N-(Hydroxybenzyl)benzamide Derivatives: Aqueous pH-Dependent Kinetics and Mechanistic Implications for the Aqueous Reactivity of Carbinolamides.

The rate constants for the aqueous reaction, between pH 0 and 14, have been determined for a series of amide substituted N-(hydroxybenzyl)benzamide derivatives, in H2O, at 25 °C, I = 1.0 M (KCl). The N-(hydroxybenzyl)benzamide derivatives were found to react via three distinct mechanisms with the kinetically dominant mechanism being dependent on the pH of the reaction solution. It has been shown that the carbinolamides react via a specific-base-catalyzed mechanism (E1cB-like) under basic and pH neutral conditions. At lower pH values, an acid-catalyzed mechanism was kinetically dominant and, last, a water reaction was postulated at pH values where neither the hydroxide-dependent nor the general-acid-catalyzed mechanism was dominant. Contrary to earlier studies with N-(hydroxymethyl)benzamide compounds, no evidence for mechanistic variation based upon the nature of the amidic substituent was observed for any of the N-(hydroxybenzyl)benzamide derivatives studied between pH values of 0-14. The rate for the acid-catalyzed reaction (kH, ρ = -1.17), the apparent second-order hydroxide rate constant (k1', ρ = 0.87), the hydroxide-independent rate (k1, ρ = 0.65), and the pKa's of the hydroxyl group of the carbinolamide (ρ = 0.23) are reported.

Fluid surface coatings for solid-state nanopores: comparison of phospholipid bilayers and archaea-inspired lipid monolayers.

In the context of sensing and characterizing single proteins with synthetic nanopores, lipid bilayer coatings provide at least four benefits: first, they minimize unwanted protein adhesion to the pore walls by exposing a zwitterionic, fluid surface. Second, they can slow down protein translocation and rotation by the opportunity to tether proteins with a lipid anchor to the fluid bilayer coating. Third, they provide the possibility to impart analyte specificity by including lipid anchors with a specific receptor or ligand in the coating. Fourth, they offer a method for tuning nanopore diameters by choice of the length of the lipid's acyl chains. The work presented here compares four properties of various lipid compositions with regard to their suitability as nanopore coatings for protein sensing experiments: (1) electrical noise during current recordings through solid-state nanopores before and after lipid coating, (2) long-term stability of the recorded current baseline and, by inference, of the coating, (3) viscosity of the coating as quantified by the lateral diffusion coefficient of lipids in the coating, and (4) the success rate of generating a suitable coating for quantitative nanopore-based resistive pulse recordings. We surveyed lipid coatings prepared from bolaamphiphilic, monolayer-forming lipids inspired by extremophile archaea and compared them to typical bilayer-forming phosphatidylcholine lipids containing various fractions of curvature-inducing lipids or cholesterol. We found that coatings from archaea-inspired lipids provide several advantages compared to conventional phospholipids; the stable, low noise baseline qualities and high viscosity make these membranes especially suitable for analysis that estimates physical protein parameters such as the net charge of proteins as they enable translocation events with sufficiently long duration to time-resolve dwell time distributions completely. The work presented here reveals that the ease or difficulty of coating a nanopore with lipid membranes did not depend significantly on the composition of the lipid mixture, but rather on the geometry and surface chemistry of the nanopore in the solid state substrate. In particular, annealing substrates containing the nanopore increased the success rate of generating stable lipid coatings.

The small molecule CA140 inhibits the neuroinflammatory response in wild-type mice and a mouse model of AD.

