Sinigrin in the rain

It is part of Hollywood folklore that somebody was once raving to Ginger Rogers about what an amazing dancer her screen partner Fred Astaire was. Ginger replied tartly that anything Fred did, she did - but backwards and in high heels! Nature has been delivering a similar put-down to chemists since time immemorial, for they know in their hearts that any molecule they can synthesise, nature can synthesise. But nature will do it purer, simpler, and quicker, and all at ambient temperature and pressure, without the use of expensive and highly poisonous catalysts, ovens, or pressure vessels.

It is just as well for humankind that plants in particular are so expert at chemical synthesis, for phytochemicals were the backbone of medicine for thousands of years. The internal and external application of decoctions, philtres, tinctures, unguents, ointments, salves and so on derived from various plants were often the only effective treatments available to old-time medics. This was fortuitous because every other weapon in their armoury arguably either did no good, eg prayer and incantation, or actually made things a damn sight worse, eg purging and bleeding.

Chemists did seem to be getting the upper hand for a while, roughly from the mid 19th century onward, with the introduction of ’modern’ drugs. And these compounds have indeed transformed the treatment of many conditions out of all recognition and continue to do so. But sadly, because of the irritating ability of bacteria and viruses to adapt and change so to counteract drugs, chemists have been having to run faster and faster just to stay in one place. And the side effects of drugs, often not anticipated by even the most careful testing, can prove disastrous. So, increasingly, medicine has been turning back to phytochemical-based remedies. Who was it said, ’what goes round, comes round’? (Probably Ginger Rogers, as she watched Fred pirouette madly past, but no matter.)

I stand in awe of the wondrous molecules that vegetables such as the humble Brussels sprout can synthesise so effortlessly. Its allyl isothiocyanate, for example, is effective against a variety of diseases, yea unto cancer itself. And I daily bless the ability of the grape to manufacture resveratrol, 3,4?,5-trihydroxystilbene, which enables me to quaff red wine with both a clear conscience and a surprisingly healthy heart, thanks to its ability to inhibit the oxidation of low density lipoproteins. But folks, you ain’t seen nothin’ yet. (No, not Ginger this time. Al Jolson said that.) As sure as God made little apples, there are lots more beneficial phytochemicals out there waiting to be discovered.

But have you ever stopped to wonder why plants obligingly stuff themselves with chemicals of great use to mankind? Well, consider the Brussels sprout again. When a hungry insect takes a bite out of the apparently defenceless vegetable, the action of myrosinase on the glucosinolate sinigrin in the ruptured cell walls liberates allyl isothiocyanate. The predator is discouraged and goes off to find something less revolting to eat. The fact that allyl isothiocyanate has been shown to impede the growth of cancer cells in humans who eat a helping of sprouts is of no consequence to the vegetable. It has its own agenda - self-preservation.

But today, there is the intriguing possibility of persuading plants to produce chemicals they wouldn’t normally bother with, by inserting into them the appropriate gene. For example, the insertion into tomatoes of the gene that enables the Arctic flounder to produce its own ’anti-freeze’ may yield frost- resistant plants. It has been shown that, using this technique, plants may be prevailed upon to produce a wide variety of potentially useful substances, eg as monomers for making novel plastics. They become, in effect, miniature chemical factories. If this catches on, it will lend a whole new meaning to the expression ’industrial plant’.