Daptomycin: Mechanism of action, mechanisms of resistance, synthesis and structure-activity relationships.

Daptomycin is a cyclic lipodepsipeptide antibiotic that is a mainstay for the treatment of serious infections caused by Gram-positive bacteria, including methicillin-resistant Streptococcus aureus and vancomycin resistant enterococci. It is one of the so-called last-resort antibiotics that are used to tackle life-threatening infections that do not respond to first-line treatments. However, resistance to daptomycin is eroding its clinical efficacy motivating the design and/or discovery of analogues that overcome resistance.

Total Synthesis of LL-A0341β.

The first total synthesis of cyclic depsipeptide antibiotic LL-A0341β (LL) is described. The configuration of the β-methyltryptophan (β-MeTrp) residue was established by preparing all four stereoisomers of Fmoc-β-MeTrp which were used for the synthesis of LL via Fmoc solid phase peptide synthesis. The most active of the four peptides was the one containing (2,3)-β-MeTrp.

The Calcium-Dependent Antibiotics: Structure-Activity Relationships and Determination of Their Lipid Target.

The calcium-dependent antibiotics (CDAs) are a group of seven closely related membrane-active cyclic lipopeptide antibiotics (cLPAs) first isolated in the early 1980s from the fermentation broth of . Their target was unknown, and the mechanism of action is uncertain. Herein, we report new routes for the synthesis of CDA4b and its analogues, explore the structure-activity relationships at its lipid tail and at positions 3, 9, and 11, and determine the CDAs' lipid target.

Tensor modeling of MRSA bacteremia cytokine and transcriptional patterns reveals coordinated, outcome-associated immunological programs.

Methicillin-resistant (MRSA) bacteremia is a common and life-threatening infection that imposes up to 30% mortality even when appropriate therapy is used. Despite in vitro efficacy determined by minimum inhibitory concentration breakpoints, antibiotics often fail to resolve these infections in vivo, resulting in persistent MRSA bacteremia. Recently, several genetic, epigenetic, and proteomic correlates of persistent outcomes have been identified.

Dissecting signaling regulators driving AXL-mediated bypass resistance and associated phenotypes by phosphosite perturbations.

Receptor tyrosine kinase (RTK)-targeted therapies are often effective but invariably limited by drug resistance. A major mechanism of acquired resistance involves "bypass" switching to alternative pathways driven by non-targeted RTKs that restore proliferation. One such RTK is AXL whose overexpression, frequently observed in bypass resistant tumors, drives both cell survival and associated malignant phenotypes such as epithelial-to-mesenchymal (EMT) transition and migration.

Multivalent, asymmetric IL-2-Fc fusions show enhanced selectivity for regulatory T cells.

The cytokine interleukin-2 (IL-2) has the potential to treat autoimmune disease but is limited by its modest specificity toward immunosuppressive regulatory T (T) cells. IL-2 receptors consist of combinations of α, β, and γ chains of variable affinity and cell specificity. Engineering IL-2 to treat autoimmunity has primarily focused on retaining binding to the relatively T-selective, high-affinity receptor while reducing binding to the less selective, low-affinity receptor.

The impact of lysyl-phosphatidylglycerol on the interaction of daptomycin with model membranes.

Daptomycin is an important clinical antibiotic for which resistance is rising. Daptomycin resistant strains of often have increased 1,2-diacyl--3-[phospho-1-(3-lysyl(1-glycerol))] (lysyl-PG) and mutations to the proteins directly involved in the synthesis and translocation of lysyl-PG are implicated in resistance mechanisms. To study the interaction of daptomycin with lysyl-DMPG-containing model membranes a new stereospecific and regioselective synthesis of lysyl-DMPG was developed.

Effect of Lipid Length and Cationic Residues on the Antibacterial and Hemolytic Activities of Paenibacterin.

Paenibacterin A1 (PA1) is a broad-spectrum, cationic cyclic lipodepsipeptide antibiotic isolated from . In this study, the roles of the cationic residues and lipid tail length on the in vitro antibacterial and hemolytic activities of PA1 was examined in the context of an active PA1 analogue, called PAK, in which the two D-Orn residues in PA1 were converted to D-Lys residues. The effect of reducing the length of the lipid tail in PAK from 15 to 12-10 carbons on the minimum inhibitory concentration (MIC) depended upon the bacteria.

A54145 Factor D Is Not Less Susceptible to Inhibition by Lung Surfactant than Daptomycin.

A54145 factor D (A5D) is a cyclic lipopeptide antibiotic that shares several structural and mechanistic features with the clinically important antibiotic daptomycin, such as their requirement for calcium and phosphatidylglycerol (PG) for activity. Studies by others have suggested that daptomycin's activity is strongly inhibited by lung surfactant while A5D's activity is not. This finding has inspired efforts, albeit unsuccessful, to develop an A5D analogue that is highly active in the presence of lung surfactant and can be used for treating community acquired pneumonia (CAP).

