Enantioselective synthesis of the aglycone of burnettramic acid A

Enantioselective total synthesis of the aglycone of burnettramic acid A, an antifungal pyrrolizidinedione with a terminally mannosylated long acyl chain produced by Aspergillus fungi, has been achieved from a known carboxylic acid by a 14-step sequence. The key steps include 2 types of asymmetric alkylation, coupling of an acetylide intermediate with (S)-epichlorohydrin to provide an acetylenic epoxide in 1 pot, and the Birch reduction to effect desulfonylation, semi-reduction of triple bond, and debenzylation in a concurrent manner. Good agreement of the synthetic aglycone with naturally occurring one in 1H and 13C nuclear magnetic resonance (NMR) spectra, coupled with previously reported unambiguous stereochemical assignment of the sugar moiety, has confirmed the structure of burnettramic acid A.

Degrasyn exhibits antibiotic activity against multi-resistant Staphylococcus aureus by modifying several essential cysteines

Degrasyn inhibits deubiquitination enzymes and has anti-cancer activity. We here show that it also exhibits antimicrobial activity against multi-resistant Staphylococcus aureus. Structure activity relationship studies demonstrate an important role of the electrophilic α-cyanoacrylamide moiety as a Michael acceptor. A suite of chemical proteomic techniques unraveled binding of this moiety to various cysteine residues of essential proteins in a reversibly covalent manner.

Targeting the endoplasmic reticulum-mitochondria interface sensitizes leukemia cells to cytostatics

Combination chemotherapy has proven to be a favorable strategy to treat acute leukemia. However, the introduction of novel compounds remains challenging and is hindered by a lack of understanding of their mechanistic interactions with established drugs. In the present study, we demonstrate a highly increased response of various acute leukemia cell lines, drug-resistant cells and patient-derived xenograft cells by combining the recently introduced protein disulfide isomerase inhibitor PS89 with cytostatics. In leukemic cells, a proteomics-based target fishing approach revealed that PS89 affects a whole network of endoplasmic reticulum homeostasis proteins. We elucidate that the strong induction of apoptosis in combination with cytostatics is orchestrated by the PS89 target B-cell receptor-associated protein 31, which transduces apoptosis signals at the endoplasmic reticulum -mitochondria interface. Activation of caspase-8 and cleavage of B-cell receptor-associated protein 31 stimulate a pro-apoptotic crosstalk including release of calcium from the endoplasmic reticulum and an increase in the levels of reactive oxygen species resulting in amplification of mitochondrial apoptosis. The findings of this study promote PS89 as a novel chemosensitizing agent for the treatment of acute leukemia and uncovers that targeting the endoplasmic reticulum - mitochondrial network of cell death is a promising approach in combination therapy.

Dual Inhibitor of Staphylococcus aureus Virulence and Biofilm Attenuates Expression of Major Toxins and Adhesins

Staphylococcus aureus is a major bacterial pathogen that invades and damages host tissue by the expression of devastating toxins. We here performed a phenotypic screen of 35 molecules that were structurally inspired by previous hydroxyamide-based S. aureus virulence inhibitors compiled from commercial sources or designed and synthesized de novo. One of the most potent compounds, AV73, not only reduced hemolytic alpha-hemolysin production in S. aureus but also impeded in vitro biofilm formation. The effect of AV73 on bacterial proteomes and extracellular protein levels was analyzed by quantitative proteomics and revealed a significant down-regulation of major virulence and biofilm promoting proteins. To elucidate the mode of action of AV73, target identification was performed using affinity-based protein profiling (AfBPP), where among others YidC was identified as a target.