Electronic circular dichroism of monomethyl [O, O, O]-phosphate and [O, O, O]-thiophosphate revisited

Phosphoryl-transfer reactions have long been of interest due to their importance in maintaining numerous cellular functions. A phosphoryl-transfer reaction results in two possible stereochemical outcomes: either retention or inversion of configuration at the transferred phosphorus atom. When the product is phosphate, isotopically-labeled [¹⁶O, ¹⁷O, ¹⁸O]-phosphate derivatives can be used to distinguish these outcomes; one oxygen must be replaced by sulfur or esterified to achieve isotopic chirality. Conventionally, stereochemical analysis of isotopically chiral phosphate has been based on ³¹P NMR spectroscopy and involves complex chemical or enzymatic transformations. An attractive alternative would be direct determination of the enantiomeric excess using chiroptical spectroscopy. (S)-Methyl-[¹⁶O, ¹⁷O, ¹⁸O]-phosphate (MePi^∗), 7 and enantiomeric [¹⁶O, ¹⁷O, ¹⁸O]-thiophosphate (TPi^∗), 10, were previously reported to exhibit weak electronic circular dichroism (ECD), although with 10 the result was considered to be uncertain. We have now re-examined the possibility that excesses of 7 and 10 enantiomers can be detected by ECD spectrometry, using both experimental and theoretical approaches. 7 and both the (R) and (S) enantiomers of 10 (10a, 10b) were synthesized by the ‘Oxford route’ and characterized by ¹H, ³¹P and ¹⁷O NMR, and by MS analysis. Weak ECD could be found for 7, with suboptimal S/N. No significant ECD could be detected for the 10 enantiomers.Time-dependent DFT (TDDFT) calculations of the electronic excitation energies and rotational strengths of the same three enantiomers were carried out using the functional B3LYP and the basis set 6-311G^∗∗. The isotopically-perturbed geometries were predicted using the anharmonic vibrational frequency calculational code in GAUSSIAN 03. In the case of 10, calculations were also carried out for the hexahydrated complex to investigate the influence of the aqueous solvent. The predicted excitation wavelengths are greater than the observed wavelengths, a not unusual result of TDDFT calculations. The predicted anisotropy ratios are 2.9 × 10⁻⁵ for 7, −5.3 × 10⁻⁶ for 10a/b, and 1.7 × 10⁻⁶ for 10a/b⋅(H₂O)₆. For 7 the predicted anisotropy ratio approximates that observed in this work, 4.5 × 10⁻⁵ at 208 nm. For 10a/b, the upper limits of the experimental anisotropy ratios (<5 × 10⁻⁶ at 225 nm, pH 9; <5 × 10⁻⁶ at 236 nm, pH 12) are comparable to the predicted magnitude of the value for 10a/b. The lower predicted value for 10a/b · (H₂O)₆ suggests that the aqueous environment affects the ECD significantly. Altogether, the TDDFT calculations together with a stereochemical analysis based on NMR and the MS data support the conclusion that the experimental ECD results for MePi^∗ and TPi^∗ may be reliable in order of magnitude.     

18O Labeling of Chlorophyll d in Acaryochloris marina Reveals That Chlorophyll a and Molecular Oxygen Are Precursors

The cyanobacterium Acaryochloris marina was cultured in the presence of either H₂¹⁸O or ¹⁸O₂, and the newly synthesized chlorophylls (Chl a and Chl d) were isolated using high performance liquid chromatography and analyzed by mass spectroscopy. In the presence of H₂¹⁸O, newly synthesized Chl a and d, both incorporated up to four isotopic ¹⁸O atoms. Time course H₂¹⁸O labeling experiments showed incorporation of isotopic ¹⁸O atoms originating from H₂¹⁸O into Chl a, with over 90% of Chl a ¹⁸O-labeled at 48 h. The incorporation of isotopic ¹⁸O atoms into Chl d upon incubation in H₂¹⁸O was slower compared with Chl a with ∼50% ¹⁸O-labeled Chl d at 115 h. The rapid turnover of newly synthesized Chl a suggested that Chl a is the direct biosynthetic precursor of Chl d. In the presence of ¹⁸O₂ gas, one isotopic ¹⁸O atom was incorporated into Chl a with approximately the same kinetic incorporation rate observed in the H₂¹⁸O labeling experiment, reaching over 90% labeling intensity at 48 h. The incorporation of two isotopic ¹⁸O atoms derived from molecular oxygen (¹⁸O₂) was observed in the extracted Chl d, and the percentage of double isotopic ¹⁸O-labeled Chl d increased in parallel with the decrease of non-isotopic-labeled Chl d. This clearly indicated that the oxygen atom in the C3¹-formyl group of Chl d is derived from dioxygen via an oxygenase-type reaction mechanism.     

