Scheme 15. GenoChemetic approaches to C–H functionalisation of small metabolites and complex natural products. Here, a halogenase is installed to complement an existing metabolic/biosynthetic pathway, the halogenated natural product is diversified through application of cross-coupling chemistries. (A) Two step approach: hairy root cultures of Catharanthus roseus are engineered to include RebH, PyrH and their concomitant reductases. A series of chlorinated and brominated analogues are produced, and cross coupling has been carried out on purified compounds and on the metabolites as components of crude extracts, enabling access to a wide portfolio of functionalised molecules.224 Cross-coupling conditions: arylboronic acid (3 equiv.), Pd(OAc)2 (5 mol%), Sphos (13 mol%), K3PO4, n-butanol, 100 °C, 10–60 min. (B and C) One pot approach, pathways constructed in heterologous hosts, with halogenation (mediated by PrnA)225 and cross-coupling occurring synchronously in the presence of the living E. coli and Streptomyces coelicolor,222 respectively.
