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D010455:Peptides / Q000737:chemistry; D011522:Protons; D012996:Solutions
D000621:Aminoisobutyric Acids; D004952:Esters; D010455:Peptides; D011522:Protons; D012996:Solutions; D004121:Dimethyl Sulfoxide