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Thiopeptides are a broad class of macrocyclic, heavily modified peptide natural products that are unified by the presence of a substituted, nitrogen-containing heterocycle core. Early work indicated that this core might be fashioned from two dehydroalanines by an enzyme-catalyzed aza-[4 + 2] cycloaddition to give a cyclic-hemiaminal intermediate. This common intermediate could then follow a reductive path toward a dehydropiperidine, as in the thiopeptide thiostrepton, or an aromatization path to yield the pyridine groups observed in many other thiopeptides. Although several of the enzymes proposed to perform this cycloaddition have been reconstituted, only pyridine products have been isolated and any hemiaminal intermediates have yet to be observed. Here, we identify the conditions and substrates that decouple the cycloaddition from subsequent steps and allow interception and characterization of this long hypothesized intermediate. Transition state modeling indicates that the key amide-iminol tautomerization is the major hurdle in an otherwise energetically favorable cycloaddition. An anionic model suggests that deprotonation and polarization of this amide bond by TbtD removes this barrier and provides a sufficient driving force for facile (stepwise) cycloaddition. This work provides evidence for a mechanistic link between disparate cyclases in thiopeptide biosynthesis.

Bacteria possess an amazing capacity to synthesize a diverse range of structurally complex, bioactive natural products known as specialized (or secondary) metabolites. Many of these specialized metabolites are used as clinical therapeutics, while others have important ecological roles in microbial communities. The biosynthetic gene clusters (BGCs) that generate these metabolites can be identified in bacterial genome sequences using their highly conserved genetic features. We analyzed an unprecedented 1,566 bacterial genomes from Bacillus species and identified nearly 20,000 BGCs. By comparing these BGCs to one another as well as a curated set of known specialized metabolite BGCs, we discovered that the majority of Bacillus natural products are comprised of a small set of highly conserved, well-distributed, known natural product compounds. Most of these metabolites have important roles influencing the physiology and development of Bacillus species. We identified, in addition to these characterized compounds, many unique, weakly conserved BGCs scattered across the genus that are predicted to encode unknown natural products. Many of these “singleton” BGCs appear to have been acquired via horizontal gene transfer. Based on this large-scale characterization of metabolite production in the Bacilli , we go on to connect the alkylpyrones, natural products that are highly conserved but previously biologically uncharacterized, to a role in Bacillus physiology: inhibiting spore development. IMPORTANCE Bacilli are capable of producing a diverse array of specialized metabolites, many of which have gained attention for their roles as signals that affect bacterial physiology and development. Up to this point, however, the Bacillus genus’s metabolic capacity has been underexplored. We undertook a deep genomic analysis of 1,566 Bacillus genomes to understand the full spectrum of metabolites that this bacterial group can make. We discovered that the majority of the specialized metabolites produced by Bacillus species are highly conserved, known compounds with important signaling roles in the physiology and development of this bacterium. Additionally, there is significant unique biosynthetic machinery distributed across the genus that might lead to new, unknown metabolites with diverse biological functions. Inspired by the findings of our genomic analysis, we speculate that the highly conserved alkylpyrones might have an important biological activity within this genus. We go on to validate this prediction by demonstrating that these natural products are developmental signals in Bacillus and act by inhibiting sporulation.

Fourteen analogs of the marine natural product largazole have been prepared and assayed against histone deacetylases (HDACs) 1, 2, 3, and 6. Olefin cross-metathesis was used to efficiently access six variants of the side-chain zinc-binding domain, while adaptation of our previously reported modular synthesis allowed probing of the macrocyclic cap group.

Details of the synthesis of the 19-methyl, 19-methylene and 19-chloro derivatives of 17α, 21-dihydroxy-pregn-4-ene-3, 20-dione from the 19-hydroxy-Δ5 intermediate 6a are reported. Incubation of the 19-methyl and 19-chloro compounds 13 and 19 with bovine adrenal homogenates produced 19-methyl-11β,17α,21-trihydroxypregn-4-ene-3, 20-dione ( 20a ) and 17α, 21-dihydroxy-11β,19-oxidopregn-4-ene-3, 20-dione ( 22a ) respectively. The incubation of the 19-methylene steroid 11a took an unexpected course and afforded after acetylation a product tentatively formulated as 17α, 21-dihydroxy-19-methyleneoxypregn-4-ene-3, 20-dione 21-acetate ( 23 ).

The conversion of 19-nortestosterone acetate into 19-norandrosta-4,7-diene-3,17-dione (X) is described. The latter compound is transformed directly into equilin by a microbiological dehydrogenation process with Corynebacterium simplex , thus representing the first synthesis of this important female sex hormone. Alternate attempts to synthesise equilin are discussed.

Dithiolopyrrolone natural products have unique structures and exhibit a broad-spectrum of antimicrobial and anticancer activities. Isolated in the late 1940s, these molecules have attracted an increasing interest towards their biosynthesis, synthesis and mechanisms of action.