New insights into the synthesis and characterization of 2‐methoxy‐3‐alkylpyrazines and their deuterated isotopologues

Abstract

A previously described synthetic route for preparation of 2-methoxy-3-alkylprazines (MPs) based on condensation of glyoxal with an a-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-[ 2 H 3 ]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 1 MS) as well as GC retention index data on two stationary phases of the most aroma relevant MPs and their deuterated isotopologues are summarized.

Rootstock, Vine Vigor, and Light Mediate Methoxypyrazine Concentrations in the Grape Bunch Rachis ofVitis viniferaL. cv. Cabernet Sauvignon

“…Deuterium-labeled and unlabeled methoxypyrazines used as analytical standards were produced via established synthetic methodologies 21,22 with modifications as previously described. 23 Synthetic products were analyzed by high resolution mass spectrometry (HRMS) and nuclear magnetic resonance (NMR) with purity determined to be >99% for all compounds (by 1 H NMR). L-Isoleucine amide hydrochloride was sourced from Chem-Impex International (Wood Dale, IL, USA), and all other chemicals purchased from Sigma-Aldrich (Castle Hill, NSW, Australia).…”

“…Solvents and reagents were of analytical reagent grade or higher. Deuterium-labeled and unlabeled methoxypyrazines used as analytical standards were produced via established synthetic methodologies , with modifications as previously described . Synthetic products were analyzed by high resolution mass spectrometry (HRMS) and nuclear magnetic resonance (NMR) with purity determined to be >99% for all compounds (by 1 H NMR).…”

Quantification of cork off-flavor compounds in natural cork stoppers and wine by multidimensional gas chromatography mass spectrometry

“…Furthermore, the migration of off-flavor compounds from cork stoppers into wine should be studied by sealing unaffected wines with off-odorous cork stoppers, followed by a storage period and finally evaluation by chemical and sensory analysis. [23][24][25]. Commercial chemicals were usually of analytical grade and used as such.…”

Wenn Nanogramm das Aroma verändern

“…Dies zeigte sich insbesondere bei der Quantifizierung der genannten 3‐Alkyl2‐methoxypyrazine im unteren ng·L—1‐Bereich. Generell sind solche Aufgaben trotz neuer Messtechniken noch immer eine besondere Herausforderung 79…”