Synthesis and biological activity of phospholipase C-resistant analogues of phosphatidylinositol 4,5-bisphosphate

Silver-Catalyzed (Z)-β-Fluoro-vinyl Iodonium Salts from Alkynes: Efficient and Selective Syntheses of Z-Monofluoroalkenes

Monofluoroalkenes are stable and lipophilic amide bioisosteres used in medicinal chemistry. However, efficient and stereoselective methods for synthesizing Z-monofluoroalkenes are underdeveloped. We envisage (Z)-β-fluoro-vinyl iodonium salts (Z-FVIs) as coupling partners for the diverse and stereoselective synthesis of Z-monofluoroalkenes. Disclosed herein is the development and application of a silver(I)-catalyzed process for accessing a broad scope of (Z)-FVIs with exclusive Z-stereoselectivity and regioselectivity from alkynes in a single step. Experimental and computational studies provide insight into the mechanism of the catalytic cycle and the role of the silver(I) catalyst, and the reactivity of (Z)-FVIs is explored through several stereospecific derivatizations.

Combining Hydrodefluorination and Defluorophosphorylation for Chemo- and Stereoselective Synthesis of gem-Fluorophosphine Alkenes

A chemo-, regio-, and stereoselective reaction of trifluoromethyl enones, phenylsilane, and phosphine oxides through a sequential hydrodefluorination and defluorophosphorylation relay is developed for the synthesis of distinctive gem-fluorophosphine alkenes. This multicomponent reaction occurred under transition-metal-free conditions with good functional group tolerance. Moreover, the preinstalled carbonyl auxiliary is important for tuning the reactivity of β-trifluoromethyl enones, thereby enabling controllable and selective functionalization of two fluorine atoms in trifluoromethylated enones.

gem-Heteroatom-Substituted Fluoroalkenes as Mimics of Amide Derivatives or Phosphates: A Comprehensive Review

gem-Heteroatom-substituted fluoroalkenes have received little attention despite their great potential in medicinal chemistry or in fine chemistry. Indeed, due to the electronic and steric similarity between the fluoroalkene moiety and the amide bond as well as the high strength of the carbon-fluorine bond, these gem-heteroatom-substituted fluoroalkenes could be envisioned as stable mimics of various important organic functions, such as phosphates, carbamates, S-thiocarbamates and ureas. We present herein an overview describing the syntheses over the last decade of heteroatom-substituted fluoroalkenes in geminal position. This review will be divided into several sections covering each the common following heteroatom: oxygen-, nitrogen-, sulfur-, phosphorus-, boron- and silicon-substituted fluoroalkenes.

Rapid Entry into Biologically Relevant α,α-Difluoroalkylphosphonates Bearing Allyl Protection-Deblocking under Ru(II)/(IV)-Catalysis

A convenient synthetic route to α,α-difluoroalkylphosphonates is described. Structurally diverse aldehydes are condensed with LiF2CP(O)(OCH2CH═CH2)2. The resultant alcohols are captured as the pentafluorophenyl thionocarbonates and efficiently deoxygenated with HSnBu3, BEt3, and O2, and then smoothly deblocked with CpRu(IV)(π-allyl)quinoline-2-carboxylate (1-2 mol %) in methanol as an allyl cation scavenger. These mild deprotection conditions provide access to free α,α-difluoroalkylphosphonates in nearly quantitative yield. This methodology is used to rapidly construct new bis-α,α-difluoroalkyl phosphonate inhibitors of PTPIB (protein phosphotyrosine phosphatase-1B).

