Biosynthesis of the validamycins:: Identification of intermediates in the biosynthesis of validamycin A by Streptomyces hygroscopicus var. limoneus
Biosynthesis of the validamycins:: Identification of intermediates in the biosynthesis of validamycin A by Streptomyces hygroscopicus var. limoneus
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DOI：
10.1021/ja003643n
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发表时间：
2001-03-28
影响因子：
15
通讯作者：
Floss, HG
中科院分区：
文献类型：
--
作者：
Dong, HJ;Mahmud, T;Floss, HG
为了研究假三糖抗生素validamcin A(1)的生物合成，以H-2-、H-3-或C-13标记的形式合成了一系列潜在的抗生素前体，并将其饲喂给吸水链霉菌变种柠檬变种。通过液体闪烁计数、氢-2-或碳-13核磁共振或选择性离子监测质谱学(SIM-MS)技术分离、纯化和分析从这些喂养实验中得到的有效霉素A。结果表明，2-epi-5-epi-valiolone(9)被特异性地结合到1中，并标记了两个环醇基团。这表明9是由开链C-7前体D-SED7-7-磷酸(5)通过类似DHQ合成酶的环化机制产生的初始环化产物。1的一个更接近的前体是valienone(11)，它也被引入到两个环醇部分中。9到11的转化包括首先异构化为5-表-valiolone(10)，它被有效地结合到1中，然后脱水，尽管也观察到Zepi-valienone(15)的掺入水平很低。11的还原提供了validone(12)，其也被特定地并入，但仅标记还原的环醇部分。连接这两个伪糖部分的氮原子的引入方式尚不清楚。虽然从发酵过程中分离出了7-氚-呋喃丙胺(8)、呋喃乙胺(2)和呋喃咪胺(3)，但它们都没有加入到1中，其中3种是最常见的。从[7-H-3]-12体内形成[7-H-3]-3的研究表明，3可能是一种途径中间体，[7-H-3]-3不掺入1是由于缺乏细胞摄取。因此，我们建议由12个胺化形成的3和11缩合形成Schiff碱，该席夫碱被还原为假二糖单元validoxylamineA(13)。将D-葡萄糖单元转移到13的4‘-位完成了1的生物合成。还讨论了在两个伪糖单元之间形成氮桥的其他可能的机制。
To study the biosynthesis of the pseudotrisaccharide antibiotic, validamycin A (1), a number of potential precursors of the antibiotic were synthesized in H-2-, H-3-, Or C-13-labeled form and fed to cultures of Streptomyces hygroscopicus var, limoneus. The resulting validamycin A from each of these feeding experiments was isolated, purified and analyzed by liquid scintillation counting, H-2- or C-13 NMR Or selective;ion monitoring mass spectrometry (SIM-MS) techniques. The results demonstrate that 2-epi-5-epi-valiolone (9) is specifically incorporated into 1 and labels both cyclitol moieties. This suggests that 9 is the initial cyclization product generated from an open-chain C-7 precursor, D-sedoheptulose 7-phosphate (5), by a DHQ synthase-like cyclization mechanism. A more proximate precursor of 1 is valienone (11), which is also incorporated into both cyclitol moieties. The conversion of 9 into 11 involves first epimerization to 5-epi-valiolone (10), which is efficiently incorporated into 1, followed by dehydration, although a low level of incorporation of Zepi-valienone (15) is also observed. Reduction of 11 affords validone (12), which is also incorporated specifically into, but labels only the reduced cyclitol moiety. The mode of introduction of the nitrogen atom linking the two pseudosaccharide moieties is not clear yet. 7-Tritiated valiolamine (8), valienamine (2), and validamine (3) were all not incorporated into 1, although each of these amines has been isolated from the fermentation, with 3 being most prevalent. Demonstration of in vivo formation of [7-H-3]validamine ([7-H-3]-3) from [7-H-3]-12 suggests that 3 may be a pathway intermediate and that the nonincorporation of [7-H-3]-3 into 1 is due to a lack of cellular uptake. We thus propose that 3, formed by amination of 12, and 11 condense to form a Schiff base, which is reduced to the pseudodisaccharide unit, validoxylamine A (13). Transfer of a D-glucose unit to the 4'-position of 13 then completes the biosynthesis of 1. Other possibilities for the mechanism of formation of the nitrogen bridge between the two pseudosaccharide units are also discussed.