Cyclic Phosphorothioate Research Articles

Synthesis of an R P-Guanosine-3′,5′-Cyclic Phosphorothioate Analogue

Synthesis of an R P-Guanosine-3′,5′-Cyclic Phosphorothioate Analogue

Preparative Synthesis of an R P-Guanosine-3',5'-Cyclic Phosphorothioate Analogue, a Drug Candidate for the Treatment of Retinal Degenerations.

Cyclic guanosine monophosphorothioate analogue 1a is currently showing potential as a drug for the treatment of inherited retinal neurodegenerations. To support ongoing preclinical and clinical work, we have developed a diastereoselective synthesis via cyclization and sulfurization of the nucleoside 5′-H-phosphonate monoester, which affords the desired RP-3′,5′-cyclic phosphorothioate in 9:1 ratio to the undesired SP-diastereomer. This route was made viable as a result of the silyl protection sequence used, which achieved >80% selectivity for 2′,5′-hydroxyls over 3′,5′-hydroxyls. Finally, the chromatography-free process allowed for a scale-up, as intermediates and the final product were isolated by crystallization to give 125 g of 1a (13.8% total yield) with over 99.9% HPLC purity.

Synthesis of 3′,5′‐Cyclic Phosphate and Thiophosphate Esters of 2′‐C‐Methyl Ribonucleosides

Abstract2′‐C‐Methylnucleosides are known to exhibit antiviral activity against Hepatitis C virus. Since the inhibitory activity depends on their intracellular conversion to 5′‐triphosphates, dosing as appropriately protected 5′‐phosphates or 5′‐phosphorothioates appears attractive. For this purpose, four potential pro‐drugs of 2′‐C‐methylguanosine, i.e., 3′,5′‐cyclic phosphorothioate of 2′‐C‐methylguanosine and 2′‐C,O6‐dimethylguanosine, 1 and 2, respectively, the S‐[(pivaloyloxy)methyl] ester of 2′‐C,O6‐dimethylguanosine 3′,5′‐cyclic phosphorothioate and the O‐methyl ester of 2′‐C,O6‐dimethylguanosine 3′,5′‐cyclic phosphate, 3 and 4, respectively, have been prepared.

The Commonly Used cGMP-dependent Protein Kinase Type I (cGKI) Inhibitor Rp-8-Br-PET-cGMPS Can Activate cGKI in Vitro and in Intact Cells

Small-molecule modulators of cGMP signaling are of interest to basic and clinical research. The cGMP-dependent protein kinase type I (cGKI) is presumably a major mediator of cGMP effects, and the cGMP analogue Rp-8-Br-PET-cGMPS (Rp-PET) (chemical name: beta-phenyl-1,N2-etheno-8-bromoguanosine-3',5'-cyclic monophosphorothioate, Rp-isomer) is currently considered one of the most permeable, selective, and potent cGKI inhibitors available for intact cell studies. Here, we have evaluated the properties of Rp-PET using cGKI-expressing and cGKI-deficient primary vascular smooth muscle cells (VSMCs), purified cGKI isozymes, and an engineered cGMP sensor protein. cGKI activity in intact VSMCs was monitored by cGMP/cGKI-stimulated cell growth and phosphorylation of vasodilator-stimulated phosphoprotein. Unexpectedly, Rp-PET (100 microm) did not efficiently antagonize activation of cGKI by the agonist 8-Br-cGMP (100 microm) in intact VSMCs. Moreover, in the absence of 8-Br-cGMP, Rp-PET (100 microm) stimulated cell growth in a cGKIalpha-dependent manner. Kinase assays with purified cGKI isozymes confirmed the previously reported inhibition of the cGMP-stimulated enzyme by Rp-PET in vitro. However, in the absence of the agonist cGMP, Rp-PET partially activated the cGKIalpha isoform. Experiments with a fluorescence resonance energy transfer-based construct harboring the cGMP binding sites of cGKI suggested that binding of Rp-PET induces a conformational change similar to the agonist cGMP. Together, these findings indicate that Rp-PET is a partial cGKIalpha agonist that under certain conditions stimulates rather than inhibits cGKI activity in vitro and in intact cells. Data obtained with Rp-PET as cGKI inhibitor should be interpreted with caution and not be used as sole evidence to dissect the role of cGKI in signaling processes.