Biochemical Characterization of the Oxygenation of Unsaturated Fatty Acids by the Dioxygenase and Hydroperoxide Isomerase of Pseudomonas aeruginosa 42A2

We have studied oxygenation of fatty acids by cell extract of Pseudomonas aeruginosa 42A2. Oleic acid ((9Z)-18:1) was transformed to (10S)-hydroperoxy-(8E)-octadecenoic acid ((10S)-HPOME) and to (7S,10S)-dihydroxy-(8E)-octadecenoic acid (7,10-DiHOME). Experiments under oxygen-18 showed that 7,10-DiHOME contained oxygen from air and was formed sequentially from (10S)-HPOME by isomerization. (10R)-HPOME was not isomerized. The (10S)-dioxygenase and hydroperoxide isomerase activities co-eluted on ion exchange chromatography and on gel filtration with an apparent molecular size of ∼50 kDa. 16:1n-7, 18:2n-6, and 20:1n-11 were also oxygenated to 7,10-dihydroxy fatty acids, and (8Z)-18:1 was oxygenated to 6,9-dihydroxy-(7E)-octadecenoic acid. A series of fatty acids with the double bond positioned closer to ((6Z)-18:1, (5Z,9Z)-18:2) or more distant from the carboxyl group ((11Z)-, (13Z)-, and (15Z)-18:1) were poor substrates. The oxygenation mechanism was studied with [7S-²H]18:1n-9, [7R-²H]18:2n-6, and [8R-²H]18:2n-6 as substrates. The pro-R hydrogen at C-8 was lost in the biosynthesis of (10S)-HPODE, whereas the pro-S hydrogen was lost and the pro-R hydrogen was retained at C-7 during biosynthesis of the 7,10-dihydroxy metabolites. Analysis of the fatty acid composition of P. aeruginosa revealed relatively large amounts of (9E/Z)-16:1 and (11E/Z)-18:1 and only traces of 18:1n-9. We found that (11Z)-18:1 (vaccenic acid) was transformed to (11S,14S)-dihydroxy-(12E)-octadecenoic acid and to a mixture of 11- and 12-HPOME, possibly due to reverse orientation of (11Z)-18:1 at the active site compared with oleic acid. The reaction mechanism of the hydroperoxide isomerase suggests catalytic similarities to cytochrome P450.     

Substituted 16α,17α-cyclohexanopregnanes: the anionic oxy-Cope rearrangement of 3β-<Emphasis Type="Italic">tert</Emphasis>-butyldimethylsilyloxy-19-hydroxy-19-vinyl-16α,17α-cyclohexapregn-5-en-20-one

(19R)-and (19S)-tert-Butyldimethylsilyl (TBS) ethers of 19-hydroxy-19-vinyl-16α,17α-cyclohexanopregn-5-en-20-ones were synthesized. These compounds containing the 1,5-oxydienoic motif were subjectedto the anionic oxy-Cope rearrangement to obtain 3β-TBS ether of 6β-(3-oxopropyl)-16α,17α-cyclohexano-19-norpregn-5(10)-en-20-one. The structures of the compounds synthesized were confirmed by the analysis of their ¹H and ¹³C NMR spectra.     

