31P NMR and computational studies on stereochemistry of conversion of phosphoramidate diesters into the corresponding phosphotriesters

31P NMR spectroscopy was used to investigate a stereochemical course of a nitrite-promoted conversion of phosphoramidate diesters into the corresponding phosphotriesters. It was found that this reaction occurred with almost complete epimerization at the phosphorus center and at the C1 atom in the amine moiety. On the basis of the 31P NMR data, a plausible mechanism for the reaction was proposed. The density functional theory calculation of the key step of the reaction, i.e., breaking of the P-N bond and formation of the P-O bond, suggested a one-step S(N)2(P) process with retention of configuration at the phosphorus center.     

Distance Measurements and Conformational Analysis of sn-2-Arachidonoylglycerol-Membrane Sample by 2H–31P REDOR NMR

The purpose of these studies is to determine the intermolecular distances that define the location, orientation, and conformation of 2-AG in palmitoyl-oleoyl-phosphatidylcholine (POPC) lipid bilayers using rotational-echo double-resonance (REDOR) NMR. All five protons on the glycerol backbone of 2-AG were replaced with ²H and the distance between the deuterons and naturally occurring ³¹P on the POPC lipid headgroup determined with REDOR. To determine the distance from each deuteron to the phosphorus, the POPC headgroup was arranged in a hexagonal array. The 2-AG intercalates between the lipid molecules and the ²H labels, resulting in an average distance of z directly above or below the center of the parallelogram of the four phosphorus atoms P₁, P₂, P₃, and P₄. For different z values, the ²H–³¹P inter-nuclear distances were 7.6–9.1 Å (²H–³¹P₁ and ²H–³¹P₃₁) and 4.4–6.7 Å (²H–³¹P₂ and ²H–³¹P₄). Each result involved the calculations and summation of 893,101 terms. Based on the curve-fitting parameters, the calculations with z = 0 fits the data the best, which means these methylene ²H atoms are at the same level as the phosphate group of the POPC lipid bilayer. Molecular dynamic simulation data suggested that the ²H atoms at the glycerol backbone of 2-AG are involved in an extended H-bonding network with the phosphorus atoms after 10-ns simulation.     

Synthesis of new ionic intermediate sitting-atop complexes of free base meso-tetraarylporphyrin and phosphorus(V) chloride under solvent free conditions

The intermediate sitting-atop (i-SAT) complexes are metalloporphyrins in which the metal ion is bonded to fewer than four nitrogen atoms in the distorted porphyrin plane. The i-SAT complexes may be considered as models for the initial steps of the metallation of the macrocycles. The new ionic intermediate sitting-atop complexes of [PCl₃(H₂t(X)pp)]Cl₂ containing phosphorus(V) was synthesized by reaction of PCl₅ and meso-tetraarylporphyrins (H₂t(X)pp) in solvent free conditions. The structure of the complexes was confirmed by (¹H, ³¹P, ¹³C) NMR, FT-IR and UV-Vis spectroscopies, elemental analysis and electrical conductometry. These data proved that only two pyrrolenine nitrogen atoms of the porphyrin act as electron donors to one phosphorus(V) center and so two pyrrolic protons remained still on the macrocycle.     

A CAUTIONARY NOTE ON THE USE OF THE 31P NMR SPECTROSCOPY IN STEREOCHEMICAL CORRELATION ANALYSIS

Stereoselectivity in condensation of protected ribonucleoside 3′-H-phosphonates with hydroxylic components was investigated using ³¹P NMR spectroscopy. The correlation between absolute configuration at the phosphorus center and the chemical shifts of the produced H-phosphonate diesters and the corresponding phosphorothioates, was studied.     

Synthesis under solvent free conditions and photoluminescence study of ionic intermediate sitting-atop complexes of meso-tetraarylporphyrins and phosphorus oxychloride

The reaction of meso-tetraarylporphyrins with phosphorus oxychloride was studied. The reaction product is the so-called intermediate sitting-atop (i-SAT) complex where two pyrrolic nitrogen atoms of the porphyrin core coordinate to the phosphorus atom and two protons on the pyrrolic nitrogen atoms remain. Selection of solvent free conditions is caused that the reaction does not progress until deprotonation step of porphyrin and stopped in the intermediate step for formation of the sitting-atop complex, [POCl₂(H₂t(X)pp)]Cl. The sitting-atop complexes were characterized by (¹H, ³¹P, ¹³C) NMR, FT-IR, UV-vis and photoluminescence spectroscopy (PL), elemental analysis and electrical conductometry. Photoluminescence study of the complexes indicates that their emission spectra are different from those of free base porphyrins.     

