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Structure elucidation of chlorophyll catabolites (phyllobilins) by ESI-mass spectrometry-Pseudo-molecular ions and fragmentation analysis of a nonfluorescent chlorophyll catabolite (NCC).

Müller T, Vergeiner S, Kräutler B - Int J Mass Spectrom (2014)

Bottom Line: The hyphenation of high performance chromatography with modern mass spectrometric techniques providing high-resolution data as well as structural information from MS/MS experiments has become a versatile tool for rapid natural product identification and characterization.A recent application of this methodology concerned the investigation of the annually occurring degradation of green plant pigments.Since the first structural elucidation of a breakdown product in the early 1990s, a number of similarly structured, tetrapyrrolic catabolites have been discovered with the help of chromatographic, spectroscopic and spectrometric methods.

View Article: PubMed Central - PubMed

Affiliation: Institute of Organic Chemistry and Center for Molecular Biosciences, University of Innsbruck, 6020 Innsbruck, Austria.

ABSTRACT

The hyphenation of high performance chromatography with modern mass spectrometric techniques providing high-resolution data as well as structural information from MS/MS experiments has become a versatile tool for rapid natural product identification and characterization. A recent application of this methodology concerned the investigation of the annually occurring degradation of green plant pigments. Since the first structural elucidation of a breakdown product in the early 1990s, a number of similarly structured, tetrapyrrolic catabolites have been discovered with the help of chromatographic, spectroscopic and spectrometric methods. A prerequisite for a satisfactory, manually operated or database supported analysis of mass spectrometric fragmentation patterns is a deeper knowledge of the underlying gas phase chemistry. Still, a thorough investigation of the common fragmentation behavior of these ubiquitous, naturally occurring chlorophyll breakdown products is lacking. This study closes the gap and gives a comprehensive overview of collision-induced fragmentation reactions of a tetrapyrrolic nonfluorescent chlorophyll catabolite, which is intended to serve as a model compound for the substance class of phyllobilins.

No MeSH data available.


Related in: MedlinePlus

Diagnostic fragmentations of sodiated (+)-ions of NCC 1: Loss of CO2 and a proposed mechanism involving the ketene functionality from the 82-methoxycarbonyl group (see Section 3.1).
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fig0045: Diagnostic fragmentations of sodiated (+)-ions of NCC 1: Loss of CO2 and a proposed mechanism involving the ketene functionality from the 82-methoxycarbonyl group (see Section 3.1).

Mentions: Typical FAB mass spectra [10,25] or ESI mass spectra [24] of polar NCCs, which carried a carboxylic acid function at ring E, showed a strong signal at (M-44 + X)+, with X = H, Na or K, indicating an efficient loss of carbon dioxide. This observation was rationalized by the presence of a reactive β-keto acid grouping in these NCCs. Surprisingly, a decarboxylation reaction in the gas phase was also observed in the MS of the NCC 1, in which a β-keto ester functionality is present. Remarkably, in the MS spectra of sodiated or potassiated 1 (Fig. 3B and C) as well as of deprotonated 1 (Fig. 4), loss of carbon dioxide was observed only from the daughter ions [M + X-CH3OH]+ with X = Na, K or [M–H–CH3OH)]− that resulted from loss of MeOH, giving a ketene group at C82. Thus, two boundary conditions need to be met for the remarkable decarboxylation to be relevant: a deprotonated carboxylic acid functionality (with sodium or potassium counter ions in the positive ion-mode) and the ketene function appear to be required. These findings suggest further activation steps to be crucial for the rapid loss of CO2. Note, the positively charged pseudo-molecular ions [M + X]+ are protonated sodium or potassium complexes of 1. In the decarboxylation the electrophilic ketene group may be attacked by the nucleophilic carboxylate. This leads to the enolate of a cyclic anhydride function (see Scheme 5; delineated for the positive ion-mode). The latter may undergo closure to a strained α-lactone ring, which is activated for an ensuing decarboxylative ring fragmentation. This hypothetical path would involve loss of the 83 carbon and one oxygen atom of the former ester function, and not of the propionate itself.


