Total Synthesis and Antibiotic Properties of Amino‐Functiona­lized Aromatic Terpenoids Related to Erogorgiaene and the Pseudopterosins

Mechanism of action of pseudopteroxazole and pseudopterosin G: Diterpenes from marine origin

Pseudopteroxazole (Ptx) and the pseudopterosins are marine natural products with promising antibacterial potential. While Ptx has attracted interest for its antimycobacterial activity, pseudopterosins are active against several clinically relevant pathogens. Both compound classes exhibit low cytotoxicity and accessibility to targeted synthesis, yet their antibacterial mechanisms remain elusive. In this study, we investigated the modes of action of Ptx and pseudopterosin G (PsG) in Bacillus subtilis employing an unbiased approach that combines gel-based proteomics with a mathematical similarity analysis of response profiles. Proteomic responses to sublethal concentrations of Ptx and PsG were compared to a library of antibiotic stress response profiles revealing that both induce a stress response characteristic for agents targeting the bacterial cell envelope by interfering with membrane-bound steps of cell wall biosynthesis. Microscopy-based assays confirmed that both compounds compromise the integrity of the bacterial cell wall without disrupting the membrane potential. Furthermore, LC-MSE analysis showed that the greater potency of PsG against B. subtilis, reflected in a lower MIC and a more pronounced proteomic response, may be rooted in a more effective association with and penetration of B. subtilis cells. We conclude that Ptx and PsG target the integrity of the gram-positive cell wall.

Marine natural products

Covering: January to the end of December 2022This review covers the literature published in 2022 for marine natural products (MNPs), with 645 citations (633 for the period January to December 2022) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, the submerged parts of mangroves and other intertidal plants. The emphasis is on new compounds (1417 in 384 papers for 2022), together with the relevant biological activities, source organisms and country of origin. Pertinent reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. An analysis of NP structure class diversity in relation to biota source and biome is discussed.

Porin-independent accumulation in Pseudomonas enables antibiotic discovery

Gram-negative antibiotic development has been hindered by a poor understanding of the types of compounds that can accumulate within these bacteria1,2. The presence of efflux pumps and substrate-specific outer-membrane porins in Pseudomonas aeruginosa renders this pathogen particularly challenging3. As a result, there are few antibiotic options for P. aeruginosa infections4 and its many porins have made the prospect of discovering general accumulation guidelines seem unlikely5. Here we assess the whole-cell accumulation of 345 diverse compounds in P. aeruginosa and Escherichia coli. Although certain positively charged compounds permeate both bacterial species, P. aeruginosa is more restrictive compared to E. coli. Computational analysis identified distinct physicochemical properties of small molecules that specifically correlate with P. aeruginosa accumulation, such as formal charge, positive polar surface area and hydrogen bond donor surface area. Mode of uptake studies revealed that most small molecules permeate P. aeruginosa using a porin-independent pathway, thus enabling discovery of general P. aeruginosa accumulation trends with important implications for future antibiotic development. Retrospective antibiotic examples confirmed these trends and these discoveries were then applied to expand the spectrum of activity of a gram-positive-only antibiotic, fusidic acid, into a version that demonstrates a dramatic improvement in antibacterial activity against P. aeruginosa. We anticipate that these discoveries will facilitate the design and development of high-permeating antipseudomonals.