Synthesis and Properties of Phosphorylated 3′-O-β-D-Ribofuranosyl-2′-deoxythymidine

Abstract

A strategy was developed for the synthesis of 3′-O-β-D-ribofuranosyl 2′-deoxythymidine derivatives using three different protecting groups, which allows the synthesis of a phosphoramidite building block for oligonucleotide synthesis. Likewise the 5′-O- and 5″-O-phosphorylated analogues were synthesized and their conformation was determined using NMR spectroscopy.     

Accumulation of Isochorismate-derived 2,3-Dihydroxybenzoic 3-O-β-d-Xyloside in Arabidopsis Resistance to Pathogens and Ageing of Leaves

An intricate network of hormone signals regulates plant development and responses to biotic and abiotic stress. Salicylic acid (SA), derived from the shikimate/isochorismate pathway, is a key hormone in resistance to biotrophic pathogens. Several SA derivatives and associated modifying enzymes have been identified and implicated in the storage and channeling of benzoic acid intermediates or as bioactive molecules. However, the range and modes of action of SA-related metabolites remain elusive. In Arabidopsis, Enhanced Disease Susceptibility 1 (EDS1) promotes SA-dependent and SA-independent responses in resistance against pathogens. Here, we used metabolite profiling of Arabidopsis wild type and eds1 mutant leaf extracts to identify molecules, other than SA, whose accumulation requires EDS1 signaling. Nuclear magnetic resonance and mass spectrometry of isolated and purified compounds revealed 2,3-dihydroxybenzoic acid (2,3-DHBA) as an isochorismate-derived secondary metabolite whose accumulation depends on EDS1 in resistance responses and during ageing of plants. 2,3-DHBA exists predominantly as a xylose-conjugated form (2-hydroxy-3-β-O-d-xylopyranosyloxy benzoic acid) that is structurally distinct from known SA-glucose conjugates. Analysis of DHBA accumulation profiles in various Arabidopsis mutants suggests an enzymatic route to 2,3-DHBA synthesis that is under the control of EDS1. We propose that components of the EDS1 pathway direct the generation or stabilization of 2,3-DHBA, which as a potentially bioactive molecule is sequestered as a xylose conjugate.     

Indole-3-methanol-β-D-glucoside and indole-3-carboxylic acid-β-D-glucoside are products of indole-3-acetic acid degradation in wheat leaf segments

The formation of glucosides of indole-3-methanol (IM) and indole-3-carboxylic acid (ICA) after application of radio-labelled indole-3-acetic acid (IAA) and IM to leaf segments of wheat and other members of the Gramineae is described. The results suggest that the decarboxylative pathway of IAA degradation leading to ICA via IM may occur in the leaf segments.     

Gas chromatographic-mass spectroscopic identification and quantification of cyclic guanosine-3′: 5′-monophosphate in maize seedlings (Zea mays)

Gas chromatographic-mass spectroscopic evidence is presented for the presence of guanosine-3′: 5′-monophosphate (cGMP) in maize seedlings. The amount of cGMP (35–72 pmol g^-1 fresh weight) was quantified as a tetra-silyl derivative using gas-chromatographic detection with reference to a silylated standard of authentic cGMP. Gas-chromatographic separation of tri-silyl adenosine-3′: 5′-monophosphate and tetra-silyl cGMP is demonstrated.     

Roles of Residues Arg-61 and Gln-38 of Human DNA Polymerase η in Bypass of Deoxyguanosine and 7,8-Dihydro-8-oxo-2′-deoxyguanosine

Like the other Y-family DNA polymerases, human DNA polymerase η (hpol η) has relatively low fidelity and is able to tolerate damage during DNA synthesis, including 7,8-dihydro-8-oxo-2′-deoxyguanosine (8-oxoG), one of the most abundant DNA lesions in the genome. Crystal structures show that Arg-61 and Gln-38 are located near the active site and may play important roles in the fidelity and efficiency of hpol η. Site-directed mutagenesis was used to replace these side chains either alone or together, and the wild type or mutant proteins were purified and tested by replicating DNA past deoxyguanosine (G) or 8-oxoG. The catalytic activity of hpol η was dramatically disrupted by the R61M and Q38A/R61A mutations, as opposed to the R61A and Q38A single mutants. Crystal structures of hpol η mutant ternary complexes reveal that polarized water molecules can mimic and partially compensate for the missing side chains of Arg-61 and Gln-38 in the Q38A/R61A mutant. The combined data indicate that the positioning and positive charge of Arg-61 synergistically contribute to the nucleotidyl transfer reaction, with additional influence exerted by Gln-38. In addition, gel filtration chromatography separated multimeric and monomeric forms of wild type and mutant hpol η, indicating the possibility that hpol η forms multimers in vivo.     