Involvement of guanylyl cyclase, protein kinase A and Na +K + ATPase in relaxations of bovine isolated bronchioles induced by GEA 3175, an NO donor

The present study was designed to investigate the role of the sodium potassium adenosine triphosphatase (the Na +K + ATPase) in relaxation of bovine isolated bronchioles by a new NO donor, GEA 3175 (3-(3-chloro-2-methylphenyl)-5-[[(4-methylphenyl)sulphonyl]amino]-)hydroxide)). Bronchioles were mounted in a wire myograph for isometric tension recordings and contracted with 5-hydroxytryptamine (5-HT) or a K + rich solution. Concentration-dependent relaxations evoked by GEA 3175 were inhibited by ouabain or K + free solution. The guanylyl cyclase inhibitor 1H-[1,2,4]-oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ, 3 μM) and ouabain (10 nM) reduced GEA 3175-evoked relaxations to the same extent without any additive effect. Iberiotoxin (10 nM), an inhibitor of large conductance Ca 2+-activated K + channels inhibited GEA 3175-evoked relaxations to the same extent as ouabain. Combining ouabain and iberiotoxin completely abolished GEA 3175 relaxation. An inhibitor of protein kinase G (PKG), Rp-β-phenyl-1,N 2-etheno-8-bromo-guanosine-3′-5′-cyclic monophosphorothioate (Rp-8-Br-PET-cGMPs), slightly reduced GEA 3175-induced relaxations. An inhibitor of cyclic AMP-dependent kinase (PKA), Rp-adenosine-3′-5′-cyclic phosphorothioate (Rp-cAMPs), inhibited the GEA 3175-induced relaxations to the same extent as ouabain. Inhibition of both PKG and PKA abolished GEA 3175 relaxation. The study provides evidence that the NO donor GEA 3175 causes guanylyl cyclase-dependent relaxations, taking place through cyclic GMP and cyclic AMP-dependent protein kinases followed by opening of large conductance Ca 2+-activated K + channels and activation of smooth muscle Na +K + ATPase.

Leptin-induced nitric oxide production in white adipocytes is mediated through PKA and MAP kinase activation

Leptin injection increases plasma levels of nitrites and/or nitrates, an index of nitric oxide (NO) production. Because plasma levels of NO are correlated with fat mass and because adipose tissue is the main source of leptin, it seems that adipose tissue plays a major role in NO release induced by leptin. Adipocytes express both leptin receptors and nitric oxide synthase (NOS; including the endothelial isoform, NOS III, and the inducible isoform, NOS II). In this study, we have demonstrated that physiological concentrations of leptin stimulate NOS activity in adipocytes. This effect of leptin is abolished by 1) AG490, an inhibitor of Janus tyrosine kinase 2/signal transducer and activator of transcription 3; 2) U0126, an inhibitor of mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (p42/p44 MAPK); and 3) N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H-89) or Rp diastereomer of adenosine 3',5'-cyclic phosphorothioate, two inhibitors of protein kinase A, but not by wortmannin, an inhibitor of phosphatidylinositol 3-kinase. Immunoblotting studies have shown that leptin fails to activate Akt but increases p42/p44 MAPK phosphorylation, an effect that is prevented by U0126 but not by H-89. Furthermore, leptin induces NOS III phosphorylation at Ser(1179) and Thr(497), but not when adipocytes are pretreated with H-89 or U0126. Finally, stimulation of adipocyte NOS activity by leptin is either unaltered when protein phosphatase 2A is inhibited by 1 nM okadaic acid or completely abolished when protein phosphatase 1 (PP1) activity is inhibited by 3 nM tautomycin, which supports a crucial role for PP1 in mediating this effect of leptin. On the whole, these experiments demonstrate that NOS activity is a novel target for leptin in adipocytes and that the leptin-induced NOS activity is at least in part the result of NOS III phosphorylations via both protein kinase A and p42/p44 MAPK activation. More generally, this study also leads to the hypothesis of NO as a potentially important factor for leptin signaling in adipocytes.

