Mechanistic studies on the effect of membrane lipid acyl chain composition on daptomycin pore formation

The final publication is available at Elsevier via https://dx.doi.org/10.1016/j.chemphyslip.2018.09.015 © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/Daptomycin is a lipopeptide antibiotic that binds and permeabilizes the cell membranes of Gram-positive bacteria. Membrane permeabilization requires both calcium and phosphatidylglycerol (PG) in the target membrane, and it correlates with the formation of an oligomer that likely comprises eight subunits, which are evenly distributed between the two membrane leaflets. In both bacterial cells and model membranes, changes in the fatty acyl composition of the membrane phospholipids can prevent permeabilization. We here used liposomes to study the effect of phospholipids containing oleoyl and other fatty acyl residues on daptomycin activity, and made the following observations: (1) Oleic acid residues inhibited permeabilization when part not only of PG, but also of other phospholipids (PC or cardiolipin). (2) When included in an otherwise daptomycin-susceptible lipid mixture, even 10% of dioleoyl lipid (DOPC) can strongly inhibit permeabilization. (3) The inhibitory effect of fatty acyl residues appears to correlate more with their chain length than with unsaturation. (4) Under all conditions tested, permeabilization coincided with octamer formation, whereas tetramers were observed on membranes that were not permeabilized. Overall, our findings further support the notion that the octamer is indeed the functional transmembrane pore, and that fatty acyl residues may prevent pore formation by preventing the alignment of tetramers across the two membrane leaflets.Natural Sciences and Engineering Research Council of Canada [250265-2013,155283-2012

Incidence and trends of blastomycosis-associated hospitalizations in the United States

We used the State Inpatient Databases from the United States Agency for Healthcare Research and Quality to provide state-specific age-adjusted blastomycosis-associated hospitalization incidence throughout the entire United States. Among the 46 states studied, states within the Mississippi and Ohio River valleys had the highest age-adjusted hospitalization incidence. Specifically, Wisconsin had the highest age-adjusted hospitalization incidence (2.9 hospitalizations per 100,000 person-years). Trends were studied in the five highest hospitalization incidence states. From 2000 to 2011, blastomycosis-associated hospitalizations increased significantly in Illinois and Kentucky with an average annual increase of 4.4% and 8.4%, respectively. Trends varied significantly by state. Overall, 64% of blastomycosis-associated hospitalizations were among men and the median age at hospitalization was 53 years. This analysis provides a complete epidemiologic description of blastomycosis-associated hospitalizations throughout the endemic area in the United States

Efficient One-Pot, Two-Component Modular Synthesis of 3,5-Disubstituted Pyrazoles

The pyrazole scaffold is one of the most prevalent and important tool in medicinal chemistry. Here, we report a method for preparing 3,5-diarylpyrazoles in good to excellent yield by reacting hydrazones of aryl aldehydes with substituted acetophenones in ethanol in the presence of dimethyl sulfoxide/cat. I2/cat. HCl. The reverse process, reacting hydrazones of substituted acetophenones with aryl aldehydes under the same conditions, also provides 3,5-diarylpyrazoles in good to excellent yields. Reaction of hydrazones of aldehydes with 2′-aryloxy ketones in the presence of cat. HCl in ethanol and the catalyst-free reaction of phenacyl bromides with hydrazones of aldehydes in ethanol also gave good to excellent yields of 3,5-diarylpyrazoles

Total Synthesis of Analogs of A54145D and A54145A₁ 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 A1 (A5A1), two cyclic lipodepsipeptide antibiotics, are reported. An on-resin cyclization strategy was employed to prepare A5A1 analogs in which Thr4, the residue involved in the depsi (ester) bond, was replaced with either diaminopropionic acid (DAPA), (2S,3R)-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. Consistent with literature reports, we found that the single substitution of either 3-hydroxyasparagine (HOAsn) or 3-methoxyaspartate (MeOAsp) with Asn or Asp, respectively, in A5D is more detrimental to activity than the double substitution where both HOAsn and MeOAsp are replaced with Asn or Asp, respectively

Total Synthesis of A54145 Factor D

An efficient total synthesis of A54145 factor D (A5D), a member of the A54145 family of cyclic lipodepsipeptide antibiotics, is reported. The peptide was constructed by attaching the peptide to the 2′-chlorotrityl polystyrene resin via Sar5 and developing conditions that avoided diketopiperazine formation upon subsequent elaboration using 9-fluorenylmethoxycarbonyl solid-phase peptide synthesis. This route allowed for facile formation of the crucial depsi bond. A branched acyclic precursor was cyclized off-resin and then globally deprotected to obtain A5D. Consistent with recent studies by others, we found that the MeOAsp residue has the 2S,3R configuration. We also established that the configuration of the stereocenter in the anteiso-undecanoyl lipid tail does not affect biological activity

Total Synthesis of A54145 Factor D

An efficient total synthesis of A54145 factor D (A5D), a member of the A54145 family of cyclic lipodepsipeptide antibiotics, is reported. The peptide was constructed by attaching the peptide to the 2′-chlorotrityl polystyrene resin via Sar5 and developing conditions that avoided diketopiperazine formation upon subsequent elaboration using 9-fluorenylmethoxycarbonyl solid-phase peptide synthesis. This route allowed for facile formation of the crucial depsi bond. A branched acyclic precursor was cyclized off-resin and then globally deprotected to obtain A5D. Consistent with recent studies by others, we found that the MeOAsp residue has the 2S,3R configuration. We also established that the configuration of the stereocenter in the anteiso-undecanoyl lipid tail does not affect biological activity

α‑Azido Esters in Depsipeptide Synthesis: C–O Bond Cleavage during Azido Group Reduction

α-Azido esters, when treated with dithiothreitol (DTT)/diisopropylethylamine (DIPEA), undergo both azido group reduction to give α-amino esters and C–O bond cleavage to give triazoles. The extent of triazole formation depends upon leaving group ability. Some C–O bond cleavage via triazole formation was also found to occur when a resin-bound peptide, which contained a terminal α-azido ester group, was treated with DTT/DIPEA. C–O bond cleavage also took place when this peptide was treated with PPh₃, PBu₃, or PMe₃; however, in these cases, C–O bond cleavage occurred via either triazole formation and/or hydrolysis of the ester bond in the iminophosphorane intermediate to give betaines. The mechanism that dominated for C–O bond cleavage depended upon the phosphine that was used for azido group reduction. C–O bond cleavage during reduction of the azido group in the peptide was minimized by performing the reduction with PBu₃ in the presence of a symmetric anhydride derived from an amino acid in dry THF followed by the addition of water. Surprisingly, these conditions provided the amine as the major product, while the expected amide was formed as a minor product. These conditions were employed in an improved synthesis of an analogue of the cyclic lipodepsipeptide antibiotic daptomycin