Formation and stability of complex organic compounds in space environments.

Complex organic compounds have been found in extraterrestrial bodies such as meteorites and comets. We confirmed the formation of complex organic compounds that contained amino acid precursors from a mixture of carbon monoxide (or methanol), ammonia and water by radiation or UV. Molecular weights of the complex organics were several thousands. Stability of the complex precursors was studied. When free amino acids were irradiated with gamma rays or synchrotron radiation, they easily decomposed. The complex precursors were, however, much more stable than free amino acid against irradiation. We propose to examine the formation and alteration of amino acid precursors in space by using exposed facility of ISS.     

Polyphenols from flowers of Magnolia coco and their anti-glycation effects

We investigated the inhibitory effects of several plant extracts on advanced glycation end-products (AGEs) formation. Among tested samples, the flower extract of Magnolia coco showed significant inhibition of AGE formation. We isolated and characterized procyanidin oligomer and four other compounds from the flowers, and evaluated their inhibitory effects on AGE formation and the AGE-derived crosslink-cleaving activity of the isolated compounds.     

The pyridoxamine action on Amadori compounds: A reexamination of its scavenging capacity and chelating effect

Amadori compounds act as precursors in the formation of advanced glycation end products (AGEs) by non-enzymatic protein glycation, which are involved in ensuing protein damage. Pyridoxamine is a potent drug against protein glycation, and can act on several pathways in the glycation process. Nevertheless, the pyridoxamine inhibition action on Amadori compounds oxidation is still unclear. In this work, we have studied the Schiff base formation between pyridoxamine and various Amadori models at pH 7.4 at 37 degrees C in the presence of NaCNBH(3). We detected an adduct formation, which suggests that pyridoxamine reacts with the carbonyl group in Amadori compounds. The significance of this mechanism is tested by comparison of the obtained kinetics rate constants with that obtained for 4-(aminomethyl)-pyridine, a structural analogue of pyridoxamine without post-Amadori action. We also study the chelating effect of pyridoxamine on metal ions. We have determined the complexation equilibrium constants between pyridoxamine, N-(1-deoxy-d-fructos-1-yl)-l-tryptophan, aminoguanidine, and ascorbic acid in the presence of Zn(2+). The results show that the strong stability of pyridoxamine complexes is the key in its post-Amadori inhibition action. On the other hand results explain the lack of inhibition of aminoguanidine (a glycation inhibitor) in the post-Amadori reactions.     

Reveromycin A biosynthesis uses RevG and RevJ for stereospecific spiroacetal formation

Spiroacetal compounds are ubiquitous in nature, and their stereospecific structures are responsible for diverse pharmaceutical activities. Elucidation of the biosynthetic mechanisms that are involved in spiroacetal formation will open the door to efficient generation of stereospecific structures that are otherwise hard to synthesize chemically. However, the biosynthesis of these compounds is poorly understood, owing to difficulties in identifying the responsible enzymes and analyzing unstable intermediates. Here we comprehensively describe the spiroacetal formation involved in the biosynthesis of reveromycin A, which inhibits bone resorption and bone metastases of tumor cells by inducing apoptosis in osteoclasts. We performed gene disruption, systematic metabolite analysis, feeding of labeled precursors and conversion studies with recombinant enzymes. We identified two key enzymes, dihydroxy ketone synthase and spiroacetal synthase, and showed in vitro reconstruction of the stereospecific spiroacetal structure from a stable acyclic precursor. Our findings provide insights into the creation of a variety of biologically active spiroacetal compounds for drug leads.     

Theoretical investigation on the heats of formation and detonation performance in polydinitroaminocubanes

A series of polydinitroaminocubanes have been designed computationally. We calculated the heats of formation, the detonation velocity (D) and detonation pressure (P) of the title compounds by density function theory (DFT) with 6-311?G** basis set. The relationship between the heats of formation and the molecular structures is discussed. The result shows that all cubane derivatives have high and positive heats of formation, which increase with increasing number of dinitroamino groups. The detonation performances of the title compound were estimated by Kamlet-Jacobs equation, and the result indicated that most cubane derivatives have good detonation performance over RDX (hexahydro-1,3,5-trinitro-1,3,5-trizine) and HMX (1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane). In addition, we also found that the heat of detonation (Q) is another very important impact in increasing detonation performance except density. The relative stabilities of the title compound are discussed in the terms of the calculated heats of formation, and the energy gaps between the frontier orbitals. The results have not only shown that these compounds may be used as high energy density compounds (HEDCs), but also provide some useful information for further investigation.     

