Structural Impact of Chelation on Phytate, a Highly Phosphorylated Biomolecule

Structural Insight on Supramolecular Polyion Salts: Inositol Hexaphosphate Enclosed in Cationic Macrocyclic Clusters

Supramolecular macrocyclic forces have been used to trap phytate, myo-inositol-1,2,3,4,5,6-hexakisphosphate, a key bioanion with multiple roles in metabolic processes. Due to the complex chemistry of six multivalent phosphates surrounding the small, cyclic inositol framework, crystallographic information of simple phytate salts has been elusive. This report represents a combined crystallographic, theoretical, and solution binding investigation of a supramolecular macrocyclic complex of phytate. Together, the results provide significant insight to phytate's intramolecular and intermolecular interactions at the microenvironment level. The macrocycle-phytate aggregates consist of phytate anionic pairs, each partly sandwiched by two 24-membered, amide/amine-based cationic macrocycles. The phytate ion pairs hold the tetrameric macrocyclic array together by six strong intermolecular hydrogen bonds. Both phytates crystallize in 1a5e phosphate conformations (one axial (P2) and five equatorial phosphates). Solution NMR binding studies in 1 : 1 DMSO-d6  : D2 O indicate 2 : 1 macrocycle:phytate associations, suggesting that the sandwich-like nature of the complex holds together in solution. DFT studies indicate the likely occurrence of dynamic intramolecular interchange of phosphate protons, as well as important roles for the axial (P2) phosphate in both intramolecular and intermolecular hydrogen bonding interactions.

Expedient synthesis and luminescence sensing of the inositol pyrophosphate cellular messenger 5-PP-InsP5

Inositol pyrophosphates are important biomolecules associated with apoptosis, cell growth and kinase regulation, yet their exact biological roles are still emerging and probes do not exist for their selective detection. We report the first molecular probe for the selective and sensitive detection of the most abundant cellular inositol pyrophosphate 5-PP-InsP5, as well as an efficient new synthesis. The probe is based on a macrocyclic Eu(iii) complex bearing two quinoline arms providing a free coordination site at the Eu(iii) metal centre. Bidentate binding of the pyrophosphate group of 5-PP-InsP5 to the Eu(iii) ion is proposed, supported by DFT calculations, giving rise to a selective enhancement in Eu(iii) emission intensity and lifetime. We demonstrate the use of time-resolved luminescence as a bioassay tool for monitoring enzymatic processes in which 5-PP-InsP5 is consumed. Our probe offers a potential screening methodology to identify drug-like compounds that modulate the activity of enzymes of inositol pyrophosphate metabolism.

Oligomeric phosphate clusters in macrocyclic channels

Thirty-six-membered ring macrocycles form sandwich-like channels for oligomeric chains of hexaphosphate clusters.

Role of metal complexation on the solubility and enzymatic hydrolysis of phytate

Phytate is a dominant form of organic phosphorus (P) in the environment. Complexation and precipitation with polyvalent metal ions can stabilize phytate, thereby significantly hinder the hydrolysis by enzymes. Here, we studied the stability and hydrolyzability of environmentally relevant metal phytate complexes (Na, Ca, Mg, Cu, Zn, Al, Fe, Al/Fe, Mn, and Cd) under different pHs, presence of metal chelators, and thermal conditions. Our results show that the order of solubility of metal phytate complexes is as follows: i) for metal species: Na, Ca, Mg > Cu, Zn, Mn, Cd > Al, Fe, ii) under different pHs: pH 5.0 > pH 7.5), and iii) in the presence of chelators: EDTA> citric acid. Phytate-metal complexes are mostly resistant towards acid hydrolysis (except Al-phytate), and dry complexes are generally stable at high pressure and temperature under autoclave conditions (except Ca phytate). Inhibition of metal complex towards enzymatic hydrolysis by Aspergillus niger phytase was variable but found to be highest in Fe phytate complex. Strong chelating agents such as EDTA are insufficient for releasing metals from the complexes unless the reduction of metals (such as Fe) occurs first. The insights gained from this research are expected to contribute to the current understanding of the fate of phytate in the presence of various metals that are commonly present in agricultural soils.

A Hydroxypyrrole Approach to 2,2'-Bi(4-pyrrolin-3-ones) and Pyrrolone-Based α-Amino Esters

A high yield synthesis of 2-amino-4-pyrrolin-3-ones including 4-pyrrolin-3-one-based amino esters by the NBS- or TfCl-mediated reaction of 3-hydroxypyrroles with amines has been developed. The reaction of 3-hydroxypyrroles with triflyl chloride in the absence of amine affords 2,2'-bi(4-pyrrolin-3-ones) in excellent yields and diastereoselectivity. The relative configuration of stereocenters in these compounds can be changed from (2RS,2'RS) to (2RS,2'SR) by the action of NaH in THF, while the reverse stereoisomerization occurs in the presence of 2,5-lutidine in MeCN. Bi(4-pyrrolin-3-ones) also can be converted to 2-amino-4-pyrrolin-3-ones in excellent yields. Bi(4-pyrrolin-3-ones) and 2-amino-4-pyrrolin-3-ones were evaluated for their antiproliferative activity toward four human tumor cell lines.