Nucleotide-evoked relaxation of rat vas deferens: possible mechanisms

ATP causes relaxation of the K +-contracted rat vas deferens. Possible sites of action were investigated. ATP and adenosine relaxed the vas deferens precontracted with 80 mM K +; EC 50 values and maximal relaxations averaged, respectively, 760 μM and 56% for ATP and 74 μM and 30% for adenosine. The adenosine P1 receptor antagonist 8-( para-sulfophenyl)theophylline (8-SPT) reduced relaxations caused by adenosine and low concentrations of ATP, as did the Rp-diastereomer of adenosine 3′,5′-cyclic phosphorothioate (Rp-cAMPS), an inhibitor of protein kinase A. The phosphodiesterase inhibitor 4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone (Ro 20-1724) augmented responses to adenosine and low concentrations of ATP. α,β-Methylene ADP, an inhibitor of 5′-nucleotidase, reduced relaxations caused by ATP to a similar extent as did 8-SPT. In the presence of an almost saturating concentration of adenosine, ATP caused further relaxation. Conversely, in the presence of ATP, adenosine had little effect. Like ATP, UTP and other nucleoside triphosphates relaxed the vas deferens. The P2 receptor antagonists reactive blue 2, acid blue 25 and 4,4′-diisothiocyanotostilbene-2,2′-disulphonate (DIDS) attenuated the relaxation caused by ATP; suramin, pyridoxalphosphate-6-azophenyl-2′,4′-disulphonate (PPADS), Evans blue, trypan blue, reactive red 2 and brilliant blue G had no effect. Three non-selective inhibitors of protein kinases, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7), staurosporine and (8 R*,9 S*,11 S*)-(−)-9-hydroxy-9-carboxy-8-methyl-2,3,9,10-tetrahydro-8,11-epoxy-1 H,8 H,11 H-2,7b,11a-triazadibenzo[ a, g]cycloocta[ cde]trinden-1-one (K-252b), markedly reduced the relaxation caused by ATP. The results indicate that adenosine, derived from enzymatic dephosphorylation, contributes to the relaxant effect of ATP, presumably by activation of a smooth muscle adenosine receptor linked to the accumulation of cAMP and activation of protein kinase A. Yet, the main part of the response to ATP is mediated by a site distinct from the adenosine receptor. The pharmacological properties of this site differ from known P2 receptor subtypes. Possibly, the nucleotide-evoked relaxation is due to a phosphoryl transfer catalyzed by an ecto-protein kinase.

EFFECTS OF ISOPROTERENOL ON SPONTANEOUS EXCITATIONS IN DETRUSOR SMOOTH MUSCLE CELLS OF THE GUINEA PIG

Because beta-adrenoceptor agonists would be a useful tool for the pharmacological treatment of unstable bladder, we investigated the cellular mechanisms underlying beta-adrenoceptor mediated inhibition on spontaneous excitation in detrusor smooth muscle. Detrusor smooth muscle bundles were isolated from guinea pig bladders. Changes in membrane potential were recorded using an intracellular recording technique. In preparations loaded with the calcium indicator fura-PE3 changes in the concentration of intracellular calcium ions were measured simultaneously with membrane potential. Effects of isoproterenol on spontaneous changes in the membrane potential and intracellular Ca(2+) were examined Detrusor smooth muscle cells exhibited spontaneous action potentials that were associated with transient increases in intracellular Ca(2+) (calcium transients). Isoproterenol, which hyperpolarized the membrane, prevented action potentials and calcium transients. This induced inhibition of calcium transients was not affected by cyclopiazonic acid. Isoproterenol induced hyperpolarization was inhibited by inhibitors of protein kinase A, N-[2-((p-bromocinnamyl)amino)ethyl]-5-isoquinolinesulfonamide, hydrochloride and Rp-adenosine-3',5'-cyclic phosphorothioate. Hyperpolarization was blocked by a solution containing 30 mM. potassium but not by a range of potassium channel blockers. Ouabain and a solution of 0.5 mM. potassium also inhibited hyperpolarization. Our results suggest that isoproterenol prevented spontaneous action potential discharges and associated calcium transients through the activation of protein kinase A. The isoproterenol induced inhibition of intracellular Ca(2+) largely depends on the prevention of spontaneous action potentials since the contribution of the intracellular calcium store was small. Isoproterenol hyperpolarizes the membrane, probably by stimulating sodium pump activity.

