13 C n.m.r. study of l‐alanine peptides

Abstract

The di‐, tri, and tetrapeptides of l‐alanine have been studied in aqueous solution by 13C n.m.r. spectroscopy at 25 and 50 MHz. By using selectively 13C enriched analogs containing either 90% 13C methyl or carbonyl carbons and measurements as a function of pH, assignment of the chemical shifts of the peptides has been made. T1 and NOE measurements of the peptides in their cationic, anionic, and zwitterionic states have been recorded as a function of concentration. The results show considerable segmental motion along the backbone carbons of the peptides, with only small changes occurring in the dynamic motions of the peptides as their charge states are altered. The lack of concentration dependence of the chemical shift and T1 values, as well as the similarity of T1 values for individual peptides in the three charge states, indicate that the peptides do not self‐associate in aqueous solution.

Fluorinated amino acids: compatibility with native protein structures and effects on protein–protein interactions

“…Mitra et al described the synthesis of tetra-L-alanine analogues containing 3 3 -F 3 Ala at positions 1, 2 and 3. 18 They tested the analogue modified at position 2 for its binding to an antipoly-L-alanine antibody and found no difference compared to the parental Ala 4 sequence. The other analogues modified at position 1 and 3 have not been investigated yet.…”

“…54 Substitution at a solvent exposed position of a monomeric b-sheets protein domain (G B1) resulted in an increased stability. 59 Senguen and co-workers used F 5 Phe to evaluate its aromatic, hydrophobic and steric effects on the self-assembly of the amyloid-b-fragment Ab (16)(17)(18)(19)(20)(21)(22). 89 This short peptide segment (Ac-KLVFFAE-NH 2 ) contains two central phenylalanine residues, and is known to pack in antiparallel b-sheets within the amyloid fibril.…”

Monofluoroalkene‐Isostere as a 19F NMR Label for the Peptide Backbone: Synthesis and Evaluation in Membrane‐Bound PGLa and (KIGAKI)3

“…The sequence from residue 8–21 was synthesized on the Rink amide resin using HBTU/HOBt/DIPEA as coupling agents as described in the supporting information. However, coupling of monofluorodipeptide isostere remained unsuccessful due to several side reactions, some of which are well‐known in the literature . All our attempts to continue the coupling of the monofluoroalkene‐based dipeptide isostere were unsuccessful (results not shown).…”