Acute manipulation of phosphoinositide levels in cells

Phosphoinositides are membrane-bound signaling phospholipids that function in a myriad of cellular processes, including membrane trafficking, cytoskeletal dynamics, ion channel and transporter function, and signal transduction. In order to better understand the role of phosphoinositides in cellular processes, different approaches to study the effects of the presence or absence of these lipids must be devised. Conventional approaches of manipulating phosphoinositide levels such as over-expression or genetic ablation of lipid enzymes cause prolonged exposure of the cells to changes in lipid levels that could result in compensatory actions by the cell or downstream alterations in cell physiology. In this chapter we present an approach used recently by various laboratories, including our own, to acutely manipulate phosphoinositide levels at target locations using chemically induced dimerization (CID) that can be spatially and temporally controlled. We discuss considerations when designing expression constructs for targeting specific cellular compartment membranes and present examples from the literature on different ways of perturbing phosphoinositide levels at particular organelle membranes using CID. In addition, we provide details on image acquisition, data collection, and data interpretation. CID technology can be applied to many lipid enzymes to broaden the understanding of the role lipid signaling plays in cell physiology.

5-Stabilized phosphatidylinositol 3,4,5-trisphosphate analogues bind Grp1 PH, inhibit phosphoinositide phosphatases, and block neutrophil migration

Metabolically stabilized analogues of PtdIns(3,4,5)P3 have shown long-lived agonist activity for cellular events and selective inhibition of lipid phosphatase activity. We describe an efficient asymmetric synthesis of two 5-phosphatase-resistant analogues of PtdIns(3,4,5)P3, the 5-methylene phosphonate (MP) and 5-phosphorothioate (PT). Furthermore, we illustrate the biochemical and biological activities of five stabilized PtdIns(3,4,5)P3 analogues in four contexts. First, the relative binding affinities of the 3-MP, 3-PT, 5-MP, 5-PT, and 3,4,5-PT3 analogues to the Grp1 PH domain are shown, as determined by NMR spectroscopy. Second, the enzymology of the five analogues is explored, showing the relative efficiency of inhibition of SHIP1, SHIP2, and phosphatase and tensin homologue deleted on chromosome 10 (PTEN), as well as the greatly reduced ability of these phosphatases to process these analogues as substrates as compared to PtdIns(3,4,5)P3. Third, exogenously delivered analogues severely impair complement factor C5a-mediated polarization and migration of murine neutrophils. Finally, the new analogues show long-lived agonist activity in mimicking insulin action in sodium transport in A6 cells.

Synthesis and biological evaluation of phosphatidylinositol phosphate affinity probes

The synthesis of the complete family of phosphatidylinositol phosphate analogues (PIPs) from five key core intermediates A-E is described. These core compounds were obtained from myo-inositol orthoformate 1 via regioselective DIBAL-H and trimethylaluminium-mediated cleavages and a resolution-protection process using camphor acetals 10. Coupling of cores A-E with phosphoramidites 34 and 38, derived from the requisite protected lipid side chains, afforded the fully-protected PIPs. Removal of the remaining protecting groups was achieved via hydrogenolysis using palladium black or palladium hydroxide on carbon in the presence of sodium bicarbonate to afford the complete family of dipalmitoyl- and amino-PIP analogues 42, 45, 50, 51, 58, 59, 67, 68, 76, 77, 82, 83, 92, 93, 99 and 100. Investigations using affinity probes incorporating these compounds have identified novel proteins involved in the PI3K intracellular signalling network and have allowed a comprehensive proteomic analysis of phosphoinositide interacting proteins.

Phosphatidylinositol 4,5-bisphosphate regulates inspiratory burst activity in the neonatal mouse preBötzinger complex

Neurons of the preBötzinger complex (preBötC) form local excitatory networks and synchronously discharge bursts of action potentials during the inspiratory phase of respiratory network activity. Synaptic input periodically evokes a Ca(2+)-activated non-specific cation current (I(CAN)) postsynaptically to generate 10-30 mV transient depolarizations, dubbed inspiratory drive potentials, which underlie inspiratory bursts. The molecular identity of I(CAN) and its regulation by intracellular signalling mechanisms during inspiratory drive potential generation remains unknown. Here we show that mRNAs coding for two members of the transient receptor potential (TRP) family of ion channels, namely TRPM4 and TRPM5, are expressed within the preBötC region of neonatal mice. Hypothesizing that the phosphoinositides maintaining TRPM4 and TRPM5 channel sensitivity to Ca(2+) may similarly influence I(CAN) and thus regulate inspiratory drive potentials, we manipulated intracellular phosphatidylinositol 4,5-bisphosphate (PIP(2)) and measured its effect on preBötC neurons in the context of ongoing respiratory-related rhythms in slice preparations. Consistent with the involvement of TRPM4 and TRPM5, excess PIP(2) augmented the inspiratory drive potential and diminution of PIP(2) reduced it; sensitivity to flufenamic acid (FFA) suggested that these effects of PIP(2) were I(CAN) mediated. Inositol 1,4,5-trisphosphate (IP(3)), the product of PIP(2) hydrolysis, ordinarily causes IP(3) receptor-mediated I(CAN) activation. Simultaneously increasing PIP(2) while blocking IP(3) receptors intracellularly counteracted the reduction in the inspiratory drive potential that normally resulted from IP(3) receptor blockade. We propose that PIP(2) protects I(CAN) from rundown by interacting directly with underlying ion channels and preventing desensitization, which may enhance the robustness of respiratory rhythm.

