2‐Methoxy‐3‐(1′‐methylpropyl)pyrazine, pea odour, from the marine bacterium Halomonas venusta

Abstract

The marine bacterium Halomonas venusta (Deleya venusta) develops a strong odour of fresh peas. Bacteria were cultivated in ZoBell medium with the addition of artificial sea water. Air was purged through the culture vessel and then trapped in a column filled with RP 18 silica gel.1 H-NMR and GC-MS analysis of the adsorbed volatile revealed 2-methoxy-3-(1 0 -methylpropyl)pyrazine (MMPP). The substance was synthesized only in the idiophase. The addition of high amounts of glycine and isoleucine to the ZoBell medium doubled the cell dry weight (1.92 g/l) and raised the yield of MMPP (9.8 mg/l). The presumed intermediate, 2,5-dioxo-3-(1-methylpropyl)piperazine, was found in the cells growing on agar plates.

The Biosynthesis of Branched Dialkylpyrazines in Myxobacteria

“…During this sequence, the N-atom of the a-amino aldehyde would be lost and replaced by an N-atom from an external source. Therefore, the Instead, a rearrangement during the condensation of two a-amino-aldehyde units 35 as shown in Scheme 7 seems more plausible and is in accord with the observed 15 Nlabeling pattern. The attack of the NH 2 group of 35 on the C¼O group of another molecule 35 leads to the tetraedric intermediate 37 that conventionally undergoes elimination of H 2 O to form an imine.…”

“…6). The ratio is roughly equal to the calculated ratio of isotopomers (57 : 29 : 14) when one fifth of the valine used by the bacteria was labeled with 15 N. The results clearly established the origin of the N-atoms in the pyrazines from valine and excluded any participation of a transamination process during the biosynthesis of 2 and 3.…”

“…To overcome this problem, feeding experiments with differently 13 C-labeled pyruvate isotopomers as metabolic precursors of glycine and valine were carried out, supporting the proposed bacterial pathway to the third class of pyrazines [13]. An identical mechanism was proposed for the formation of 2-methoxy-3-(1-methylpropyl)pyrazine in Halomonas venusta that showed increased formation of the respective piperazinedione intermediate when glycine and isoleucine were supplied [15].…”

“…The final oxidation furnishes the rearranged pyrazine 3, without requirement for an external N-atom. Therefore, the 15 Nlabeling patterns in compounds 2 and 3 remain identical.…”

“…]-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.…”