Discriminating between the six isomers of dicaffeoylquinic acid by LC-MSn
Discriminating between the six isomers of dicaffeoylquinic acid by LC-MSn
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DOI：
10.1021/jf050046h
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发表时间：
2005-05-18
影响因子：
6.1
通讯作者：
Kuhnert, N
中科院分区：
文献类型：
--
作者：
Clifford, MN;Knight, S;Kuhnert, N
使用LC-MS 4研究了所有六种二咖啡酰奎宁酸（diCQA）的裂解行为。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，在片段化过程中去除咖啡酰残基的容易程度为1近似于5 > 3 > 4。很少研究的1，4-二咖啡酰奎宁酸观察到的独特的片段化涉及C1咖啡酰残基的消除，导致奎宁酸部分的芳构化的重复脱水，及其脱羧。有人建议，这一过程是由C1羧基质子化的C5羟基在倒椅构象，然后由其质子化的C1咖啡酰残基在有利的椅子构象。1-咖啡酰奎尼酸的碎片与市售的5-咖啡酰奎尼酸的碎片无法区分，但这两种异构体可以通过它们在反相填料上的简易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关键已被扩展到容纳1-caffeoylquinic酸和1-acyl dicaffeoylquinic酸。
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 approximate to 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.