Designing Protease-Triggered Protein Cages.

Proteins that self-assemble into enclosed polyhedral cages, both naturally and by design, are garnering attention for their prospective utility in the fields of medicine and biotechnology. Notably, their potential for encapsulation and surface display are attractive for experiments that require protection and targeted delivery of cargo. The ability to control their opening or disassembly would greatly advance the development of protein nanocages into widespread molecular tools.

Establishing the Structure-Activity Relationship between Phosphatidylglycerol and Daptomycin.

Daptomycin is a clinical antibiotic used to treat serious infections caused by Gram-positive bacteria. Although there is debate about the action mechanism of daptomycin, it is known that daptomycin requires both calcium and phosphatidylglycerol (PG) to exert its antibacterial effect. Despite the importance and uniqueness of the interaction of daptomycin with PG, very little is known about this interaction or the nascent daptomycin-PG complex.

Discovery of Highly Active Derivatives of Daptomycin by Assessing the Effect of Amino Acid Substitutions at Positions 8 and 11 on a Daptomycin Analogue.

Daptomycin is an important antibiotic used for treating serious infections caused by Gram-positive bacteria including methicillin-resistant (MRSA) and vancomycin-resistant enterococci. Establishing structure-activity relationships of daptomycin is important for developing new daptomycin-based antibiotics with expanded clinical applications and for tackling the ever-increasing problem of antimicrobial resistance. Toward this end, Dap-K6-E12-W13, an active analogue of daptomycin in which the uncommon amino acids in daptomycin are replaced with their common counterparts, was used as a model system for studying the effect of amino acid variation at positions 8 and 11 on in vitro biological activity against a model organism, , and calcium-dependent insertion into model membranes.

The Chiral Target of Daptomycin Is the 2R,2'S Stereoisomer of Phosphatidylglycerol.

Daptomycin (dap) is an important antibiotic that interacts with the bacterial membrane lipid phosphatidylglycerol (PG) in a calcium-dependent manner. The enantiomer of dap (ent-dap) was synthesized and was found to be 85-fold less active than dap against B. subtilis, indicating that dap interacts with a chiral target as part of its mechanism of action.

Tensor-structured decomposition improves systems serology analysis.

Systems serology provides a broad view of humoral immunity by profiling both the antigen-binding and Fc properties of antibodies. These studies contain structured biophysical profiling across disease-relevant antigen targets, alongside additional measurements made for single antigens or in an antigen-generic manner. Identifying patterns in these measurements helps guide vaccine and therapeutic antibody development, improve our understanding of diseases, and discover conserved regulatory mechanisms.

Enantioselective Synthesis and Application of Small and Environmentally Sensitive Fluorescent Amino Acids for Probing Biological Interactions.

Environmentally sensitive fluorescent amino acids (FlAAs) have been used extensively to probe biological interactions. However, most of these amino acids are large and do not resemble amino acid side chains. Here, we report the enantioselective synthesis of two small and environmentally sensitive fluorescent amino acids bearing 7-dialkylaminocoumarin side chains by alkylation of a Ni(II) glycine Schiff base complex.

Synthesis of β-Hydroxy-α,α-difluorosulfonamides from Carbanions of Difluoromethanesulfonamides.

The synthesis of β-hydroxy-α,α-difluorosulfonamides was achieved by reacting difluoromethanesulfonamides with KHMDS in the presence of an aldehyde or ketone. The reaction exhibited a dramatic counterion effect with KHMDS or NaHMDS usually giving excellent yields in minutes, while lithium bases gave little or no product. Excellent yields and high diastereomeric ratios were achieved with -benzyl--phenylfluorenyl (PhF)-protected chiral amino aldehydes derived from amino acids.

Solid-Phase Total Synthesis of Dehydrotryptophan-Bearing Cyclic Peptides Tunicyclin B, Sclerotide A, CDA3a, and CDA4a using a Protected β-Hydroxytryptophan Building Block.

A new approach to the synthesis of -dehydrotryptophan (ΔTrp) peptides is described. This approach uses Fmoc-β-HOTrp(Boc)(TBS)-OH as a building block, which is readily prepared in high yield and incorporated into peptides using solid-phase Fmoc chemistry. The -butyldimethylsilyl-protected indolic alcohol is eliminated during global deprotection/resin cleavage to give ΔTrp peptides exclusively as the thermodynamically favored Z isomer.

A high-yielding solid-phase total synthesis of daptomycin using a Fmoc SPPS stable kynurenine synthon.