Synthesis and separation of diastereomers of uridine 2′,3′-cyclic boranophosphate

The first boron-containing 2′,3′-cyclic phosphate-modified analogue, uridine 2′,3′-cyclic boranophosphate (2′,3′-cyclic-UMPB), was synthesized. 5′- O-Protected uridine was cyclophosphorylated by diphenyl H-phosphonate to yield uridine 2′,3′-cyclic H-phosphonate, which upon silylation followed by boronation and subsequent acid treatment gave 2′,3′-cyclic-UMPB in high yield. The two diastereomers of 2′,3′-cyclic-UMPB were separated by HPLC. An alternative method for synthesis of uridine 2′,3′-cyclic phosphorothioate (2′,3′-cyclic-UMPS) via H-phosphonate was also described.

Complex actions of protein kinase A inhibitors on mitogenesis of bovine coronary artery smooth muscle cells

This study investigates the possible modulation of platelet-derived growth factor-(PDGF, 20 ng/ml)-induced DNA synthesis in bovine coronary artery smooth muscle cells by the protein kinase A inhibitors Rp-adenosine-3′,5′-cyclic phosphorothioate (Rp-cAMPS, 0.03–10 μM) and { N-[2-(( p-bromocinnamyl)amino)ethyl]-5-isoquinolinesulfonamide, HCl} (H-89, 0.01–1 μM). Rp-cAMPS concentration dependently enhanced PDGF-induced DNA synthesis. In contrast, no potentiation of PDGF-induced DNA synthesis was seen with H-89. However, H-89 but not Rp-cAMPS, inhibited p42/p44 mitogen-activated protein kinase phosphorylation. Thus, Rp-cAMPS, but not H-89, unmasks inhibitory actions of protein kinase A on PDGF-induced mitogenesis of vascular smooth muscle cells. Low specificity may limit the use of H-89 as protein kinase A inhibitor.

Preparation and cleavage reactions of 3′-thiouridylyl-(3′→5′)-uridine

3′-Thiouridylyl-(3′→5′)-uridine [(Us)pU] 3 is prepared by coupling together the disulfide 14 and the 5′-H-phosphonate 18, and then removing the protecting groups. (Us)pU 3 readily undergoes cleavage in 0.05 mol dm−3 sodium glycinate buffer (pH 10.06) at 50 °C to give, in the first instance, uridine 4 and 3′-thiouridine 2′,3′-cyclic phosphorothioate 21; in glacial acetic acid at 30 °C, it rapidly undergoes cleavage in essentially the same way. The behaviour of (Us)pU 3 is compared with that of uridylyl-(3′→5′)-uridine (UpU) 1a under the same basic and acidic reaction conditions. (Us)pU 3 and 3′-thiouridine 2′,3′-cyclic phosphorothioate 21 are both substrates for ribonuclease A; (Us)pU 3 is a substrate for Crotalus adamanteus snake venom phosphodiesterase but not for calf spleen phosphodiesterase.

Adrenaline enhances LPS-induced IL-10 synthesis: evidence for protein kinase A-mediated pathway

