Institut für Organische Chemie, Technische Universität Braunschweig, Hagenring 30, Braunschweig.
Chem Biodivers. 2010 Sep;7(9):2129-44. doi: 10.1002/cbdv.201000158.
The biosynthesis of the volatiles 2,5- and 2,6-diisopropylpyrazine (2 and 3, resp.) released by the myxobacteria Nannocystis exedens subsp. cinnabarina (Na c29) and Chondromyces crocatus (strains Cm c2 and Cm c5) was studied. Isotopically labeled precursors and proposed pathway intermediates were fed to agar plate cultures of the myxobacteria. Subsequently, the volatiles were collected by use of a closed loop stripping apparatus (CLSA), and incorporation into the pyrazines was followed by GC/MS analysis. [(2)H(8)]Valine was smoothly incorporated into both pyrazines clearly establishing their origin from the amino acid pool. The cyclic dipeptide valine anhydride (16)--a potential intermediate on the biosynthetic pathway to branched dialkylpyrazines--was synthesized containing (2)H(1) labels in specific positions. Feeding of [(2)H(16)]-16 and [(2)H(12)]-16 in both valine subunits mainly resulted in the formation of pyrazines derived from only one labeled amino acid, whereas only traces of the expected pyrazines with two labeled subunits were found. To investigate the origin of nitrogen in the pyrazines, a feeding experiment with [(15)N]valine was performed, resulting in the incorporation of the (15)N label. The results contradict a biosynthetic pathway via cyclic dipeptides, but rather point to a pathway on which valine is reduced to valine aldehyde. Its dimerization to 2,5-diisopropyldihydropyrazine 36 and subsequent oxidation results in 2. The proposed biosynthetic pathway neatly fits the results of earlier labeling studies and also explains the formation of the regioisomer 2,6-diisopropylpyrazine 3 by isomerization during the first condensation step of two molecules valine aldehyde. A general biosynthetic pathway to different classes of pyrazines is presented.
研究了粘细菌 Nannocystis exedens subsp. cinnabarina（Na c29）和 Chondromyces crocatus（菌株 Cm c2 和 Cm c5）释放的挥发性物质 2,5-和 2,6-二异丙基吡嗪（2 和 3）的生物合成。用同位素标记的前体和提议的途径中间体喂养粘细菌的琼脂平板培养物。随后，使用闭路剥离装置（CLSA）收集挥发性物质，并通过 GC/MS 分析跟踪其掺入吡嗪中。[(2)H(8)]缬氨酸顺利掺入到两种吡嗪中，清楚地确定了它们来自氨基酸库的来源。环状二肽缬氨酸酐（16）——支链二烷基吡嗪生物合成途径上的潜在中间体——被合成，其中包含特定位置的(2)H(1)标记。在两个缬氨酸亚基中喂养[(2)H(16)]-16 和 [(2)H(12)]-16 主要导致仅形成来自一个标记氨基酸的吡嗪，而仅发现预期的具有两个标记亚基的吡嗪的痕迹。为了研究吡嗪中氮的来源，进行了[(15)N]缬氨酸的喂养实验，导致掺入(15)N 标记。结果与通过环状二肽的生物合成途径相矛盾，但更指向缬氨酸还原为缬氨酸醛的途径。其二聚化生成 2,5-二异丙基二氢吡嗪 36 并随后氧化生成 2。所提出的生物合成途径恰好符合早期标记研究的结果，并且还解释了在两个分子缬氨酸醛的第一缩合步骤期间异构化形成 2,6-二异丙基吡嗪 3 的区域异构体的形成。提出了不同类别的吡嗪的一般生物合成途径。
