Chiral shift reagent analysis of enantioselectivity in baker's yeast reductions of ethyl acetoacetate: An NMR experiment

Nuclear Magnetic Resonance spectra were acquired on 300 MHz or 400 MHz Bruker Avance III spectrometers fitted with BBFO probeheads (300 or 400 MHz, and 75 or 100 MHz for 1H and 13C, respectively). Chemical shifts were reported in parts per million relative to the solvent residual peak (1 H) or to the central peak of the solvent signal (13 C). The spectra were processed on Bruker Topspin 4.0.7. Note about process parameters in 1 H NMR: All 1 H NMR spectra without Eu(hfc) 3 were obtain with exponential line broadening of FID signal (command "efp"), with Line Broadening parameter set at 0.3 Hz (command "lb" set to 0.3). It improved signal-to-nose ratio, but to the detriment of the resolution. To determine enantiomeric ratio of 3 with Eu(hfc) 3 , it was needed to improve resolution of the spectra : they were obtain with Gaussian broadening of FID signal (command "gfp") with Line Broadening parameter set to-1 Hz (command "lb" set to-1), and Gaussian maximum position set to 0.3 (command "gb" set to 0.3). It explains distortions in figure S7 and figure S10. FTIR spectra (ATR) were performed on samples using a AGILENT Cary 630 FTIR Spectrometer Optical rotation were performed on POLARTRONIC E polarimeter, using chloroform as solvent and a 10-cm long polarimeter tube. All reagents were used as received, without further purification. Anhydrous THF and LiAlH 4 solution 1M in THF were purchased from Sigma-Aldrich ans and were used as received by students. Flash column chromatography separations were achieved on silica gel (Merck-Geduran Si 60, 63-200 μm).m). download file view on ChemRxiv SI Michael Addition ChemEdu Tiano.pdf (1.55 MiB) Enantioselective Michael addition : an experimental introduction to asymmetric synthesis

“…It coordinates weakly with esters and ketones. Since Eu 3+ is paramagnetic, it induces large chemical shift changes, even in substoichiometric quantities …”

Section: Experimental Overviewmentioning

confidence: 99%

Enantioselective Michael Addition: An Experimental Introduction to Asymmetric Synthesis

Tiano

2020

“…Enantiomeric excess was determined by polarimetry and peak integrations of gas chromatograms using a chiral cyclodextrin-based column. Alternatively, a NMR chiral shift reagent could be used (9). A 2:1 ratio of enantiomers was obtained by all of the students performing the sodium borohydride-tartaric acid reaction.…”

Section: Our Experimentsmentioning

confidence: 99%

Chiral Compounds and Green Chemistry in Undergraduate Organic Laboratories: Reduction of a Ketone by Sodium Borohydride and Baker's Yeast

Pohl¹,

Clague²,

Schwarz³

2002

We describe an integrated set of experiments for the undergraduate organic laboratory that allows students to compare and contrast biological and chemical means of introducing chirality into a molecule. The racemic reduction of ethyl acetoacetate with sodium borohydride and the same reduction in the presence of a tartaric acid ligand are described, and a capillary gas chromatography column packed with a chiral material for product analysis is introduced. The results of these two hydride reactions are compared with the results of a common undergraduate experiment, the baker's yeast reduction of ethyl acetoacetate.

“…These analogies have served well to clarify this question and should prove helpful in explaining related topics involving averaging observations. The subject is especially relevant as seen by several recent articles on chiral and achiral LSR (13,14).…”

Section: Ft-(substratementioning

confidence: 99%

Chiral lanthanide NMR shift reagents and equilibria with substrate enantiomers: Rationale for the observed signals

Rothchild¹

1989