The aim of the present study was to investigate the role of cAMP in enhanced IL-10 synthesis in human mononuclear cells. Adrenaline is known to act via the α- and β-adrenergic receptors which are coupled to adenylyl cyclase. The effects of cAMP elevation on IL-10 synthesis were studied at the protein level by ELISA and at the level of mRNA by RT\\PCR. In this in vitro model adrenaline enhanced the LPS-induced synthesis of IL-10 with parallel suppression of TNF synthesis. These effects were demonstrated both at the protein level and the level of mRNA. To analyze the role of cAMP we antagonized this effect by application of (Rp)-cAMPS, a diastereomer of adenosine-3′,5′-cyclic phosphorothioate, known to inhibit competitively the cAMP-induced activation of protein kinase A. Simultaneous addition of adrenaline and (Rp)-cAMPS led to a reversal of IL-10 synthesis to values induced by LPS stimulation alone. The kinetic analysis in LPS-stimulated mononuclear cells revealed a significant delay of IL-10 synthesis starting after 7 h compared with TNF synthesis which showed the first significant increase at 90 min. Finally, the combination of adrenaline and exogenous IL-10 led to a more pronounced suppression of TNF synthesis after LPS stimulation compared to suppression by IL-10 or adrenaline alone. The present results suggest the role of protein kinase A activation for adrenaline-induced IL-10 synthesis in human mononuclear cells. Additionally, based on the kinetic analysis and further experiments described in the literature, endogenous IL-10 could contribute to the adrenaline-induced suppression of TNF synthesis after prolonged incubation. These in vitro results could explain the suppression of TNF plasma concentration after parallel infusion of LPS and epinephrine compared to LPS infusion alone as has been demonstrated in a first human study.

Protein kinase A-mediated inhibition of gamma interferon-induced tyrosine phosphorylation of Janus kinases and latent cytoplasmic transcription factors in human monocytes by Ehrlichia chaffeensis.

Ehrlichia chaffeensis, an obligatory intracellular bacterium of monocytes or macrophages, is the etiologic agent of human monocytic ehrlichiosis. Our previous study showed that gamma interferon (IFN-gamma) added prior to or at early stage of infection inhibited infection of human monocytes with E. chaffeensis; however, after 24 h of infection, IFN-gamma had no antiehrlichial effect. To test whether ehrlichial infection disrupts Janus kinase (Jak) and signal transducer and activator of transcription (Stat) signaling induced by IFN-gamma, tyrosine phosphorylation of Stat1, Jak1, and Jak2 in E. chaffeensis-infected THP-1 cells was examined by immunoprecipitation followed by immunoblot analysis. Viable E. chaffeensis organisms blocked tyrosine phosphorylation of Stat1, Jak1, and Jak2 in response to IFN-gamma within 30 min of infection. Similar results were obtained with human peripheral blood monocytes infected with E. chaffeensis. Heat or proteinase K treatment but not periodate treatment of E. chaffeensis abrogated the inhibitory effect, suggesting that protein factor(s) of E. chaffeensis is responsible for the inhibition of IFN-gamma-induced tyrosine phosphorylation. Preincubation of E. chaffeensis with the Fab fragment of dog anti-E. chaffeensis immunoglobulin G also abrogated the inhibitory effect. On the other hand, monodansylcadaverine, which does not block binding but blocks internalization of ehrlichiae into macrophages, did not have any influence on the tyrosine phosphorylation. These results indicate that ehrlichial binding to host cells is sufficient to inhibit Stat1 tyrosine phosphorylation induced by IFN-gamma. Protein kinase A (PKA) activity in THP-1 cells increased approximately 25-fold within 30 min of infection with E. chaffeensis. In THP-1 cells pretreated with a PKA inhibitor, Rp isomer of adenosine 3',5'-cyclic phosphorothioate, E. chaffeensis-induced inhibition of Stat1 tyrosine phosphorylation was partially abrogated. These results suggest that E. chaffeensis blocks IFN-gamma-induced tyrosine phosphorylation of Jak and Stat through raising PKA activity in THP-1 cells, which may be an important survival mechanism of ehrlichiae within the host cell.

Effects of protein phosphatase and kinase inhibitors on Ca2+ and Cl- currents in guinea pig ventricular myocytes.