Optimization of a series of quinazolinone-derived antagonists of CXCR3

The evaluation of the CXCR3 antagonist AMG 487 in clinic trials was complicated due to the formation of an active metabolite. In this Letter, we will discuss the further optimization of the quinazolinone series that led to the discovery of compounds devoid of the formation of the active metabolite that was seen with AMG 487. In addition, these compounds also feature increased potency and good pharmacokinetic properties. We will also discuss the efficacy of the lead compound 34 in a mouse model of cellular recruitment induced by bleomycin.     

Effects of daphnodorin A, daphnodorin B and daphnodorin C on human chymase-dependent angiotensin II formation.

We investigated whether daphnodorin A, daphnodorin B and daphnodorin C inhibited human chymase-dependent angiotensin II-forming activity. Although the structures of these compounds are very similar, daphnodorin A completely inhibited angiotensin II formation generated by chymase, while daphnodorin B partially inhibited and daphnodorin C did not. On the other hand, these daphnodorins did not affect angiotensin converting enzyme-dependent angiotensin II formation. Furthermore, these daphnodorins did not inhibit purified human tryptase, which, like chymase, is contained in mast cells. Therefore, daphnodorin A, but not daphnodorin B and daphnodorin C, may specifically inhibit the chymase-dependent angiotensin II formation, and such differences between inhibitory effects of these compounds to human chymase may be useful for the development of human chymase inhibitor.     

Hydrolysis of cyclosporin A: Identification of 1,11 seco-cyclosporin A and 4,5 secoisoCyclosporin A by FAB-MS/MS

We have previously reported that treatment of CsA with aqueous HCl gives rise to the formation of a number of water-soluble compounds. Two of these were identified from their FAB-MS/MS spectra as open-chain nona- and decapeptides. We describe here the identification of two other main compounds deriving from the same treatment. Identification was rendered possible from the comparison of their FAB-MS/MS spectra with those of methyl and acetyl derivatives. The two compounds are water-soluble, open-chain undecapeptides corresponding to 1,11 seco-CsA and of 4,5 seco-isoCsA, respectively.     

Inhibition of Ribonuclease A by polyphenols present in green tea

We report the effect of the natural polyphenolic compounds from green tea on the catalytic activity of Ribonuclease A (RNase A). The compounds behave as noncompetitive inhibitors of the protein with inhibition constants ranging from 80-1300 microM. The dissociation constants range from 50-150 microM for the RNase A-polyphenol complexes as determined by ultraviolet (UV) and circular dichroism (CD) studies. We have also investigated the changes in the secondary structure of RNase A on complex formation by CD and Fourier transformed infrared (FTIR) spectroscopy. The presence of the gallate moiety has been shown to be important for the inhibition of enzymatic activity. Docking studies for these compounds indicate that the preferred site of binding is the region encompassing residues 34-39 with possible hydrogen bonding with Lys 7 and Arg 10. Finally we have also looked at changes in the accessible surface area of the interacting residues on complex formation for an insight into the residues involved in the interaction.     

Cytokinin receptors are involved in alkamide regulation of root and shoot development in Arabidopsis