Stepwise selective oxidation of tris(2-(diphenylphosphino)ethyl)phosphine on thiolato palladium(II) complexes

One of the equatorially coordinated terminal phosphorus atoms of tris(2-(diphenylphosphino)ethyl)phosphine (pp₃) ligand on the five-coordinate trigonal-bipyramidal palladium(II) complex, [Pd(4-Cltp)(pp₃)](BF₄) (4-Cltp = 4-chlorothiophenolate), was selectively oxidized by photolysis to form the four-coordinate square-planar complex. Further selective oxidation of another coordinated terminal phosphorus atom proceeded quantitatively by the substitution reaction with 4-chlorothiophenolate. The solid state structures of these stepwise-oxidized square-planar complexes were determined by X-ray crystal structure analyses, and the structures of the starting trigonal-bipyramidal and the oxidized complexes in solution have been characterized by ³¹P NMR spectroscopy.     

Biotransformations of 2-hydroxy-2-(ethoxyphenylphosphinyl)acetic acid and the determination of the absolute configuration of all isomers

2-Hydroxy-2-(ethoxyphenylphosphinyl)acetic acid, a new type of organophosphorus compound possessing two stereogenic centers, was investigated. Racemic 2-butyryloxy-2-(ethoxyphenylphosphinyl)acetic acid was synthesized and hydrolyzed using four bacterial species as biocatalysts. In all cases the reaction was more or less stereoselective and isomers bearing a phosphorus atom with an (S_P)-configuration were hydrolyzed preferentially. The observed ¹H and ³¹P NMR chemical shifts of Mosher esters of 2-hydroxy-2-(ethoxyphenylphosphinyl)acetic acid were correlated with the configurations of both stereogenic centers of all four stereoisomers.     

31P NMR Studies of the Binding of the Oligonucleotide (Ap)3A to an Oligodeoxythymidylate Covalently Linked to an Acridine Derivative

Abstract

³¹P NMR was used to study the specific interaction of an oligodeoxynucleotide containing four thymines and covalently attached to an acridine derivative through its 3-phosphate [(Tp)₄(CH₂)₅Acr] with a complementary oligoribonucleotide (Ap)₃A.³¹P-¹H and ¹H-¹H chemical shift correlation spectroscopies were jointly used to provide the assignment of the phosphorus resonances. A downfield shift of two phosphorus resonances of (Tp)₄(CH₂)₅Acr and of two phosphorus resonances of (Ap)₄A was observed upon complex formation. The assignment of the phosphorus resonances which are downfield shifted allowed us to propose a model involving an equilibrium between several 1:1 complexes where the acridine ring is intercalated between different A.T base pairs.     

Characterization of a Phospholipid Adduct Formed in Sprague Dawley Rats by Chloroform Metabolism: NMR Studies

The formation of a covalent adduct to a single phospholipid by the oxidative chloroform metabolite, phosgene, is demonstrated in liver mitochondria of phenobarbital-pretreated Sprague Dawley (SD) rats treated with CHCl₃. The densitometric analysis of the phosphorus stained extracted phospholipids showed that the formation of this adduct in liver mitochondria is accompanied by a decrease of phosphatidylethanolamine and cardiolipin. The characterization of this adduct was performed with a multinuclear NMR approach by comparison with the decreased phospholipids. Treatment of rats with [¹³C]chloroform resulted in an intense ¹³C NMR peak from either an esteric or amidic carbonyl. Very strong similarities in fatty acid composition were found between phosphatidylethanolamine and the phosgene-modified PL, using ¹³C and ¹H NMR spectroscopy. A multiplet at 3.91 ppm coupled to a signal at 3.41 ppm was shown by two-dimensional ¹H NMR in the adduct spectrum. This cross peak was interpreted as arising from the shifted resonances of the two PE head group methylene groups, due to the binding with phosgene. ³¹P spectrum of the adduct was identical to that of phosphatidylethanolamine. We concluded that the chloroform adduct is a modified phosphatidylethanolamine, with the phosgene-derived carbonyl bound to the amine of the head group. © 1997 John Wiley & Sons, Inc. J Biochem Toxicol 12: 93–102, 1998     