It is well-established that in heart, both the L-type Ca2+ channel and the cystic fibrosis transmembrane conductance regulator Cl- channel are regulated by cAMP-dependent phosphorylation. However, it is not clear whether both of these channels are regulated in concert by protein kinase A (PKA) or whether there are mechanisms that independently control the phosphorylation of these two PKA targets. The purpose of this study was to compare the effects of various protein phosphatase and protein kinase inhibitors on these two ionic currents (ICa and ICl) in guinea pig ventricular myocytes to gain insight into these questions. We found that both the stimulation and washout of the effects of isoproterenol on ICl are about twice as fast as the effects on ICa, probably because the dephosphorylation reaction for ICl is faster than that for ICa. In contrast, inhibition of protein phosphatases with 10 microM microcystin stimulated both ICa and ICl, but the stimulation of ICl was much slower and smaller than the stimulation of ICa. The effect of microcystin was inhibited by staurosporine (Ki = 171.5 and 161 nM for ICa and ICl, respectively), suggesting that the stimulation was due to a kinase. The kinase was not protein kinase C (PKC) because it was not inhibited by the specific pseudosubstrate inhibitor of PKC, PKC(19-31), and it was not PKA because it was not inhibited by adenosine 3',5'-cyclic phosphorothioate. These results suggest that although both the Ca2+ and Cl- channels are regulated by cAMP-dependent phosphorylation, another protein kinase may also regulate these channels, and the kinetics of the response of the channels to phosphorylation can be modulated independently by protein phosphatases.

Triggering of CD23b antigen by anti‐CD23 monoclonal antibodies induces interleukin‐10 production by human macrophages

The aim of this study was to evaluate the capacity of human macrophages to produce interleukin (IL)-10 upon stimulation of membrane CD23. An anti-CD23 monoclonal antibody (mAb) was found to elicit the expression of the specific mRNA for IL-10 in CD23-bearing macrophages, and to induce a time-dependent production of this cytokine with a maximal effect reached after 12 h. Inasmuch as we previously reported that CD23 ligation evoked the generation of nitric oxide and of cAMP, the effect of the Rp diastereoisomer of adenosine 3', 5'-cyclic phosphorothioate (Rp-cAMP, an inhibitor of the cAMP pathway) and of NG-monomethyl-L-arginine (L-NMMA, an inhibitor of the nitric oxide pathway) were evaluated on CD23-induced IL-10 production. In the presence of Rp-cAMP, the CD23-induced production of IL-10 and of the pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) was totally abrogated, whereas, in the presence of L-NMMA, IL-10 production was enhanced and TNF-alpha production was suppressed. In addition, neutralization of IL-10 with an anti-IL-10 mAb increased both the magnitude and duration of CD23-driven TNF-alpha production. Such an inducing effect was observed with different anti-CD23 mAb (clone 135, MHM6 and 25), indicating that the triggering of the CD23 molecule at the surface of human macrophages induced the generation of IL-10 through a cAMP-dependent mechanism. Concomitantly this generation of IL-10 was down-regulated by nitric oxide, which was also produced after triggering of the CD23 antigen. Taken together these data indicated that human macrophages produced IL-10 after triggering of the CD23 molecule and that this production could regulate the inflammatory state of these cells.

Evidence that Ca/calmodulin-dependent protein kinase mediates the modulation of the Ca 2+ -dependent K + current, I AHP , by acetylcholine, but not by glutamate, in hippocampal neurons

Muscarinic and metabotropic glutamate receptor agonists increase the excitability of hippocampal and other cortical neurons by suppressing the Ca2+-activated K+current, IAHP, which underlies the slow afterhyperpolarization (AHP) and spike frequency adaptation. We have examined the mechanism of action of a muscarinic agonist (carbachol) and a metabotropic glutamate receptor agonist (1-Aminocyclopentane-trans-1,3-dicarboxylic acid; t-ACPD) on IAHP in hippocampal CA1 neurons in slices, by using highly specific protein kinase inhibitors. We found that inhibition of protein kinase A (PKA) with the adenosine 3',5'-cyclic monophosphate (cAMP) analogue Rp-adenosine-3',5'-cyclic phosphorothioate Rp-cAMPS, did not prevent the muscarinic and glutamatergic suppression of IAHP. In contrast, two specific peptide inhibitors of Ca2+/calmodulin-dependent protein kinase II (CaM-K II), each partially blocked the effect of carbachol, but not the effect of t-ACPD on IAHP. We conclude that CaM-K II, but not PKA, is involved in mediating the muscarinic suppression of IAHP, although other pathways may also contribute. In contrast, neither CaM-K II nor PKA seems to mediate the metabotropic glutamate receptor action on IAHP.

