Differentiation of diastereomeric N‐aryltetrahydropyrano/tetrahydrofuranochromenylamines under electron ionization and chemical ionization conditions

Abstract

A series of diastereomeric 4S,5S,6R/S-tetrahydropyrano- and 3S,4S,5R/S-tetrahydrofuranochromenylamine derivatives (a/b isomers; 1-26) has been studied under electron ionization (EI) and chemical ionization (CI) conditions. The EI mass spectra of all diastereomeric compounds show two characteristic fragment ions, of which one is formed by retro-Diels-Alder (RDA) reaction from the molecular ion, retaining the charge on the diene fragment, and the other [M-(HNAr)]+ ion by a simple radical loss. The RDA process is more favorable in all b isomers, whereas the radical loss is dominant in all a isomers; based on these two ions it is easy to differentiate the two diastereomers. The collision-induced dissociation (CID) spectra of all the molecular ions also show the same trend, which reflects the stereoselectivity in the formation of the two characteristic fragment ions. The results of theoretical calculations performed are in accordance with the experimental observations. The CI experiments (methane and isobutane) on all the diastereomeric compounds also enabled the differentiation of the isomers.

Stereochemical effects in fragmentation of diastereoisomers of protected diethyl 1,2-diamino-alkylphosphonates

“…In some cases, differences in the abundances or formation of specific fragment ions can be observed in mass spectra especially when electron ionization (EI) has been applied as an ionization technique. Soft ionization techniques (chemical ionization (CI), fast atom bombardment (FAB), liquid secondary ion mass spectrometry (LSI) or electrospray (ESI)) give abundant protonated or cationized molecules from which stereochemical information can be obtained by collision‐induced dissociation (CID) 3–5. Investigation of fragmentation stereochemistry can be useful for better understanding of the factors influencing differences in the fragmentation of diastereoisomers of new compounds.…”

Differentiation of the diastereomeric synthetic precursors of isofebrifugine and febrifugine by electrospray ionization tandem mass spectrometry

“…However, to the best of our knowledge, there are no studies on the differentiation of these precursors by mass spectrometric methods. Mass spectrometry is a proven tool in the analysis of stereoisomers employing a wide range of ionization and tandem mass spectrometric techniques 14–16. We have reported the differentiation of several diastereomeric compounds using electron ionization (EI), chemical ionization (CI) and electrospray ionization (ESI) 17, 18.…”

Mass Spectrometry in India

“…As a continuation of this work, Prabhakar et al at IICT addressed the differentiation of diastereomers of biological or synthetic importance, such as hydroxy brevicomins, conduramine derivatives, precursors of febrifugene/ isofebrifugene and a-sulfanyl b-amino acid derivatives. [93][94][95][96][97] A few sets of structural isomers, substituted diaryl ethers and benzoxazolinones, were also differentiated. 98,99 Prabhakar and colleagues demonstrated the occurrence of EI-induced Claisen rearrangements and Newman-Kwart rearrangements with the aid of high-resolution mass spectrometry (HRMS) and MS/MS.…”