P{H} NMR studies of the nonoxidative chlorination of poly(1,12-dodecane phosphonate) and subsequent coordination and nucleophilic reactions

Quantitative ³¹P{¹H} NMR spectroscopic studies demonstrate that dichloro(2,4,6-tribromophenoxy)(2,2′-biphenoxy)phosphorane, (TBPO)(DP)PCl₂, quantitatively converts poly(1,12-dodecylene phosphonate) into the corresponding poly(1,12-dodecylene chlorophosphite). NMR analysis indicates that the reaction is quantitative and the polymer remains intact. The poly(1,12-dodecylene chlorophosphite) chlorophosphite has been characterized by its reactions with acetonitrilepentacarbonyltungsten(0), W(CO)₅(CH₃CN), and subsequent nucleophilic displacement reactions at the coordinated chlorophosphite group. Quantitative ³¹P{¹H} NMR spectroscopic studies demonstrate that the polymer chain remains intact throughout the coordination and nucleophilic reactions. All of the reactions are quantitative by NMR spectroscopy, the synthesis of the (TBPO)(DP)PCl₂ and the subsequent nonoxidative chlorination reactions can be carried out in one pot, and the byproduct of the reaction does not interfere with the reactions or cleave the polymer chains.     

31P Magnetic relaxation studies of yeast transfer RNAPhe.

The molecular mechanism of thermal unfolding of yeast tRNA^Phe in 20 mM NaCl, 1 mM EDTA, and 10 mM MgSO₄, pH 7.1 ± 0.1, has been examined by ³¹P magnetic relaxation and the nuclear Overhauser effect methods at 40.48 MHz in the temperature range of 22.5–80°C. Two partially resolved ³¹P resonance peaks of yeast tRNA^Phe have been found to behave distinctively different in their longitudinal relaxation times. Individual intensities of the two partially resolved peaks have been quantitatively estimated by the use of relaxation data and the nuclear Overhauser effect as a function of temperature. The results of these observations largely support the earlier suggestion by Guéron and Shulman that the high- and low-field parts of the main ³¹P resonance cluster originate from phosphorus nuclei belonging to the double-helical and nonhelical regions of the tRNA, respectively. The spin-lattice relaxation of the phosphorus nucleus has been found to be determined dominantly by the dipolar interaction with the surrounding ribose protons at this observing frequency. Rotational correlation times for the two portions of the ribose-phosphate backbone of the tRNA have been separately deduced from the quantitative treatment of the ³¹P nuclear spin-lattice relaxation times (T₁) and the nuclear Overhauser effect. The result indicates that the two portions undergo internal motions at distinctively different rates of 10⁸–10¹⁰ sec^?1 order in the temperature range of 22.5–80°C, and that the thermal activation of these motions occurs at least in three distinctive steps, i.e., 22.5–31, 31–40, and 40–80°C. The rates of the internal motions and the associated activation energies in respective steps give some insight into the thermo-induced change of the yeast tRNA^Phe structure.     

Protonation and dimerization reactions of cyclopentadienylrhodiumcarbonylphosphine and phosphite derivatives

Eight cyclopentadienylrhodiumcarbonylphosphine and phosphite complexes have been prepared and their IR, ¹H, and ³¹P NMR spectra recorded. A good correlation between carbonyl stretching frequencies and rhodium-phosphorous coupling constants has been observed. Reaction of these compounds with trifluorosulfonic acid, HCF₃SO₃, forms the expected cationic rhodium-hydride species which were examined using ¹H and ³¹P NMR spectroscopy. Similar reactions between trifluoroacetic acid, HCF₃CO₂, and the phosphine compounds gave evidence of rapid proton exchange at the metal. Reaction between trifluoroacetic acid and cyclopentadienylrhodiumcarbonylphosphite compounds yielded new sets of rhodium-hydride resonances which were shown to be due to the formation of dinuclear rhodium complexes and cyclopentadienylrhodiumbis(phosphite) complexes which arise under the reaction conditions. A Scheme for the formation of these reaction products is presented which is consistent with all of the experimental data.     