Alkamides and N-acilethanolamides are a class of lipid compounds related to animal endocannabinoids of wide distribution in plants. We investigated the structural features required for alkamides to regulate plant development by comparing the root responses of Arabidopsis (Arabidopsis thaliana) seedlings to a range of natural and synthetic compounds. The length of the acyl chain and the amide moiety were found to play a crucial role in their biological activity. From the different compounds tested, N-isobutyl decanamide, a small saturated alkamide, was found to be the most active in regulating primary root growth and lateral root formation. Proliferative-promoting activity of alkamide treatment was evidenced by formation of callus-like structures in primary roots, ectopic blades along petioles of rosette leaves, and disorganized tumorous tissue originating from the leaf lamina. Ectopic organ formation by N-isobutyl decanamide treatment was related to altered expression of the cell division marker CycB1:uidA and an enhanced expression of the cytokinin-inducible marker ARR5:uidA both in roots and in shoots. The involvement of cytokinins in mediating the observed activity of alkamides was tested using Arabidopsis mutants lacking one, two, or three of the putative cytokinin receptors CRE1, AHK2, and AHK3. The triple cytokinin receptor mutant was insensitive to N-isobutyl decanamide treatment, showing absence of callus-like structures in roots, the lack of lateral root proliferation, and absence of ectopic outgrowths in leaves under elevated levels of this alkamide. Taken together our results suggest that alkamides and N-acylethanolamides may belong to a class of endogenous signaling compounds that interact with a cytokinin-signaling pathway to control meristematic activity and differentiation processes during plant development.     

Exploring the potential of 3'-O-carboxy esters of thymidine as inhibitors of ribonuclease A and angiogenin

In this study, compounds with a carboxy ester in lieu of the phosphate ester at the 3'-position have been employed to inhibit the ribonucleolytic activity of ribonuclease A (RNase A). Phosphates at the 3'-position of pyrimidine bases are well-known inhibitors of the protein. We have investigated the inhibition of RNase A by 3'-O-carboxy esters of thymidine. The compounds behave as competitive inhibitors with inhibition constants ranging from 42 to 95 microM. The mode of inhibition has also been confirmed by (1)H NMR studies of the active site histidines of RNase A. Docking studies have further substantiated the experimental results. The compounds are also found to inhibit the ribonucleolytic activity of angiogenin, a homologous protein and potent inducer of blood vessel formation.     

Regulatory role of heparin compounds with low molecular ligands of blood in plasma and thromocyte hemostasis

Aanalysis of the literature and our own research on the physiological effects of complex compounds of heparin with low molecular ligands (amino acids, regulatory peptides) is presented. It is proved that anticoagulative effects in blood flow were conditioned by the interaction of heparin with glioproline, immunopeptides, and other low molecular substances with formation of complex compounds. The presence of structural regions of binding of heparin and other components is established. It is indicated that in the blood of animals heparin complexes with low molecular ligands possess protective anticoagulative and antithrombotic effects. We made an attempt to reveal the possible mechanism of anticoagulative-fibrinolytic and antithrombotic action of complex compounds of heparin in the organism.     

Amine oxidase-like activity of polyphenols. Mechanism and properties.

Polyphenols in several oxidation systems gained amine oxidase-like activity, probably due to the formation of the corresponding quinones. In the presence of Cu(II), o- and p-phenolic compounds exhibited amine oxidase-like activity, whereas only the o-phenolic compounds showed the activity in the presence of 1,1-diphenyl-2-picrylhydrazyl radical. The activity was determined by measuring the conversion of benzylamine to benzaldehyde by HPLC. Moreover, gallic acid, chlorogenic acid, and caffeic acid, which are plant polyphenols, converted the lysine residue of bovine serum albumin to alpha-amino-adipic semialdehyde residue, indicating lysyl oxidase-like activity. We also characterized the activity of pyrocatechol, hydroquinone, and pyrogallol in the presence of Cu(II). The oxidative deamination was accelerated at a higher pH, and required O2 and transition metal ions. Furthermore, EDTA markedly inhibited the reaction but not beta-aminopropionitrile, which is a specific inhibitor of lysyl oxidase. Catalase significantly inhibited the oxidation, implying the participation of hydroxyl radical in the reaction, but superoxide dismutase stimulated the oxidation, probably due to its radical formation activity. We discussed the mechanism of the oxidative deamination by polyphenols and the possible significance of the activity for biological systems.     