BACKGROUND: Neuroinflammation is associated with neurodegenerative diseases, including Alzheimer's disease (AD). Thus, modulating the neuroinflammatory response represents a potential therapeutic strategy for treating neurodegenerative diseases. Several recent studies have shown that dopamine (DA) and its receptors are expressed in immune cells and are involved in the neuroinflammatory response. Thus, we recently developed and synthesized a non-self-polymerizing analog of DA (CA140) and examined the effect of CA140 on neuroinflammation. METHODS: To determine the effects of CA140 on the neuroinflammatory response, BV2 microglial cells were pretreated with lipopolysaccharide (LPS, 1 µg/mL), followed by treatment with CA140 (10 µM) and analysis by reverse transcription-polymerase chain reaction (RT-PCR). To examine whether CA140 alters the neuroinflammatory response in vivo, wild-type mice were injected with both LPS (10 mg/kg, intraperitoneally (i.p.)) and CA140 (30 mg/kg, i.p.), and immunohistochemistry was performed. In addition, familial AD (5xFAD) mice were injected with CA140 or vehicle daily for 2 weeks and examined for microglial and astrocyte activation. RESULTS: Pre- or post-treatment with CA140 differentially regulated proinflammatory responses in LPS-stimulated microglia and astrocytes. Interestingly, CA140 regulated D1R levels to alter LPS-induced proinflammatory responses. CA140 significantly downregulated LPS-induced phosphorylation of ERK and STAT3 in BV2 microglia cells. In addition, CA140-injected wild-type mice exhibited significantly decreased LPS-induced microglial and astrocyte activation. Moreover, CA140-injected 5xFAD mice exhibited significantly reduced microglial and astrocyte activation. CONCLUSIONS: CA140 may be beneficial for preventing and treating neuroinflammatory-related diseases, including AD.

Thiol-Triggered Release of Intraliposomal Content from Liposomes Made of Extremophile-Inspired Tetraether Lipids.

Liposomal drug-delivery systems have been used for delivery of drugs to targeted tissues while reducing unwanted side effects. DOXIL, for instance, is a liposomal formulation of the anticancer agent doxorubicin (DOX) that has been used to address problems associated with nonspecific toxicity of free DOX. However, while this liposomal formulation allows for a more-stable circulation of doxorubicin in the body compared to free drug, the efficacy for cancer therapy is reduced in comparison with systemic injections of free drug. A robust liposomal system that can be triggered to release DOX in cancer cells could mitigate problems associated with reduced drug efficacy. In this work, we present a serum-stable, cholesterol-integrated tetraether lipid comprising of a cleavable disulfide bond, {GcGT(S-S)PC-CH}, that is designed to respond to the reducing environment of the cell to trigger the release intraliposomal content upon cellular uptake by cancer cells. A cell viability assay revealed that DOX- loaded liposomes composed of pure GcGT(S-S)PC-CH lipids were ∼20 times more toxic than DOXIL, with an IC50 value comparable to that of free DOX. The low inherent membrane-leakage properties of GcGT(S-S)PC-CH liposomes in the presence of serum, combined with an intracellular triggered release of encapsulated cargo, represents a promising approach for developing improved drug-delivery formulations for the treatment of cancer and possibly other diseases.

Hybrid Lipids Inspired by Extremophiles and Eukaryotes Afford Serum-Stable Membranes with Low Leakage.

This paper presents a new hybrid lipid that fuses the ideas of molecular tethering of lipid tails used by archaea and the integration of cholesterol groups used by eukaryotes, thereby leveraging two strategies employed by nature to increase lipid packing in membranes. Liposomes comprised of pure hybrid lipids exhibited a 5-30-fold decrease in membrane leakage of small ions and molecules compared to liposomes that used only one strategy (lipid tethering or cholesterol incorporation) to increase membrane integrity. Molecular dynamics simulations reveal that tethering of lipid tails and integration of cholesterol both reduce the disorder in lipid tails and time-dependent variance in area per lipid within a membrane, leading to tighter lipid packing. These hybrid lipid membranes have exceptional stability in serum, yet can support functional ion channels, can serve as a substrate for phospholipase enzymes, and can be used for liposomal delivery of molecules into living cells.

Evaluation of tetraether lipid-based liposomal carriers for encapsulation and retention of nucleoside-based drugs.

