Whether L version and D version peptides should have identical NMR, especially in the state of self-assembly have to have identical NMR?
How to use HRMS to confirm L version or D version peptides?
For example, compounds 1 and 2 are shown in the attachment. Could you explain it with these two compounds as examples
Hello Xia Wu
With NMR you cannot distinguish between two enantiomers, the L and D form have the same NMR spectrum. You need to convert one enantiomer into a diastereomer. Alternatively you can use chiral derivatizing agents CDA or chiral solvating agents (CSA).
Also HRMS is not suitable to distinguish between both peptides, HRMS just give you the information about the mass and not about the stereochemistry. But you can use CD spectroscopy.
Mr. Wu,
By means of conventional NMR measurements there is unable to determnine enantiomers both qualitatively and quantitatively. There is needed chiral orienting medium.
By means of mass spectrometry such analysis can be carried out using (i) chiral chromatography as a preliminary analysis; or by (ii) quantifying the experimental variable ''intensity'' of the MS fragment ions of the enantiomers.
Mr. Lamping,
The mass spectrometry (MS) provides information not only about m/z-values, but also the variable 'intensity' of MS peak.
The mass spectrometric instrumentation does not provide information only about the elemental composition. There is 'elemental analysis' for such purposes.
Please, consider more recent trends in the quantitative mass spectrometry, providing absolute quantification of the MS intensity values of the MS peak
(These are references [1,2].)
Such quantification is capable of determining enantiomers not only qualitytively, but also quantitatively.
[1] Stochastic Dynamic Mass Spectrometric Approach to Quantify Reserpine in Solution; Bojidarka Ivanova, Michael Spiteller
Analytical Chemistry Letters, 10 (2020) 703-721; Received 13 Oct 2020, Accepted 16 Dec 2020, Published online: 28 Jan 2021
Download citation https://doi.org/10.1080/22297928.2020.1865834
[2] Steroids, 164 (2020) 108750
Stochastic dynamic mass spectrometric quantification of steroids in mixture — Part II; Bojidarka Ivanova, Michael Spiteller
The method is our own authored contribution (to me and my co-author's according to the shown authorship.)
Dear Xia..
you can not discriminate FULL L (e.g. LLL) from full D (DDD), but as has been pointed out by Matthias, you can discriminate LLL from e.g DLL or LDL or LLD (which in turn cannot be discriminated from DDL) ....there is a exception for Thr amino acid, because this has a 2nd stereocenter in the side-chain....
I hope this helps....
Alfred
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