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The chemical synthesis of N-acyl indoles is hindered by the poor nucleophilicity of indolic nitrogen, necessitating the use of strongly basic reaction conditions that encumber elaboration of highly functionalized scaffolds. Herein, we describe the total chemoenzymatic synthesis of the bulbiferamide natural products by the biochemical activity reconstitution of a nonribosomal peptide synthetase assembly line-derived (NRPS-derived) thioesterase that neatly installs the macrocyclizing indolylamide. The enzyme represents a starting point for biocatalytic access to macrocyclic indolylamide peptides and natural products. 

Streptomycesspecies are renowned for their ability to produce bioactive natural products (NPs) via biosynthetic gene clusters (BGCs). However, many BGCs remain transcriptionally silent under standard laboratory conditions. Among the key regulatory mechanisms for NP biosynthesis are theγ‐butyrolactone (GBL) signaling molecules, which have been widely studied for their role in repressor‐molecule circuits. While theS. coelicolorbutanolides (SCBs) and A‐factor fromS. griseushave been extensively studied, the virginiae butanolides (VBs) fromS. virginiae,which alleviate repression of the biosynthesis of the antibiotic virginiamycins via binding to the cluster situated TetR‐like repressor BarA, remain understudied. This is in large part due to limited access to enantiopure VBs. Herein, we report a diastereoselective and diversifiable route to access the VB hormones, starting from a protected (R)‐paraconyl alcohol intermediate. A library of VB derivatives was synthesized and tested for their ability to alleviate repression of BarA using a newly developed green fluorescent protein (GFP) reporter assay. The synthesis and assay described herein established the most quantitative structure–activity relationship (SAR) analysis of the VBs to date. Overall, this study provides new tools for probing NP regulation inStreptomycesand enables new strategies for BGC activation using synthetic GBL molecules. 

Actinobacteria are a large and diverse group of bacteria that are known to produce a wide range of secondary metabolites, many of which have important biological activities, including antibiotics, anti-cancer agents, and immunosuppressants. The biosynthesis of these compounds is often highly regulated with many natural products (NPs) being produced at very low levels in laboratory settings. Environmental factors, such as small molecule elicitors, can induce the production of secondary metabolites. Specifically, they can increase titers of known NPs as well as enabling discovery of novel NPs typically produced at undetectable levels. These elicitors can be NPs, including antibiotics or hormones, or synthetic compounds. In recent years, there has been a growing interest in the use of small molecule elicitors to induce the production of secondary metabolites from actinobacteria, especially for the discovery of NPs from “silent” biosynthetic gene clusters. This review aims to highlight classes of molecules that induce secondary metabolite production in actinobacteria and to describe the potential mechanisms of induction. 

Bacteria produce natural products (NPs) via biosynthetic gene clusters. Unfortunately, many biosynthetic gene clusters are silent under traditional laboratory conditions. To access novel NPs, a better understanding of their regulation is needed. γ-Butyrolactones, including the A-factor and Streptomyces coelicolor butanolides, SCBs, are a major class of Streptomyces’ hormones. Study of these hormones has been limited due to challenges in accessing them in stereochemically pure forms. Herein, we describe an efficient route to (R)-paraconyl alcohol, a key intermediate for these molecules, as well as a biocatalytic method to access the exocyclic hydroxyl group that differentiates A-factor-type from SCB-type hormones. Utilizing these methods, a library of hormones have been synthesized and tested in a green fluorescent protein reporter assay for their ability to relieve repression by the repressor ScbR. This allowed the most quantitative structure–activity relationship of γ-butyrolactones and a cognate repressor to date. Bioinformatics analysis strongly suggests that many other repressors of NP biosynthesis likely bind similar molecules. This efficient, diversifiable synthesis will enable further investigation of the regulation of NP biosynthesis.