Potential Rearrangements in the Reaction Catalyzed by the Indole Prenyltransferase FtmPT1

Abstract

The indole prenyltransferase FtmPT1 catalyzes the C-2 normal prenylation of brevianamide F (cyclo-L-Trp-L-Pro) to give tryprostatin B. A previous structural analysis and studies with alternate substrates suggest that the reaction might not proceed through a direct C-2 attack, but could involve a C-3 prenylation followed by a rearrangement. In this work we investigated the reactivity of FtmPT1 with tryptophan, 5-hydroxybrevianamide, and 2-methylbrevianamide, and isolated products that had been reverse prenylated at C-3 and normal prenylated at N-1, C-3, or C-4. The formation of these products can be rationalized through mechanisms involving either an initial C-3 normal or C-3 reverse prenylation. In addition, we demonstrate that a C-3 reverse prenylated indole can undergo a nonenzymatic aza-Cope rearrangement at 37 °C to give an N-1 normal prenylated product. Together, these studies broaden the known product scope of this interesting catalyst and suggest that alternative mechanisms might be operating.

Mechanistic studies on the indole prenyltransferases

“…14,[28][29][30] In addition, with alternate substrates, products containing prenylation at unexpected sites are oen observed. 25,[31][32][33] While fewer studies have focused on mechanism, recent work in this area is addressing the way in which enzymes with similar active sites catalyze both normal and reverse prenylations at a variety of positions on the indole ring. This highlight article will focus on recent mechanistic and structural studies that have been performed on the indole prenyltransferases.…”

Structure and specificity of a permissive bacterial C-prenyltransferase

“…Based on this newly observed catalytic capability, similar DAP-based prenylation assays with six other representative PTs (Supplementary Figs. 17 and 18, Supplementary Table 7) revealed both FgaPT2 [an indole C-4 C -PT 17 ] and CdpNPT [an indole reverse C-3 C -PT, originally annotated as a N -PT 18 ] to also successfully catalyze DAP prenylation [65% and 75% (Supplementary Figs. 19 and 20) conversion, respectively].…”

Origin of Product Selectivity in a Prenyl Transfer Reaction from the Same Intermediate: Exploration of Multiple FtmPT1-Catalyzed Prenyl Transfer Pathways

“…20 Recently, a number of experimental papers on fungal indole PTs exploring their regioselectivity have been published. 23−26 Multiple reaction channels are possible, so the fundamental question is how one reaction channel is favored over another by the characteristics of the active site of the protein catalyst involved. Importantly, once the C–O bond in DMAPP is cleaved, the dimethylallyl carbocation can react at one of two ends of the molecule: the less sterically crowded C5 position or the more crowded C2 site (see Figure 1).…”