CD Spectra in Methanol ofβ-Oligopeptides Consisting ofβ-Amino Acids with Functionalized Side Chains, with Alternating Configuration, and with Geminal Backbone Substituents - Fingerprints of New Secondary Structures?

Abstract

Dedicated to Professor Richard Neidlein on the occasion of his 70th birthday b-Hexa-, b-hepta-, and b-nonapeptides, 1 ± 6, which carry functionalized side chains (CO 2 R, CO À 2 , (CH 2 ) 4 NH 3 , CH 2 ÀCHCH 2 ) consisting of b 3 -amino-acid residues of alternating configuration, or which carry geminal substituents in the 2-or 3-positions of all residues, have been synthesized (Schemes 1 ± 3), and their CD spectra in MeOH are reported (Figs. 2 ± 6). Strong Cotton effects (V > 10 5 ) are indicative of the presence of chiral secondary structures. It is suggested by simple modelling (Fig. 1) that the new b-peptides should not be able to fold to the familiar 3 14 -helical structures. Still, three of them (3, 4, and 5) give rise to CD spectra matching those of b-peptides that are known to be present as (M)-or (P)-3 14 -helices in MeOH solution. While possible folding motifs (Figs. 3,b, and 7) of the new b-peptides have been identified in crystal structures, an interpretation of the CD spectra has to be postponed until NMR solution structures become available. A list of all b-peptides giving rise to CD spectra with a minimum near 215 nm is included (Table).

The Miraculous CD Spectra (and Secondary Structures?) ofβ-Peptides as They Grow Longer, Preliminary Communication

“…14 ) For the NMR-solution structure of 1 in MeOH and H 2 O, see [7]. 15 ) For lists of characteristic CD patterns of b-peptides see Table 3 in [10] and the Table in [11]. CD spectra of the b-peptides 1 (in MeOH and in H 2 O) and 2 (in MeOH) 16 ) are in accord with our experience and expectation (Fig.…”

“…This leads to b-peptides of excellent solubility 10 secondary structure), we have now synthesized the all-b 3 -tetracosapeptide 4 (Scheme and Fig. 1) 11 ).…”

Synthesis and Solution Conformation of Homo-β-peptides Consisting of N-Mannofuranosyl-3-ulosonic acids

“…For example β 3,3 -oligomers from Seebach's group show CD pattern with a weak trough around 230 nm and two peaks at 215 and 200 nm. 45 The presence of the additional signal at 215 nm makes the general shape different and as a consequence do not allow any future comparison. The polyproline I helix and oligomers of (S)-nipecotic acids also feature CD signals above 225 nm, until 232 nm in aliphatic alcohol,s 46 but their whole spectra are once again different from those that characterize our oligomers.…”

NMR-Structural Investigations of a β3-Dodecapeptide with Proteinogenic Side Chains in Methanol and in Aqueous Solutions

“…For certain b-peptides, CD spectra have been correlated with secondary structures 4 ). It has been established by numerous CD measurements and corresponding NMR investigations that b-peptides consisting of l-b 3 -amino acids exhibit a characteristic CD pattern with a negative Cotton effect near 215 nm, zero-crossing between 205 and 210 nm, and a positive peak near 200 nm, a pattern that was assigned to a left-handed (M) 3 14 -helical structure [41] [42]. The b-peptide 1 exhibits the CD spectrum shown in Fig.…”