Organic synthesis - chemistry as it is done in the laboratory or manufacturing plant - traditionally uses a step-by-step approach. In a typical sequence, a starting material A is converted into a final product D, and intermediate products B and C have to be isolated and purified in each conversion step. Such multistep organic syntheses are still quite common in today's fine chemical industry, and they suffer from several disadvantages. They are often carried out noncatalytically using relatively large amounts of reagents that produce many kilograms of waste per kilo of final product. The separation and purification steps needed after each conversion step produce waste heat as energy is consumed. They require extra energy to overcome the thermodynamic hurdles to produce and isolate intermediates Band C if they lie in high-energy states.
On the other hand, biosynthesis - chemistry as Nature performs it in the cells of organisms - goes through a multistep cascade to convert starting material A to final product D without separation of intermediates B and C. Such multistep combined syntheses are common in everyday life. They are carried out in a fully catalytic way by using enzymes with relatively limited amounts of reagents (cofactors) and thus produce much less waste. The mutual compatibility and high selectivity of the enzymatic conversions make it possible to proceed without intermediate recovery steps. They save energy by avoiding the separation and isolation of intermediates B and C.
The potential power of combined catalytic conversions to overcome thermodynamic hurdles in multistep syntheses is demonstrated here for the well-known glycolysis pathway.
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