Negative Ion Mass Spectral Fragmentation of N-Alkoxycarbonyl-1-Aminoarylmethyl Phosphonic Monoesters under Electrospray Ionization Conditions

Abstract

The negative ion mass spectrometry of N-benzyloxycarbonyl and N-ethoxycarbonyl 1-aminoarylmethylphosphonic methyl, ethyl, and phenyl monoesters was investigated under electrospray ionization conditions. Their fragmentation pathways are proposed and supported by collisional activated dissociation product-ion spectrometry. All of the deprotonated molecules preferentially eliminate a molecule of benzyl alcohol or ethanol first to yield isocyanato-alkylphosphonate anions, which further generate phosphonate ions by the loss of carbon monoxide, phenol or alcohol, carbon monoxide plus arenes. The isocyanato-sulfonate anions can further cyclize to generate 3-aryl-2-phenoxy-1,2,4-oxaphosphazolidine-2,5-dione amide anions, which can undergo rearrangements by the loss of carbon dioxide, metaphosphorous acid phenyl ester, or carbon dioxide plus metaphosphorous acid phenyl ester, respectively, to give rise to nitrogen-containing anions. The title compounds show an obviously different fragmentation in the negative ion mode from that in the positive ion mode under the electrospray ionization conditions.

GRAPHICAL ABSTRACT

Keywords:

• Aminoalkylphosphonate
• ESI-MS ⁿ
• fragmentation
• negative ion mode
• ring contraction

Acknowledgments

The project was supported by the Chinese National Natural Science Foundation (Nos. 20092013 and 20772005) and the Beijing Natural Science Foundation (2092022).