B. Larsen, D. Christensen, A. Holm
Jul 1, 1993
Citations
0
Influential Citations
35
Citations
Journal
Journal of the American Chemical Society
Abstract
The stepwise solid-phase synthesis of the peptide H-(Ala) 6 -Lys-OH on a polyacrylamide gel resin was followed by near-infrared (NIR) Fourier-transform (FT) Raman spectroscopy. In particular, this investigation involved the use of Fmoc as the N-α-protecting group. The deprotection of the Fmoc group by standard methods could be quantitatively followed. The deprotection was essentially complete until a number of alanine residues in multiples of six were reached, with nearly one-third of the peptide chains left protected after the standard piperidine treatment. Even a prolonged deprotection time did not result in a complete deprotection of the Fmoc group. This phenomenon could be attributed to the formation of secondary structures, which were indicated by structurally sensitive Raman bands, with particular focus on the amide III bands. The Fmoc group was found to have a clear influence upon the secondary structure, supporting mainly a β-sheet conformation, whereas more coiled forms were found for the deprotected samples. Preliminary studies with the use of Boc as the N-α-protecting group showed that this group had essentially no importance for the secondary structure of the pendent peptide chains. Investigation of peptides containing both D- and L-chiral forms of alanine supported the hypothesis that the presence of the Fmoc group influences the secondary structure. The swelled forms of the sequence Fmoc-(Ala) 6 -Lys(Boc)-OR in DMSO or DMF showed different secondary structures, indicating different interactions between the peptide chains and the two solvents. Our studies show that Raman spectroscopy is a nondestructive analytical tool which allows a recording of spectra while the peptide is directly bound to the solid support under normal synthetic conditions