Design of an in vitro biocatalytic cascade for the manufacture of islatravir

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Science  06 Dec 2019:
Vol. 366, Issue 6470, pp. 1255-1259
DOI: 10.1126/science.aay8484

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Maximal efficiency from enzyme cascades

Enzymes are highly selective catalysts that can be useful for specific transformations in organic synthesis. Huffman et al. combined designer enzymes in a multistep cascade reaction (see the Perspective by O'Reilly and Ryan). The approach eliminates purification steps, recycles expensive cofactors, and couples favorable and unfavorable reactions. With the target molecule islatravir, an experimental HIV drug, they optimized five enzymes by directed evolution to be compatible with unnatural substrates and stable in the reaction conditions. Stereochemical purity was amplified at every enzymatic step, and the final synthesis was both atom economical and efficient.

Science, this issue p. 1255; see also p. 1199


Enzyme-catalyzed reactions have begun to transform pharmaceutical manufacturing, offering levels of selectivity and tunability that can dramatically improve chemical synthesis. Combining enzymatic reactions into multistep biocatalytic cascades brings additional benefits. Cascades avoid the waste generated by purification of intermediates. They also allow reactions to be linked together to overcome an unfavorable equilibrium or avoid the accumulation of unstable or inhibitory intermediates. We report an in vitro biocatalytic cascade synthesis of the investigational HIV treatment islatravir. Five enzymes were engineered through directed evolution to act on non-natural substrates. These were combined with four auxiliary enzymes to construct islatravir from simple building blocks in a three-step biocatalytic cascade. The overall synthesis requires fewer than half the number of steps of the previously reported routes.

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