Although liposomal nanoparticles are one of the most versatile class of drug delivery systems, stable liposomal formulation of small neutral drug molecules still constitutes a challenge due to the low drug retention of current lipid membrane technologies. In this study, we evaluate the encapsulation and retention of seven nucleoside analog-based drugs in liposomes made of archaea-inspired tetraether lipids, which are known to enhance packing and membrane robustness compared to conventional bilayer-forming lipids. Liposomes comprised of the pure tetraether lipid generally showed improved retention of drugs (up to 4-fold) compared with liposomes made from a commercially available diacyl lipid. Interestingly, we did not find a significant correlation between the liposomal leakage rates of the molecules with typical parameters used to assess lipophilicity of drugs (such logD or topological polar surface area), suggesting that specific structural elements of the drug molecules can have a dominant effect on leakage from liposomes over general lipophilic character.

Characterization of drug encapsulation and retention in archaea-inspired tetraether liposomes.

The passive leakage of small molecules across membranes is a major limitation of liposomal drug formulations. Here, we evaluate the leakage of 3 clinically used chemotherapeutic agents (cytarabine, methotrexate and vincristine) encapsulated in liposomes comprised of a synthetic, archaea-inspired, membrane-spanning tetraether lipid. Liposomes comprised of the pure tetraether lipid exhibited superior retention of both a neutrally and positively charged drug (up to an ∼9-fold decrease in the rate of drug leakage) compared to liposomes formed from a commercial diacyl lipid, while exhibiting a similar retention of a negatively charged drug that did not appreciably leak from either type of liposome. We also demonstrate that liposomes made of the archaea-inspired lipid can be used for the delivery of encapsulated small molecules into living cells.

Effects of Lipid Tethering in Extremophile-Inspired Membranes on H(+)/OH(-) Flux at Room Temperature.

This work explores the proton/hydroxide permeability (PH+/OH-) of membranes that were made of synthetic extremophile-inspired phospholipids with systematically varied structural elements. A fluorescence-based permeability assay was optimized to determine the effects on the PH+/OH- through liposome membranes with variations in the following lipid attributes: transmembrane tethering, tether length, and the presence of isoprenoid methyl groups on one or both lipid tails. All permeability assays were performed in the presence of a low concentration of valinomycin (10 nM) to prevent buildup of a membrane potential without artificially increasing the measured PH+/OH-. Surprisingly, the presence of a transmembrane tether did not impact PH+/OH- at room temperature. Among tethered lipid monolayers, PH+/OH- increased with increasing tether length if the number of carbons in the untethered acyl tail was constant. Untethered lipids with two isoprenoid methyl tails led to lower PH+/OH- values than lipids with only one or no isoprenoid tails. Molecular dynamics simulations revealed a strong positive correlation between the probability of observing water molecules in the hydrophobic core of these lipid membranes and their proton permeability. We propose that water penetration as revealed by molecular dynamics may provide a general strategy for predicting proton permeability through various lipid membranes without the need for experimentation.

Effect of Headgroups on Small-Ion Permeability across Archaea-Inspired Tetraether Lipid Membranes.

This paper examines the effects of four different polar headgroups on small-ion membrane permeability from liposomes comprised of Archaea-inspired glycerolmonoalkyl glycerol tetraether (GMGT) lipids. We found that the membrane-leakage rate across GMGT lipid membranes varied by a factor of ≤1.6 as a function of headgroup structure. However, the leakage rates of small ions across membranes comprised of commercial bilayer-forming 1-palmitoyl-2-oleoyl-sn-glycerol (PO) lipids varied by as much as 32-fold within the same series of headgroups. These results demonstrate that membrane leakage from GMGT lipids is less influenced by headgroup structure, making it possible to tailor the structure of the polar headgroups on GMGT lipids while retaining predictable leakage properties of membranes comprised of these tethered lipids.

Cyclohexane Rings Reduce Membrane Permeability to Small Ions in Archaea-Inspired Tetraether Lipids.

