Organoleptic properties of some alkyl-substituted alkoxy- and alkylthiopyrazines

Abstract

2-Methoxy-3-isobutylpyrazine has previously been reported to be an extremely potent flavoring material with a characteristic aroma of bell peppers. Twenty-one compounds structurally related to this molecule have been synthesized in an attempt to determine structural variations of the molecule which may be made and still retain the intense bell pepper note. For this flavor effect, the alkyl chain can vary from CB to at least CS; the effect is reduced by Cg. Replacing the methoxy group by ethoxy markedly reduces the effect, and it disappears with butoxy substitution. Adding a second alkyl function on the ring reduces the bell pepper character. The effect is not limited to the 2,3 isomer, since the 2,6 isomer possesses a similar note. A most surprising result is the fact that the oxygen of the methoxy group may be replaced by sulfur with little change in character.The compound having the characteristic aroma of bell peppers was identified as 2-methoxy-3-isobutylpyrazine (structure I, R1 = isobutyl) and was shown to possess an extremely low odor threshold (Buttery et al., 1969). Subsequently this compound was also reported in peas (Murray et al., 1970), in galbanum oil (Bramwell et al., 1969), and in coffee (Friedel et al., 1971). Due to the potency and unusual character of this compound, several reports have been published which describe the synthesis and odor properties of structurally related compounds (Seifert et al., 1970(Seifert et al., , 1972. This report extends the previous work for the purpose of further defining the basic chemical structure which is responsible for the intense bell pepper note.There are a number of ways of modifying the basic 2-methoxy-3-isobutylpyrazine molecule. The effect of varying alkyl chain length of R1 in structure I is one obvious choice. Other ways of varying the molecule include: investigating other positional isomers (structures I1 and VI); preparing the dialkyl-substituted methoxy compounds (111); replacing the methoxy by higher alkoxy (IV); and replacing the oxygen by sulfur (V and VI).Gas-Liquid Chromatography. Since the synthetic procedures described below result in a mixture of the 2,3-General Foods' Technical Center, White Plains, New York 10625. and 2,6-chloroalkylpyrazine isomers (Lutz et al., 1964), final purification of the desired isomer was achieved by gas-liquid chromatography. The samples were purified on a Ys in. X 6 ft column packed with 10% DEGS on 60/80 mesh Anakrom ABS in a Perkin-Elmer Model 900 gas chromatograph. Helium carrier gas flow was 30 ml/min and detection was by flame ionization. Temperature programming was utilized and the purified compound was trapped by condensation in a Dry Ice-cooled melting point capillary tube.General Synthetic Procedure. 2-C hloro-3-methylpyrazine containing a small amount of 2-chloro-6-methylpyrazine was prepared as described in the literature (Hirschberg and Spoerri, 1961;Lutz et al., 1964). This mixture was converted to the corresponding alkoxymethylpyrazine or thioalkoxy-methylpyrazine by reaction with the appropriate ...

Identification of hydroxymethylpyrazines using mass spectrometry

“…Various pyrazines have been identified in bacterial odours, and recently, more structurally complex derivatives have been discovered from biotransformation reactions by microorganisms as well as in orchid–wasp pollination chemistry . In natural systems, pyrazines are often present in minute amounts, and the threshold for humans to smell and taste these compounds is extremely low . As these compounds are active in such low concentrations and are often present as blends, the key method of analysis and structural elucidation is gas chromatography–mass spectrometry (GC–MS).…”

Existence of Different Origins for Methoxypyrazines of Grapes and Wines

“…The sensory detection threshold of sec-butylmethoxypyrazine and isopropyl methoxypyrazine are very similar to that of isobutylmethoxypyrazine, but the sec-butyl-and isopropyl-components are relatively minor methoxypyrazines, typically 10% or less of the isobutylmethoxypyrazine concentration. This suggests that they are less important to wine flavor than isobutylmethoxypyrazine; although isopropyl methoxypyrazine may be more important, in red wine, than its sensory detection threshold suggests (9), and its more earthy aroma (3, 9,14,15) may contribute to nuances of wine aroma.…”

“…Of all the methoxypyrazines so far mentioned, it has an aroma most similar to raw potatoes (16) and synthetic material adds potato flavor to processed potato products (18). It is also described as earthy (15), and it has a sensory detection threshold of 425 ng/L (17). Given its aroma, it is not surprising that its possible occurrence in potatoes has been the subject of several studies.…”

Musty/earthy aromas

“…Pyrazines as a flavor compound class possess diverse sensory properties (22), ranging from roasted and nutty for alkyl derivatives to musty /earthy for certain alkoxypyrazines (23). The compound most often cited in this latter category is 2-methoxy-3-isopropylpyrazine, although closely related structures possess similar odor properties (24,25).…”