First direct discrimination of chiral phosphine selenide (P=Se) derivatives by multinuclear magnetic resonance spectroscopy in the presence of a chiral dirhodium complex

Enantiomeric ratios of compounds with P=Se functionalities (phosphine selenides) can easily be determined by (1)H, (13)C, (31)P, and (77)Se NMR spectroscopic inspection of their diastereomeric complexes with (R)-Rh(2)(MTPA)(4) (MTPA-H identical with methoxytrifluoromethylphenylacetic acid; Mosher's acid). This is the first facile and rapid spectroscopic method for chiral recognition in this class of compounds. Whereas most complexation shifts Delta(delta) are moderate or even negligible, significant signal dispersions Delta(nu) can be observed. Some rationalization for the adduct formation mode is presented. NMR spectral characteristics of the free P=Se compounds 1-5 are described.     

Chiral separation and CD characterisation of enantiomeric cyclotriphosphazene derivatives

The gem-disubstituted cyclotriphosphazene 1 reacted with piperazine (pip) to give the piperazine-bridged derivative 2, which is expected to exist in meso and racemic forms because the two PCl (pip) groups are stereogenic. The proton-decoupled (31)P NMR spectrum of 2 gave rise to two similar sets of ABX signals in a 1:1 ratio, consistent with formation of diastereoisomers. The meso and racemic forms of compound 2 were separated by column chromatography on silica gel and characterised by elemental analysis, mass spectrometry, (31)P NMR spectroscopy, and X-ray crystallography. Using HPLC with a chiral stationary phase, the racemic form of compound 2 was further separated into enantiomers, which were characterised by circular dichroism (CD) spectroscopy. This is the first report of the separation of enantiomers in the field of cyclophosphazene chemistry and hence the first CD spectra of derivatives in which the cyclophosphazene ring is at the chiral centre.     

The dirhodium-method in the determination of absolute configurations of phospholene chalcogenides

The 1H, 13C, and 31P NMR signals of six chiral phospholene chalcogenides (X = O, S, Se) are duplicated in the presence of one mole equivalent of the chiral auxiliary Rh2[(R)-MTPA]4 (diastereomeric dispersion Deltanu; in Hz). The samples were investigated as nonracemic mixtures of enantiomers with known absolute configurations so that signs can be attributed to the Deltanu-values and each signal set can be assigned to the respective enantiomer. The signs are uniform--in particular those of 1H nuclei--and nearly independent of the nature of the chalcogen atom. Thus, if the absolute configuration of one compound is known, it is possible to derive absolute configurations in the whole series (correlation method).     

Chiral phospholene and phospholane chalcogenides: stereochemistry and chiral recognition by multinuclear NMR spectroscopy of their Rh2[(R)-MTPA]4 adducts

Full NMR spectral assignments of the phospholene chalcogenides 1-12 are presented and their stereochemistry proven. The enantiomeric ratio of any of these compounds can be monitored easily by adding one mole equivalent of the chiral auxiliary Rh(2)[(R)-MTPA](4) (MTPA-H identical with Mosher's acid) and subsequent NMR inspection. Some surprisingly large diastereomeric signal dispersion is observed in the (1)H NMR spectra of the adducts, leading to the conclusion that intramolecular anisotropy interaction between groups inside the ligand molecules exists. The dependence of dispersion effects on the nature of the chalcogenide atom is investigated.     

First direct discrimination of chiral phosphorus thionate (P=S) derivatives by multinuclear magnetic resonance spectroscopy in the presence of a chiral dirhodium complex

Enantiomeric ratios of compounds with P=S functionalities can be determined by 1H, 13C, and 31P NMR spectroscopic inspection of their diastereomeric complexes with (R)-Rh2(MTPA)4 (MTPA-H identical with methoxytrifluoromethylphenylacetic acid; Mosher's acid). This is the first facile and rapid spectroscopic method for chiral recognition in this class of compounds. Whereas complexation shifts Deltadelta are moderate or even negligible, significant signal dispersions Delta(nu) can be observed. Some rationalization about the complexation mode is presented. The NMR spectral characteristics of the free P=S compounds 1-9 are described in detail.     