Synthesis and evaluation of 6-(3-[18F]fluoro-2-hydroxypropyl)-substituted 2-pyridylbenzothiophenes and 2-pyridylbenzothiazoles as potential PET tracers for imaging Aβ plaques

3-[¹⁸F]Fluoro-2-hydroxypropyl substituted compounds were synthesized and evaluated as novel ¹⁸F-labeled PET tracers for imaging Aβ plaque in a living brain. All compounds exhibited high binding affinities toward the synthetic Aβ_1–42 aggregate and/or Alzheimer’s disease brain homogenate. In the microPET study with normal mice, the 3-[¹⁸F]fluoro-2-hydroxypropyl substituted compounds resulted in fast brain washout by reducing the lipophilicities of the compounds. Intriguingly, (S)-configured PET tracers, (S)-[¹⁸F]1b and (S)-[¹⁸F]1c, exhibited a 2.8 and 4.0-fold faster brain washout rate at a peak/30 min in the mouse brain than the corresponding (R)-configured PET tracers despite there being no meaningful difference in binding affinities toward Aβ plaque. A further evaluation of (S)-[¹⁸F]1c with healthy rhesus monkeys also revealed excellent clearance from the frontal cortex with ratios of 7.0, 16.0, 30.0 and 49.0 at a peak/30, 60, 90, and 120 min, respectively. These results suggest that (S)-[¹⁸F]1c may be a potential PET tracer for imaging Aβ plaque in a living brain.     

Infrared and raman study of matrix isolated M(SO2) molecules. The structure of the molecular ion SO2−

The IR and Raman spectra of Cs(SO₂), K(SO₂) and Na(SO₂) molecules were studied by ³²S/³⁴S and ¹⁶O/¹⁸O isotopic substitution technique. These molecules have a planar ring configuration of C_2v symmetry with the OSO angle equal to 109°±5° and the SO bond length of 0.149±0.001 nm. The alkali metal atom interacts symmetrically with the oxygen atoms of the SO₂⁻ group. The doubling observed for the vibrations of Cs(S¹⁶O¹⁸O) was attributed to a matrix effect.     

Synthesis and preliminary biological evaluation of a novel P2X7R radioligand [18F]IUR-1601

The reference standard IUR-1601 ((S)-N-(2-chloro-3-(trifluoromethyl)benzyl)-1-(2-fluoroethyl)-5-oxopyrrolidine-2-carboxamide) was synthesized from tert-butyl (S)-5-oxopyrrolidine-2-carboxylate, fluoroethylbromide, and 2-chloro-3-(trifluoromethyl)benzylamine with overall chemical yield 12% in three steps. The target tracer [¹⁸F]IUR-1601 ((S)-N-(2-chloro-3-(trifluoromethyl)benzyl)-1-(2-[¹⁸F]fluoroethyl)-5-oxopyrrolidine-2-carboxamide) was synthesized from desmethyl-GSK1482160 with 2-[¹⁸F]fluoroethyl tosylate, prepared from 1,2-ethylene glycol-bis-tosylate and K[¹⁸F]F/Kryptofix2.2.2, in two steps and isolated by HPLC combined with SPE in 1–3% decay corrected radiochemical yield. The radiochemical purity was >99%, and the molar activity at end of bombardment (EOB) was 74–370?GBq/μmol. The potency of IUR-1601 in comparison with GSK1482160 was determined by a radioligand competitive binding assay using [¹¹C]GSK1482160, and the binding affinity K_i values for IUR-1601 and GSK1482160 are 4.31 and 5.14?nM, respectively.     

The stereochemical course of yeast hexokinase-catalysed phosphoryl transfer by using adenosine 5''[gamma(S)-16O,17O,18O]triphosphate as substrate.

Adenosine 5'[gamma(S)-16O, 17O, 18O]triphosphate has been synthesized and used to determine the stereochemical course of phosphoryl transfer catalysed by yeast hexokinase. The chirality at phosphorus of the D-glucose 6-[16O,17O,18O]phosphate formed was analysed, after cyclization and methylation, by 31P n.m.r. spectroscopy. The phosphoryl transfer was found to occur with inversion of configuration, with a stereoselectivity in excess of 94%. The simplest interpretation of this result is that the phosphoryl group is transferred between substrates in the enzyme-substrate ternary complex by an 'in line' mechanism.     

