A chemo-enzymatic oxidation cascade to activate C-H bonds with in situ generated H2O2.

Continuous low-level supply or in situ generation of hydrogen peroxide (H2O2) is essential for the stability of unspecific peroxygenases, which are deemed ideal biocatalysts for the selective activation of C-H bonds. To envisage potential large scale applications of combined catalytic systems the reactions need to be simple, efficient and produce minimal by-products. We show that gold-palladium nanoparticles supported on TiO2 or carbon have sufficient activity at ambient temperature and pressure to generate H2O2 from H2 and O2 and supply the oxidant to the engineered unspecific heme-thiolate peroxygenase PaDa-I. This tandem catalyst combination facilitates efficient oxidation of a range of C-H bonds to hydroxylated products in one reaction vessel with only water as a by-product under conditions that could be easily scaled.

Hierarchical filters determine community assembly of urban species pools.

The majority of humanity now lives in cities or towns, with this proportion expected to continue increasing for the foreseeable future. As novel ecosystems, urban areas offer an ideal opportunity to examine multi-scalar processes involved in community assembly as well as the role of human activities in modulating environmental drivers of biodiversity. Although ecologists have made great strides in recent decades at documenting ecological relationships in urban areas, much remains unknown, and we still need to identify the major ecological factors, aside from habitat loss, behind the persistence or extinction of species and guilds of species in cities. Given this paucity of knowledge, there is an immediate need to facilitate collaborative, interdisciplinary research on the patterns and drivers of biodiversity in cities at multiple spatial scales. In this review, we introduce a new conceptual framework for understanding the filtering processes that mold diversity of urban floras and faunas. We hypothesize that the following hierarchical series of filters influence species distributions in cities: (1) regional climatic and biogeographical factors; (2) human facilitation; (3) urban form and development history; (4) socioeconomic and cultural factors; and (5) species interactions. In addition to these filters, life history and functional traits of species are important in determining community assembly and act at multiple spatial scales. Using these filters as a conceptual framework can help frame future research needed to elucidate processes of community assembly in urban areas. Understanding how humans influence community structure and processes will aid in the management, design, and planning of our cities to best support biodiversity.

Growth inhibition of drug-resistant species of Plasmodium falciparum by domain structured N1,N2-derivatized hydrazines: denticity effects, redox switches, and reductant-driven redox-cycling.

Six analogs of bidentate 1-[pyridoxylidene]-2-phenyl]hydrazine, twelve analogs of N2O-tridentate 1-[pyridoxylidene]-2-[heteroaryl]hydrazine, and four O2N-tridentate analogs of 1-[pyridoxylidene]-2-[heteroaroyl] hydrazines were synthesized and characterized. Their solutions in water and DMSO were assayed in vitro for activity against a chloroquine-resistant species of P. falciparum obtained from Hadassah Hospital Blood Bank in Jerusalem. The O2N-tridentate group was essentially inactive, whereas the bidentate group, with N and O liganding atoms, exhibited slight activity against late-stage trophozoites and schizonts of P. falciparum. The N2O-tridentate group, by contrast, was remarkably active against resistant P. falciparum, highlighting the importance of the Denticity Effect in this system. It is assumed that the pyridoxal-based chelator acts as an iron redox mediator, controlling the first coordination sphere and, therefore, the immediate chemical environment of the iron. Chelation of iron-(II) presumably facilitates its oxidation..The Fe(II) --> Fe(III) intra-electron transfer, may be viewed as a switch ("redox switch"), controlling the thermodynamic stability and kinetic lability of the coordination shell. The redox-switch is accompanied by the appearance of a carbon-based Fe-(III)-chelate radical, capable of donating its free electron to the parasite-DNA, thus causing death. The antimalarial N2O-tridentate Fe(III)-chelates appear to be prone to redox-switch, and tend to be converted into their Fe(II) species, whereas the inactive O2N-tridentate analogs apparently cannot do so.

Inhibition of in vitro lymphoproliferation by three novel iron chelators of the pyridoxal and salicyl aldehyde hydrazone classes.

The capacity of three novel iron chelators, namely 1-[N-ethoxycarbonylmethylpyridoxylidenium]-2-[2'-pyridyl]hydrazine bromide (EPH), 1-[5'-bromosalicylidene]-2-[2"-pyridyl]hydrazine (BsPH), and 1-pyridoxylidene-2-[1'-phthalazyl]hydrazine dihydrochloride (PPhH), to inhibit the proliferation of mitogen-stimulated murine lymph node cells was examined in vitro. All three are of the aryl hydrazone class, the prototype of which is pyridoxal isonicotinoyl hydrazone. The chelators inhibited lymphoproliferation at low micromolar concentrations. EPH and PPhH had an inhibitory capacity comparable to that of desferrioxamine (IC(50): 3 and 2 microM, respectively), whereas BsPH was more potent (IC(50) < 1 microM). The inhibitory effects of the chelator were not due to cell cytotoxicity and could be abrogated by pretreating the chelator with iron. Time-course studies established a site of action for the chelators at the G(1)/S phase transition. These agents warrant further investigation for their potential as immunosuppressants.