Effect of Hypoglycemic Encephalopathy upon Amino Acids, High-Energy Phosphates, and pHi in the Rat Brain In Vivo: Detection by Sequential 1H and 31P NMR Spectroscopy

Metabolic alterations in amino acids, high-energy phosphates, and intracellular pH during and after insulin hypoglycemia in the rat brain was studied in vivo by 1H and 31P nuclear magnetic resonance (NMR) spectroscopy. Sequential accumulations of 1H and 31P spectra were obtained from a double-tuned surface coil positioned over the exposed skull of a rat while the electroencephalogram was recorded continuously. The transition to EEG silence was accompanied by rapid declines in phosphocreatine, nucleoside triphosphate, and an increase in inorganic orthophosphate in 31P spectra. In 1H spectra acquired during the same time interval, the resonances of glutamate and glutamine decreased in intensity while a progressive increase in aspartate was observed. Following glucose administration, glutamate and aspartate returned to control levels (recovery half-time, 8 min); recovery of glutamine was incomplete. An increase in lactate was detected in the 1H spectrum during recovery but it was not associated with any change in the intracellular pH as assessed in the corresponding 31P spectrum. Phosphocreatine returned to control levels following glucose administration, in contrast to nucleoside triphosphate and inorganic orthophosphate which recovered to only 80% and 200% of their control levels, respectively. These results show that the changes in cerebral amino acids and high-energy phosphates detected by alternating the collection of 1H and 31P spectra allow for a detailed assessment of the metabolic response of the hypoglycemic brain in vivo.     

Determination of the enantiomeric excess of chiral carboxylic acids by 31P NMR with phosphorylated derivatizing agents from C2-symmetrical diamines containing the (S)-alpha-phenylethyl group

The use of P(III) and P(V) organophosphorus derivatizing agents prepared from C(2) symmetrical (1R,2R)- and (1S,2S)-trans-N,N'-bis-[(S)-alpha-phenylethyl]-cyclohexane-1,2-diamines 1 and 2, as well as (1R,2R)- and (1S,2S)-trans-N,N'-bis-[(S)-alpha-phenylethyl]-4-cyclohexene-1,2-diamines 3 and 4 for the determination of enantiomeric composition of chiral carboxylic acids by (31)P NMR, is described.     

Phosphorylation as a method of tuning the enantiodiscrimination potency of quinine--an NMR study

Quinines phosphorylated at the C-9 hydroxyl group (diphenyl and diethyl phosphates) were synthesized and validated as novel effective chiral solvating agents in two alternative methods based on (1)H and (31)P NMR spectroscopy. Tested with a representative set of racemic analytes, the title compounds induced shift nonequivalence effects in (1)H NMR signals with values up to 0.1-0.2 ppm for 3,5-dinitrobenzoyl-substituted amino acids. In terms of enantiodifferentiation extent and application range, introduction of a phosphate group was proven to be superior compared to the action of nonmodified quinine. Interestingly, a temperature decrease to reach the slow exchange conditions also produced nonequivalences in the (31)P NMR spectra of the selectors. Comprehensive NMR analysis showed the existence of two conformations (closed 1 and 2) for both quinines in their free forms and the open 3 arrangement for the protonated ones. The crystal structure of diethylphosphorylquinine hydrochloride dichloromethane hemisolvate revealed a similar conformation to that observed in solution. Structures of complexes of phosphorylated quinines with selected ligands were determined with the use of NMR-based molecular modeling studies.     

