Structural Diversification of Hapalindole and Fischerindole Natural Products via Cascade Biocatalysis

Abstract

Hapalindoles and related compounds (ambiguines, fischerindoles, welwitindolinones) are a diverse class of indole alkaloid natural products. They are typically isolated from the Stigonematales order of cyanobacteria and possess a broad scope of biological activities. Recently the biosynthetic pathway for assembly of these metabolites has been elucidated. In order to generate the core ring system, l-tryptophan is converted into the cis-indole isonitrile subunit before being prenylated with geranyl pyrophosphate at the C-3 position. A class of cyclases (Stig) catalyzes a three-step process, including a Cope rearrangement, 6-exo-trig cyclization, and electrophilic aromatic substitution, to create a polycyclic core. The formation of the initial alkaloid is followed by diverse late-stage tailoring reactions mediated by additional biosynthetic enzymes to give rise to a wide array of structural variations observed in this compound class. Herein, we demonstrate the versatility and utility of the Fam prenyltransferase and Stig cyclases toward the core structural diversification of this family of indole alkaloids. Through the synthesis of cis-indole isonitrile subunit derivatives, and with the aid of protein engineering and computational analysis, we have employed cascade biocatalysis to generate a range of derivatives and gained insights into the basis for substrate flexibility in this system.

The Time and Place for Nature in Drug Discovery

“…Similarly, a detailed understanding of the biosynthetic pathways leading to polyketides facilitated their production using microbial hosts . In this approach, pathways comprising multiple genes/biocatalysts are assembled to convert simple feedstocks into both the natural product and also analogues via mutasynthesis . However, these “biosynthetic” enzymes tend to be characterized by relatively low turnover rates and also narrow substrate scope, precluding their more general application as biocatalysts for target molecule synthesis.…”

Cooperative Biocatalysis Enables Assembly of a Prenylated Indole Alkaloid

“…Next, we created a library of variously functionalized indole isonitrile/nitrile derivatives to test HpiC1 cyclase flexibility and its ability to create 11‐DMAC analogs. Previous work had shown that halogenated and oxygenated cis‐ indole isonitrile derivatives could be accepted by various Stig cyclases to produce both hapalindole and fischerindole compounds [19,20] . Derivatives were synthesized via a Horner‐Wadsworth‐Emmons (HWE) olefination on indole‐3‐carbaldehydes ( 6 a – n ) to afford cis ‐indole isonitrile substrates ( 1 a – n ) following the previously optimized procedure (Table 1).…”

Synthesized 3-(2-isocyano-6-methylbenzyl)-1H-indole Enhanced Susceptibility of Serratia marcescens to Kanamycinby Occluding Quorum Sensing

“…The indol-isonitrile derivatives often as a reaction intermediate or reactive material in organic chemistry (Hohlman et al 2021), such as synthesized biologically intriguing pyroglutamic acids (Isaacson et al 2007). But few studies focus on their own biological activity.…”