Assimilation of exogenous 2′-14C-indole-3-acetic acid and 3′-14C-tryptophan exposed to the roots of three wheat varieties

This study was conducted to determine if plants can assimilate indole-3-acetic acid (IAA) from rooting media and if exogenous L-tryptophan (L-TRP) can be assimilated and converted by plants into auxins. The addition of 2-¹⁴C-IAA (3.7 kBq plant^-1) to wheat (Triticum aestivum L.) seedlings of three varieties grown in nutrient solution resulted in the uptake (avg.=7.6%) of labelled IAA. Most of the label IAA was recovered in the shoot (avg.=7.2%) with little accumulation in the root (avg.=0.43%). A portion of the assimilated IAA-label in the plant was identified by co-chromatography and UV spectral confirmation as IAA-glycine and IAA-aspartic acid conjugates. Little of the assimilated IAA label was found as free IAA in the wheat plants. These same assimilation patterns were observed when 2-¹⁴C-IAA was added to wheat plants grown in sterile and nonsterile soil. In contrast, the wheat varieties assimilated considerably less (avg.=1.3%) of the added microbial IAA precursor, 3-¹⁴C-L-TRP (3.7 kBq plant^-1) and thus much lower amounts of IAA conjugates were detected. Glasshouse soil experiments revealed that 2 out of 3 wheat varieties had increased growth rates and increased yields when L-TRP (10^-5 and 10^-7 M) was added to the root zone. It is surmised that this positive response is a result of microbial auxin production within the rhizosphere upon the addition of the precursor, L-TRP. The amino acid composition of the root exudates plays a critical role in microbial production of auxins in the rhizosphere. This study showed that wheat roots can assimilate IAA from their rooting media, which will supplement the endogenous IAA levels in the shoot tissue and may positively influence plant growth and subsequent yield.     

Biosynthesis of indole-3-acetic acid in tomato shoots: Measurement,mass-spectral identification and incorporation of −2H from −2H2O into indole-3-acetic acid,d- and l-tryptophan,indole-3-pyruvate and tryptamine

Indole-3-acetic acid (IAA) and its putative precursors, l- and d-tryptophan, indole-3-pyruvate, and tryptamine were isolated from tomato (Lycopersicon esculentum (L.) Mill.) shoots, identified by mass spectrometry, and measured using capillary gas chromatography with an electron capture detector and radioactive internal standards. Average amounts present were 7.9ng · (g FW)^–-1 IAA, 5.7ng · (g FW)^–-1 indole-3-pyruvate, 132 ng · (g FW)^–-1 tryptamine, 103 ng · (g FW)^–-1 d-tryptophan, and 2250 ng · (g FW)^–-1 l-tryptophan. Indole-3-acetaldoxime was not found; detection limits were less than 1ng · (g FW)^–-1. When tomato shoots were incubated for 6, 10 and 21 h in 30% ^–2H₂O, up to four positions in IAA, l- and d-tryptophan, tryptamine and indole-3-pyruvate became labelled with ^–2H. Compounds became labelled rapidly with 10% of IAA molecules containing ^–2H after 6 h. The percentage of labelled molecules of IAA and l-tryptophan increased up to 10 h but then decreased again, correlating with an increase in the total shoot tryptophan and presumably a result of protein hydrolysis in the excised, slowly senescing tissue. The amount of ^–2H in d-tryptophan also showed an increase followed by a decrease, but the proportion of labelled molecules was much less than in l-tryptophan and IAA. Tryptamine became labelled initially at a similar rate to IAA but continued to accumulate ^–2H up to 21 h. We conclude that tryptamine is synthesized from a different pool of tryptophan from that used in IAA synthesis, and is not a major endogenous precursor of IAA in tomato shoots. Indole-3-pyruvate was the most heavily labelled compound after 6 and 10 h incubation (21-h data not available). Furthermore, the proportion of ^–2H-labelled indole-3-pyruvate molecules was quantitatively consistent with the amount of label in IAA. On the other hand, a quantitative comparison of the IAA turnover rate and the rate of ^–2H incorporation into both l- and d-tryptophan indicates that IAA is not made from the total shoot pool of either l- or d-tryptophan. Instead IAA appears to be synthesized from a restricted pool which is turning over rapidly and which has access to both newly synthesized tryptophan and that from protein hydrolysis.Abbreviations GC-ecd gas chromatography with electroncapture detector - GC-MS combined gas chromatography-mass spectrometry - HPLC high-performance liquid chromatography - IAA indole-3-acetic acid - IAOX indole-3-acetaldoxime - IPyA indole-3-pyruvate - PFB pentafluorobenzyl - R_T retention time - TNH₂ tryptamine - Trp tryptophan - SIM selected ion monitoring We wish to thank Ms. Sue Alford for running the mass spectra and Dr Harry Young for advice with the mass spectrometry. The work was supported by grants from the University of Auckland Research Committee and the C. Alma Baker Trust fund. The mass spectrometer was supported jointly by the University Grants Commitee (NZ) and the DSIR Division of Horticulture and Processing.     