Unique 31P Spectral Response to the Formation of a Specific Restriction Enzyme–DNA Complex

Protein-induced distortion is a dramatic but not universally observed feature of sequence-specific DNA interactions. This is illustrated by the crystal structures of restriction enzyme–DNA complexes: While some of these structures exhibit DNA distortion, others do not. Among the latter is PvuII endonuclease, a small enzyme that is also amenable to NMR spectroscopic studies. Here ³¹P NMR spectroscopy is applied to demonstrate the unique spectral response of DNA to sequence-specific protein interactions. The ³¹P NMR spectrum of a noncognate DNA exhibits only spectral broadening upon the addition of enzyme. However, when enzyme is added to target DNA, a number of ³¹P resonances shift dramatically. The magnitudes of the chemical shifts (2–3 ppm) are among the largest observed. Site-specific substitution with phosphoramidates and phosphorothioates are used analyze these effects. While such spectral features have been interpreted as indicative of DNA backbone distortions, FRET analysis indicates that this does not occur in PvuII-cognate DNA complexes in solution. The distinct ³¹P spectral signature observed for cognate DNA mirrors that observed for the enzyme, underscoring the unique features of cognate complex formation.     

Using 31P NMR Spectroscopy at 14.1 Tesla to Investigate PARP-1 Associated Energy Failure and Metabolic Rescue in Cerebrocortical Slices

PARP-1 activation by H(2)O(2) in an acute preparation of superfused, respiring, neonatal cerebrocortical slices was assessed from PAR-polymer formation detected with immunohistochemistry and Western blotting. (31)P NMR spectroscopy at 14.1 Tesla of perchloric acid slice extracts was used to assess energy failure in a 1-h H(2)O(2) exposure as well as in a subsequent 4-h recovery period where the superfusate had no H(2)O(2) and specifically chosen metabolic substrates. Although more data are needed to fully characterize different bioenergetic responses, a high NMR spectral resolution (PCr full-width at half-max approximately.01 ppm) and narrow widths for most metabolites (<.2 ppm) permitted accurate quantifications of spectrally resolved resonances for ADP, ATP, NAD(+)/NADH, and other high energy phosphates. It appears possible to use brain slices to quantitatively study PARP-related, NAD-associated energy failure, and rescue with TCA metabolites.     

Comparison of glucose fermentation by suspended and gel-entrapped yeast cells: An in vivo nuclear magnetic resonance study

Phosphorus-31 nuclear magnetic resonance ((31)P NMR) was used to compare the anaerobic metabolism of glucose by suspended and gel-entrapped Saccharomyces bayanus cells. The fermentation of glucose was carried out in a reaction system with continuous circulation through the NMR sample tube. The intracellular pH and the levels of some phosphorylated compounds were the levels of some phosphorylated compounds were noninvasively monitored by (31)P NMR while glucose, fermentation products, and biomass were determined by analytic techniques comparisons showed that no significant differences are observed in the relative concentrations in the spectra, but distinct profiles for the variation of both intracellular and extracellular pH are found. The internal pH of immobilized cells is maintained at a constant value throughout the fermentation as opposed to freely suspended cells for which a steady decrease in the internal pH occurs. A faster and stronger acidification is also observed in the external medium of the assays with suspended cells. Furthermore, higher yields for ethanol and biomass production and lower yields of fermentation by-products are obtained with immobilized cells. It is concluded that the higher intracellular pH achieved in the presence of the gel matrix had a regulatory effect on the metabolism which favored the ethanol production pathway. (c) 1993 John Wiley & Sons, Inc.     

Identifying stereoisomers of the asymmetric hydrogenation catalyst [Me-BPE-Rh(COD)]+BF4 -

The performance of a catalyst used in asymmetric synthesis is likely to be dependent upon its stereoisomeric purity. An impurity was detectable by (31)P NMR in early development batches of the asymmetric hydrogenation catalyst [(S,S)-Me-BPE-Rh(COD)](+)BF(4) (-) made from the ligand bis((2S,5S)-2,5-dimethylphospholano)ethane [(S,S)-Me-BPE]. Its identity as a stereoisomer with one chiral and one meso-phospholane ring was deduced by comparison of the (31)P NMR spectra and GC traces of the ligand with a deliberately synthesized mixture of isomers. Interestingly, the impurity corresponded to a trans-meso isomer formed by thermal (200 degrees C) pyramidal inversion at phosphorus of the initially synthesized cis-meso-phospholane when the ligand was purified by distillation. Low levels of this trans-meso/chiral impurity do not significantly impair the enantioselectivity of the rhodium complex as an asymmetric hydrogenation catalyst, but high levels of stereochemical impurities resulted in a loss of both enantioselectivity and activity. Therefore it is indeed important to establish that a catalyst used in asymmetric catalysis is sufficiently stereoisomerically pure. Owing to strict control of the stereochemical purity of the key hexane-2,5-diol intermediate, the impurity is not detected in production batches.     