Extremophile archaeal organisms overcome problems of membrane permeability by producing lipids with structural elements that putatively improve membrane integrity compared to lipids from other life forms. Herein, we describe a series of lipids that mimic some key structural features of archaeal lipids, such as: 1) single tethering of lipid tails to create fully transmembrane tetraether lipids and 2) the incorporation of small rings into these tethered segments. We found that membranes formed from pure tetraether lipids leaked small ions at a rate that was about two orders of magnitude slower than common bilayer-forming lipids. Incorporation of cyclopentane rings into the tetraether lipids did not affect membrane leakage, whereas a cyclohexane ring reduced leakage by an additional 40 %. These results show that mimicking certain structural features of natural archaeal lipids results in improved membrane integrity, which may help overcome limitations of many current lipid-based technologies.

(6R)-2-tert-Butyl-6-[(4R,5S)-3-isopropyl-4-methyl-5-phenyl-oxazolidin-2-yl]phenol.

In the title compound, C(23)H(31)NO(2), the lone pair on the nitro-gen atom is oriented to facilitate intra-molecular hydrogen bonding with the hydr-oxy group residing on the phenyl substituent. The five-membered ring adopts an envelope confornmation with the O atom at the flap. The absolute stereochemistry was verified by measurement of optical activity using a digital polarimeter.

Fusion of Bipolar Tetraether Lipid Membranes Without Enhanced Leakage of Small Molecules.

A major challenge in liposomal research is to minimize the leakage of encapsulated cargo from either uncontrolled passive permeability across the liposomal membrane or upon fusion with other membranes. We previously showed that liposomes made from pure Archaea-inspired bipolar tetraether lipids exhibit exceptionally low permeability of encapsulated small molecules due to their capability to form more tightly packed membranes compared to typical monopolar lipids. Here, we demonstrate that liposomes made of synthetic bipolar tetraether lipids can also undergo membrane fusion, which is commonly accompanied by content leakage of liposomes when using typical bilayer-forming lipids. Importantly, we demonstrate calcium-mediated fusion events between liposome made of glycerolmonoalkyl glycerol tetraether lipids with phosphatidic acid headgroups (GMGTPA) occur without liposome content release, which contrasts with liposomes made of bilayer-forming EggPA lipids that displayed ~80% of content release under the same fusogenic conditions. NMR spectroscopy studies of a deuterated analog of GMGTPA lipids reveal the presence of multiple rigid and dynamic conformations, which provide evidence for the possibility of these lipids to form intermediate states typically associated with membrane fusion events. The results support that biomimetic GMGT lipids possess several attractive properties (e.g., low permeability and non-leaky fusion capability) for further development in liposome-based technologies.

One-Pot Electrochemical Nickel-Catalyzed Decarboxylative Sp2-Sp3 Cross-Coupling.

A one-pot electrochemical nickel-catalyzed decarboxylative sp2-sp3 cross-coupling reaction has been developed using redox-active esters prepared in situ from alkyl carboxylates and  N-hydroxyphthalimide tetramethyluronium hexafluorophosphate (PITU). This undivided cell one-pot method enables C-C bond formation using inexpensive, benchtop-stable reagents with isolated yields up to 95% with good functional group tolerance, which includes nitrile, ketone, ester, alkene and selectivity over other aromatic halogens.

Entropic effects enable life at extreme temperatures.

Maintaining membrane integrity is a challenge at extreme temperatures. Biochemical synthesis of membrane-spanning lipids is one adaptation that organisms such as thermophilic archaea have evolved to meet this challenge and preserve vital cellular function at high temperatures. The molecular-level details of how these tethered lipids affect membrane dynamics and function, however, remain unclear. Using synthetic monolayer-forming lipids with transmembrane tethers, here, we reveal that lipid tethering makes membrane permeation an entropically controlled process that helps to limit membrane leakage at elevated temperatures relative to bilayer-forming lipid membranes. All-atom molecular dynamics simulations support a view that permeation through membranes made of tethered lipids reduces the torsional entropy of the lipids and leads to tighter lipid packing, providing a molecular interpretation for the increased transition-state entropy of leakage.