The oxidized form of cholesterol 3β-hydroxy-5-oxo-5,6-secocholestan-6-al induces structural and thermotropic changes in phospholipid membranes

The effect of an oxidized form of cholesterol, 3β-hydroxy-5-oxo-5,6-secocholestan-6-al on the thermotropic and structural properties of phospholipid membranes was investigated by differential scanning calorimetry and X-ray diffraction and compared with that of cholesterol. The phospholipids studied included 1-palmitoyl-2-oleoylphosphatidylserine, dipalmitoleoylphosphatidylethanolamine, 1-palmitoyl-2-oleoylphosphatidylethanolamine, dipalmitoleoylphosphatidylcholine, 1-palmitoyl-2-oleoylphosphatidylcholine. Depending on the constituent phospholipids, the oxidized cholesterol is observed to shift phase transitions, disrupt stacking, modify interbilayer spacings and promote increased negative membrane curvature. We determined by absorption spectroscopy that the amino group of phosphatidylserine forms a Schiff base with the aldehyde group of the 3β-hydroxy-5-oxo-5,6-secocholestan-6-al as was previously found for the amino group of phosphatidylethanolamine. This result strengthens the biologically significant finding that not only amino groups of proteins but also amino groups of phospholipids are able to form a Schiff base with oxidized cholesterol. The marked triangular shape of the Schiff base complex with phosphatidylethanolamine may explain how 3β-hydroxy-5-oxo-5,6-secocholestan-6-al can promote increased negative curvature in the hexagonal phase, as compared to cholesterol, even though its increased polarity would favor a location closer to the interface with water.     

Occurrence of Stereoisomers of 1-(2′-Pyrrolidinethione-3′-yl)-1,2,3,4- tetrahydro-β-carboline-3-carboxylic Acid in Fermented Radish Roots and Their Different Mutagenic Properties

Stereoisomers of the tetrahydro-β-carboline derivative, 1-(2′-pyrrolidinethione-3′-yl)-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid (PTCC), were formed from L-tryptophan with 4-methylthio-3-butenyl isothiocyanate, and their mutagenic properties and contents in different types of the radish products were studied. The isomers were identified as (1S ^*, 3S ^*, 3′R ^*)- and (1R ^*, 3S ^*, 3′R ^*)-PTCCs; the former was found as the major compound but had no mutagenic activity, while the latter was mutagenic toward Salmonella typhimurium TA 98 in the presence of a rat microsomal fraction. Both (1S ^*, 3S ^*, 3′R ^*)- and (1R ^*, 3S ^*, 3′R ^*)-PTCC were detected in a ratio of about 4:1 in a product fermented for 8 months, but only a trace was apparent in products manufactured within a few weeks.     

