Applications of New Mass Spectral Techniques

该项目的目标是开发新的质谱技术，以提供创新和/或更快速的解决方案，解决涉及（1）化学结构测定，（2）复杂混合物分析和（3）生物系统中痕量成分的测量。基质辅助激光解吸电离（MALDI）质谱、电喷雾电离质谱（ESI/MS）、串联质谱（MS/MS）、液相色谱-质谱联用（LC/MS）、毛细管电泳-质谱联用（CE/MS）和精确质量测量是当前感兴趣的技术。在线样品浓缩技术正在研究作为一个前奏接口CE纳米电喷雾电离质谱分析细胞内的核苷酸代谢物。作为一种将CE与高分辨率MALDI/MS和源后衰变裂解分析相结合的离线方法，也正在研究同位素级CE。一个合作的质谱和分子模拟研究已经开始调查的因素控制碱金属离子阳离子化过程中从液相电离（ESI/MS和FAB/MS）。在正常情况下，碱金属离子阳离子化是不可取的，因为它可以降低灵敏度和/或复杂的光谱解释。然而，对于某些类别的化合物，如寡糖和倍半萜类化合物，选择性和受控的阳离子化可以赋予分析优势。抗疟天然产物青蒿素的衍生物，包括一系列具有抗肿瘤活性的三恶烷二聚体，由于它们需要碱金属离子阳离子化才能获得有用的质谱，因此被用作模型化合物。我们对二氢青蒿素的初步研究表明，加合物的形成是阳离子和电离技术选择性的。该化合物的分子模拟计算表明气相阳离子化的结合能与质谱中观察到的结合能相反。在预测结果与观察到的钾离子络合物形成相对应之前，需要考虑液体基质中的阳离子溶剂化。因此，似乎在从液相电离期间形成的阳离子加合物至少部分地代表基质中分析物的状态。 采用快速原子轰击质谱法（FAB/MS）通过新化合物和合成中间体的结构表征来支持LMC合成工作。基于二酰基甘油环内酯模板的合成类似物的组合文库的快速质谱表征策略正在评估和实施使用FAB/MS。目标是在一天内对所有96个文库组分进行结构表征。通过三维数据库检索确认被鉴定为HIV-1整合酶抑制剂的化合物的结构特性的研究仍在继续。利用质谱和核磁共振分析进行结构表征和纯度测定，评价NCI化学数据库中化合物质量的项目已经完成。统计和聚类方法已被用来选择300种化合物，这些化合物代表了这个具有超过250，000种结构的小分子数据库的结构多样性。还获得了由38种市售化合物组成的验证集，并作为内部质量控制进行了分析。由于检测的化合物中有31%被评定为不可接受（没有光谱证据表明样品中存在超过50%的所需化合物或污染物），因此在使用该数据库中的化合物时必须小心。一系列新的细胞毒性异喹啉醌和亚氨基醌分离的海洋苔藓虫Caulibugula intermis已通过准确的质量分析，其结构解析的一部分。

The objective of this project is development of new mass spectral techniques in order to provide innovative and/or more rapid solutions to problems involving (1) chemical structure determination, (2) complex mixture analysis and (3) measurement of trace components in biological systems. Matrix-assisted laser desorption ionization (MALDI) mass spectrometry, electrospray ionization mass spectrometry (ESI/MS), tandem mass spectrometry (MS/MS), combined liquid chromatography-mass spectrometry (LC/MS), combined capillary electrophoresis-mass spectrometry (CE/MS) and accurate mass measurement are the techniques of current interest. On-line sample concentration techniques are being investigated as a prelude to interfacing CE to nano-electrospray ionization mass spectrometry for the analysis of intracellular nucleotide metabolites. Preparative-scale CE is also being investigated as an off-line method for combining CE with high resolution MALDI/MS and post-source decay fragmentation analysis. A collaborative mass spectrometric and molecular modeling study has been initiated to investigate the factors controlling alkali metal ion cationization during ionization from the liquid phase (ESI/MS and FAB/MS). Under normal circumstances, alkali metal ion cationization is not desirable because it can decrease sensitivity and/or complicate spectral interpretation. However, for certain classes of compounds, such as oligosaccharides and sesquiterpenoids, selective and controlled cationization can confer an analytical advantage. Derivatives of the antimarial natural product artemisinin (qinghaosu), including a series of trioxane dimers with antitumor activity, are being used as model compounds since they require alkali metal ion cationization to obtain useful mass spectra. Our initial investigation focusing on dihyroartemisinin shows that adduct formation is cation and ionization technique selective. Molecular modeling calculations for this compound indicate binding energies for gas phase cationization that are the opposite of what is observed in the mass spectra. A consideration of cation solvation in the liquid matrix is required before the predicted results correspond to the potassium ion complex formation that is observed. Thus it appears that cation adducts formed during ionization from a liquid phase represent at least partially the state of the analyte in the matrix. Fast atom bombardment mass spectrometry (FAB/MS) is employed to support the LMC synthetic effort through structural characterization of new compounds and synthetic intermediates. Strategies for the rapid mass spectral characterization of combinatorial libraries of synthetic analogues based on the diacylglycerol cyclic lactone template are being evaluated and implemented using FAB/MS. The goal is the structural characterization of all 96 library components in a single day. Studies to confirm the structural identity of compounds identified as HIV-1 integrase inhibitors through 3-dimensional database searching continue. A project to evaluate the quality of compounds in the NCI chemical database using MS and NMR analysis for structural characterization and determination of purity has been completed. Statistical and clustering methods have been used to select 300 compounds representative of the structural diversity of this publically accessible, small molecule database of over 250,000 structures for analysis. A validation set consisting of 38 of these compounds that are commercially available has also been obtained and analyzed as an internal quality control. Since 31% of the compounds examined have been rated as unacceptable (no spectral evidence for the presence of the desired compound or contaminants exceed 50% of the sample), care must be exercised in using compounds from this database. A series of novel cytotoxic isoquinoline quinones and iminoquinones isolated from the marine bryozoan Caulibugula intermis have been characterized by accurate mass analysis as part of their structural elucidation.