Novel inhibitors of advanced glycation endproducts

A number of natural or synthetic compounds as AGE inhibitors have been proposed, discovered or currently being advanced by others and us. We have identified two new classes of aromatic compounds; aryl- (and heterocyclic) ureido and aryl (and heterocyclic) carboxamido phenoxyisobutyric acids, and benzoic acid derivatives and related compounds, as potential inhibitors of glycation and AGE formation. Some of these novel compounds also showed "AGE-breaking" activities in vitro. Current evidence is that chelation of transition metals and/or trapping or indirect inhibition of formation of reactive carbonyl compounds are involved in the mechanisms of action of these novel AGE inhibitors and breakers. Here, we review the inhibitors of glycation and AGE-breakers published to date and present the results of our in vitro and in vivo investigations on a number of these novel AGE inhibitors. These AGE-inhibitors and AGE-breakers may find therapeutic use in the treatment of diseases that AGE formation and accumulation may be responsible for their pathogenesis such as diabetes, Alzheimer's, rheumatoid arthritis, and atherosclerosis.     

Adenosine 3',5'-monophosphate formation by preparations of rat liver soluble guanylate cyclase activated with nitric oxide, nitrosyl ferroheme, S-nitrosothiols, and other nitroso compounds

Cyclic AMP formation from ATP was stimulated by unpurified and partially purified soluble hepatic guanylate cyclase in the presence of nitric oxide (NO) or compounds containing a nitroso moiety such as nitroprusside, N-methyl-N-nitro-N-nitrosoguanidine (MNNG), nitrosyl ferroheme, and S-nitrosothiols. Cyclic AMP formation was undetectable in the absence of NO or nitroso compounds and was not stimulated by fluoride or glucagon, indicating the absence of adenylate cyclase activity. The nitroso compounds failed to activate, whereas fluoride or glucagon activated, adenylate cyclase in washed rat liver membrane fractions. Cyclic GMP formation from GTP was markedly stimulated by the soluble hepatic fraction in the presence of NO or nitroso compounds. Cyclic AMP formation by partially purified guanylate cyclase was competitively inhibited by GTP and cyclic GMP formation is well-known to be competitively inhibited by ATP. Therefore, it appears that activated guanylate cyclase, rather than adenylate cyclase, was responsible for the formation of cyclic AMP from ATP. Formation of cyclic AMP of cyclic GMP was enhanced by thiols, inhibited by hemoproteins and oxidants, and required the addition of either Mg2+ or Mn2+. Further, several nitrosyl ferroheme compounds and S-nitrosothiols stimulated the formation of both cyclic AMP and cyclic GMP by the soluble hepatic fraction. These observations support the view that soluble guanylate cyclase is capable, under certain well-defined conditions, of catalyzing the conversion of ATP to cyclic AMP.     

Phenolsulfonphthalein, but not phenolphthalein, inhibits amyloid fibril formation: implications for the modulation of amyloid self-assembly

The study of the mechanism of amyloid fibril formation and its inhibition is of key medical importance due to the lack of amyloid assembly inhibitors that are approved for clinical use. We have previously demonstrated the potent inhibitory potential of phenolsulfonphthalein, a nontoxic compound that was approved for diagnostic use in human subjects, on aggregation of islet amyloid polypeptide (IAPP) that is associated with type 2 diabetes. Here, we extend our studies on the mechanism of action of phenolsulfonphthalein by comparing its antiamyloidogenic effect to a very similar compound that is also approved for human use, phenolphthalein. While these compounds have very similar primary chemical structures, they significantly differ in their three-dimensional conformation. Our results clearly demonstrated that these two compounds had completely different inhibitory potencies: While phenolsulfonphthalein was a very potent inhibitor of amyloid fibril formation by IAPP, phenolphthalein did not show significant antiamyloidogenic activity. This behavior was observed with a short amyloid fragment of IAPP and also with the full-length polypeptide. The NMR spectrum of IAPP 20-29 in the presence of phenolsulfonphthalein showed chemical shift deviations that were different from the unbound or phenolphthalein-bound peptide. Differential activity was also observed in the inhibition of insulin amyloid formation by these two compounds, and density-gradient experiments clearly demonstrated the different inhibitory effect of the two compounds on the formation of prefibrillar assemblies. Taken together, our studies suggest that the three-dimensional arrangement of the polyphenol phenolsulfonphthalein has a central role in its amyloid formation inhibition activity.     