Reactivity of a 2‘-Thio Nucleotide Analog

The chemical reactivity of ribonucleotide analog 2‘-deoxy-2‘-thiouridine 3‘-(p-nitrophenyl phosphate) (1), in which the 2‘ hydroxyl is replaced with a 2‘-thiol group, has been characterized. The major reaction pathway for 1, as monitored by 31P NMR spectroscopy, is transphosphorylation to afford 2‘,3‘-cyclic phosphorothioate 3, followed by hydrolysis of 3 to produce 2‘-deoxy-2‘-thiouridine 2‘-phosphorothioate (4). Thus, the reaction pathway of 1 is similar to that of the hydrolysis of ribonucleotides, yet there are significant differences. The pH−rate profile for transphosphorylation of 1 was determined by monitoring the formation of p-nitrophenol or p-nitrophenolate by UV−visible spectroscopy. Analysis of the profile reveals the attacking nucleophile to be thiolate, and the pKa of the 2‘-thiol was determined to be 8.3 ± 0.1. At pH 7.4, the thiol-containing ribonucleotide analog 1 is hydrolyzed at an observed rate 27-fold slower than its 2‘-hydroxyl counterpart. These results indicate that the rate of thi...

Nitric oxide inhibits angiotensin II-induced migration of rat aortic smooth muscle cell. Role of cyclic-nucleotides and angiotensin1 receptors.

Nitric oxide (NO) and angiotensin II (AII) can effect vascular smooth muscle cell (SMC) proliferation. However, the effects of such agents on SMC migration, an equally important phenomenon with regard to vascular pathophysiology, have received little attention. The objectives of the present study were: (a) to determine whether NO inhibits AII-induced migration of vascular SMCs; (b) to investigate the mechanism of the interaction of NO and AII on SMC migration; and (c) to evaluate the AII receptor subtype that mediates AII-induced SMC migration. Migration of rat SMCs was evaluated using a modified Boydens Chamber (transwell inserts with gelatin-coated polycarbonate membranes, 8 microns pore size). AII stimulated SMC migration in a concentration-dependent manner, and this effect was inhibited by sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP). In the presence of L-arginine, but not D-arginine, IL-1 beta, an inducer of inducible NO synthase, also inhibited AII-induced SMC migration, and this effect was prevented by the NO-synthase inhibitor, N-nitro-L-arginine methyl ester. The effects of NO donors on AII-induced SMC migration were mimicked by 8-bromo-cGMP. Also, the antimigratory effects of SNAP were partially inhibited by LY83583 (an inhibitor of soluble guanylyl cyclase) and by KT5823 (an inhibitor of cGMP-dependent protein kinase). Although 8-bromo-cAMP (cAMP) also mimicked the antimigratory effects of NO donors, the antimigratory effects of SNAP were not altered by 2',5'-dideoxyadenosine (an inhibitor of adenyl cyclase) or by (R)-p-adenosine-3',5'-cyclic phosphorothioate (an inhibitor of the cAMP-dependent protein kinase). Low concentrations of the subtype AT1-receptor antagonist CGP 48933, but not the subtype AT2-receptor antagonist CGP 42112, blocked AII-induced SMC migration. These findings indicate that (a) NO inhibits AII-induced migration of vascular SMCs; (b) the antimigratory effect of NO is mediated in part via a cGMP-dependent mechanism; and (c) AII stimulates SMC migration via an AT1 receptor.

The specific type IV phosphodiesterase inhibitor rolipram differentially regulates the proinflammatory mediators TNF-α and nitric oxide

We compared the effect of the specific type IV phosphodiesterase inhibitor rolipram on intracellular cAMP concentration, nitric oxide (NO) and tumour necrosis factor-α (TNF) formation in the murine macrophage cell line RAW 264.7. We found a dose-dependent increase of nitrite accumulation in LPS-stimulated macrophages from 17.5 to 25.1 μM nitrite with rolipram, whereas TNF synthesis was suppressed to less than 30% of control. This was accompanied by an increase from 7.4 to a maximum of 10.5 nM cAMP in RAW cells incubated with rolipram. These results were confirmed with the stable cAMP analogue ( S)- p-adenosine 3′,5′-cyclic phosphorothioate [( S)- p-cAMPS]. These findings demonstrate that elevation of cAMP in RAW 264.7 cells by rolipram decreases TNF synthesis and increases NO formation.

