3-Hydroxybenzene 1,2,4-Trisphosphate, a Novel Second Messenger Mimic and unusual Substrate for Type-I myo-Inositol 1,4,5-Trisphosphate 5-Phosphatase: Synthesis and Physicochemistry

Regioisomeric Family of Novel Fluorescent Substrates for SHIP2

SHIP2 (SH2-domain containing inositol 5-phosphatase type 2) is a canonical 5-phosphatase, which, through its catalytic action on PtdInsP₃, regulates the PI3K/Akt pathway and metabolic action of insulin. It is a drug target, but there is limited evidence of inhibition of SHIP2 by small molecules in the literature. With the goal to investigate inhibition, we report a homologous family of synthetic, chromophoric benzene phosphate substrates of SHIP2 that display the headgroup regiochemical hallmarks of the physiological inositide substrates that have proved difficult to crystallize with 5-phosphatases. Using time-dependent density functional theory (TD-DFT), we explore the intrinsic fluorescence of these novel substrates and show how fluorescence can be used to assay enzyme activity. The TD-DFT approach promises to inform rational design of enhanced active site probes for the broadest family of inositide-binding/metabolizing proteins, while maintaining the regiochemical properties of bona fide inositide substrates.

Advances in microspeciation of drugs and biomolecules: Species-specific concentrations, acid-base properties and related parameters

The pharmacokinetic and pharmacodynamic behaviour of drugs and the interacting biomolecules are highly influenced by their species-specific physico-chemical properties. The first of such bio-relevant, structure-dependent properties were the species-specific acid-base constants and the co-dependent concentrations, but the past decade brought significant advances to previously uncharted territories, including the experimental determination of species-specific partition coefficients, solubilities and redox equilibrium constants. This review gives an overview of the types and definitions of species-specific physico-chemical and analytical properties. We survey the pertinent literature, the fundamental relationships, and summarize some of our recent work that enabled the determination of species-specific partition coefficients for coexisting, inseparable protonation isomers and pH-independent, microscopic redox equilibrium constants. The thorough insight provided by these species-specific properties improves our understanding of the submolecular mechanism of pharmacokinetic processes. As a result, there are some pieces of clear-cut evidence of practical significance. A few of them are as follows: - passive diffusion into lipophilic media is not necessarily predominated by the non-charged species, contrary to the widespread misbelief. - the reactive microspecies in structure-controlled, highly specific biochemical reactions is not necessarily the major one. - a preventive defence system against oxidative stress can be based upon thiol-disulfide equilibria of custom-tailored redox potentials.

Scavenger receptor-recognized and enzyme-responsive nanoprobe for fluorescent labeling of lysosomes in live cells

Lysosomal imaging represents a potent tool for investigating the organization of related cellular events and their modulation via diagnostic and therapeutic approaches. However, specific labeling of the lysosome in live cells is a significant challenge. Taking advantage of the inherent lysosomal entry of nanoparticles and unique digestive inclusions in the lysosome, we developed a nanoparticle-based, enzyme-switchable fluorescence OFF-ON strategy for specific labeling of the lysosome and further imaging of extracellular acidification-induced lysosome trafficking in living cells. The nanoprobe comprised a 16 nm spherical gold nanoparticle as the core and an enzyme-responsive oligomer of fluorescein-conjugated oligo(4-vinyl-phenyl phosphate) as the shell. Due to quenching of the core gold nanoparticle, the nanoprobe was non-fluorescent. After incubation with cancer cells, the nanoprobe was rapidly internalized via scavenger receptor-mediated endocytosis and significantly shuffled into the lysosome. The nanoprobe specifically lighted up the lysosome owing to lysosome-induced fluorescence enhancement. Specifically, digestive inclusions in the lysosome hydrolyzed and released gold-quenched fluorescein molecules, leading to significant augmentation of fluorescence. On account of specific lysosomal labeling, the nanoprobe effectively facilitated imaging of a 4-6 μm anterograde trafficking event of the lysosome from the perinuclear region to the cell surface when an acidic extracellular environment developed. Our findings collectively highlight the use of nanoprobes for lysosomal imaging.

