The Legionella autoinducer LAI-1 is delivered by outer membrane vesicles to promote interbacterial and interkingdom signaling.

Legionella pneumophila is an environmental bacterium, which replicates in amoeba but also in macrophages, and causes a life-threatening pneumonia called Legionnaires' disease. The opportunistic pathogen employs the α-hydroxy-ketone compound Legionella autoinducer-1 (LAI-1) for intraspecies and interkingdom signaling. LAI-1 is produced by the autoinducer synthase Legionella quorum sensing A (LqsA), but it is not known, how LAI-1 is released by the pathogen. Here, we use a Vibrio cholerae luminescence reporter strain and liquid chromatography-tandem mass spectrometry to detect bacteria-produced and synthetic LAI-1. Ectopic production of LqsA in Escherichia coli generated LAI-1, which partitions to outer membrane vesicles (OMVs) and increases OMV size. These E. coli OMVs trigger luminescence of the V. cholerae reporter strain and inhibit the migration of Dictyostelium discoideum amoeba. Overexpression of lqsA in L.pneumophila under the control of strong stationary phase promoters (PflaA or P6SRNA), but not under control of its endogenous promoter (PlqsA), produces LAI-1, which is detected in purified OMVs. These L. pneumophila OMVs trigger luminescence of the Vibrio reporter strain and inhibit D. discoideum migration. L. pneumophila OMVs are smaller upon overexpression of lqsA or upon addition of LAI-1 to growing bacteria, and therefore, LqsA affects OMV production. The overexpression of lqsA but not a catalytically inactive mutant promotes intracellular replication of L. pneumophila in macrophages, indicating that intracellularly produced LA1-1 modulates the interaction in favor of the pathogen. Taken together, we provide evidence that L. pneumophila LAI-1 is secreted through OMVs and promotes interbacterial communication and interactions with eukaryotic host cells.

Al(III)-Promoted Formation of All-Carbon Quaternary Centers from Aliphatic Tertiary Chlorides and Alkynyl Silanes.

Despite the accessibility of numerous alkynes through coupling or substitution reactions, the synthesis of trialkyl-substituted alkynes is still a major challenge. Within this context, we reexplored the electrophilic alkynyl substitution between tertiary aliphatic chlorides and silylated alkynes. We were able to demonstrate that this approach is significantly more general than originally demonstrated by Capozzi and even tolerates several functional groups. Furthermore, we report diastereoselective reactions which in some instances gave excellent diastereoselectivity (dr >95:5).

Utilization of 13C NMR Carbon Shifts for the Attribution of Diastereomers in Methyl-Substituted Cyclohexanes.

In this report, we address the challenge of assigning diastereomers for methyl cyclohexanes, particularly those with quaternary centers, which remains nontrivial despite modern NMR techniques. By utilizing a HSQC NMR experiment to identify methyl-carbons coupled with a simple conformational analysis, we identified an effective and quite general method for assigning stereochemistry, even in cases where diastereomeric mixtures are inseparable.