Le Pogam Pierre, Boustie Joël, Richomme Pascal, Denis Antoine, Schinkovitz Andreas
Institut d'Électronique et de Télécommunications de Rennes, Université de Rennes 1, UMR CNRS 6164, 263 Avenue du Général Leclerc, 35042, Rennes Cedex, France.
Institut des Sciences Chimiques de Rennes, Université de Rennes 1, UMR CNRS 6226, 2 Avenue du Professeur Léon Bernard, 35043, Rennes Cedex, France.
Rapid Commun Mass Spectrom. 2017 Dec 15;31(23):1993-2002. doi: 10.1002/rcm.7980.
Light-absorbing secondary metabolites from lichens were recently reported to exhibit promising Laser Desorption Ionization (LDI) properties, enabling their direct detection from crude lichen extracts. In addition, many of them display close structural homologies to commercial Matrix-Assisted Laser Desorption Ionization (MALDI) matrices, which is incentive for the evaluation of their matrical properties. The current study systematically evaluated the matrix effects of several structural classes of lichen metabolites: monoaromatic compounds, quinone derivatives, dibenzofuran-related molecules and the shikimate-derived vulpinic acid. Their matrical properties were tested against a wide range of structurally diverse analytes including alkaloids, coumarins, flavonoids and peptides.
Triplicate automatic positive-ion mode MALDI analyses were carried out and ionization efficiencies were compared with those of structurally related reference matrices (i.e. DHB, HCCA, dithranol and usnic acid) in terms of (i) analyte absolute intensities and (ii) Matrix Suppressing Effect (MSE) scores.
Monoaromatic lichen metabolites revealed matrical properties similar to those of DHB when obtained under comparable experimental conditions. Likewise, anthraquinone metabolites triggered ionization of tested analytes in a similar way to the structurally related dithranol. Finally, dibenzofuran derivatives displayed a broad ionization profile, reminiscent of that of (+)-usnic acid.
Lichen metabolites exhibit interesting MALDI matrix properties, especially for medium and low molecular weight analytes. For many of the tested molecules, matrix ion formation was very limited. This proof-of-concept study paves the way for follow-up investigations to assess the matrix properties of lichen metabolites against a wider array of analytes as well as adapting experimental settings to individually optimize the performance of successfully tested candidates.
最近有报道称，地衣中吸收光的次生代谢产物具有良好的激光解吸电离（LDI）特性，能够直接从地衣粗提物中检测到它们。此外，其中许多次生代谢产物与商业基质辅助激光解吸电离（MALDI）基质具有相似的结构同源性，这促使人们对其基质特性进行评估。本研究系统地评估了几类地衣代谢产物的基质效应：单芳族化合物、醌衍生物、二苯并呋喃相关分子以及莽草酸衍生的狐衣酸。针对包括生物碱、香豆素、黄酮类化合物和肽在内的多种结构各异的分析物，测试了它们的基质特性。
进行了三次重复的自动正离子模式MALDI分析，并根据（i）分析物绝对强度和（ii）基质抑制效应（MSE）得分，将电离效率与结构相关的参考基质（即2,5-二羟基苯甲酸、α-氰基-4-羟基肉桂酸、地蒽酚和松萝酸）进行比较。
在可比的实验条件下获得的单芳族地衣代谢产物显示出与2,5-二羟基苯甲酸相似的基质特性。同样，蒽醌代谢产物以与结构相关的地蒽酚相似的方式引发测试分析物的电离。最后，二苯并呋喃衍生物显示出广泛的电离谱，类似于（+）-松萝酸。
地衣代谢产物表现出有趣的MALDI基质特性，特别是对于中低分子量的分析物。对于许多测试分子，基质离子的形成非常有限。这项概念验证研究为后续研究铺平了道路，后续研究将评估地衣代谢产物针对更广泛的分析物的基质特性，并调整实验设置以单独优化成功测试的候选物的性能。
