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- Title
How To Stabilize or Break β-Peptidic Helices by Disulfide Bridges: Synthesis and CD Investigation of β-Peptides with Cysteine and Homocysteine Side Chains.
- Authors
Jacobi, Albrecht; Seebach, Dieter
- Abstract
all- L- β3-Penta-, hexa-, and heptapeptides with the proteinogenic side chains of valine, leucine, serine, cysteine, and methionine have been prepared by previously described procedures ( 12, 13, 14, 15; Schemes 2 - 5). Thioether cleavage with Na/NH3 in β-HMet residues has also provided a β3-hexapeptide with homocysteine (CH2CH2S) side chains ( 13e). The HS−(CH2) n groups were positioned on the β-peptidic backbone in such a way that, upon disulfide-bridge formation, the corresponding β-peptide was expected to maintain either a 31-helical secondary structure ( 1, 2) ( Fig. 1) or to be forced to adopt another conformation ( 3, 4). The 13-, 17-, 19-, and 21-membered-ring macrocyclic disulfide derivatives and their open-chain precursors, as well as all synthetic intermediates, were purified (crystallization, flash or preparative HPL chromatography; Fig. 5) and fully characterized (m.p., [ α]D, CD, IR, NMR, FAB or ESI mass spectroscopy, and elemental analysis, whenever possible; Fig. 2 and Exper. Part). The structures in MeOH and H2O of the new β-peptides were studied by CD spectroscopy ( Figs. 3 and 4), where the characteristic 215-nm-trough/200-nm-peak pattern was used as an indicator for the presence or absence of ( M)- 31-helical conformations. A CH2−S2−CH2 and, somewhat less so, a (CH2)2−S2−(CH2)2 bracket between residues i and i+3 ( 1 vs. 12d, and 2 vs. 13e in Fig. 3) give rise to CD spectra which are compatible with the presence of 31-helical structures, while CH2−S2−CH2 brackets between residues i and i+2 ( 3 vs. 14c) or i and i+4 ( 4 vs. 15c in Fig. 4) do not.
- Publication
Helvetica Chimica Acta, 1999, Vol 82, Issue 8, p1150
- ISSN
0018-019X
- Publication type
Article
- DOI
10.1002/(SICI)1522-2675(19990804)82:8<1150::AID-HLCA1150>3.0.CO;2-O