Total synthesis of cerebrosides: (2S, 3R, 4E)-1-O-β-d-galactopyranosyl-N-(2′R and 2′S)-2′-hydroxytetracosanoylsphingenine

Total syntheses of both (2S, 3R, 4E)-1-O-β-d-galactopyranosyl-N-(2′R)-2′-hydroxytetracosanoylsphingenine 23 and the (2′S) stereoisomer were performed in an unambiguous way by employing either (2S, 3R, 4E)-N-(2′R)-2′-(tert-butyl-diphenylsilyloxy)tetracosanoylsphingenine or its (2′S) stereoisomer as the key glycosyl acceptors. The synthetic cerebroside 23 was shown to be identical with the natural product through comparison of their 400-MHz, ¹H-n.m.r. spectra, thus providing synthetic evidence for the 2′R configuration of the natural cerebroside.     

Selective synthesis of cerebrosides: (2S, 3R, 4E)-1-O-β-d-galactopyranosyl-N-(2′R and 2′S)-2′-hydroxytetracosanoyl-sphingenine

The cerebrosides were first isolated by Thudicum in 1874 and the structures were established by Carteret al. in 1950 (for review, see [2]). In 1961 Shapiro and Flowers [3] reported the first total synthesis of a cerebroside1 (Fig. 1) which was identified with the natural sample, only through comparison of their i.r. data. In order to confirm the absolute configuration at C-2 of natural cerebroside1, we describe here an unambiguous synthesis of two stereoisomeric cerebrosides1 and2, and found that the¹H-NMR spectra of the synthetic1 (Fig. 2) was completely identical with that of the natural cerebroside reported recently by Dabrowskiet al. [4].In planning the synthetic route, the target structures1 and2 were disconnected at the dotted lines to give three key synthetic intermediates3, 4 and5 or6 (Fig. 1).Abbreviations Bu butyl - Ph phenyl - t-BuPh₂SiCl t-butyldiphenylsilyl chloride - MTPA -methoxy--trifluoromethylphenylacetic acid - THF tetrahydrofuran Part 36 in the series Synthetic Studies on Cell-surface Glycans, for part 35, see [1]     

5-O-β-d-galactopyranosyl-7-methoxy-3′,4′-dihydroxy-4-phenylcoumarin,an inhibitor of photophosphorylation in spinach chloroplasts

5-O--d-galactopyranosyl-7-methoxy-3,4-dihydroxy-4-phenylcoumarin isolated from Exostema caribaeum (Rubiaceae) has been found to act as an energy-transfer inhibitor in spinach chloroplasts. ATP synthesis and phosphorylating (coupled) electron flow were inhibited by 89 and 72%, respectively, at a concentration of 400 M. H⁺-uptake, basal and uncoupled electron transport were not affected by the coumarin. The light-activated Mg⁺²-ATPase activity from bound membrane thylakoid chloroplasts was slightly inhibited by the coumarin. Also, the heat-activated Ca⁺²-ATPase activity of the isolated coupling factor protein was insensitive to this compound. In chloroplasts partially stripped of coupling factor 1 by an EDTA treatment, the coumarin showed a restoration of the proton uptake process. These results suggest that the 4-phenylcoumarin under investigation inhibited phosphorylation in chloroplasts by specifically blocking the transport of protons through a membrane-bound component or a carrier channel (CF_O) located in a hydrophobic region at or near the functional binding site for the coupling factor 1.Abbreviations CF₁ chloroplast coupling factor 1 - CF_O coupling factor zero - DCCD dicyclohexylcarbodiimide - DTT dithiothreitol - EDTA ethylene-diaminetetraacetic acid - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulphonic acid - MES 2-(N-morpholino) ethanesulphonic acid - TCA trichloroacetic acid Taken in part from PhD thesis of M.R. Calera.     

