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首页> 外文期刊>Journal of Agricultural and Food Chemistry >Discriminating between the six isomers of dicaffeoylquinic acid by LC-MSn
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Discriminating between the six isomers of dicaffeoylquinic acid by LC-MSn

机译：LC-MSn区分二咖啡酰奎尼酸的六个异构体

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摘要

The fragmentation behavior of all six dicaffeoylquinic acids (diCQA) has been investigated using LC-MS4. It is possible to discriminate between each of the isomers including those for which commercial standards are not available. For diCQA, the ease of removal of the caffeoyl residue during fragmentation is 1 ≈ 5 > 3 > 4. The distinctive fragmentation observed for the little-studied 1,4- dicaffeoylquinic acid involves elimination of the C1 caffeoyl residue, repeated dehydrations leading to the aromatization of the quinic acid moiety, and its decarboxylation. It is suggested that this process is initiated by the C1 carboxyl protonating the C5 hydroxyl in the inverted chair conformer, followed by its protonating the C1 caffeoyl residue in the favored chair conformation. The fragmentation of 1-caffeoylquinic acid is indistinguishable from that of the commercially available 5-caffeoylquinic acid, but these two isomers can be distinguished easily by their facile chromatographic resolution on reversed phase packings. The hierarchical key previously developed for characterizing chlorogenic acids has been extended to accommodate 1-caffeoylquinic acid and the 1-acyl dicaffeoylquinic acids.
机译：使用LC-MS4已研究了所有六个二咖啡酰奎尼酸（diCQA）的断裂行为。可以区分每种异构体，包括那些没有商业标准的异构体。对于diCQA，片段化过程中去除咖啡酰残基的难易程度为1＆AP; 5＆GT; 3＆GT; 4.对于研究较少的1,4-二咖啡酰奎尼酸，观察到的独特断裂涉及消除C1咖啡酰残基，反复脱水导致奎尼酸部分的芳构化及其脱羧作用。提示此过程是通过C1羧基使倒置的椅子构象异构体中的C5羟基质子化，然后以C1的咖啡酰残基以有利的椅子构象进行质子化而引发的。 1-咖啡酰基奎宁酸的片段化与市售的5-咖啡酰基奎宁酸的片段没有区别，但是这两种异构体可以通过它们在反相填料上的简便色谱分离而容易地区分。先前开发的用于表征绿原酸的分级键已扩展为可容纳1-咖啡酰基奎宁酸和1-酰基二咖啡酰基奎宁酸。

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