Domain-structured N1,N2-derivatized hydrazines as inhibitors of ribonucleoside diphosphate reductase: redox-cycling considerations.

Eight analogues of 1-[5-halogenosalicylidene]-2-[2'-pyridinoyl]hydrazine and -[2'-pyridyl]hydrazine, four of 1-[pyridoxylidene]-2-[2'-pyridinoyl]hydrazine, seven of 1-[pyridoxylidene]-2-[2'-pyridyl]hydrazine, and one each of 1, 2-bis[pyridoxylidene]diaminoethane and bis[pyridoxylidenehydrazino]phthalazine were synthesized. Their solutions in DMF were assayed for activity against the metalloenzyme ribonucleoside diphosphate reductase (RdR), prepared from a subcutaneously growing murine tumor (sarcoma 180) implanted in B6D2F3 male mice. The 14C-labeled CDP reductase was assayed by the modified method of Takeda and Weber, in which [14C]cytidine was separated from deoxycytidine by thin-layer chromatography (TLC) on cellulose foil. Distribution of radioactivity was assessed with an automatic TLC linear analyzer. Of the 31 compounds tested, 13 were essentially inactive, 7 were highly active against RdR, and the remaining 20 were slightly more active than hydroxyurea (used as a reference compound). The mechanism of inhibition is discussed in terms of three alternative pathways, initiated by sequestration of iron embedded in the R1 subunit of the metalloenzyme to form a C-centered chelate radical (via redox cycling). Alternatively, the latter could either reduce the tyrosyl radical or intercept radicals generated in the reduction process.

In vitro effects of three iron chelators on mitogen-activated lymphocytes: identification of differences in their mechanisms of action.

The effects of three iron chelators (ADR-529/ICRF-187; omadine/pyrithione; and a newly synthesized pyridoxal-based iron chelator, SAG-15) on cultured BALB/c murine lymph node cells stimulated with phorbol myristate acetate and ionomycin have been investigated. All three agents were found to inhibit [3H]-thymidine incorporation after 66-72 h incubation. Pretreatment of ADR-529 and omadine with Fe(III) or Fe(II) ions did not prevent their inhibitory effects. However, pretreatment of SAG-15 with Fe(II) or Fe(III) ions led to a significant increase in the ID50. Time-course studies of cell viability and thymidine incorporation demonstrated that the inhibitory effect of omadine was attributable to cell killing while for ADR-529 and SAG-15 there were both cytostatic and cytotoxic effects. Cell cycle analysis showed that treatment of cells with ADR-529 led to arrest in G2/M while treatment with SAG-15 led to a G0/G1 arrest. Iron has an obligatory role in T-lymphocyte activation that may be related to the formation of reactive oxygen species. SAG-15 is a new iron chelator that will help in the elucidation of the precise role of iron in lymphoproliferation. Since SAG-15 is an extremely effective iron chelator in vivo it has potential as an immunosuppressive agent.

Fe (II)-chelates based on redox-active pyridoxal-betaines as C-centered radicals causing single- and double-strand scissions to DNA.

The ability of 1-[N-Ethoxycarbonylmethylpridoxylidenium]-2-[2'- pyridyl]hydrazine bromide code name - [L2.9 = L+,X-]-FE(II) chelate [L2-9-Fe(II)] to induce breaks both in the 43kb linear double-strand lambda phage DNA, and in the 4363 base pair supercoiled pBR322 plasmid DNA is herein described. Neither the free ligand nor FE(II) alone demonstrated any effect on the DNA. The cleaving ability is shown to occur instantaneously under strictly anaerobic conditions, either in the presence or absence of the enzyme catalase. It is also shown to be dose dependent. Thus, at lambda DNA:L2-9-Fe(II) molar ratio of 3.7:1.0, the linear DNA is randomly cleaved into fragments ranging from 23.1kb to 4.3kb, whereas at approximately 1:1 molar ratio, the range extends down to 2.5kb fragments. By contrast, at 1:2.7 [plasmid DNA]: chelate-Fe(II) molar ratio, a single-strand nick was observed, and a double strand break was noted at a 1:50 ratio [( plasmid DNA]: chelate-Fe(II). A multi-stage redox cycling involving a carbon-centered (L,X-)-Fe(III) radical capable of transferring an electron to the DNA to form high unstable [DNA].- anion-radical is invoked to explain the degradation of the chain macromolecule. Possible modes for regeneration of the chelate-Fe(III) radical both at the cell-free and at the cell levels are proposed.

Growth inhibition of Plasmodium falciparum involving carbon centered iron-chelate radical (L., X-)-Fe(III) based on pyridoxal-betaine. A novel type of antimalarials active against chloroquine-resistant parasites.