Synthesis, characteristics and biological activity of pentacoordinated spirophosphoranes derived from amino acids

Summary. The reactions of phosphorus trichloride with various amino acids afford the pentacoordinated spirophosphoranes. The reaction procedures were traced by ³¹P NMR spectra techniques. A new crystal structure of alanine derivative was characterized, which is a slightly distorted TBP structure. Besides, this kind of spirophosphoranes are potent inhibitors to tyrosinase.     

Characterization of the 31P NMR spectrum of Manduca sexta and effects of antimetabolites

High resolution ³¹P nuclear magnetic resonance spectroscopy (NMR) was successfully applied to 5th instar larvae of Manduca sexta. Conditions for in vivo analysis under non-saturating conditions are described. The ³¹P NMR spectrum of intact larvae was composed of six peaks. Their resonance frequencies are reported relative to orthophosphoric acid. Analysis of tissue extracts demonstrated the in vivo peaks to be composed of the β phosphorus resonance of nucleotide triphosphates (NTP) at −19.36 ppm; α phosphorus of NTP and nucleotide diphosphates (NDP) at −10.51 ppm; β and γ phosphorus of NDP and NTP, respectively, at −5.42 ppm; phosphoarginine (PA) at −3.45 ppm; inorganic phosphate (Pi) at +2.76 ppm and sugar phosphates at +3.34 ppm. The major sugar phosphate present in fat body extracts was trehalose-6-phosphate and this was the major phosphorus component of the spectrum of hemolymph. The spin-lattice relaxation times for each in vivo peak were determined.Titration of aqueous fat body and hemolymph extracts was carried out and the relationship between the chemical shift of Pi and pH determined. On this basis the pH of the hemolymph was estimated at approx. 6.7.The metabolic inhibitors, iodoacetate and dinitrophenol, had significant effects on the ³¹P NMR spectrum of intact larvae. Administration of iodoacetate caused a rapid increase in the levels of sugar phosphates together with decreases in NTP and PA. Dinitrophenol also caused declines in the relative levels of NTP and PA but sugar phosphates decreased as well. The experiments demonstrated the potential of in vivo NMR analysis for metabolic studies on high energy phosphate metabolites in M. sexta.     

In Situ Revealing the Electroactivity of P?O and P?C Bonds in Hard Carbon for High‐Capacity and Long‐Life Li/K‐Ion Batteries

The low capacity and unsatisfactory rate capability of hard carbon still restricts its practical application for Li/K‐ion batteries. Herein, a low‐cost and large‐scale method is developed to fabricate phosphorus‐doped hard carbon (PHC‐700) by crosslinking phosphoric acid and epoxy resin and followed by annealing at 700 °C. H₃PO₄ acts not only as a crosslinker to solidify epoxy resin for promoting the degree of graphitization and lowering the specific surface area, but also as phosphorus source for forming P? C and P? O bonds, thus providing more active sites for Li/K storage. As a result, the PHC‐700 electrode delivers a highly reversible capacity of 1294.8 mA h g^?1 at 0.1 A g^?1 and a capacity of 214 mA h g^?1 after 10 000 cycles at 10 A g^?1. As for potassium‐ion batteries, PHC‐700 exhibits a reversible capacity of 381.9 mA h g^?1 at 0.1 A g^?1 and a capacity of 260 mA h g^?1 after 1000 cycles at 0.2 A g^?1. In situ Raman and in situ NMR measurements reveal that the P‐containing bonds can enhance the adsorption to alkali metal ions, and the P? C bond can participate in electrochemical redox reaction by forming Li_x PC_y . Additionally, P‐doped hard carbon shows better structural/interfacial stability for improved long‐term cycling stability.     

