N-烷基酰胺类化合物电喷雾质谱裂解机制的研究

为阐明维吾尔族药阿纳其根中N-烷基酰胺类成分的质谱裂解机制,采用电喷雾离子源(ESI)正离子模式进行多级碎片解析,对阿纳其根中分离得到5种N-烷基酰胺类成分:十-2E,4E-二烯酸-异丁基胺,十一-2E,4E-二烯-8,10二炔酸-苯乙胺,十-2E,4E-二烯酸-4-羟基苯乙胺,十二-2E,4E-二烯酸-4-羟基苯乙胺和十四-2E,4E-二烯酸-4-羟基苯乙胺,应用密度泛函(DFT)法比较不同裂解方式的优化结构,并分析其可能的质谱裂解机制。结果表明,在正离子模式下,5种N-烷基酰胺类成分均易形成[M+H]+准分子离子,并进一步发生N-位的α裂解,丢失酰胺结构中胺部分、羰基以及水等而形成碎片离子。该类化合物的裂解规律可为N-烷基酰胺类化合物的结构鉴定和定量分析奠定理论基础。

Fragmentation Pathways and Patterns of N-Alkylamides by ESI-MSn

There are 4 main types of N-alkylamides in Anacyclus pyrethrum DC., namely, isobutylamide (IBA),N-Me isobutylamide (N-Me IBA), 2-phenylethylamide (2-PEA) and 4-hydroxyphenylethylamide (4-OH PEA). However, there was very few research on the fragmentation pathways ofN-alkylamides by now. In order to obtain accurate and comprehensive information about the fragmentation pathways of N-alkylamides, 5 kinds of N-alkylamides were analyzed by HPLC-ESI-MSⁿ. They are identified as deca-2E, 4E-dienoicacid isobutylamideylamide, undeca-2E, 4E-diene-8, 10-diynoic acid phenylethylamide, deca-2E, 4E-dienoicacid 4-hydroxyphenylethlamide, dodeca-2E, 4E-dienoicacid 4-hydroxyphenyl-ethylamide and tetradeca-2E, 4E-dienoic acid 4-hydroxyphenylethylamide. Multi-stage mass spectrum diagrams of five N-alkylamides were obtained in positive ion mode. Simultaneously, the method of quantum computational chemistry was adopted to verify their fragmentation pathways. Characteristic fragment ions were identified and the patterns were deduced further. The fragmentation patterns and structural assignment of ‘isobutylamides (IBA)’type, ‘2-phenylethylamide(2-PEA)’ type and ‘4-hydroxyphenylethyl-amides (4-OH PEA)’ type in ESI-MSⁿ under positive ion mode were summarized. The results show that fiveN-alkylamides have the similar fragmentation pathway, ［M+H］⁺ is prone to α-cracking in N-position at the first, loss of 28(CO), 18(H₂O) subsequently. These compounds have strong pyrolysis rules and the study can provide reference forN-alkylamides in structural identification and quantitative analysis.