The Biosynthesis of Branched Dialkylpyrazines in Myxobacteria

Abstract

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.

Biological Activity of Volatiles from Marine and Terrestrial Bacteria

“…Their potential receptors are not known because only few bacterial communication mechanisms have been established so far (see Introduction). Finally, in some cases they may also serve as a means of detoxification, as recently proposed for some pyrazines[34]. Interestingly, the pyrazines show almost no antimicrobial activity.…”

Significance and Transformation of 3-Alkyl-2-Methoxypyrazines Through Grapes to Wine: Olfactory Properties, Metabolism, Biochemical Regulation, and the HP–MP Cycle

“…Another pathway was proposed and validated with the isotope labeling approach [54]. Cheng et al [55] confirmed these results and proposed a novel and widely-accepted biosynthetic pathway for IPMP (Figure 4(Ab) and Figure 5) that is consistent with the results of Nawrath [56] (Figure 4 Studies on the formation of the pyrazine ring in plants are scarcely found. On an Académie Amorim in 2003, Roujou de Boubée [57] issued the studies on IBMP in grapes and wines.…”

“…The proposed biosynthesis pathways of pyrazines (A) and the hypothesized pathway and precursors for 3-alkyl-2-methoxypyrazines in grapes and wine (B). (A-a) is from Murray et al[46], (A-b) from Cheng et al[55], and (A-c) from Nawrath et al[56]. The colors of red and blue display the origination of hemical groups.…”

Plasma Membrane Fusion Is Specifically Impacted by the Molecular Structure of Membrane Sterols During Vegetative Development of Neurospora crassa

“…In brief, sterols were isolated from frozen, ground mycelia using a 3:1 (v/v) mixture of chloroform and methanol, subsequent saponification with 10% (w/v) potassium hydroxide in methanol, followed by extraction in n-hexane. Sterol extracts were derivatized with 2,2,2trifluoro-N-methyl-N-(trimethylsilyl) acetamide (MSTFA) and analyzed by gas chromatography/mass spectrometry (GC/MS) as described in (Nawrath et al 2010). The sterol biosynthesis intermediates were identified by comparing their mass spectra with data available from databases and the literature.…”