Microbial Stereoselective Oxidation of 2-methyl-1,3-propanediol to (R)-β-hydroxyisobutyric Acid in Aqueous/organic Biphasic Systems

The aim of this work was to evaluate (R)-&#103-hydroxyisobutyric acid (HIBA) production by microbial stereoselective oxidation of 2-methyl-1,3 propanediol under different conditions, and to compare the performance of this bioconversion in traditional aqueous media and aqueous/organic biphasic media. The oxidation is a two-step reaction with hydroxyisobutanal as an intermediate. Among the operational factors tested, pH and aeration were those, which most significantly affected the biocatalytic activity. Enantiomeric excesses higher than 95% were consistently obtained. For substrate concentrations above 50 mg ml^?1 a slight substrate inhibition was observed. Product inhibition was much stronger, and together with the decrease of the pH during the bioconversion was the most important limiting factor in long-term bioconversions. Kinetic parameters were determined for different pH values. A compromise pH value of 4 was determined to be the optimum for HIBA production and simultaneous extraction with an organic phase of trioctyl phosphine oxide (TOPO) in isooctane.     

Production of rosmarinic acid and a new rosmarinic acid 3′-O-β-D-glucoside in suspension cultures of the hornwort Anthoceros agrestis Paton

Cell suspension cultures of the hornwort Anthoceros agrestis Paton (Anthocerotaceae) were cultivated and characterized in CB-media containing 2 and 4% sucrose. The suspension cells accumulated rosmarinic acid up to 5.1% of the cell dry weight as well as caffeoyl-4'-hydroxyphenyllactate. Moreover, a more hydrophilic compound was detected which was isolated and identified as rosmarinic acid 3'-O-beta-D-glucoside, a new rosmarinic acid derivative. This new rosmarinic acid derivative was found up to 1.0% of the cell dry weight in suspension cells of A. agrestis.     

HPLC as a Tool to Study the Kinetics of Parallel and Consecutive Reactions: Competitive Interconversion,Dephosphorylation, Deamination and Depyrimidination of Cytidine 2′- and 3′-Monophosphates in Aqueous Acid

Abstract

The applicability of HPLC as a method to study the kinetics of complicated reaction systems of nucleosides and nucleotides has been demonstrated by using the hydrolytic reactions of cytidine 2′- and 3′-monophosphates as an example.     

Low 8-oxo-7,8-dihydro-2′-deoxyguanosine levels and influence of genetic background in an Andean population exposed to high levels of arsenic

BackgroundArsenic (As) causes oxidative stress through generation of reactive oxygen species. 8-Oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodG), a sensitive marker of oxidative DNA damage, has been associated with As exposure in some studies, but not in others, possibly due to population-specific genetic factors.ObjectivesTo evaluate the association between As and 8-oxodG in urine in a population with a low urinary monomethylated As (%MMA) and high dimethylated As (%DMA), as well as the genetic impact on (a) 8-oxodG concentrations and (b) the association between As and 8-oxodG.Materials and methodsWomen (N = 108) in the Argentinean Andes were interviewed and urine was analyzed for arsenic metabolites (ICPMS) and 8-oxodG (LC–MS/MS). Twenty-seven polymorphisms in genes related to oxidative stress and one in As(+III)methyltransferase (AS3MT) were studied.ResultsMedian concentration of 8-oxodG was 4.7 nmol/L (adjusted for specific weight; range 1.6–13, corresponding to 1.7 μg/g creatinine, range 0.57–4.8) and of total urinary As metabolites (U-As) 290 μg/L (range 94–720; 380 μg/g creatinine, range 140–1100). Concentrations of 8-oxodG were positively associated with %MMA (strongest association, p = 0.013), and weakly associated with U-As (positively) and %DMA (negatively). These associations were strengthened when taking ethnicity into account, possibly reflecting genetic differences in As metabolism and genes regulating oxidative stress and DNA maintenance. A genetic influence on 8-oxodG concentrations was seen for polymorphisms in apurinic/apyrimidinic endonuclease 1 (APEX1), DNA-methyltransferases 1 and 3b (DNMT1, DNMT3B), thioredoxin reductase 1 (TXNRD1) and 2 (TXNRD2) and glutaredoxin (GLRX).ConclusionDespite high As exposure, the concentrations of 8-oxodG in this population were low compared with other As-exposed populations studied. The strongest association was found for %MMA, stressing that some inconsistencies between As and 8-oxodG partly depend on population variations in As metabolism. We found evidence of genetic impact on 8-oxodG concentrations.     

