Prenylation of diverse indole derivatives by the fungal aromatic prenyltransferase RePT

Abstract

Prenylation is a widespread natural modification of compounds that serves to functionalize and often enhance the bioactivity of plant and microbial secondary metabolites, including indole derivatives. In this study, we aimed to expand the library of prenylated indoles using RePT, a fungal (i.e. Rasamsonia emersonii) aromatic prenyltransferase from the dimethylallyl tryptophan synthase (DMATS) family. Previous work showed that RePT readily C7- and N1-prenylated l-tryptophan, and O-prenylated l-tyrosine and a number of phenolic stilbenes. Here, we investigated its regioselectivity further with 23 indole substrates, including tryptophan derivatives with varying C4-C7 substituents and several C3-substituted indoles. High conversion was observed primarily with fluorinated tryptophans and unsubstituted indole. Product analysis by UHPLC-PDA-ESI-MSⁿ and NMR revealed that RePT mainly catalyzed either normal prenylation at C7 or reverse prenylation at N1 on a series of halogenated tryptophans. The regioselectivity observed for several substrates was strongly influenced by the position of the halogen substituent, particularly fluorine, which displayed its characteristic ortho-/para-directing effect. In the absence of the amino acid moiety, RePT’s regioselectivity in some cases shifted from its typical preference, leading to prenylation at alternative positions such as C3 and C6. These findings showcase the versatility of RePT for modifying diverse indole derivatives and demonstrate, for the first time, halogen-induced steering of the regioselectivity of DMATS to facilitate synthesis of bioactive prenylated compounds and intermediates.