Alkylpyrazines, examples

These compounds are formed by addition of lithium alkyls to alkylpyrazines, followed by hydrolysis (see Section V,A). They readily oxidize to pyrazines on exposure to air. Some early examples of 1,4-dihydropyrazines have recently been shown to have 1,2-dihydro structures.384 ... 

This listing is a major subcategory of condensations, not only from a synthetic point of view, but also in respect of the occurrence of many alkylpyrazines in foodstuffs by the self-condensation of natural a-aminoacids from protein with subsequent elaboration (114). The following synthetic examples illustrate the types of N—C—C synthons that may be used. 

Alkylpyrazines may be oxidized to pyrazine aldehydes, ketones, or carboxylic acids. They may also undergo nuclear oxidation (covered piecemeal in most other chapters), oxidative hydroxylation, epoxidation, and so on. Such reactions are illustrated in the following examples ... 

The reduction of alkenyl- or alkynylpyrazines to alkylpyrazines has been covered in Section 3.2.I.4. The remaining reactions in this category comprise nuclear reduction or N-debenzylation, as illustrated in the following examples ... 

Several minor reactions of alkylpyrazines are illustrated in the following examples ... 

Several important preparative routes to pyrazinecarboxylic acids have been discussed already by primary synthesis (Chapters 1 and 2), by oxidation of alkylpyrazines (Section 3.2.4.1), by the indirect ( ) oxidation of halogenoalkylpyrazines (end of Section 4.4), and by oxidation ofhydroxyalkylpyrazines (Section 5.2.2). The remaining methods of preparation are indicated in the following classified examples ... 

The primary syntheses of pyrazine JV-oxides from aliphatic components only are described in this chapter. The preparations of pyrazine JV-oxides by oxidation of pyrazines are dealt with under the reactions of the appropriately substituted pyrazines for example, those of pyrazine and alkylpyrazine TV-oxides are described in Chapter IV, and of halogenopyrazine JV-oxides in Chapter V. The cleavage of JV-oxides of pteridines and related systems to aminopyrazine JV-oxides is described in Section VIII.3A(2). 

Alkylpyrazines occur frequently as flavor constituents in foodstufis that imdergo heating, for example, coffee and meat. They are probably formed by a Maillard reaction between amino acids and carbohydrates. Alkylpyrazines also act as alarm pheromones in ants. Coelenterazine (35) is a bioluminiscent natural product isolated from a jellyfish [293]. 

Most of the reactions that occur in amino acids also take place in peptides and proteins. Heterocyclic products are formed when the N-terminal amino acid is involved in the ring formation. Products such as N-3 substituted 2-alkylpyrazin-2-ones form, for example, in reactions of peptides with glyoxal (2-128, and = peptide residues). 

---