Synthesis and X-ray crystal structures of organotri(2-furyl)phosphonium salts: effects of 2-furyl substituents at phosphorus on intramolecular nitrogen to phosphorus hypervalent coordinative interactions

The synthesis of tri(2-furyl)(8-quinolylmethyl)phosphonium bromide and 2-[2-tri(2-furyl)phosphoniophenyl]benzimidazole perchlorate is described, the latter involving a nickel(II)-catalysed displacement of bromine from 2-(2-bromophenyl)benzimidazole by tri(2-furyl)phosphine. X-ray structural studies of the phosphoniobenzimidazole salt reveals the existence of a significant hypervalent coordinative interaction between heterocyclic nitrogen and the phosphonium centre, which also appears to be retained in solution, the ³¹P NMR spectrum showing a significantly shielded phosphorus atom, δ³¹P=ca. 40 ppm in CDCl₃. The structure of the phosphoniophenylbenzimidazole cation reveals major distortion of bond angles about phosphorus away from the idealised tetrahedral angles expected for a tetraarylphosphonium salt, in the range 102-116°. Three of the angles are reduced below the tetrahedral angle and three are increased, the structure about phosphorus approaching that of a trigonal bipyramid, in which the heterocyclic imino nitrogen forms part of a five-membered ring spanning apical-equatorial positions. The apical axis of the trigonal bipyramid is formed by this nitrogen atom and one of the 2-furyl groups, the apical axial bond angle (N2-P-C14) being an average of 178°. The remaining 2-furyl groups occupy equatorial positions, along with the phenyl ring. Significantly, the nitrogen-phosphorus distance is an average of 2.67 Å (for two independent molecules in the unit cell), being the shortest observed in structures of this type, a consequence of the electron-withdrawing properties of the 2-furyl substituents at phosphorus. The structure also shows edge to face associations of 2-furyl substituents of one cation with the phenyl ring of the benzimidazole unit of another cation. The perchlorate anion is hydrogen-bonded to the nitrogen bearing the hydrogen atom in the benzimidazole ring system. In contrast, the N-P interaction in the quinolylmethylphosphonium salt is much less developed, with an N-P distance of 3.511 Å, although there is considerable deformation of bond angles at phosphorus. The crystal structure is dominated by the existence of hydrogen-bonded interactions between the cation, anion and a molecule of water, and by face to face interactions between cations. Both salts undergo loss of a 2-furyl group on treatment with hydroxide ion.     

Structural characterization of the head-to-head isomers of the [Pd2(Ph2Ppy)2Cl2] and [PtPd(Ph2Ppy)2I2] complexes (Ph2Ppy = 2-(diphenylphosphino)pyridine)

The molecular structures of the thermodynamically unstable head-to-head isomers, HH-[Pd₂(Ph₂Ppy)₂Cl₂] and HH-[PtPd(Ph₂Ppy)₂I₂], have been determined by single crystal X-ray diffraction. The two complexes have proved to be isostructural. The severe distortions of the bond angles from the ideal square planar geometry around the metal centers ligating the trans phosphorus donor atoms are indicative of a more pronounced internal strain in the HH isomers as compared to the HT counterparts. The enhanced internal strain is thought to be the major driving force responsible for the spontaneous conversion of the head-to-head isomers to their head-to-tail congeners. ¹³C NMR spectra in solution phase as well as solid-state ³¹P MAS NMR spectra have proved to be informative regarding the orientation of the asymmetric Ph₂Ppy ligands.     

AMP promotes oxygen consumption and ATP synthesis in heart mitochondria through the adenylate kinase reaction: an NMR spectroscopy and polarography study

Adenylate kinase plays an important role in cellular energy homeostasis by catalysing the interconversion of adenine nucleotides. The goal of present study was to evaluate the contribution of the adenylate kinase reaction to oxidative ATP synthesis by direct measurements of ATP using ³¹P NMR spectroscopy. Results show that AMP can stimulate ATP synthesis in the presence or absence of ADP. In particular, addition of 1 mM AMP to the 0.6 mM ADP superfusion system of isolated superfused mitochondria (contained and maintained in agarose beads) led to a 25% increase in ATP synthesis as measured by the increase in βATP signal. More importantly, we show that AMP can support ATP synthesis in the absence of ADP, demonstrated as follows. Superfusion of mitochondria without ADP led to the disappearance of ATP γ, α and β signals and the increase of P_i. Addition of AMP to the medium restored the production of ATP, as demonstrated by the reappearance of γ, α and β ATP signals, in conjunction with a decrease in P_i, which is being used for ATP synthesis. Polarographic studies showed Mg²⁺ dependence of this process, confirming the specificity of the adenylate kinase reaction. Furthermore, data obtained from this study demonstrate, for the first time, that different aspects of the adenylate kinase reaction can be evaluated with ³¹P NMR spectroscopy. Copyright © 2015 John Wiley & Sons, Ltd. SIGNIFICANCE OF RESEARCH PARAGRAPH The data generated in the present study indicate that ³¹P NMR spectroscopy can effectively be used to study the adenylate kinase reaction under a variety of conditions. This is important because understanding of adenylate kinase function and/or malfunction is essential to understanding its role in health and disease. The data obtained with ³¹P NMR were confirmed by polarographic studies, which further strengthens the robustness of the NMR findings. In summary, ³¹P NMR spectroscopy provides a sensitive tool to study adenylate kinase activity in different physiological and pathophysiological conditions, including but not exclusive of, cancer, ischemic injury, hemolytic anemia and neurological problems such as sensorineural deafness.     