NMR chiral discrimination of chalcogen containing secondary alcohols

Here, we report the general strategies by which NMR spectroscopy can be used to determine the enantiopurity and absolute configuration of chalcogen containing secondary alcohols, including the evaluation of the use of chiral solvating and chiral derivatizing agents. The BINOL/DMAP ternary complex demonstrated a simple and fast protocol for determining enantiopurity. The drug Naproxen afforded a stable, nonhygroscopic, and readily available chiral derivatizing agent (CDA) for NMR chiral discrimination of chalcogen containing secondary alcohols. The chiral recognition by CDA and chiral solvating agent (CSA) was assessed using ¹H, ⁷⁷Se‐{1H}, and ¹²⁵Te‐{1H} NMR spectroscopy. A simple model for the assignment of the absolute configuration from NMR data is presented.     

Synthesis and enantiomeric analysis of cyclotriphosphazene derivatives with one centre of chirality

A series of chiral cyclotriphosphazene compounds 2-9 in which the spiro 3-amino-1-propanoxy moiety provides the one centre of chirality have been synthesised and characterised by elemental analysis, MS, ¹H and ³¹P NMR spectroscopies. The enantiomers of newly synthesised compounds have been analysed by the changes in the ³¹P NMR spectra on addition of a Chiral Solvating Agent (CSA), (S)-(+)-2,2,2-trifluoro-1-(9′-anthryl)ethanol. HPLC methods have been developed for the enantiomeric separations of chiral cyclotriphosphazenes containing one centre of chirality. It is found that chiral HPLC gave a good resolution of enantiomers of the racemic compounds 2-9 with resolution factors between 2.49 and 7.50 making them good candidates for enantiomeric separations and determination of absolute configuration.     

Reevaluation of the phospholipid composition in membranes of adult human lenses by P NMR and MALDI MS

The phospholipid composition of adult human lens membranes differs dramatically from that of any other mammalian membrane. Due to minimal cell turnover, cells in the nucleus of the human lens may be considered as the longest lived cells in our body. This work reassesses previous assignments of phospholipid ³¹P NMR resonances in adult human lenses. The new assignments are based not only on chemical shifts but also on temperature coefficients. By addition of known phospholipids and examination by matrix-assisted laser desorption/ionization mass spectrometry, several misassigned resonances have been corrected. The revised composition reveals the possible presence of ceramide-1-phosphate and dihydroceramide-1-phosphate. Among glycerophospholipids, the most abundant one does not correspond to phosphatidylglycerol but may be due to the lysoform of alkyl-acyl analogs of phosphatidylethanolamine. Besides sphingophospholipids, adult human lens membranes contain significant amounts of ether (1-O-alkyl) glycerophospholipids and their corresponding lysoforms.     

Determination of optical purity of 3,5-dimethoxybenzoyl-leucine diethylamide by chiral chromatography and 1H and 13C NMR spectroscopy

(R)-N-3,5-dinitrobenzoyl (DNB) leucine derived chiral selector was used as an HPLC chiral stationary phase for the resolution of various racemic amino acids derivatives. In this study, determination of optical purity of an amino acid derivative was performed by chiral high performance liquid chromatography and 1H and 13C NMR spectroscopy by using the DNB leucine derived chiral selector. The accuracy and precision of each optical purity value are calculated and the data are compared to each other.     

