Bioretrosynthesis is a technique for synthesizing organic chemicals from inexpensive precursors and evolved enzymes.
[1] For each precursor, the enzyme is evolved using induced mutations and natural selection to produce a more productive version.
The evolutionary process can be repeated over multiple generations until acceptable productivity is achieved.
[2] The mutant genes were inserted into Escherichia coli bacteria and used to produce (now-mutant) enzymes.
[2] A third retrogression allowed them to start with the simple and inexpensive sugar named dideoxyribose and produce didanosine in a three-step sequence.