The unique alternation of conformationally different (‘chair’-‘saddle’) eight-membered metallocycles [Cd2S4P2] in the chains of cadmium dialkyldithiophosphates: C, P, Cd CP/MAS NMR and single-crystal X-ray diffraction studies

O,O′-Dipropyldithiophosphate and O,O′-dibutyldithiophosphate (Dtph) cadmium(II) complexes were prepared and studied by means of heteronuclear ³¹P, ¹¹³Cd, ³¹C CP/MAS NMR spectroscopy and single-crystal X-ray diffraction. Linear-chain polynuclear structures have been established for both cadmium(II) complexes, in which each pair of equivalent dithiophosphate groups, playing the same bridging structural function, asymmetrically links the neighbouring cadmium atoms. One remarkable structural feature of the synthesised cadmium(II) compounds is defined by the alternation of two types of conformationally different (‘chair’-‘saddle’) eight-membered rings [Cd₂S₄P₂] in the polymeric chains. Therefore, in both ³¹P NMR and XRD data, the bridging dithiophosphate ligands exhibit structural inequivalence in pairs. The structural states of both Dtph ligands and cadmium atoms have been characterised by the ³¹P and ¹¹³Cd chemical shift tensors, which display a profound axially symmetric and mainly rhombic characters, respectively. All experimental ³¹P resonances were assigned to the phosphorus structural sites in both resolved structures.     

The interaction of nemorubicin metabolite PNU-159682 with DNA fragments d(CGTACG)2, d(CGATCG)2 and d(CGCGCG)2 shows a strong but reversible binding to G:C base pairs

The antitumor anthracycline nemorubicin is converted by human liver microsomes to a major metabolite, PNU-159682 (PNU), which was found to be much more potent than its parent drug toward cultured tumor cells and in vivo tumor models. The mechanism of action of nemorubicin appears different from other anthracyclines and until now is the object of studies. In fact PNU is deemed to play a dominant, but still unclear, role in the in vivo antitumor activity of nemorubicin. The interaction of PNU with the oligonucleotides d(CGTACG)₂, d(CGATCG)₂ and d(CGCGCG)₂ was studied with a combined use of ¹H and ³¹P NMR spectroscopy and by ESI-mass experiments. The NMR studies allowed to establish that the intercalation between the base pairs of the duplex leads to very stable complexes and at the same time to exclude the formation of covalent bonds. Melting experiments monitored by NMR, allowed to observe with high accuracy the behaviour of the imine protons with temperature, and the results showed that the re-annealing occurs after melting. The formation of reversible complexes was confirmed by HPLC–tandem mass spectra, also combined with endonuclease P1digestion. The MS/MS spectra showed the loss of neutral PNU before breaking the double helix, a behaviour typical of intercalators. After digestion with the enzyme, the spectra did not show any compound with PNU bound to the bases. The evidence of a reversible process appears from both proton and phosphorus NOESY spectra of PNU bound to d(CGTACG)₂ and to d(CGATCG)₂. The dissociation rate constants (k_off) of the slow step of the intercalation process, measured by ³¹P NMR NOE-exchange experiments, showed that the kinetics of the process is slower for PNU than for doxorubicin and nemorubicin, leading to a 10- to 20-fold increase of the residence time of PNU into the intercalation sites, with respect to doxorubicin. A relevant number of NOE interactions allowed to derive a model of the complexes in solution from restrained MD calculations. The conformation of PNU bound to the oligonucleotides was also derived from the coupling constant values.