Characterization of Growing Microorganisms in Soil by Stable Isotope Probing with H218O

A new approach to characterize growing microorganisms in environmental samples based on labeling microbial DNA with H₂¹⁸O is described. To test if sufficient amounts of ¹⁸O could be incorporated into DNA to use water as a labeling substrate for stable isotope probing, Escherichia coli DNA was labeled by cultivating bacteria in Luria broth with H₂¹⁸O and labeled DNA was separated from [¹⁶O]DNA on a cesium chloride gradient. Soil samples were incubated with H₂¹⁸O for 6, 14, or 21 days, and isopycnic centrifugation of the soil DNA showed the formation of two bands after 6 days and three bands after 14 or 21 days, indicating that ¹⁸O can be used in the stable isotope probing of soil samples. DNA extracted from soil incubated for 21 days with H₂¹⁸O was fractionated after isopycnic centrifugation and DNA from 17 subsamples was used in terminal restriction fragment length polymorphism (TRFLP) analysis of bacterial 16S rRNA genes. The TRFLP patterns clustered into three groups that corresponded to the three DNA bands. The fraction of total fluorescence contributed by individual terminal restriction fragments (TRF) to a TRFLP pattern varied across the 17 subsamples so that a TRF was more prominent in only one of the three bands. Labeling soil DNA with H₂¹⁸O allows the identification of newly grown cells. In addition, cells that survive but do not divide during an incubation period can also be characterized with this new technique because their DNA remains without the label.     

Resonance Raman Studies of Co—O2 and O—O Stretching Vibrations in Oxy-Cobalt Hemes

Strong evidence suggests that the stretching vibration of the bound oxygen can be perturbed by an accidentally degenerate porphyrin ring mode, resulting in two split frequencies. In the Co(II)(TpivPP) (pyridine) ¹⁸O₂ complex, we demonstrate that the ν(¹⁸O—¹⁸O) mode, after being shifted from its ν(¹⁶O—¹⁶O) value at 1,156 cm^-1, undergoes a resonance interaction with the 1,080 cm^-1 porphyrin mode, giving rise to two lines at 1,067 and 1,089 cm^-1. In the O₂ complex of Co(II) mesoporphyrin IX-substituted sperm whale myoglobin, we observed a dramatic intensity increase at 1,132 cm^-1 upon ¹⁶O₂ → ¹⁸O₂ substitution, which is due to the reappearance of the 1,132-cm^-1 porphyrin mode after the removal of resonance conditions. A decrease in O₂ binding affinity, caused by the proximal base tension, corresponds to an increase in the Co—O₂ stretching frequency. The ν(Co—O₂) at 527 cm^-1 for the low affinity Co(II)(TpivPP)(1,2-Me₂Im) O₂ complex is 11 cm^-1 higher than the 516-cm^-1 value for the high affinity complex (with N-MeIm replacing 1,2-Me₂Im). However, in the corresponding iron complexes the reverse behavior is observed, i.e., the ν(Fe—O₂) decreases for the (1,2-Me₂Im) complex. There is a 24-cm^-1 difference in the Co—O₂ stretching frequencies between Co(II)(TpivPP)(N-MeIm)O₂ (at 516 cm^-1) and oxy meso CoMb (at 540 cm^-1), suggesting a protein induced distortion of the Co—O—O linkage. However, the values for ν(Fe—O₂) are nearly identical between Fe(II)(TpivPP)(N-MeIm)O₂ (at 571 cm^-1) and oxy Mb (at 573 cm^-1), indicating that O₂ binds to myoglobin in the same manner as in the sterically unhindered “picket fence” complex. Evidence is presented that suggests the presence of two dioxygen stretching frequencies due to two different conformers in each of the N-MeIm and 1,2-Me₂Im complex of oxy Co(II)(TpivPP).     

Enzymatic formation of (20R, 22R)-20,22-dihydroxycholesterol from cholesterol and a mixture of 16O2 and 18O2: random incorporation of oxygen atoms

[4-¹⁴C]Cholesterol was incubated with an adrenocortical preparation in the presence of ¹⁶O₂ and ¹⁸O₂ devoid of significant ¹⁶O¹⁸O. Isolated (20R,22R)-20,22-dihydroxycholesterol was converted to a trimethylsilyl derivative and analyzed by gas chromatography - mass spectrometry to determine the isotope distribution of the oxygen atoms at C-20 and C-22. The ions of $\text{m}\text{e}$ 289, 291, and 293 (comprising the C₈ C-20 to C-27 side-chain and containing, respectively, ¹⁶O₂, ¹⁶O¹⁸O, and ¹⁸O₂) exhibited a binomial distribution indicating that the oxygen atoms of the vicinal glycol were drawn at random from the atomic pool of the oxygen molecules. If both side-chain hydroxyl groups had originated from the atoms of the same oxygen molecule, the ion of $\text{m}\text{e}$ 291 would have been absent.     

