Pseudomonas aeruginosa is a major cause of nosocomial infections and also leads to severe exacerbations in cystic fibrosis or chronic obstructive pulmonary disease. Three intertwined quorum sensing systems control virulence of P. aeruginosa, with the rhl circuit playing the leading role in late and chronic infections. The majority of traits controlled by rhl transcription factor RhlR depend on PqsE, a dispensable thioesterase in Pseudomonas Quinolone Signal (PQS) biosynthesis that interferes with RhlR through an enigmatic mechanism likely involving direct interaction of both proteins. Here we show that PqsE and RhlR form a 2:2 protein complex that, together with RhlR agonist N-butanoyl-L-homoserine lactone (C4-HSL), solubilizes RhlR and thereby renders the otherwise insoluble transcription factor active. We determine crystal structures of the complex and identify residues essential for the interaction. To corroborate the chaperone-like activity of PqsE, we design stability-optimized variants of RhlR that bypass the need for C4-HSL and PqsE in activating PqsE/RhlR-controlled processes of P. aeruginosa. Together, our data provide insight into the unique regulatory role of PqsE and lay groundwork for developing new P. aeruginosa-specific pharmaceuticals.

Herein, we broaden the application scope of (cyclopentadienone)iron complexes 1 in C=N bond reduction. The catalytic scope of pre‐catalyst 1b, which is more active than the “Knölker complex” (1a) and other members of its family, has been expanded to the catalytic transfer hydrogenation (CTH) of a wider range of aldimines and ketimines, either pre‐isolated or generated in situ. The kinetics of 1b‐promoted CTH of ketimine S1 were assessed, showing a pseudo‐first order profile, with TOF = 6.07 h–1 at 50 % conversion. Moreover, the chiral complex 1c and its analog 1d were employed in the enantioselective reduction of ketimines and reductive amination of ketones, giving fair to good yields and moderate enantioselectivity.

Tris(acetylacetonato) iron(III) [Fe(acac)3] is an indispensable reagent in synthetic chemistry. Its applications range from hydrogen atom transfer to cross-coupling reactions and to use as a Lewis acid. Consequently, the exceptional utility of Fe(acac)3 has been demonstrated in several total syntheses. This short review summarizes the applications of Fe(acac)3 in methodology and catalysis and highlights its use for the synthesis of medicinally relevant structures and in natural product syntheses.1 Introduction2 Hydrogen Atom Transfer (HAT)3 Oxidations and Radical Transformations4 Synthesis and Use of Alkynes and Allenes5 Cross-Couplings and Cycloisomerizations6 Borylations7 Miscellaneous Reactions8 Conclusions

The first bioinspired and protecting group free total synthesis of the antibacterial sesquiterpenoid antroalbocin A has been achieved in five linear steps from a literature-known intermediate with an overall yield of 6.7%. An intramolecular Robinson annulation gave rapid access to the tricyclic enone as starting material for a photochemical domino process of deconjugation and sigmatropic 1,3-acyl shift. Herein we further describe studies towards the use of photolytic sigmatropic 1,3-acyl shifts in the synthesis of bridged terpenoid building blocks.Antroalbocin A (1), isolated in 2018 from the higher fungus Antrodiella albocinnamomea by Liu and co-workers, is a new antibacterial sesquiterpenoid. [1] Its unique structure shows a novel bridged 5/5/6 tricyclic system with three all carbon quaternary centers. Two of them are located in both bridgehead positions.

Dedicated to Prof. Cesare Gennari on the occasion of his 70th birthday.