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Stereochemistry of norditerpenoid alkaloids by liquid chromatography/atmospheric pressure chemical ionization mass spectrometry
Author(s) -
Wada Koji,
Mori Takao,
Kawahara Norio
Publication year - 2000
Publication title -
journal of mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 1076-5174
DOI - 10.1002/(sici)1096-9888(200003)35:3<432::aid-jms954>3.0.co;2-6
Subject(s) - chemistry , atmospheric pressure chemical ionization , mass spectrometry , fragmentation (computing) , protonation , chemical ionization , ion , mass spectrum , analytical chemistry (journal) , ionization , acetonitrile , deuterium , alkaloid , molecule , chromatography , stereochemistry , organic chemistry , physics , quantum mechanics , computer science , operating system
High‐performance liquid chromatography/atmospheric pressure chemical ionization mass spectrometry (HPLC/APCI‐MS) is a very promising approach to structural investigations of positional isomers and stereoisomers. This method was applied successfully to stereoisomeric norditerpenoid alkaloids differing in configuration at C‐6. APCI‐MS allowed the easy and precise control of energy deposition by varying the drift voltage. Comparison of the breakdown curves, observed by changing the potential difference between the first electrode and the second electrode of the APCI ion source, revealed the stereochemical dependence of different fragmentations. Comparison of the APCI spectra showed that the abundance of fragment ions was significantly higher for C‐6β alkaloid than for C‐6α alkaloid. The axial positions of the corresponding substituents (6‐methoxyl and 8‐hydroxyl) strongly suggested a 1,3‐diaxial interaction effect of the fragmentation. The characteristic fragment ions were formed by the loss of water or acetic acid at position 8, irrespective of the stereochemistry at position 6. The possibility of distinct fragmentation mechanisms depending on the stereochemistry of the precursor ion could be discerned by recording the spectra in a deuterated solvent system of 0.05 M ammonium acetate in D 2 O–acetonitrile–tetrahydrofuran. Loss of D 2 O from the precursor ion gave the fragment ion. This result indicated that the proton of protonation was included in the leaving water molecule. The peak intensity ratio R = [M + H] + /[M + H − H 2 O] + manifested the stereochemical differentiation of alkaloids at position 6. Copyright © 2000 John Wiley & Sons, Ltd.