A high-yielding total synthesis of daptomycin, an important clinical antibiotic, is described. Key to the development of this synthesis was the elucidation of a Camps cyclization reaction that occurs in the solid-phase when conventionally used kynurenine (Kyn) synthons, such as Fmoc-l-Kyn(Boc,CHO)-OH and Fmoc-l-Kyn(CHO,CHO)-OH, are exposed to 20% 2-methylpiperidine (2MP)/DMF. During the synthesis of daptomycin, this side reaction was accompanied by intractable peptide decomposition, which resulted in a low yield of Dap and a 4-quinolone containing peptide.

Thermoresponsive Starch for the Flocculation of Oil Sands Mature Fine Tailings.

The reclamation of land and recovery of water from tailing ponds created during bitumen extraction from oil sands is a major technical and environmental challenge. In the current study, thermoresponsive hydroxybutylated (HB) corn starch (HB-CS) and potato starch (HB-PS), with lower critical solution temperatures (LCSTs) ranging from 36 to 45 °C, were examined as flocculants for oil sands mature fine tailings (MFT). The ability of different doses of the HB-CS and HB-PS to flocculate 2 and 10 wt % MFT, prepared by diluting 35 wt % MFT in tap water, in terms of the initial settling rate (ISR), supernatant turbidity (ST), sediment solids content (SSC), and water recovery (WR), was examined at temperatures below and above their LCSTs.

Correction: Measurement and models accounting for cell death capture hidden variation in compound response.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Highly efficient and enantioselective syntheses of (2S,3R)-3-alkyl- and alkenylglutamates from Fmoc-protected Garner's aldehyde.

A 6-step enantioselective synthesis of (2S,3R)-3-alkyl/alkenylglutamates, including the biologically significant amino acid, (2S,3R)-3-methylglutamate, protected for Fmoc SPPS, is reported. Overall yields range from 52-65%. Key to the success of these syntheses was the development of a high-yielding 2-step synthesis of Fmoc Garner's aldehyde followed by a Horner-Wadsworth-Emmons reaction to give the corresponding Fmoc Garner's enoate in a 94% yield.

Measurement and models accounting for cell death capture hidden variation in compound response.

Cancer cell sensitivity or resistance is almost universally quantified through a direct or surrogate measure of cell number. However, compound responses can occur through many distinct phenotypic outcomes, including changes in cell growth, apoptosis, and non-apoptotic cell death. These outcomes have divergent effects on the tumor microenvironment, immune response, and resistance mechanisms.

Mild, Rapid, and Chemoselective Procedure for the Introduction of the 9-Phenyl-9-fluorenyl Protecting Group into Amines, Acids, Alcohols, Sulfonamides, Amides, and Thiols.

The 9-phenyl-9-fluorenyl (PhF) group has been used as an N protecting group of amino acids and their derivatives mainly as a result of its ability to prevent racemization. However, installing this group using the standard protocol, which employs 9-bromo-9-phenylfluorene/KPO/Pb(NO), often takes days and yields can be variable. Here, we demonstrate that the PhF group can be introduced into the amino group of Weinreb's amides and methyl esters of amino acids, as well as into alcohols and carboxylic acids, rapidly and in excellent yields, using 9-chloro-9-phenylfluorene (PhFCl)/-methylmorpholine (NMM)/AgNO.

Total Synthesis of Analogs of A54145D and A54145A for Structure-Activity Relationship Studies.

The total solid-phase synthesis and in vitro biological activity of a series of analogs of A54145 factor D (A5D) and A54145 factor A (A5A), two cyclic lipodepsipeptide antibiotics, are reported. An on-resin cyclization strategy was employed to prepare A5A analogs in which Thr4, the residue involved in the depsi (ester) bond, was replaced with either diaminopropionic acid (DAPA), (2,3)-diaminobutyric acid (DABA), or serine, effectively replacing the ring-closing ester bond with an amide linkage or with a primary ester. Antibacterial studies with these four analogs revealed that, contrary to a previous report, replacing the ester bond with an amide bond significantly reduces biological activity, and that both the ester bond and the methyl group at the γ-position of Thr4 are crucial for activity.

Discovery of 5-aryl-3-thiophen-2-yl-1H-pyrazoles as a new class of Hsp90 inhibitors in hepatocellular carcinoma.

Although hepatocellular carcinoma (HCC)-related mortality has increased over the past decades, treatment options are still very limited, underlining the need for developing new therapeutic strategies. The molecular chaperone heat shock protein 90 (Hsp90) plays a key role in post-translational maturation of many oncogenic client proteins that are important for survival and proliferation of cancer cells. Thus, inhibitors of Hsp90 are promising targets for many cancer types.