The stimulants in tea and coffee are methylated purines

An important stimulant for many is a fully methylated purine present in tea and coffee— caffeine. Caffeine is a crystalline substance easily extracted from coffee or tea with organic solvents. It is extracted industrially with supercritical CO2 (or, if you prefer, ‘nature’s effervescence’) to make decaffeinated tea and coffee. If we, as chemists, were to add those methyl groups we would choose to use a reagent such as methyl iodide, but nature uses a much more complicated molecule. There is a great deal of methylating going on in living things—and the methyl groups are usually added by (S)-adenosyl methionine (or SAM), formed by reaction of methionine with ATP. This is a good reaction because sulfur is a good soft nucleophile, triphosphate is a good leaving group, and substitution at primary carbon is easy.

SAM is a sulfonium salt and could be attacked by nucleophiles at three different carbon atoms. Two are primary centres—good for SN2 reactions—but the third is the methyl group, which is even better. Many nucleophiles attack SAM in this way. In the coffee plant, theobro mine (a purine also found in cocoa) is converted into caffeine with a molecule of SAM. The methylation occurs on nitrogen partly because this preserves both the aromatic ring and the amide functionality and also because the enzyme involved brings the two molecules together in the right orientation for N-methylation.

At this point we should just point out something that it’s easy to forget: there is only one chemistry. There is no magic in biological chemistry, and nature uses the same chemical principles as we do in the chemical laboratory. All the mechanisms that you have studied so far will help you to draw mechanisms for biological reactions and most reactions that you have met have their counterparts in nature. The difference is that nature is very, very good at chemistry, and we humans are only just learning. We still do much more sophisticated reactions inside our bodies without thinking about them than we can do outside our bodies with all the most powerful ideas available to us in the 21st century.

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المزيد

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ماذا يحدث لجسمك عند شرب عصير البطيخ بانتظام؟

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المعادن الحيوية قد تنضب خلال 10 سنوات.. دراسة صادمة ؟

"إنستغرام" يستنسخ خاصية شائعة من منافسه "سناب شات"

رواد فضاء يغادرون محطة الفضاء الدولية بعد مهمة استمرت 5 أشهر

"كريساليس".. سفينة فضائية ستسافر بالبشر إلى أعماق النجوم ؟!

المزيد

مواضيع ذات صلة

Cyclic nucleosides and stereochemistry

HIV and AIDS are treated with modifi ed nucleosides Modified nucleosides

Life begins with nucleic acids

Aldol reactions catalysed by proline

Organocatalysis

Asymmetric dihydroxylation

Catalytic asymmetric reduction of ketones

Chiral reagents

Enantiomeric excess

Alkylation of enolates

Resolution can be used to separate enantiomers

Nature is asymmetric