Degradation rates of organic phosphorus in lake sediment

Phosphorus (P) binding groups were identified in phytoplankton, settling particles, and sediment profiles by ³¹P NMR spectroscopy from the Swedish mesotrophic Lake Erken. The ³¹P NMR analysis revealed that polyphosphates and pyrophosphates were abundant in the water column, but rapidly mineralized in the sediment. Orthophosphate monoesters and teichoic acids degraded more slowly than DNA-P, polyphosphates, and P lipids. Humic acids and organic acids from phytoplankton were precipitated from the NaOH extract by acidification and identified by ³¹P NMR spectroscopy. The precipitated P was significantly more recalcitrant than the P compound groups remaining in solution, but does not constitute a major sink of P as it did not reach a stable concentration with depth, which indicates that it may eventually be degraded. Since P also precipitated from phytoplankton, the origin of humic-P can not be related solely to allochthonous P.     

Influence of temperature on 31P NMR chemical shifts of phospholipids and their metabolites I. In chloroform-methanol-water

Spectral overlap of ³¹P NMR resonances and the lack of reproducibility in chemical shifts corresponding to phospholipids in organic solvents challenge the accuracy of band assignments and quantification. To alleviate these problems, the use of temperature coefficients is proposed. Changes in temperature enable the resolution of overlapped resonances and provide a facile approach for the computation of temperature coefficients. The coefficients were evaluated for various glycero- and sphingo-phospholipids. Their values suggest that differences in H-bonding between the phosphate and the head groups are responsible for the changes of chemical shift with temperature. Among parent phospholipids, and in addition to sphingomyelin, the smallest temperature coefficient values (closest to zero) were observed for phosphatidylcholine, phosphatidylglycerol, dihydrosphingomyelin, and cardiolipin. The highest values were exhibited by phospholipids with protonated head groups, such as phosphatidylserine and phosphatidylethanolamine. The lowest and, in fact, negative values were measured for phospholipids with an exposed phosphate group: phosphatidic acid, ceramide-1-phosphate, and dihydroceramide-1-phosphate. Diacyl, alkyl-acyl, and alkenyl-acyl phospholipids with the same head group exhibited comparable coefficients but differed slightly in chemical shifts. Compared to their parent glycerophospholipids, all lyso analogs had greater temperature coefficients, possibly due to the presence of an extra OH capable of forming a H-bond with the phosphate group.     

Absolute Configuration and Enantiodifferentiation of a Hemicryptophane Incorporating an Azaphosphatrane Moiety

The hemicryptophane racemate (±)‐ M-1 , P-1 was optically resolved by semipreparative HPLC on Chiralpak IC column. The absolute configuration of each isolated enantiomer was established from the analysis of their electronic circular dichroism spectra. Enantiodifferentiation of the chiral cationic cage (±)‐ M-1 , P-1 was evidenced in solution using Δ‐TRISPHAT as chiral solvating agent, and the diastereomeric associations were observed in ¹H and ³¹P NMR spectra. Chirality 24:1077–1081, 2012. © 2012 Wiley Periodicals, Inc.     

Tripodal polyphosphine ligands in silver (I) coordination chemistry: Mononuclear cf. polynuclear complex dependence vis-a-vis counterion and ligand to metal ratio

1:2, 1:1, 3:2 and 6:2 AgX:L adducts (where L is a tridentate phosphine, in detail: 1,1,1-tris(diphenylphosphinomethyl)ethane (Me-triphos) and bis(2-diphenylphosphinoethyl)phenylphosphine (Ph-triphos), X = O₃SCF₃, O₃SCH₃, BF₄ or O₂CCF₃) have been synthesized and characterized by IR, NMR (¹H, ³¹P and ¹⁹F) and ESI MS spectroscopy. The stoichiometry of the complexes is strongly dependent on the ligand to metal ratio employed and also on the nature of the counterion. ³¹P NMR (solution) data also show the complexes existing in solution, in some cases, however, disproportionating to adducts of different nuclearity. Oligonuclear species have been detected through ESI MS spectroscopy that has been demonstrated as a powerful tool for the identification of the solution species. AgBF₄:Me-triphos (1:2) has been structurally characterized as [Ag(P,P′-Me-triphos)₂](BF₄) · H₂O · 7/2 MeOH, while Ag(O₃SCF₃): Ph-triphos: H₂O (6:2:4) is a spectacular two-dimensional polymer.