Lastly, the combination of multiple enzymatic steps in onepot cascades 31 , sometimes combined with chemical reactions steps, has also found several recent applications in natural product synthesis, particularly for the rapid construction of molecular complexity. The main appeal of this approach is the smooth combination of multiple reaction steps in one pot, including those which may be incompatible by purely chemical means. Typically, cascade strategies grant significant savings in time and resources by circumventing the need for intermediate work-up steps, in addition to the possibility to drive (potentially unfavorable) equilibrium reactions to completion. For instance, following the impressive example of the development of a three-step biocatalytic cascade for the synthesis of the nucleoside analogue Islatravir, Merck recently developed a chemoenzymatic cascade towards the nucleoside analogue Molnupiravir, an investigational antiviral agent for the treatment of COVID-19. Following 5-acylation of ribose using an immobilized lipase, a five-enzyme cascade for 1phosphorylation and nucleobase installation with an engineered MTR kinase and an engineered uridine phosphorylase in combination with auxiliary enzymes for phosphate donor recycling yielded 5′-acyl uridine selectively. Chemical oxime formation completed this chemoenzymatic synthesis of Molnupiravir, which is not only 70% shorter compared to the initial chemical route, but also 7-fold higher yielding. In an alternative approach towards the same nucleoside analogue, the groups of Lovelock, Turner and Green employed an engineered cytidine deaminase for the installation of the N-hydroxyl group in cytidine by relying on the promiscuous activity of the enzyme with hydroxylamine. In addition to these examples, our group recently demonstrated the diversification of nucleoside analogues bearing alkylated sugar moieties through the use of hyperthermostable nucleoside phosphorylases. The inherent thermodynamic constrains in such phosphorolysis systems could either be manipulated by reaction engineering or selective product removal through strategies such as in situ formation of borate esters. In a remarkable example from the Allemann group, the chemo-enzymatic synthesis of natural as well as non-natural linear terpene precursors and terpene analogs has been demonstrated. Starting from prenol or prenol-based precursors, the corresponding diphosphates were accessed through sequential enzymatic phosphorylation in a one-pot cascade using two kinases together with an ATP recycling system relying on phosphoenolpyruvate. Extending this cascade with different prenyl transferases allowed easy access to methylated as well as hydroxylated farnesyldiphosphate derivatives. Upon further extension with terpene synthases, several sesquiterpenes and non-natural analogues thereof were obtained with impressive selectivity. Similarly, Tang and coworkers developed a cell-free biosynthetic cascade comprising a total of nine enzymes for the efficient production of the plant monoterpene nepetalactol from geraniol at a product titer of up to 1 g/L. 40 Key to the successful combination of the different enzymes in one pot was the selection of enzymes with orthogonal cofactor specificities and suitable, highly-selective cofactor regeneration systems. Efficient cofactor supply was also crucial in the cascade synthesis of methylated natural and non-natural tetrahydroisoquinoline alkaloids as reported by the Hailes group. Starting from L-tyrosine, (S)-norcoclaurine was generated in situ using four different enzymes, and further methylated in one pot by SAMdependent O-and N-methyltransferases exhibiting exceptional regioselectivities. Here, the necessary (but instable) SAM cofactor was formed in situ from L-methionine and ATP using a methionine adenosyltransferase, while the resulting S-adenosylhomocysteine by-product arising from methyl transfer had to be removed through enzymecatalyzed degradation to circumvent inhibition of the methyltransferases.