Atherton-Todd reaction: mechanism, scope and applications

Initially, the Atherton–Todd (AT) reaction was applied for the synthesis of phosphoramidates by reacting dialkyl phosphite with a primary amine in the presence of carbon tetrachloride. These reaction conditions were subsequently modified with the aim to optimize them and the reaction was extended to different nucleophiles. The mechanism of this reaction led to controversial reports over the past years and is adequately discussed. We also present the scope of the AT reaction. Finally, we investigate the AT reaction by means of exemplary applications, which mainly concern three topics. First, we discuss the activation of a phenol group as a phosphate which allows for subsequent transformations such as cross coupling and reduction. Next, we examine the AT reaction applied to produce fire retardant compounds. In the last section, we investigate the use of the AT reaction for the production of compounds employed for biological applications. The selected examples to illustrate the applications of the Atherton–Todd reaction mainly cover the past 15 years.

Evolution of an oxidative dearomatization enabled total synthesis of vinigrol

The evolution of the synthetic strategy resulting in a total synthesis of vinigrol is presented. Oxidative dearomatization/intramolecular Diels-Alder cycloaddition has served as the successful cornerstone for all of the approaches. Extensive radical cyclization efforts to form the tetracyclic core resulted in interesting and surprising reaction outcomes, none of which could be advanced to vinigrol. These cyclization obstacles were successfully overcome by using Heck instead of radical cyclizations. The total synthesis features a trifluoroethyl ether protecting group being used for the first time in organic synthesis. The logic of its selection and the group's importance beyond protecting the C8a hydroxyl group is presented along with a discussion of strategies for its removal. Because of the compact tetracyclic cage the route is built around many unusual reaction observations and solutions have emerged. For example, a first of its kind Grob fragmentation reaction featuring a trifluoroethyl leaving group has been uncovered, interesting interrupted selenium dioxide allylic oxidations have been observed as well as intriguing catalyst and counterion dependent directed hydrogenations.

Multivalent benzene polyphosphate derivatives are non-Ca2+-mobilizing Ins(1,4,5)P3 receptor antagonists

Inositol 1,4,5-trisphosphate [Ins(1,4,5)P31] mobilizes intracellular Ca2+ through the Ins(1,4,5)P3 receptor [InsP3R]. Although some progress has been made in the design of synthetic InsP3R partial agonists and antagonists, there are still few examples of useful small molecule competitive antagonists. A "multivalent" approach is explored and new dimeric polyphosphorylated aromatic derivatives were designed, synthesized and biologically evaluated. The established weak InsP3R ligand benzene 1,2,4-trisphosphate [Bz(1,2,4)P32] is dimerized through its 5-position in two different ways, first directly as the biphenyl derivative biphenyl 2,2',4,4',5,5'-hexakisphosphate, [BiPh(2,2',4,4',5,5')P68] and with its regioisomeric biphenyl 3,3',4,4',5,5'-hexakisphosphate [BiPh(3,3',4,4',5,5')P611]. Secondly, a linker motif is introduced in a flexible ethylene-bridged dimer (9) with its corresponding 1,2-bisphosphate dimer (10), both loosely analogous to the very weak antagonist 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA 7). In permeabilized L15 fibroblasts overexpressing type 1 InsP3R, BiPh(2,2',4,4',5,5')P6 (8) inhibits Ins(1,4,5)P3-induced Ca2+ release in a apparently competitive fashion [IC50 187 nM] and the Bz(1,2,4)P3 dimer (9) is only slightly weaker [IC50 380 nM]. Compounds were also evaluated against type I Ins(1,4,5)P3 5-phosphatase. All compounds are resistant to dephosphorylation, with BiPh(2,2',4,4',5,5')P6 (8), being the most effective inhibitor of any biphenyl derivative synthesized to date [IC50 480 nM] and the Bz(1,2,4)P3 ethylene dimer (9) weaker [IC50 3.55 μM]. BiPh(3,3',4,4',5,5')P6 (11) also inhibits 5-phosphatase [IC50 730 nM] and exhibits unexpected Ca2+ releasing activity [EC50 800 nM]. Thus, relocation of only a single mirrored phenyl phosphate group in (11) from that of antagonist (8) does not markedly change enzyme inhibitory activity, but elicits a dramatic switch in Ca2+-releasing activity. Such new agents demonstrate the power of the multivalent approach and may be useful to investigate the chemical biology of signaling through InsP3R and as templates for further design.