Regulation of transient receptor potential (TRP) channels by phosphoinositides

This review summarizes the modulation of transient receptor potential (TRP) channels, by phosphoinositides. TRP channels are characterized by polymodal activation and a surprising complexity of regulation mechanisms. Possibly, most if not all TRP channels are modulated by phosphoinositides. Modulation by phosphatidylinositol 4,5-biphosphate (PIP(2)) has been shown in detail for TRP vanilloid (TRPV) 1, TRPV5, TRP melastatin (TRPM) 4, TRPM5, TRPM7, TRPM8, TRP polycystin 2, and the Drosophila TPR-like (TRPL) channels. This review describes mechanisms of modulation of TRP channels mainly by PIP(2) and discusses some future challenges of this fascinating topic.

Stabilized phosphatidylinositol-5-phosphate analogues as ligands for the nuclear protein ING2: chemistry, biology, and molecular modeling

The interaction of PtdIns(5)P with the tumor suppressor protein ING2 has been implicated in the regulation of chromatin modification. To enhance the stability of PtdIns(5)P for studies of the biological role in vivo, two phosphatase-resistant moieties were used to replace the labile 5-phosphate. The total asymmetric synthesis of the 5-methylenephosphonate (MP) and 5-phosphothionate (PT) analogues of PtdIns(5)P is described herein, and the resulting metabolically stabilized lipid analogues were evaluated in three ways. First, liposomes containing either the dioleoyl MP or PT analogues bound to recombinant ING2 similar to liposomes containing dipalmitoyl PtdIns(5)P, indicating that the replacement of the hydrolyzable 5-phosphate group does not compromise the binding. Second, the dioleoyl MP and PT PtdIns(5)P analogues were equivalent to dipalmitoyl PtdIns(5)P in augmenting cell death induced by a DNA double-strand break in HT1080 cells. Finally, molecular modeling and docking of the MP or PT analogues to the C-terminus PtdInsP-binding region of ING2 (consisting of a PHD finger and a polybasic region) revealed a number of complementary surface and electrostatic contacts between the lipids and ING2.

Visualization and manipulation of phosphoinositide dynamics in live cells using engineered protein domains

There is hardly a membrane-associated molecular event that is not regulated by phosphoinositides, a minor but critically important class of phospholipids of cellular membranes. The rapid formation, elimination, and conversion of these lipids in specific membrane compartments are ensured by a wealthy number of inositol lipid kinases and phosphatases with unique localization and regulatory properties. The existence of multiple inositol lipid pools have been indicated by metabolic labeling studies, but the level of functional compartmentalization revealed by the identification of numerous protein effectors acted upon by phosphoinositides could not have been foreseen. The changing perception of inositides from just serving as lipid precursors of second messengers to becoming highly dynamic local membrane-bound regulators poses new challenges concerning the detection of their rapid localized changes. Moreover, it is increasingly evident that manipulation of lipids in highly defined compartments would be a highly superior approach to soaking the cells with a particular phosphoinositide when studying the local regulation of the lipid on any effectors. In this review, we will summarize our efforts to improve our tools in studying phosphoinositide dynamics and discuss our views on the values of these methods compared to other options currently used or being explored.