Interaction of 4-arylcoumarin analogues of combretastatins with microtubule network of HBL100 cells and binding to tubulin

The synthesis of different 4-arylcoumarin analogues of combretastatin A-4 led to the identification of two new compounds (1 and 2) with potent cytotoxic activity on a CEM leukemia cell line and a third one completely inactive (compound 3). It was suggested that the cytotoxicity of compounds 1 and 2 may be related to their interaction with microtubules and tubulin, since these compounds inhibit microtubule formation from purified tubulin in vitro [Bailly et al. (2003) J. Med. Chem. 46 (25), 5437-5444]. In the present study, tubulin was identified as the main target of these molecules. We studied structure-activity relationships of these compounds using biological experiments specific for tubulin binding. The modification of cell cycle progression induced by compounds 1 and 2 was characterized by an apoptotic induction on human breast cells (HBL100). In addition, these two molecules disturbed cell survival by depolymerizing the microtubule network, leading to a mitotic block. We then determined the thermodynamic parameters of their interaction with purified tubulin by fluorescence spectroscopy and isothermal microcalorimetry. These results, together with a superimposition of the molecule on colchicine in the X-ray-determined three-dimensional structure model of tubulin-colchicine complex, allowed us to identify the pharmacophore of the combretastatin A-4 analogues responsible for their biological activity.     

Carnosine and related dipeptides protect human ceruloplasmin against peroxyl radical-mediated modification

Ceruloplasmin (CP) is the major plasma antioxidant and copper transport protein. In a previous study, we showed that the aggregation of human ceruloplasmin was induced by peroxyl radicals. We investigated the effects of antioxidant dipeptides carnosine, homocarnosine and anserine on peroxyl radical-mediated ceruloplasmin modification. Carnosine, homocarnosine and anserine significantly inhibited the aggregation of CP induced by peroxyl radicals. When CP was incubated with peroxyl radicals in the presence of three compounds, ferroxidase activity, as measured by the activity staining method, was protected. All three compounds also inhibited the formation of dityrosine in peroxyl radicals-treated CP. The results suggest that carnosine and related compounds act as peroxyl radical scavenger to protect the protein modification. It is proposed that carnosine and related peptides might be explored as potential therapeutic agents for pathologies that involve CP modification mediated by peroxyl radicals generated in the lipid peroxidation.     

Structural and functional characteristics of various forms of red pigment of yeast Saccharomyces cerevisiae and its synthetic analog

Structural and functional characteristics of the yeast red pigment (product of polymerization of N¹-(β-D-ribofuranosyl)-5-aminoimidazole), isolated from ade1 mutant cells of Saccharomyces cerevisiae and its deribosylated derivatives (obtained by acid hydrolysis) and its synthetic pigment analogue (product of polymerization of N¹-methyl-5-aminoimidazole in vitro) were obtained. Products of in vitro polymerization were identified using mass spectrometry. The ability of these pigments to inhibit amyloid formation using insulin fibrils was compared. All the studied compounds are able to interact with amyloids and inhibit their growth. Electron and atomic force microscopy revealed a common feature inherent in the insulin fibrils formed in the presence of these compounds—they are merged into conglomerates more stable and resistant to the effects of ultrasound than are insulin aggregates grown without pigments. We suggest that all these compounds can cause coalescence of fibrils partially blocking the loose ends and, thereby, inhibit attachment of monomers and formation of new fibrils.     

Synthesis and antioxidant properties of novel benzimidazole derivatives

Some novel benzimidazole derivatives carrying thiosemicarbazide and triazole moieties at the N1 position were synthesized and their in vitro effects on rat liver microsomal NADPH-dependent lipid peroxidation (LP) levels determined by measuring the formation of 2-thiobarbituric acid reactive substance. The free radical scavenging properties of the compounds were also examined in vitro by determining the capacity to scavenge superoxide anion formation and the interaction with the stable free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH). The compounds showed a significant effect in the above tests except to scavenge superoxide anion formation.