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"Click" analytics for "click" chemistry - A simple method for calibration-free evaluation of online NMR spectra

  • Driven mostly by the search for chemical syntheses under biocompatible conditions, so called "click" chemistry rapidly became a growing field of research. The resulting simple one-pot reactions are so far only scarcely accompanied by an adequate optimization via comparably straightforward and robust analysis techniques possessing short set-up times. Here, we report on a fast and reliable calibration-free online NMR monitoring approach for technical mixtures. It combines a versatile fluidic system, continuous-flow measurement of H-1 spectra with a time interval of 20 s per spectrum, and a robust, fully automated algorithm to interpret the obtained data. As a proof-of-concept, the thiol-ene coupling between N-boc cysteine methyl ester and ally] alcohol was conducted in a variety of non-deuterated solvents while its time-resolved behaviour was characterized with step tracer experiments. Overlapping signals in online spectra during thiol-ene coupling could be deconvoluted with a spectral model using indirect hard modeling and wereDriven mostly by the search for chemical syntheses under biocompatible conditions, so called "click" chemistry rapidly became a growing field of research. The resulting simple one-pot reactions are so far only scarcely accompanied by an adequate optimization via comparably straightforward and robust analysis techniques possessing short set-up times. Here, we report on a fast and reliable calibration-free online NMR monitoring approach for technical mixtures. It combines a versatile fluidic system, continuous-flow measurement of H-1 spectra with a time interval of 20 s per spectrum, and a robust, fully automated algorithm to interpret the obtained data. As a proof-of-concept, the thiol-ene coupling between N-boc cysteine methyl ester and ally] alcohol was conducted in a variety of non-deuterated solvents while its time-resolved behaviour was characterized with step tracer experiments. Overlapping signals in online spectra during thiol-ene coupling could be deconvoluted with a spectral model using indirect hard modeling and were subsequently converted to either molar ratios (using a calibration free approach) or absolute concentrations (using 1-point calibration). For various solvents the kinetic constant k for pseudo-first order reaction was estimated to be 3.9 h(-1) at 25 degrees C. The obtained results were compared with direct integration of non-overlapping signals and showed good agreement with the implemented mass balance. (C) 2017 Elsevier Inc. All rights reserved.show moreshow less

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Metadaten
Author details:Aleksandra Michalik-Onichimowska, Simon Kern, Jens RiedelORCiD, Ulrich Panne, Rudibert King, Michael MaiwaldORCiD
DOI:https://doi.org/10.1016/j.jmr.2017.02.018
ISSN:1090-7807
ISSN:1096-0856
Pubmed ID:https://pubmed.ncbi.nlm.nih.gov/28288418
Title of parent work (English):Journal of magnetic resonance
Publisher:Elsevier
Place of publishing:San Diego
Publication type:Article
Language:English
Year of first publication:2017
Publication year:2017
Release date:2020/04/20
Tag:Automated data evaluation; NMR spectroscopy; Reaction monitoring; Thiol-ene click chemistry
Volume:277
Number of pages:8
First page:154
Last Page:161
Funding institution:Excellence Initiative of the German Research Foundation (DFG); European
Organizational units:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Chemie
Peer review:Referiert
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