Evidence for 18O labeling of photorespiratory CO2 in photoautotrophic cell cultures of higher plants illuminated in the presence of 18O2

The ¹⁸O-enrichment of CO₂ produced in the light or during the post-illumination burst was measured by mass spectrometry when a photoautotrophic cell suspension of Euphorbia characias L. was placed in photorespiratory conditions in the presence of molecular ¹⁸O₂. The only ¹⁸O-labeled species produced was C¹⁸O¹⁶O; no C¹⁸O¹⁸O could be detected. Production of C¹⁸O¹⁶O ceased after addition of two inhibitors of the photosynthetic carbon-oxidation cycle, aminooxyacetate or aminoacetonitrile, and was inhibited by high levels of CO₂. The average enrichment during the post-illumination burst was estimated to be 46 ± 15% of the enrichment of the O₂ present during the preceding light period. Addition of exogenous carbonic anhydrase, by catalyzing the exchange between CO₂ and H₂O, drastically diminished the ¹⁸O-enrichment of the produced CO₂. The very low carbonio-anhydrase level of the photoautotrophic cell suspension probably explains why the ¹⁸O labeling of photorespiratory CO₂ could be observed for the first time. These data allow the establishment of a direct link between O₂ consumption and CO₂ production in the light, and the conclusion that CO₂ produced in the light results, at least partially, from the mitochondrial decarboxylation of the glycine pool synthesized through the photosynthetic carbon-oxidation cycle. Analysis of the C¹⁸O¹⁶O and CO₂ kinetics provides a direct and reliable way to assess in vivo the real contribution of photorespiratory metabolism to CO₂ production in the light.     

Coordinated 2-halo-l,3,2-dioxaphosphorinane ligands. I. syntheses and 13C, 17O, 31P and 95Mo NMR and IR spectroscopic characterization of some molybdenum pentacarbonyl complexes of 2-substituted-5, 5-dimethyl-1,3, 2-dioxaphosphorinanes

A study of the reactions of Mo(CO)₅(P(OCH₂- CMe₂CH₂0)X) (X = C1, Br) with a variety of nucleophiles of the type HER (E = NH, O, S; R = H, alkyl, aryl) is reported. The mechanism of these reactions is shown to be S_N2, and the significantly slower rates of reactions of n-propylamine with the above complexes relative to the rate of reaction of n-propylamine with Mo(CO)₅(Ph₂PC1) is discussed.The ¹³C, ¹⁷O, ³¹P and ⁹⁵Mo NMR data and infrared data for these complexes are presented. Good correlations between chemical shifts of the cis and trans CO¹³C and trans CO¹⁷0 NMR resonances, CO infrared stretching force constants and the magnitudes of ¹J_Mop and ²J_PC (trans CO) are observed and the reasons for these correlations are discussed.The correlations between the chemical shifts of NMR-active nuclei in the Mo(CO)₅(P(OCH₂CMe₂- CH₂O)ER) complexes with the chemical shifts of similar nuclei in the Mo(CO)₅(Ph₂PER) complexes fange from excellent to very poor. This indicates that the effects of-the P-substituents on the chemical shifts of the NMR-active nuclei in these complexes are not additive.     

Synthesis and characterization of the asymmetrically coordinated dinuclear complex [{L(Ph2acac)FeIII}(μ-O){FeIII(Cl4-cat)L}](ClO4) and its one-electron reduced and oxidized forms. Models for dinuclear non-heme active sites

