Yamagaki Tohru, Nobuhara Mika
Suntory Institute for Bioorganic Research, Suntory Foundation for Life Sciences, 8-1-1 Seikadai, Seika-Cho, Soraku-Gun, Kyoto 619-0284 Japan.
J Am Soc Mass Spectrom. 2025 Feb 5;36(2):329-339. doi: 10.1021/jasms.4c00405. Epub 2025 Jan 4.
In this study, we analyzed purine derivatives using multimatrix variation matrix-assisted laser desorption ionization mass spectrometry (MALDI MS) with α-cyano-4-hydroxycinnamic acid (CHCA), 1,5-diaminonaphtalene (DAN), 5-formylsalicylic acid (FSA), and 5-nitrosalicylic acid (NSA) as matrices. Further, we focused on the abstraction/attachment of hydrogen from/to analytes and detected [M - H], [M + 2H] and/or [M + 3H] in MALDI MS spectra of compounds containing nitrogen and/or carbonyl oxygen. Although [M - H] generation of purine compounds in MALDI MS with conventional matrices was challenging, NSA-MALDI MS effectively yielded the [M - H]species of purine derivatives compared with CHCA, FSA, and DAN, and the [M - H]/[M + H] ratios reflected their structures, such as the substituting groups and positions. We speculated that the molecular ion [M] generated and the subsequent hydrogen radical abstraction proceeded by NSA matrix from the α-carbon of the amine group. The nitro group (-NO) of NSA can withdraw hydrogen radicals in photochemical reactions. The [M - H] of adenosine, guanosine, and inosine suggested that hydrogen abstraction occurred in the ribose unit. The xanthine isomer of paraxanthine was distinguished from those of theophylline and theobromine using their [M - H]/[M + H] ratios obtained with NSA-MALDI MS. Additionally, [M + 2H] generated in DAN-MALDI MS of xanthine derivatives due to their carbonyl groups. The relative abundances of [M + 2H] of xanthine derivatives were much higher than those of the other purine derivatives such as adenine derivatives which generated [M + 3H] in their DAN-MALDI MS. DAN induced the hydrogen attachment of purine compounds because the amine group (-NH) of DAN can give hydrogen radicals in photochemical reactions. NSA- and DAN-MALDI MS characterized purine derivatives and were useful for their structure categorization.
在本研究中，我们使用α-氰基-4-羟基肉桂酸（CHCA）、1,5-二氨基萘（DAN）、5-甲酰基水杨酸（FSA）和5-亚硝基水杨酸（NSA）作为基质，通过多基质变化基质辅助激光解吸电离质谱（MALDI MS）分析嘌呤衍生物。此外，我们关注了分析物上氢的夺取/附着情况，并在含氮和/或羰基氧的化合物的MALDI MS谱图中检测到了[M - H]、[M + 2H]和/或[M + 3H]。虽然在使用传统基质的MALDI MS中，嘌呤化合物生成[M - H]具有挑战性，但与CHCA、FSA和DAN相比，NSA-MALDI MS能有效地产生嘌呤衍生物的[M - H]物种，且[M - H]/[M + H]比值反映了它们的结构，如取代基和位置。我们推测，NSA基质从胺基的α-碳上产生分子离子[M]并随后进行氢自由基夺取。NSA的硝基（-NO）可在光化学反应中夺取氢自由基。腺苷、鸟苷和肌苷的[M - H]表明氢夺取发生在核糖单元中。使用NSA-MALDI MS获得的[M - H]/[M + H]比值，可将对甲氧基黄嘌呤的黄嘌呤异构体与茶碱和可可碱的异构体区分开来。此外，由于黄嘌呤衍生物的羰基，在其DAN-MALDI MS中会生成[M + 2H]。黄嘌呤衍生物的[M + 2H]相对丰度远高于其他嘌呤衍生物，如在其DAN-MALDI MS中生成[M + 3H]的腺嘌呤衍生物。DAN可诱导嘌呤化合物的氢附着，因为DAN的胺基（-NH）可在光化学反应中提供氢自由基。NSA-和DAN-MALDI MS可对嘌呤衍生物进行表征，有助于其结构分类。
