- Rapid Optical Determination of Enantiomeric Excess, Diastereomeric Excess, and Total Concentration Using Dynamic-Covalent Assemblies: A Demonstration Using 2-Aminocyclohexanol and Chemometrics
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Optical analysis of reaction parameters such as enantiomeric excess (ee), diastereomeric excess (de), and yield are becoming increasingly useful as assays for differing functional groups become available. These assays typically exploit reversible covalent or noncovalent assemblies that impart optical signals, commonly circular dichroism (CD), that are indicative of the stereochemistry and ee at a stereocenter proximal to the functional group of interest. Very few assays have been reported that determine ee and de when two stereocenters are present, and none have targeted two different functional groups that are vicinal and lack chromophores entirely. Using a CD assay that targets chiral secondary alcohols, a separate CD assay for chiral primary amines, a UV-vis assay for de, and a fluorescence assay for concentration, we demonstrate a work-flow for speciation of the enantiomers and diastereomers of 2-Aminocyclohexanol as a test-bed analyte. Because of the fact the functional groups are vicinal, we found that the ee determination at the two stereocenters is influenced by the adjacent center, and this led us to implement a chemometric patterning approach, resulting in a 4% absolute error in full speciation of the four stereoisomers. The procedure presented herein would allow for the total speciation of around 96 reactions in 27 min using a high-Throughput experimentation routine. While 2-Aminocyclohexanol is used to demonstrate the methods, the general workflow should be amenable to analysis of other stereoisomers when two stereocenters are present.
- Herrera, Brenden T.,Moor, Sarah R.,McVeigh, Matthew,Roesner, Emily K.,Marini, Federico,Anslyn, Eric V.
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supporting information
p. 11151 - 11160
(2019/08/07)
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- Lipophilic oligopeptides for chemo- and enantioselective acyl transfer reactions onto alcohols
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Inspired by the extraordinary selectivities of acylases, we envisioned the use of lipophilic oligopeptidic organocatalysts for the acylative kinetic resolution/desymmetrization of rac- and meso-cycloalkane-1,2-diols. Here we describe in a full account the discovery and development process from the theoretical concept to the final catalyst, including scope and limitations. Competition experiments with various alcohols and electrophiles show the full potential of the employed oligopeptides. Additionally, we utilized NMR and IR-spectroscopic methods as well as computations to shed light on the factors responsible for the selectivity. The catalyst system can be readily modified to a multicatalyst by adding other catalytically active amino acids to the peptide backbone, enabling the stereoselective one-pot synthesis of complex molecules from simple starting materials.
- Mueller, Christian E.,Zell, Daniela,Hrdina, Radim,Wende, Raffael C.,Wanka, Lukas,Schuler, Soeren M. M.,Schreiner, Peter R.
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p. 8465 - 8484
(2013/09/24)
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- Backbone modification of β-hairpin-forming tetrapeptides in asymmetric acyl transfer reactions
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Synthetic oligopeptides as mimics of enzymes have been increasingly exploited as catalysts for asymmetric reactions, but highly effective oligopeptide catalysts with relatively low molecular weight are still in great demand. In this paper, we showed the conformational engineering of the β-hairpin-forming tetrapeptide 4 which was first reported by Miller's group as the catalyst for the asymmetric acyl transfer reaction of trans-2-(N-acetylamino)cyclohexan-1-ol (krel = 28). Through our backbone modification strategy, thioamide and sulfonamide as the isosteres of amide were introduced in the β-hairpin secondary structure. The thioxo peptides also adopt β-hairpin conformations as the oxopeptide supported by the combined use of NMR, IR, and X-ray techniques. Thioxo tetrapeptide 14 formed a more constrained β-hairpin conformation and therefore delivered much higher enantioselectivity (krel = 109) in the same reaction. Moreover, the examination of the conformational changes of tetrapeptide 8 upon the protonation of the Nπ-methylhistidine moiety provided evidence to explain the variation of its catalytic efficiency in the asymmetric acyl-transfer reaction.
- Chen, Peng,Qu, Jin
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scheme or table
p. 2994 - 3004
(2011/07/08)
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- Fluorescence-based screening of asymmetric acylation catalysts through parallel enantiomer analysis. Identification of a catalyst for tertiary alcohol resolution
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A technique for high-throughput screening of kinetic resolution catalysts is reported. The method relies on carrying simultaneous kinetic resolutions in a multiwell plate format wherein each well contains a unique catalyst and a small amount of a pH-activated fluorescent sensor (3). By conducting experiments such that each catalyst is evaluated in parallel in the presence of each isolated enantiomer, an indication of catalyst activity is obtained on a per enantiomer basis. Catalysts that are highly active for one enantiomer but modestly active for another are then reevaluated in conventional kinetic resolutions. From these screens, a highly selective krel = 46) pentapeptide (4) was obtained for a model secondary alcohol (1). In addition, peptide 10 was found to afford excellent selectivities (krel > 20) for a number of alcohol substrates (9a-9f) in the traditionally challenging tertiary class.
- Jarvo,Evans,Copeland,Miller
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p. 5522 - 5527
(2007/10/03)
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- Asymmetric acylation reactions catalyzed by conformationally biased octapeptides
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Octapeptides capable of adopting β-hairpin conformations have been found to function as efficient catalysts for the kinetic resolution of certain racemic secondary alcohols. Parallel solid phase synthesis of a series of peptides with the common feature of the D-Pro-Gly sequence at the turn region (i+3 to i+4) was carried out to yield a family of octapeptide catalysts. The peptides were then screened for their efficiency in a number of enantioselective acylation reactions. (C) 2000 Elsevier Science Ltd.
- Jarvo, Elizabeth R.,Vasbinder, Melissa M.,Miller, Scott J.
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p. 9773 - 9779
(2007/10/03)
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