Reporter 433, 15 March 1999

Chemical breakthrough promises purer medicine

University researchers have developed a technique for producing cleaner and purer medicines based on a process for taking the caffeine out of coffee beans.

Impurities of the type causing the side-effects of thalidomide can be virtually eliminated with the new technique.

Their method uses pressurised carbon dioxide as a solvent, because it allows chemical reactions which usually create a mixture of products to produce only one. Project leaders Chris Rayner and Tony Clifford believe it could change the way pharmaceuticals are manufactured in the future.

"If the effect is general for a wide range of chemical reactions - and so far we think it is - the method will offer fundamental advantages to companies manufacturing fine chemicals," said Dr Rayner.

At high pressures and temperatures 'supercritical' carbon dioxide behaves like both a gas and liquid, dissolving chemicals such as caffeine. Subtle changes in the temperature and pressure then alter the mixture of products formed in chemical reactions.

This is particularly important with pharmaceutical chemicals, as certain reactions yield two near-identical 'chiral' forms of the same product. These can have radically different effects inside the body, giving medicines unexpected side-effects if the rogue chiral twin is not removed. The side-effects of thalidomide were caused in this way, by the alternative chiral form of a drug used to prevent morning sickness in pregnant women. The new technique fine-tunes the synthesis to produce very little of the unwanted - and potentially dangerous - version.

The process is also far friendlier to the environment than some of the industrial solvents currently in use. After use the carbon dioxide can simply be released into the atmosphere.

The team's research was initially prompted by these environmental benefits, although they quickly realised the new method came with a stronger selling point.

"Most companies want to make their processes more eco-friendly but the increased cost needs to be outweighed by real advantages," said Dr Rayner. "This is greener, cheaper and more efficient, so everybody wins."

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