The synthesis and reactivity of new 2-( N, N-diisopropylamino)-3-methylsulfonyl-1,3,2-benzoxazaphospholes. The utility of the 5-chloro analogue in the one-pot synthesis of oligothiophosphates: [Ap sppA, Ap spppA, ppp5′A2′p s5′A, m 7Gp sppA, Ap spppp, Ap spp

The synthesis of 2-( N, N-diisopropylamino)-2,3-dihydro-3-methylsulfonyl-1,3,2-benzoxazaphospholes 22, 23 and 24 is reported. Their reactivities have been investigated using a variety of acid catalyst under conditions normally employed in phosphoramidite chemistry for oligonucleotide synthesis. The rate (k) of activation of 22, 23 and 24 by acid catalysis with N-methylanilinium hydrochloride (MAC) to their protonated species 25A, 26A and 27A, respectively, (Scheme 2) has been estimated to be 6.813 × 10 −7mol −1min −1, 1.237 × 10 −6mol −1min −1 and 1.972 × 10 −7mol −1min −1 at 18°C with a ratio of the rates as 0.56 : 1 : 0.16. The 5-chlorobenzoxazaphosphole 23 selectively activated by MAC gave the intermediate 2-(N-methylanilinium)-5-chlorobenzoxazaphosphole 26A (∼90% by NMR), which was then reacted with alcohols (nucleosides) to generate the reactive 2-alkoxybenzoxazaphosphole 30 (Scheme 4) or 33–35 (Scheme 5) (∼70% by NMR). We have then shown that 33–35 (Scheme 5) react with binucleophilic reagents, ADP, ATP or pyrophosphate, to generate the corresponding P 1-alkoxycyclometatriphosphite intermediate 36, 37, 50, 52 or 54. These intermediates were then sulfurised to form the P 1-alkoxy-1-thiocyclotriphosphate intermediates 38, 39, 51, 53 and 55, which were ring-opened by hydrolysis. Thus these steps constituted a one-pot multicomponent reaction (MCR) leading to the synthesis of R P and S P mixtures of each of the mono-thioanalogues of naturally-occurring oligophosphates: Ap sppA ( 43) (10%), Ap spppA ( 45) (19%), ppp5′A2′p s5′A ( 46) (24%), the cap structure m 7Gp sppA ( 47) (3%), Ap spppp ( 42) (23%), Ap spp ( 41) (33%) and Ap sp ( 40) (7%). The reaction of putative 34 and ADP gave the desired 43 (10%) along with pp5′A2′p s 5′A ( 44) (5%). The reaction sequences from 34 and ATP gave 45 (19%) and ppp5′A2′p s5′A ( 46) (24%). The proposed reaction mechanism for the synthesis of 43, 45 and 47 proceeds via the corresponding (dinucleoside 5′)-cyclometatriphosphite intermediates 50, 54, 52 and the (dinucleoside 5′)-1-thiocyclotriphosphate intermediates 51, 55, 53. The existence of these cyclic P(III) and P(V) intermediates were supported by 31P- and 1H-NMR spectroscopy. We here also demonstrate that 5-chlorobenzoxazaphosphole 23 can be used to synthesise a protected ribonucleoside 2′,3′-cyclic phosphorothioate block 28, a protected ribonucleoside 3′-(O-(4-chloro-2-mesylsulfonamido)phenyl phosphorothioate diester block 29 and bis(2-deoxyadenosine-5′)-thymidine-3′-monophosphate 32. The correct coupling of the nucleoside residues to the oligophosphate chain in 43, 45 & 47 has unequivocally been assessed by 2D 31P- 31P and 1H- 31P correlation spectroscopy.