Chain Entropy Beats Hydrogen Bonds to Unfold and Thread Dialcohol Phosphates inside Cyanostar Macrocycles To Form [3]Pseudorotaxanes

The recognition of substituted phosphates underpins many processes including DNA binding, enantioselective catalysis, and recently template-directed rotaxane synthesis. Beyond ATP and a few commercial substrates, however, little is known about how substituents effect organophosphate recognition. Here, we examined alcohol substituents and their impact on recognition by cyanostar macrocycles. The organophosphates were disubstituted by alcohols of various chain lengths, dipropanol, dihexanol, and didecanol phosphate, each accessed using modular solid-phases syntheses. Based on the known size-selective binding of phosphates by π-stacked dimers of cyanostars, threaded [3]pseudorotaxanes were anticipated. While seen with butyl substituents, pseudorotaxane formation was disrupted by competitive OH···O- hydrogen bonding between both terminal hydroxyls and the anionic phosphate unit. Crystallography also showed formation of a backfolded propanol conformation resulting in an 8-membered ring and a perched cyanostar assembly. Motivated by established entropic penalties accompanying ring formation, we reinstated [3]pseudorotaxanes by extending the size of the substituent to hexanol and decanol. Chain entropy overcomes the enthalpically favored OH···O- contacts to favor random-coil conformations required for seamless, high-fidelity threading of dihexanol and didecanol phosphates inside cyanostars. These studies highlight how chain length and functional groups on phosphate's substituents can be powerful design tools to regulate binding and control assembly formation during phosphate recognition.

Snapshots of "crystalline" salt-water solutions of inositol hexaphosphate conformers

Supramolecular insight to intra- and inter-ionic interactions in two inositol hexaphosphate conformers as a function of pH was enabled by NMR and crystallographic studies. These findings also shed light on the complex interactive roles of extended salt-water arrays through the crystal "solution" lattice.

Revisiting phytate-element interactions: implications for iron, zinc and calcium bioavailability, with emphasis on legumes

Myo-Inositol hexakisphosphate or phytic acid concentration is a prominent factor known to impede divalent element bioavailability in vegetal foods including legumes. Both in vivo and in vitro studies have suggested that phytic acid and other plant-based constituents may synergistically form insoluble complexes affecting bioavailability of essential elements. This review provides an overview of existing investigations on the role of phytic acid in the binding, solubility and bioavailability of iron, zinc and calcium with a focus on legumes. Given the presence of various interference factors within legume matrices, current findings suggest that the commonly adapted approach of using phytic acid-element molar ratios as a bioavailability predictor may only be valid in limited circumstances. In particular, differences between protein properties and molar concentrations of other interacting ions are likely responsible for the observed poor correlations. The role of phytate degradation in element bioavailability has been previously examined, and in this review we re-emphasize its importance as a tool to enhance mineral bioavailability of mineral fortified legume crops. Food processing strategies to achieve phytate reduction were identified as promising tools to increase mineral bioavailability and included germination and fermentation, particularly when other bioavailability promoters (e.g. NaCl) are simultaneously added.

Supramolecular traps for highly phosphorylated inositol sources of phosphorus

Structurally elusive inositol hexakisphosphates have been trapped in host-guest sandwiches between two picolinamide macrocycles that remain intact in solution, aided by hydrogen bonds and electrostatic interactions. This first report of macrocyclic complexes of inositol hexakisphosphates provides structural insight to significant biosources of phosphorus that impact the global phosphorus cycle.

Solution Studies and Crystal Structures of Heteropolynuclear Potassium/Copper Complexes with Phytate and Aromatic Polyamines: Self-Assembly through Coordinative and Supramolecular Interactions

Phytate (L^12- ) is a relevant natural product. It interacts strongly with biologically relevant cations, due to the high negative charge exhibited in a wide pH range. The synthesis and crystal structures of the mixed-ligand Cu(II) polynuclear complexes K(H₂ tptz)_0.5 [Cu(H₈ L)(tptz)] ⋅ 3.6H₂ O (1), K(H₂ O)₃ {[Cu(H₂ O)(bpca)]₃ (H₈ L)} ⋅ 1.75H₂ O (2), and K_1.5 (H₂ O)₂ [Cu(bpca)](H_9.5 L) ⋅ 8H₂ O (3) (tptz=2,4,6-tri(pyridin-2-yl)-1,3,5-triazine; Hbpca=bis(2-pyridylcarbonyl) amine) are reported herein. They were obtained by the use of an aromatic rigid amine, which satisfies some of the metal coordination sites and promotes the hierarchical assembly of 2D polymeric structures. Speciation of phytate-Cu(II)-Hbpca system and determination of complex stability constants were performed by means of potentiometric titrations, in 0.15 M NMe₄ Cl at 37.0 °C, showing that, even in solution, this system is able to produce highly aggregated complexes, such as [Cu₃ (bpca)₃ (H₇ L)]^2- . Furthermore, the Cu(II)-mediated tptz hydrolysis was studied by UV-vis spectroscopy at room temperature in 0.15 M NMe₄ Cl. Based on the equilibrium results and with the aid of molecular modelling tools, a plausible self-assembly process for 2 and 3 could be proposed.