Trigonelline reactions

Fig. 8.14. Stepwise activation of dihydrotrigonelline-based chemical delivery systems, first by oxidation to a pyridinium cation (Reaction a), and then by hydrolysis to trigonelline and the drug ROH (Reaction b). Direct hydrolysis (Reaction c) is slow in comparison to the Reactions...

It was formed in the pyrolysis of proline and 4-hydroxyproline (Merritt et al., 1970) and is one of the pyrolysis products of trigonelline (Viani and Horman, 1974). Baltes and Bochmann (1987b) found 1-methylpyrrole in all their serine/threonine/sucrose reactions as well as in coffee. 

For Viani and Horman (1974), pyridine represents 25% of the pyrolysis products of a trigonelline monohydrate sample. Pyridine has been found in model reactions between glucose and amino acids (Kato et al., 1973b), when heating serine and/or threonine with or without sucrose under coffee-roasting conditions (Baltes and Bochmann, 1987d who found it also in coffee). Mottram (1991) explained the possible formation of pyridine by reaction of ammonia on 2,4-pentadienal. 

This is based on the reaction of derivatives of pyridine with cyanogen bromide in the presence of an aromatic amine giving specific colors. Amines commonly used are 2-naphthylamine-i-sulfonic acid, />-aminoacetophenone, iV-methyl-aminophenol sulphate, aniline and />-naphthylamine. The reaction gives a yellowish-green color which is measured photometrically. The color is soluble in amyl alcohol which can be used to extract it from water solutions, but is not stable unless a phosphate buffer of pH 6.i is used. This method is not specific for nicotinic acid since other pyridine derivatives and derivatives of nicotinic acid such as trigonelline, nicotinuric acid and nicotine give a similar color. 

Jencks (1969) has pointed out that the role of the enzyme itself is particularly difficult to understand in bimolecular displacement reactions in which general acid-base catalysis would give little advantage, or is not possible. As examples of such reactions Jencks included methyl transfer from S-adenosylmethionine to nicotinic acid to form the N-meth-yl pyridinium, trigonelline (Joshi and Handler, 1960), or to methionine to form the new sulfonium, S-methylmethionine (Greene and Davis,... 

Further flavour components of coffee (and other foods) are different quinoKnes (8-173) and isoquinolines (8-174), which result from trigonelline. Some pyridines (aminoimidazopyridines) and quinoKnes (aminoimidazoquinolines) produced in the Maillard reaction are classified as processing food contaminants (see Section 12.2.1). 

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