The asymmetrically coordinated complex [{L(Ph₂acac)Fe^III}(μ-O){Fe^III(Cl₄-cat)L}](BPh₄)·1.5toluene has been synthesized and structurally characterized (Ph₂acac^–=1,3-diphenylpropane-1,3-dionate, Cl₄-cat^2–=tetrachlorocatecholate, L=1,4,7-trimethyl-1,4,7-triazacyclononane). This species can be electrochemically oxidized and reduced by one electron, respectively, yielding two species which both have an S=1/2 ground state. It is shown that the oxidation is ligand-centered, affording a coordinated semiquinonate(1–) ligand with S=1/2 which is antiferromagnetically coupled to a high-spin Fe^III ion (S=5/2) yielding an S=2 state which, in turn, is antiferromagnetically coupled (through the oxo bridge) to the second high-spin Fe^III ion (S=5/2) yielding the observed S=1/2 ground state. In contrast, the reduction is metal-centered generating a mixed-valent species with an [Fe^III-O-Fe^II]³⁺ core; intramolecular antiferromagnetic coupling again produces an S=1/2 ground state. The symmetrical complex [{LFe^III(Ph₂acac)}₂(μ-O)](ClO₄)₂ has also been synthesized, as have the mononuclear species [LFe^II(Ph₂acac)Cl] and [LFe^III(aacac)Cl](ClO₄)·1 mesitylene [aacac^–=3-(9-anthryl)acetylacetonate(1–)], all of which have been characterized by X-ray crystallography. The magnetism, the Mössbauer-, EPR-, and UV-VIS-spectra and the electrochemistry of complexes are reported.     

Neutron scattering study of the 13 S fragment of 16 S RNA and its complex with ribosomal protein S4

A fragment with a molecular weight of 170,000 and a sedimentation coefficient of 13 S which is capable of specifically binding ribosomal protein S4 has been obtained by digestion of Escherichia coli 16 S RNA with ribonuclease A. The 13 S fragment of 16 S RNA and its complex with protein S4 have been studied by different physical methods; in the first place, by neutron scattering. It has been shown that this fragment is very compact in solution. The radii of gyration of this fragment (50 ± 3 Å) and of protein S4 within the complex (17 ± 3 Å) coincide, within the limits of experimental error, with the radii of gyration for the free RNA fragment (47 ± 2 Å) and the free ribosomal protein S4 in solution (18 ± 2 Å). Hence the conclusion is drawn that the compactness of the RNA fragment and the ribosomal protein does not change on complex formation. The compact 13 S fragment of 16 S RNA is shown to be contrast-matched in solvent containing 70% ²H₂O which corresponds to a value for the partial specific volume of RNA of 0.537 cm³/g.     

Synthesis and evaluation of myxochelin analogues as antimetastatic agents

Myxochelin A (1) is an inhibitor of tumor cell invasion produced by the bacterium belonging to the genus Nonomuraea. In order to obtain more potent inhibitors, a series of myxochelin analogues [2 and (S)-3–17] were synthesized through the coupling of lysine or diaminoalkane derivatives and appropriately protected hydroxybenzoate, followed by modification of functional groups and deprotection. These compounds were evaluated for their inhibitory activity against invasion of murine colon 26-L5 carcinoma cells. Among the synthetic analogues tested, compound (S)-6 which possesses carbamoyl group at C-1 was found to be the most potent antiinvasive agent and is considered to be a promising lead molecule for the antimetastasis. Compound (S)-6 was also shown to inhibit gelatinase activities of MMP-2 and MMP-9 and in vivo lung metastasis in mice.     

Synthesis and evaluation of 18F-labeled mitiglinide derivatives as positron emission tomography tracers for β-cell imaging

Measuring changes in β-cell mass in vivo during progression of diabetes mellitus is important for understanding the pathogenesis, facilitating early diagnosis, and developing novel therapeutics for this disease. However, a non-invasive method has not been developed. A novel series of mitiglinide derivatives (o-FMIT, m-FMIT and p-FMIT; FMITs) were synthesized and their binding affinity for the sulfonylurea receptor 1 (SUR1) of pancreatic islets were evaluated by inhibition studies. (+)-(S)-o-FMIT had the highest affinity of our synthesized FMITs (IC₅₀ = 1.8 μM). (+)-(S)-o-[¹⁸F]FMIT was obtained with radiochemical yield of 18% by radiofluorination of racemic precursor 7, hydrolysis, and optical resolution with chiral HPLC; its radiochemical purity was >99%. In biodistribution experiments using normal mice, (+)-(S)-o-[¹⁸F]FMIT showed 1.94 ± 0.42% ID/g of pancreatic uptake at 5 min p.i., and decreases in radioactivity in the liver (located close to the pancreas) was relatively rapid. Ex vivo autoradiography experiments using pancreatic sections confirmed accumulation of (+)-(S)-o-[¹⁸F]FMIT in pancreatic β-cells. These results suggest that (+)-(S)-o-[¹⁸F]FMIT meets the basic requirements for an radiotracer, and could be a candidate positron emission tomography tracer for in vivo imaging of pancreatic β-cells.     

