Regioselective Biocatalytic C4‐Prenylation of Unprotected Tryptophan Derivatives

Abstract

Regioselective carbonÀ carbon bond formation belongs to the challenging tasks in organic synthesis. In this context, CÀ C bond formation catalyzed by 4-dimethylallyltryptophan synthases (4-DMATSs) represents a possible tool to regioselectively synthesize C4-prenylated indole derivatives without site-specific preactivation and circumventing the need of protection groups as used in chemical synthetic approaches. In this study, a toolbox of 4-DMATSs to produce a set of 4-dimethylallyl tryptophan and indole derivatives was identified. Using three wild-type enzymes as well as variants, various C5-substituted tryptophan derivatives as well as N-methyl tryptophan were successfully prenylated with conversions up to 90 %. Even truncated tryptophan derivatives like tryptamine and 3-indole propanoic acid were regioselectively prenylated in position C4. The acceptance of C5-substituted tryptophan derivatives was improved up to 5-fold by generating variants (e. g. T108S). The feasibility of semi-preparative prenylation of selected tryptophan derivatives was successfully demonstrated on 100 mg scale at 15 mM substrate concentration, allowing to reduce the previously published multistep chemical synthetic sequence to just a single step.

Non-Native Site-Selective Enzyme Catalysis

“…376 A related 4-DMATS enzyme from the organism A. japonicus was recently found to accept a variety of tryptophan derivatives with exceptional site selectivity in high yields even at relatively high substrate loadings. 377 The 4-DMATS enzymes were the first prenyltransferases to be characterized, and shortly thereafter, the 7-DMATS analogue from A. f umigatus was discovered. 378 This enzyme has a broader substrate scope than FgaPT2.…”

“…While these substrates were typically prenylated in low yield, this enzyme was later found to be competent for the site-selective prenylation of cyclo- l -Trp- l -Tyr and other diketopiperazines, albeit at higher enzyme loading . A related 4-DMATS enzyme from the organism A. japonicus was recently found to accept a variety of tryptophan derivatives with exceptional site selectivity in high yields even at relatively high substrate loadings …”

Non-Native Site-Selective Enzyme Catalysis

“…374 A related 4-DMATS enzyme from the organism A. japonicus was recently found to accept a variety of tryptophan derivatives with exceptional site selectivity in high yields even at relatively high substrate loadings. 375 The 4-DMATS enzymes were the first prenyltransferases to be characterized, and shortly thereafter the 7-DMATS analogue from A. fumigatus was discovered. 376 This enzyme has a broader substrate scope than FgaPT2.…”

Structure‐Guided Mutagenesis Reveals the Catalytic Residue that Controls the Regiospecificity of C6‐Indole Prenyltransferases

“…[18][19][20] IPTs have shown to facilitate the synthesis of a complex natural product alkaloid [21] as well as the semipreparative synthesis of regiospecific l-and d-indole derivatives. [22] Different IPTs have been functionally characterized that catalyze the CÀ H bond activation at each of the non-fusion carbons including C6 via Friedel-Crafts alkylation. [23,24] In this regard, PriB is a promiscuous C6 IPT that accommodates various indole-derived compounds and achieves a C1' normal prenylation reaction (Figure 1B, 3 a).…”

“…IPTs have relaxed acceptor and donor specificities allowing them to be used as a valuable tool for indole late‐stage functionalization and labelling [18–20] . IPTs have shown to facilitate the synthesis of a complex natural product alkaloid [21] as well as the semipreparative synthesis of regiospecific l ‐ and d ‐indole derivatives [22] …”