Malaria parasites have been shown to be more susceptible to oxidative stress than their host erythrocytes. In the present work, a chloroquine resistant malaria parasite, Plasmodium falciparum (FCR-3) was found to be susceptible in vitro to a pyridoxal based iron chelator--(1-[N-ethoxycarbonylmethylpyridoxlidenium]-2-[2'-pyridyl ] hydrazine bromide--(code named L2-9). 2h exposure to 20 microM L2-9 was sufficient to irreversibly inhibit parasite growth. Desferrioxamine blocked the drug effect, indicating the requirement for iron. Oxygen however, was not essential. Spectrophotometric analysis showed that under anoxic conditions, L2-9-Fe(II) chelate undergoes an intramolecular redox reaction which presumably involves a one electron transfer and is expected to result in the formation of free radical. Spin trapping coupled to electron spin resonance (ESR) studies of L2-9-iron chelate showed that L2-9-Fe(II) produced free radicals both in the presence and absence of cells, while L2-9-Fe(III) produced free radicals only in the presence of actively metabolising cells.

Inhibition of Plasmodium falciparum growth by a synthetic iron chelator.

The susceptibility of the chloroquine-resistant malaria parasite Plasmodium falciparum (FCR-3) to a pyridoxal-based iron chelator was tested. 10 microM of the chelator 1[N-ethoxycarbonylmethyl-pyridoxy-lidenium]-2-[2'-pyri dyl] hydrazine bromide (code name L2-9) effectively inhibited growth in vitro of the parasites. Presaturation of the chelator with either ferric or ferrous iron partially blocked the inhibitory effect. Two hours' exposure of parasites to 20 microM L2-9 was sufficient to inhibit their growth irreversibly. Desferrioxamine blocked the inhibitory effect of L2-9. It is suggested that the chelator may be acting by generating free radicals in complexing intracellular iron.

Syntheses of iron bis(pyridoxal isonicotinoylhydrazone)s and the in vivo iron-removal properties of some pyridoxal derivatives.

Pyridoxal isonicotinoylhydrazone (PINH; 1) and its isomeric O-acetates (E and Z) were synthesized and complexed with ferrous ions to afford the hitherto unisolated chelates iron(II) bis(pyridoxal isonicotinoylhydrazone)s (11) and iron(II) bis(O-acetylpyridoxal isonicotinoylhydrazone)s (12). The analytical and spectroscopic data of the new coordination compounds are presented. In addition, a series of imino derivatives of pyridoxal of structures 2-3 and 5-10 have been prepared and tested in vivo as chelators of storage iron, and the cumulative net excretion of radioiron in urine and in feces was estimated. This study reestablishes that PINH is a potent iron chelator in vivo comparable in efficiency with parenteral desferrioxamine (DF) and indicates that it requires further attention.

Antiviral compounds. 1. Structure-activity relationship of some antiviral enediones derived from aldehydo sugars.

A series of aldehydo sugars was subjected to condensation reactions with active methylene compounds. Acetylacetone was condensed with 2,4-O-benzylidene-3,5-O-dibenzoyl-D-ribose (1), 2,4:3,5-O-dibenzylidene-D-ribose (6), 2,3,4,5-tetraacetyl-D-ribose (7), and 2,3,4,5,6-pentaacetyl-D-glucose (9) to yield 3-ylidene-2,4-pentanedione derivatives 2, 11, 12, and 13, respectively. Sugar derivatives 1 and 6 were also condensed with benzoylacetone to give 14 and 18, with acetoacetanilide to give 16 and 19, with malononitrile to give 17 and 20, and with alpha-(gamma-butyrolactonylidene)triphenylphosphorane to give 21 and 22, respectively. Condensation of 1 with dibenzoylmethane gave 15. The double bond in compounds 2 and 11 was saturated by hydrogenation to give 23 and 24. All alpha, beta-unsaturated carbonyl compounds obtained exhibited antiviral activity and cytotoxicity. Compound 11 was found to have the most significant and selective antiviral activity against herpes simplex virus.

Mechanism of in vivo iron chelation by pyridoxal isonicotinoyl hydrazone and other imino derivatives of pyridoxal.

The source of iron chelated in vivo by the new iron-chelating agent PIH and its mechanism of excretion have been studied in normal and hypertransfused rats. PIH is able to chelate iron from both parenchymal and RE iron stores. Unlike DF, which promotes both urinary and fecal iron excretion, in this model PIH-induced iron excretion is limited almost entirely to the gut. Response to PIH is directly related to dosage, and oral doses ranging from 125 to 500 mg/kg/day are well tolerated. Six additional imino derivatives of pyridoxal have been studied, but none of these new compounds was as effective as PIH. Our study indicates that oral PIH is comparable in efficiency with parenteral DF and is of potential usefulness in the management of iron overload.