Conformational Properties of Poly(L-azetidine-2-carboxylic acid) in Solution as Studied by Carbon-13 and Proton Nuclear Magnetic Resonance Spectroscopy

Abstract

The proton and magnetic resonance spectra of poly(~-azetidine-2-carboxylic acid) were determined in water and in formic acid. The 100-MHz 'H nmr spectra do not give evidence of cis-trans isomerism in the two solvents. On the other hand, the 220-MHz 'H nmr spectrum in water shows two peaks for the aCH proton. 13C nmr spectra show two separate peaks for each carbon atom, .which are assigned to cis and trans isomers of the amide bond. Some model compounds have been examined to aid this assignment. The percentage of the cis isomer decreases from water to formic acid and increases upon addition of CaC12 to the water solution. High yields of high molecular weight poly(~-azetidine-2-carboxylic acid) (mol wt = 23,000) have been obtained by the polymeric selfcondensation of the (Aze)s pentachlorophenyl ester trifluoroacetate.

13C‐NMR sequence analysis 8. Investigation on piperazine‐containing copolyamides

“…Thus, it turned out that in every case the signals of carbons anti to the carbonyl oxygen shift downfield compared with those of the syn position. Other authors report similar results (18,19). Hence, we assume that the 13C signals of piperazine show an analogous behavior.…”

Azetidine-Derived Amino Acids versus Proline Derivatives. Alternative Trends in Reverse Turn Induction

“…It is known that proline serves as a turn inducer in natural peptides and proteins, with a high frequency of occurrence in the ( i + 1) position of β-turn motifs. , Moreover, it has been shown that the α-alkylation of Pro, as in α-MePro, provides further stabilization of β-turn conformations in linear peptides ,− have pointed out the propensity for β-bend formation of the Aze-containing peptides, but with higher flexibility compared to Pro analogues. We have recently performed a conformational analysis of 2-alkyl-2-carboxy azetidines, when incorporated at the i + 1 position of simplified model tetrapeptides, and showed that these non-proteinogenic amino acids possess an unexpected ability to induce γ-turn conformations .…”

“…Cl 2(1:60). HPLC: t R ) 16.03 min (cis isomer) and18.75 min (trans isomer) (A:B ) 15:85). [R] D -113.13 (c 0.98, CHCl 3 ).1 H NMR (CDCl 3 ): cis/trans isomers ratio: 1:5.…”

Conformational Preferences of Proline Analogues with Different Ring Size

“…The replacement of Pro with Aze causes to inhibit the growth of Escherichia coli and the seedlings of mung bean ( Phaseolus aureus ) . In spite of similar chemical structures, the replacement of Pro with Aze has resulted in remarkable changes in structures and biological properties of polyproline, , collagen, − peptides, , and proteins. − In particular, the addition of Aze to budding yeast cells induces the protein misfolding and selectively activates the heat shock factor that is required for the subsequent G 1 arrest of the cell cycle . The incorporation of Aze in place of Pro in the C-terminus of YbeL protein from E. coli significantly suppresses tagging by SsrA, an RNA molecule contained in all eubacteria …”