Benzene polyphosphates as tools for cell signalling: inhibition of inositol 1,4,5-trisphosphate 5-phosphatase and interaction with the PH domain of protein kinase Balpha

Novel benzene polyphosphates were synthesised as inositol polyphosphate mimics and evaluated against type-I inositol 1,4,5-trisphosphate 5-phosphatase, which only binds soluble inositol polyphosphates, and against the PH domain of protein kinase Balpha (PKBalpha), which can bind both soluble inositol polyphosphates and inositol phospholipids. The most potent trisphosphate 5-phosphatase inhibitor is benzene 1,2,4-trisphosphate (2, IC(50) of 14 microM), a potential mimic of D-myo-inositol 1,4,5-trisphosphate, whereas the most potent tetrakisphosphate Ins(1,4,5)P(3) 5-phosphatase inhibitor is benzene 1,2,4,5-tetrakisphosphate, with an IC(50) of 4 microM. Biphenyl 2,3',4,5',6-pentakisphosphate (4) was the most potent inhibitor evaluated against type I Ins(1,4,5)P(3) 5-phosphatase (IC(50) of 1 microM). All new benzene polyphosphates are resistant to dephosphorylation by type I Ins(1,4,5)P(3) 5-phosphatase. Unexpectedly, all benzene polyphosphates studied bind to the PH domain of PKBalpha with apparent higher affinity than to type I Ins(1,4,5)P(3) 5-phosphatase. The most potent ligand for the PKBalpha PH domain, measured by inhibition of biotinylated diC(8)-PtdIns(3,4)P(2) binding, is biphenyl 2,3',4,5',6-pentakisphosphate (4, K(i)=27 nm). The approximately 80-fold enhancement of binding relative to parent benzene trisphosphate is explained by the involvement of a cation-pi interaction. These new molecular tools will be of potential use in structural and cell signalling studies.

Biphenyl 2,3′,4,5′,6‐pentakisphosphate, a novel inositol polyphosphate surrogate, modulates Ca2+responses in rat hepatocytes

Benzene polyphosphates containing phosphate groups on one ring are Ins(1,4,5)P3 5-phosphatase inhibitors when evaluated against type-I Ins(1,4,5)P3 5-phosphatase. A novel biphenyl derivative, biphenyl 2,3',4,5',6-pentakisphosphate, with five phosphate groups on two rings was synthesized: It inhibited the activity of two inositol 5-phosphatases: type I and SHIP2 with Ins(1,3,4,5)P4 as substrate. The inhibition was competitive with respect to the substrate. IC50 value measured in rat hepatocytes, which contains the native Ins(1,4,5)P3 5-phosphatase, was in the micromolar range at 1.0 microM Ins(1,4,5)P3 as substrate. Biphenyl 2,3',4,5',6-pentakisphosphate did not affect the activity of Ins(1,4,5)P3 3-kinase A in the 5-100 microM range. Surprisingly, experimental evidence supports an effect of biphenyl 2,3',4,5',6-pentakisphosphate at the level of the Ins(1,4,5)P3 receptor. Finally, when injected into rat hepatocytes, the analog affected the frequency of Ca2+ oscillations in a positive or negative way depending on its concentration. At very high concentrations of the analog, Ca2+ oscillations were even suppressed. These data were interpreted as a dual effect of the biphenyl 2,3',4,5',6-pentakisphosphate on cytosolic [Ca2+] increases: an activation effect through an increase in Ins(1,4,5)P3 level via Ins(1,4,5)P3 5-phosphatase inhibition and an inhibitory effect, which was exerted directly on the Ins(1,4,5)P3 receptor. Thus, our data show for the first time that the frequency of Ca2+ oscillations in response to a Ca2+-mobilizing agonist can be controlled by inhibitors of type-I Ins(1,4,5)P3 5-phosphatase.