Theobromine-producing plants

Many antibiotics produced by various microorganisms are nucleosides (2). Among these are nebularine, cordycepin, and nucleocidin. The only known purines in higher plants shown to be involved In allelopathy are caffeine, theophylline, paraxanthine, and theobromine from the coffee tree... 

Caffeine is present in coffee, tea, and chocolate. These plant-derived beverages and foods also contain the other methylxanthines, which some scientists say serve as defense chemicals for leaves and berries produced in climates where there is no winter to kill off chewing bugs. Tea contains mostly caffeine, with small amounts of theophylline and theobromine, but tea is a weaker plant extract than the stronger brew, coffee. Theobromine is the primary methylxanthine found in cocoa, which also contains a small amount of caffeine per cup. Caffeine content ranges from as little as 5 mg in a cup of hot cocoa to 300 mg in 6 oz (177 ml) of espresso. Colas have about 50 mg per 12 fl oz (355 ml). 

The organic analyses contained traces of theobromine, or 3, 7-dimethylxanthine (Fig. 5.10), a caffeine-like chemical abundant in the cacao bean, but not produced in abundance by other plants. Theobromine is a smoking-gun indicator for cacao and chocolate. Henderson and others were able to find theobromine traces in pots from northern Honduras, as old as 1000 to 1400 bc. 

Camellia (Thea) sinensis (tea) and Cqffea arabica (coffee) plants. Caffeine was formed rapidly by extracts of green coffee berries, but little by more mature ones, and not at all by seedlings. Biosynthesis of caffein proceeds from 7-methylxanthosine in the presence of an active purine nucleoside phosphorylase or 7-methyl-A -nucleoside hydrolase. Methionine and 5-adenosylmethionine serve as precursors for the methyl groups of purine alkaloids. These act in the presence of methyltransferases on 7-methylxanthine (38) and theobromine (31) to produce caffeine. A pathway for the origin of these compounds in coffee and tea plants has been proposed (Suzuki et al., 1992 Waller and Dermer, 1981) (Fig. 37.10). 

Alkylations and other types of transformation may, however, also proceed with free purines. In Dictyostelium for instance, dimethylallyl pyrophosphate condenses with AMP to produce isopentenyl adenine. In mammalian tissue 3-methyladenine is formed from adenine, and in plants theobromine and caffeine... 

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