A previously described synthetic route for preparation of 2-methoxy-3-alkylprazines (MPs) based on condensation of glyoxal with an α-amino acid amide, followed by methylation with iodomethane yields 3-alkyl-1-methyl-1H-pyrazin-2-ones (N-methyl derivatives), rather than the designated 2-methoxy-3-alkylpyrazines (O-methyl derivatives). Despite similar nuclear magnetic resonance and mass spectral properties, gas chromatographic (GC) retention indices differ significantly, indicating chemical difference. With the example of 3-sec-butyl-1-methyl-1H-pyrazin-2-one and its 3-sec-butyl-1-[2H3]methyl-1H-pyrazin-2-one isotopologue, the position of the methyl group introduced could be assigned unambiguously, using heteronuclear multiple bond correlation (HMBC) NMR experiments. For future characterization, the spectroscopic (NMR, EI+MS) as well as GC retention index data on two stationary phases of the most aroma relevant MPs and their deuterated isotopologues are summarized. Copyright © 2011 John Wiley & Sons, Ltd.
前面描述的合成路线是基于
乙二醛与
α-氨基酸酰胺缩合制备2-甲氧基-3-烷基
吡嗪(MP),然后用
碘甲烷甲基化,得到3-烷基-1-甲基-1H-
吡嗪-2-酮(N-甲基衍
生物),而不是指定的2-甲氧基-3-烷基
吡嗪(O-甲基衍
生物)。尽管核磁共振和质谱特性相似,但气相色谱(GC)保留指数差异显著,表明
化学差异。以3-仲丁基-1-甲基-1H-
吡嗪-2-酮及其3-仲丁基-1-[2H3]甲基-1H-
吡嗪-2-酮同位素为例,使用异核多键相关(HMBC)核磁共振实验可以明确地确定引入的甲基的位置。对于未来的表征,总结了与香气最相关的MP及其
氘代同位素的两个固定相的光谱(NMR,EI + MS)以及GC保留指数数据。版权 © 2011 John Wiley & Sons, Ltd.