Identification of New Regions in HIV-1 gp120 Variable 2 and 3 Loops that Bind to α4β7 Integrin Receptor

Background

The gut mucosal homing integrin receptor α4β7 present on activated CD4⁺ T cells interacts with the HIV-1 gp120 second variable loop (V2). Case control analysis of the RV144 phase III vaccine trial demonstrated that plasma IgG binding antibodies specific to scaffolded proteins expressing the first and second variable regions (V1V2) of HIV envelope protein gp120 containing the α4β7 binding motif correlated inversely with risk of infection. Subsequently antibodies to the V3 region were also shown to correlate with protection. The integrin receptor α4β7 was shown to interact with the LDI/V motif on V2 loop but recent studies suggest that additional regions of V2 loop could interact with the α4β7. Thus, there may be several regions on the V2 and possibly V3 loops that may be involved in this binding. Using a cell line, that constitutively expressed α4β7 receptors but lacked CD4, we examined the contribution of V2 and V3 loops and the ability of V2 peptide-, V2 integrin-, V3-specific monoclonal antibodies (mAbs), and purified IgG from RV144 vaccinees to block the V2/V3-α4β7 interaction.

Results

We demonstrate that α4β7 on RPMI8866 cells bound specifically to its natural ligand mucosal addressin cell adhesion molecule-1 (MAdCAM-1) as well as to cyclic-V2 and cyclic-V3 peptides. This binding was inhibited by anti-α4β7-specific monoclonal antibody (mAb) ACT-1, mAbs specific to either V2 or V3 loops, and by purified primary virions or infectious molecular clones expressing envelopes from acute or chronic subtypes A, C, and CRF01_AE viruses. Plasma from HIV-1 infected Thai individuals as well as purified IgG from uninfected RV144 vaccinees inhibited (0–50%) the binding of V2 and V3 peptides to α4β7.

Conclusion

Our results indicate that in addition to the tripeptide LDI/V motif, other regions of the V2 and V3 loops of gp120 were involved in binding to α4β7 receptors and this interaction was blocked by anti-V2 peptide, anti-V2 integrin, and anti-V3 antibodies. The ability of purified IgG from some of the uninfected RV144 vaccinees to inhibit α4β7 raises the hypothesis that anti-V2 and anti-V3 antibodies may play a role in blocking the gp120-α4β7 interaction after vaccination and thus prevent HIV-1 acquisition.     

Opposing Roles of Dopamine D1 and D2 Receptors in Nigral γ-[3H]Aminobutyric Acid Release?

This study examined the effects of dopamine D1 and D2 receptor agonists and antagonists on the spontaneous and calcium-dependent, K+-induced release of gamma-[3H]aminobutyric acid [( 3H]GABA) accumulated by slices of rat substantia nigra. SKF 38393 (D1 agonist) and dopamine (dual D1/D2 agonist) were without effect on [3H]GABA efflux by themselves (1-40 microM), or in the presence of the phosphodiesterase inhibitor isobutylmethylxanthine (IBMX) (0.5 mM), but potentiated evoked release in the presence of forskolin (0.5 microM), an adenylate cyclase activator. These increases in release were prevented by the D1 antagonist SCH 23390 (0.5 microM), but not by the D2 antagonist metoclopramide (0.5 microM). Higher concentrations of forskolin (10-40 microM) augmented stimulus-evoked [3H]GABA release directly, whereas dibutyryl cyclic AMP (100-200 microM) depressed it. Apomorphine, noradrenaline, and 5-hydroxytryptamine (1-40 microM) had no effect. The D2 stimulants lisuride, RU 24213, LY 171555, and bromocriptine dose-dependently inhibited depolarisation-induced but not basal [3H]GABA outflow. These inhibitory responses were not modified by the additional presence of SKF 38393 (10 microM) or SCH 23390 (1 microM), or by injection of 6-hydroxydopamine into the medial forebrain bundle 42 days earlier, but were attenuated by metoclopramide (0.5 microM). Higher amounts (10 microM) of SCH 23390, metoclopramide, or other D2 antagonists (loxapine, haloperidol) reduced evoked GABA release by themselves, probably by nonspecific mechanisms. These results suggest D1 and D2 receptors may have opposing effects on nigral GABA output and could explain the variable effects of mixed D1/D2 dopaminomimetics in earlier release and electrophysiological experiments.