Membrane channel forming polypeptides. 270-MHz hydrogen-1 nuclear magnetic resonance studies on the conformation of the 11-21 fragment of suzukacillin.

270-MHz 1H NMR studies on the synthetic suzukacillin fragments Boc-Leu-Aib-Gly-Leu-Aib-OMe (13-17), Boc-Gln-Aib-Leu-Aib-Gly-Leu-Aib-OBz (11 -17), Boc-Leu-Aib-Gly-Leu-Aib-Pro-Val-Aib-Aib-OMe (13-21), and Boc-Gln-Aib-Leu-Aib-Gly-Leu-Aib-Pro-Val-Aib-Aib-OMe (11-21) have been carried out in CDCl3 and (CD3)2SO. The intramolecularly hydrogen-bonded amide hydrogens in these peptides have been identified by using solvent titration experiments and temperature coefficients of NH chemical shifts in (CD3)2SO. The peptides are shown to favor conformations stabilized by intramolecular 4 leads to 1 hydrogen bonds. The 11-21 fragment adopts a highly folded, largely 310 helical conformation stabilized by seven intramolecular hydrogen bonds. An eighth NH group [Gly(5)] appears to be involved in a weaker interaction. Evidence for the possible participation of the Gln side-chain carboxamide group in hydrogen bonding to the peptide backbone is also presented.