Steroidal Saponins from the Rhizomes of Aspidistra typica

Eleven new furostanol saponins, typaspidosides B-L (1–11), one new spirostanol saponin, typaspidoside M (12), and five known spirostanol saponins, 25S-atropuroside (13), neoaspidistrin (14), (25S)-pratioside D₁ (15), 25S-aspidistrin (16) and 25S-neosibiricoside (17) were isolated from the rhizomes of Aspidistra typica Baill. The structures of the new compounds were established using 1D and 2D NMR (¹H-¹H COSY, HMQC, HMBC and ROESY) spectroscopy, high resolution mass spectrometry, and chemical methods. The aglycones of 1–3 (unusual furostanol saponins with opened E ring type), 9 and 10 (the methoxyl substituent at C-23 position) were found, identified from natural products for the first time. Moreover, the anti-HIV activities of the isolated steroidal glycosides were assessed, and compounds 13, 14, 16 and 17 exhibited high active against HIV-1.     

Study on the properties of the S3-state by mass spectrometry in the filamentous cyanobacterium Oscillatoria chalybea

In the present paper we analyzed the properties of the S₃-state in the filamentous cyanobacterium Oscillatoria chalybea by mass spectrometry. In this organism a substantial O₂-signal due to a single flash is observed even after extensive dark adaptation (20 min). This signal can be measured by mass spectrometry as well as amperometrically on an oxygen electrode and is not due to an interference of respiratory and photosynthetic electron transport in the prokaryotic membrane. The mass spectrometric analysis shows that, if S₃ is generated by two flashes in a medium containing only H₂¹⁶O, addition of H₂¹⁸O and subsequent firing of a third flash yields O₂ evolution labelled with ¹⁸O. It appears that the isotopic composition of the O₂ evolved corresponds to the isotopic composition of the water in the suspension. This experiment shows that water oxidation does not proceed via an oxygen precursor or water derivatives bound to the S₃-state. This conclusion has been reached shortly before ours by Radmer and Ollinger [15] in the reverse marker experiment. From our study with O. chalybea it appears that freshly generated S₃ can be distinguished from metastable S₃ by the mass spectrometric method. It looks as if in contrast to freshly generated S₃ metastable S₃ contained bound unexchangeable water or an oxidized water derivative.     

Hydrogen bond supramolecular self-assembly in nickel(II) dithiophosphates, Ni[S2P(OR)2]2, R = sec-Bu, iso-Bu, and their bis(pyrazole) adducts

The reaction between nickel(II) nitrate and potassium phosphorus-1,1-dithiolates (di-sec-butyl and di-iso-butyl) in methanol yields 2:1 complexes which were characterized by FT-IR and NMR spectroscopy. 2:1 pyrazole adducts of both compounds were also obtained.The X-ray diffraction analysis of the compounds reveals square planar, four-coordination geometry for the homoleptic compounds and a six-coordinated distorted octahedral geometry for the adducts. In Ni[S₂P(OBu^s)₂]₂ the molecules are associated through C-H?O hydrogen bonds (2.652 Å), and in Ni[S₂P(OBuⁱ)₂]₂ the molecules are associated through C-H?S hydrogen bonds (2.948 Å). The pyrazole adducts are associated through N-H?O bonds and N-H?S bonds from the pyrazole nitrogen atoms, to form supramolecular assemblies. Thus, Ni[S₂P(OBu^s)₂(Pz)₂]₂ (Pz = pyrazole) forms bi-dimensional layers through N-H?O and N-H?S bonds (2.502 and 2.965 Å, respectively), whereas Ni[S₂P(OBuⁱ)₂(Pz)₂]₂ forms linear chains with N-H?S bonds 2.728 Å. The dithiophosphato groups behave as isobidentate chelating ligands.