Synthesis of Imidazoles from Fatty 1,2‐Diketones

Isolation, structure elucidation, total synthesis, and biosynthesis of dermazolium A, an antibacterial imidazolium metabolite of a vaginal bacterium Dermabacter vaginalis

Dermabacter vaginalis is a human-derived bacterium isolated from vaginal fluid of a Korean female in 2016. Although several human-related species in Dermabacter genus have been reported there are few studies on their bioactive metabolites. Dermazolium A (1), a rare imidazolium metabolite, was isolated from D. vaginalis along with five known metabolites (2-6) and their chemical structures were determined by NMR, HRMS, and MS/MS data analysis. Feeding experiments using predicted precursors and biomimetic total synthesis of 1 corroborated its structure and led to suggestion of biosynthetic pathway of 1. Antibacterial tests on the isolated compounds showed that 1 is a mild antibacterial agent with MIC values of 41 µg/mL against methicillin-resistant Staphylococcus aureus (MRSA) USA300, Lacticaseibacillus paracasei subsp. paracasei KCTC 3510 and Brevibacterium epidermidis KCTC 3090.

Understanding desaturation/hydroxylation activity of castor stearoyl Δ9-Desaturase through rational mutagenesis

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Rationally designed mutations in the Δ⁹ desaturase promoted hydroxylation activity.

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Proton and electron transfer to the active site is crucial for the Δ⁹D to desaturate

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Detailed analysis of all enzymatic products of the Δ⁹D was carried out

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Insight into the chemo-, and stereoselectivity of non-heme diiron enzymes was obtained

A recently proposed reaction mechanism of soluble Δ⁹ desaturase (Δ⁹D) allowed us to identify auxiliary residues His203, Asp101, Thr206 and Cys222 localized near the di-iron active site that are supposedly involved in the proton transfer (PT) to and from the active site. The PT, along with the electron transfer (ET), seems to be crucial for efficient desaturation. Thus, perturbing the major PT chains is expected to impair the native reaction and (potentially) amplify minor reaction channels, such as the substrate hydroxylation. To verify this hypothesis, we mutated the four residues mentioned above into their counterparts present in a soluble methane monooxygenase (sMMO), and determined the reaction products of mutants. We found that the mutations significantly promote residual monohydroxylation activities on stearoyl-CoA, often at the expense of native desaturation activity. The favored hydroxylation positions are C₉, followed by C₁₀ and C₁₁. Reactions with unsaturated substrate, oleoyl-CoA, yield erythro-9,10-diol, cis-9,10-epoxide and a mixture of allylic alcohols. Additionally, using 9- and 11-hydroxystearoyl-CoA, we showed that the desaturation reaction can proceed only with the hydroxyl group at position C₁₁, whereas the hydroxylation reaction is possible in both cases, i.e. with hydroxyl at position C₉ or C₁₁. Despite the fact that the overall outcome of hydroxylation is rather modest and that it is mostly the desaturation/hydroxylation ratio that is affected, our results broaden understanding of the origin of chemo- and stereoselectivity of the Δ⁹D and provide further insight into the catalytic action of the NHFe₂ enzymes.