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首页> 外文期刊>Journal of mass spectrometry: JMS >Characterization of N~α-Fmoc-protected ureidopeptides by electrospray ionization tandem mass spectrometry (ESI-MS/MS): Differentiation of positional isomers
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Characterization of N~α-Fmoc-protected ureidopeptides by electrospray ionization tandem mass spectrometry (ESI-MS/MS): Differentiation of positional isomers

机译：电喷雾电离串联质谱（ESI-MS / MS）表征N〜α-Fmoc保护的尿肽肽：位置异构体的区别

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摘要

Four pairs of positional isomers of ureidopeptides, FmocNH-CH(R _1)-φ(NH-CO-NH)-CH(R_2)-OY and FmocNH-CH(R _2)-φ(NH-CO-NH)-CH(R_1)-OY (Fmoc = [(9-fluorenyl methyl)oxy]carbonyl; R_1 = H, alkyl; R_2 = alkyl, H and Y = CH_3/H), have been characterized and differentiated by both positive and negative ion electrospray ionization (ESI) ion-trap tandem mass spectrometry (MS/MS). The major fragmentation noticed in MS/MS of all these compounds is due to -N-CH(R)-N-bond cleavage to form the characteristic N- and C-terminus fragment ions. The protonated ureidopeptide acids derived from glycine at the N-terminus form protonated (9H-fluoren-9-yl)methyl carbamate ion at m/z 240 which is absent for the corresponding esters. Another interesting fragmentation noticed in ureidopeptides derived from glycine at the N-terminus is an unusual loss of 61 units from an intermediate fragment ion FmocNH = CH_2~+ (m/z 252). A mechanism involving an ion-neutral complex and a direct loss of NH_3 and CO_2 is proposed for this process. Whereas ureidopeptides derived from alanine, leucine and phenylalanine at the N-terminus eliminate CO_2 followed by corresponding imine to form (9H-fluoren-9-yl)methyl cation (C_(14)H_(11)~+) from FmocNH = CHR~+. In addition, characteristic immonium ions are also observed. The deprotonated ureidopeptide acids dissociate differently from the protonated ureidopeptides. The [M - H]~- ions of ureidopeptide acids undergo a McLafferty-type rearrangement followed by the loss of CO_2 to form an abundant [M - H - Fmoc + H]~- which is absent for protonated ureidopeptides. Thus, the present study provides information on mass spectral characterization of ureidopeptides and distinguishes the positional isomers.
机译：四对脲肽位置异构体FmocNH-CH（R _1）-φ（NH-CO-NH）-CH（R_2）-OY和FmocNH-CH（R _2）-φ（NH-CO-NH）-CH （R_1）-OY（Fmoc = [（9-芴基甲基）氧基]羰基; R_1 = H，烷基; R_2 =烷基，H和Y = CH_3 / H），已通过正离子和负离子电喷雾进行了表征和区分电离（ESI）离子阱串联质谱（MS / MS）。 MS / MS中所有这些化合物的主要片段化是由于-N-CH（R）-N键断裂形成了特征性的N和C末端片段离子。在N /末端衍生自甘氨酸的质子化的尿苷肽酸在m / z 240处形成质子化的（9H-芴-9-基）甲基氨基甲酸酯离子，其对于相应的酯不存在。在N端衍生自甘氨酸的尿苷肽中发现的另一个有趣的片段化是中间片段离子FmocNH = CH_2〜+（m / z 252）导致的61个单位的异常丢失。提出了一种涉及离子中性配合物以及NH_3和CO_2直接损失的机理。而在N端衍生自丙氨酸，亮氨酸和苯丙氨酸的尿肽则消除CO_2，然后消除相应的亚胺，从FmocNH = CHR〜形成（9H-芴-9-基）甲基阳离子（C_（14）H_（11）〜+）。 +。另外，还观察到特征性的铵离子。去质子化的尿肽肽酸与质子化的尿肽肽解离的方式不同。尿苷肽酸的[M-H]〜-离子经历McLafferty型重排，然后损失CO_2形成大量的[M-H-Fmoc + H]〜-，而质子化的尿苷肽没有。因此，本研究提供了有关尿苷肽质谱表征的信息，并区分了位置异构体。

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