We report on a detailed NMR spectroscopic study of the catalyst-substrate interaction of a highly enantioselective oligopeptide catalyst that is used for the kinetic resolution of trans-cycloalkane-1,2-diols via monoacylation. The extraordinary selectivity has been rationalized by molecular dynamics as well as density functional theory (DFT) computations. Herein we describe the conformational analysis of the organocatalyst studied by a combination of nuclear Overhauser effect (NOE) and residual dipolar coupling (RDC)-based methods that resulted in an ensemble of four final conformers. To corroborate the proposed mechanism, we also investigated the catalyst in mixtures with both trans-cyclohexane-1,2-diol enantiomers separately, using advanced NMR methods such as T relaxation time and diffusion-ordered spectroscopy (DOSY) measurements to probe molecular aggregation. We determined intramolecular distance changes within the catalyst after diol addition from quantitative NOE data. Finally, we developed a pure shift EASY ROESY experiment using PSYCHE homodecoupling to directly observe intermolecular NOE contacts between the trans-1,2-diol and the cyclohexyl moiety of the catalyst hidden by spectral overlap in conventional spectra. All experimental NMR data support the results proposed by earlier computations including the proposed key role of dispersion interaction.

Poly(aspartic acid esters) are known to form either right-or left-handed α-helices depending on the ester group in the side chain, on solvent and/or on temperature. Polyphenethyl-l-aspartates (PPLA) exhibit a helix reversal from the right- to the left-handed form with increasing temperature. We have recently reported the application of polyphenethylaspartates as helically chiral alignment media. The thermoresponsivity observed for these polymers offers the possibility to measure different orientations of analytes before and after helix reversal of the alignment medium at 373 K. Herein we present a synthesized copolymer of phenethyl- and benzylaspartate as a new alignment medium undergoing this helix reversal at 303-313 K. Thus, the measurement of residual dipolar couplings (RDC) before and after the helix reversal is allowed for at ambient temperatures. A complete sign change of all H- C RDCs was observed, which is close to the highest possible difference in NMR spectra.

Lyotropic liquid crystalline phases of poly-β-phenethylaspartates are presented as new helically chiral enantiodifferentiating alignment media with thermoresponsive properties. In addition to displaying the highest enantiodifferentiation observed for homopolypeptides, the alignment media undergo a temperature induced helix reversal without perturbing the nematic phase. This offers the opportunity to measure residual dipolar couplings (RDCs) in high and low temperature helix conformation (P- and M-helix) in one polymer. Thus different mean orientations of a chiral analyte can be determined within the same sample. Furthermore, we investigated whether the resulting media are diastereomeric and whether we are able to obtain information about the alignment process.

Herein, we report the preparation of lyotropic liquid crystalline (LLC) phases of poly-β-benzyl-L-aspartate (PBLA), a polymer that has not been known to form LLC phases before. Compared to other L-configured polypeptides usually forming right-handed helices, PBLA forms left-handed helices. The LLC phase behavior was observed for PBLA in a specific range of molecular weights, exclusively. Living polymerization allowed for this excellent control over the molecular weight. Furthermore, the LLC phase was used as a host matrix for two chiral analytesisopinocampheol and β-pineneused as probes. The interaction between these probes and the polypeptide was measured indirectly using NMR spectroscopy by investigation of the resulting orientation of probes in general and the enantiodifferentiation of the chiral analytes in particular. By comparison of the orientation induced on the probes by PBLA and the well-known poly-β-benzyl-Lglutamate, the effect of side-chain flexibility and conformation of the polypeptides on the alignment process are discussed.

Wir stellen eine umfassende NMR‐spektroskopische Untersuchung der Katalysator‐Substrat‐Wechselwirkungen eines hochselektiven Oligopeptid‐Katalysators vor, welcher für die kinetische Racematspaltung von trans‐Cycloalkan‐1,2‐diolen via Monoacylierung verwendet wird. Die außerordentliche Selektivität wurde basierend auf Molekulardynamik‐Simulationen sowie DFT‐Rechnungen erklärt. In dieser Arbeit beschreiben wir die Konformationsanalyse des Organokatalysators durch Kombination des Kern‐Overhauser‐Effekts (NOE) mit residualen dipolaren Kopplungen (RDC), wobei ein Ensemble aus vier Konformeren erhalten wurde. Zur Bestätigung des postulierten Mechanismus untersuchten wir den Katalysator in Mischungen mit dem jeweiligen Enantiomer des trans‐Cyclohexan‐1,2‐diols. Zur Charakterisierung der molekularen Aggregation wurden weiterführende NMR‐Methoden, wie die Messung von T1‐Relaxationszeiten und DOSY‐Experimente, angewendet. Bei der Messung quantitativer NOEs konnte eine Änderung der intramolekularen Abstände innerhalb des Katalysators nach Zugabe des Diols festgestellt werden. Schließlich erlaubte die Entwicklung eines pure‐shift‐EASY‐ROESY‐Experiments auf der Basis von PSYCHE‐Homoentkopplung die direkte Beobachtung intermolekularer NOE‐Kontakte zwischen dem trans‐1,2‐Diol und dem Cyclohexyl‐Rest des Katalysators, welche zuvor aufgrund von Signalüberlagerung in konventionellen NMR‐Spektren nicht beobachtbar waren. Sämtliche experimentellen NMR‐Daten bestätigen die zuvor durch Berechnungen aufgestellten Modelle. Dies beinhaltet auch die vorgeschlagene Schlüsselrolle von Dispersionswechselwirkungen.