Structure elucidation of chlorophyll catabolites (phyllobilins) by ESI-mass spectrometry-Pseudo-molecular ions and fragmentation analysis of a nonfluorescent chlorophyll catabolite (NCC).

Müller T, Vergeiner S, Kräutler B - Int J Mass Spectrom (2014)

Diagnostic fragmentations of sodiated (+)-ions of NCC 1: Loss of CO2 and a proposed mechanism involving the ketene functionality from the 82-methoxycarbonyl group (see Section 3.1).
© Copyright Policy - CC BY-NC-ND
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4375672&req=5

fig0045: Diagnostic fragmentations of sodiated (+)-ions of NCC 1: Loss of CO2 and a proposed mechanism involving the ketene functionality from the 82-methoxycarbonyl group (see Section 3.1).
Mentions: Typical FAB mass spectra [10,25] or ESI mass spectra [24] of polar NCCs, which carried a carboxylic acid function at ring E, showed a strong signal at (M-44 + X)+, with X = H, Na or K, indicating an efficient loss of carbon dioxide. This observation was rationalized by the presence of a reactive β-keto acid grouping in these NCCs. Surprisingly, a decarboxylation reaction in the gas phase was also observed in the MS of the NCC 1, in which a β-keto ester functionality is present. Remarkably, in the MS spectra of sodiated or potassiated 1 (Fig. 3B and C) as well as of deprotonated 1 (Fig. 4), loss of carbon dioxide was observed only from the daughter ions [M + X-CH3OH]+ with X = Na, K or [M–H–CH3OH)]− that resulted from loss of MeOH, giving a ketene group at C82. Thus, two boundary conditions need to be met for the remarkable decarboxylation to be relevant: a deprotonated carboxylic acid functionality (with sodium or potassium counter ions in the positive ion-mode) and the ketene function appear to be required. These findings suggest further activation steps to be crucial for the rapid loss of CO2. Note, the positively charged pseudo-molecular ions [M + X]+ are protonated sodium or potassium complexes of 1. In the decarboxylation the electrophilic ketene group may be attacked by the nucleophilic carboxylate. This leads to the enolate of a cyclic anhydride function (see Scheme 5; delineated for the positive ion-mode). The latter may undergo closure to a strained α-lactone ring, which is activated for an ensuing decarboxylative ring fragmentation. This hypothetical path would involve loss of the 83 carbon and one oxygen atom of the former ester function, and not of the propionate itself.

Bottom Line: The hyphenation of high performance chromatography with modern mass spectrometric techniques providing high-resolution data as well as structural information from MS/MS experiments has become a versatile tool for rapid natural product identification and characterization.A recent application of this methodology concerned the investigation of the annually occurring degradation of green plant pigments.Since the first structural elucidation of a breakdown product in the early 1990s, a number of similarly structured, tetrapyrrolic catabolites have been discovered with the help of chromatographic, spectroscopic and spectrometric methods.

View Article: PubMed Central - PubMed

Affiliation: Institute of Organic Chemistry and Center for Molecular Biosciences, University of Innsbruck, 6020 Innsbruck, Austria.

ABSTRACT

The hyphenation of high performance chromatography with modern mass spectrometric techniques providing high-resolution data as well as structural information from MS/MS experiments has become a versatile tool for rapid natural product identification and characterization. A recent application of this methodology concerned the investigation of the annually occurring degradation of green plant pigments. Since the first structural elucidation of a breakdown product in the early 1990s, a number of similarly structured, tetrapyrrolic catabolites have been discovered with the help of chromatographic, spectroscopic and spectrometric methods. A prerequisite for a satisfactory, manually operated or database supported analysis of mass spectrometric fragmentation patterns is a deeper knowledge of the underlying gas phase chemistry. Still, a thorough investigation of the common fragmentation behavior of these ubiquitous, naturally occurring chlorophyll breakdown products is lacking. This study closes the gap and gives a comprehensive overview of collision-induced fragmentation reactions of a tetrapyrrolic nonfluorescent chlorophyll catabolite, which is intended to serve as a model compound for the substance class of phyllobilins.

No MeSH data available.


Related in: MedlinePlus