SEARCH · PubMed Health
Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
A series of N-[omega-[N-alkyl-N-(phenylmethyl)amino]alkyl]-3-arylpropenamides was prepared and tested for its inhibitory activities on acetylcholinesterase. Some in the series were found to be potent inhibitors. The structure-activity relationships were discussed in detail.
The aim of this study was to determine whether the final enzymes in the two biosynthetic pathways for platelet-activating factor (PAF) (the 'de novo' and the 'membrane remodelling' pathways) are present in mouse embryos, zygotes and oocytes. The enzymes are dithiothreitol-insensitive cytidinediphosphocholine: 1-O-alkyl-2-acetyl-sn-glycerol cholinephosphotransferase (cholinephosphotransferase) in the de novo pathway and acetyl-coenzyme A:1-O-alkyl-2-lyso-sn-glycero-3-phosphocholine acetyltransferase (acetyltransferase) in the membrane remodelling pathway. Activity of both enzymes was detected in the unfertilized oocyte, the zygote and also in the preimplantation embryo (48, 72 and 96 h after the ovulatory injection of hCG). In both cases the activity was destroyed by boiling and increased linearly with incubation time and the concentration of embryo homogenate present, indicating that the reactions were catalysed by enzymes. The product of the reactions was confirmed as PAF using HPLC and structural analyses by enzymatic digestion. Cholinephosphotransferase required Mg2+ and was inhibited by Ca2+, while acetyltransferase required the presence of NaF (a phosphatase inhibitor). The activity of cholinephosphotransferase was similar in unfertilized oocytes and zygotes, and did not change significantly with advancing developmental stage in preimplantation embryos. Acetyltransferase had a significantly lower specific activity (0.078 +/- 0.044 fmol PAF per oocyte per min, mean +/- SEM) in unfertilized oocytes than in zygotes of corresponding age (0.358 +/- 0.097 fmol PAF per zygote per min) (P < 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)
Synthesis of new 7-(substituted)amino-1-alkyl-2-aryl-1H-2,3-dihydroimidazo[1,2-a]py rimidin-5- ones bearing the 4-arylpiperazin-1-yl moiety connected by ethyl or acetoyl two-carbonyl chain extension was described. The arylpiperazinyl moiety was introduced by alkylation or acylation with corresponding halogeno-derivatives. Preliminary pharmacological screening showed the 7-(substituted)-amino derivatives of the system investigated to exhibit the CNS activity lesser than that of the 7-amino derivatives and to have no effect on the serotonin neurotransmission pathway.
From 5-cyano-3-chloro-2-pyrazinecarboxamide) (II) hydrolysis in acid medium) yielded 3-chloro-2,5-pyrazinedicarboxamide (III), which in a reaction with sodium hydrogensulfide in dimethyl-formamide) yielded 3-mercapto-2,5-pyrazinedicarboxamide (IV). This compound through condensations with alkyl- and arylhalogenides in triethylamine) yielded 3-alkyl(or aryl) thio-2,5-pyrazinedicarboxamides of type I. The structure of compounds was confirmed by elemental analysis, IR and 1H NMR spectra. A microbiological evaluation was carried out; the antituberculous effect of these compounds is not higher than that of pyrazinamide.
1-Alkyl-2-acetyl-sn-glycero-3-phosphocholine (alkylacetyl-GPC, platelet activating factor (PAF] can be biosynthesized either by acetylation of alkyllyso-GPC through a remodeling pathway or by the transfer of phosphocholine to alkylacetyl-sn-glycerol (alkylacetyl-G) via a putative de novo pathway involving a dithiothreitol-insensitive cholinephosphotransferase. However, the relevance of the de novo pathway in the biosynthesis of PAF depends on the existence of enzymes that can directly synthesize alkylacetyl-G from 1-alkyl-2-lyso-sn-glycero-3-P (alkyllyso-GP) or some other source. In this study, we demonstrated that microsomal preparations of rat spleen can synthesize alkylacetyl-GP by an alkyllyso-GP:acetyl-CoA acetyltransferase and that this intermediate is subsequently dephosphorylated by an alkylacetyl-GP phosphohydrolase to generate alkylacetyl-G. The properties of alkyllyso-GP:acetyl-CoA acetyltransferase were characterized under conditions where the contaminating activity of alkylacetyl-GP phosphohydrolase was minimal; this was accomplished by inhibiting the phosphohydrolase with the addition of sodium vanadate and sodium fluoride to the assay mixtures and incubating at relatively low temperatures (23 degrees C). Alkyllyso-GP:acetyl-CoA acetyltransferase had a pH optimum of 8.4 at 23 degrees C and was located in the microsomal fraction. The apparent Km for acetyl-CoA under these conditions was 226 microM and the optimal concentration of alkyllyso-GP ranged between 16 and 25 microM. Based on pH optima, substrate inhibition studies, and sensitivities to preincubation temperatures of the microsomes, it appears that alkyllyso-GP:acetyl-CoA acetyltransferase differs from the acetyltransferase responsible for the transfer of acetate from acetyl-CoA to alkyllyso-GPC to form PAF. A variety of tissues had high activities of alkyllyso-GP:acetyl-CoA acetyltransferase, which indicates that this pathway is operational in many cell types. Our results document the existence of a complete de novo biosynthetic pathway for the assembly of PAF, and this route could be responsible for maintaining physiological levels of platelet activating factor for normal cell function.
The O-alkyl cleavage enzyme is important for the metabolism of cytotoxic alkyl-lysophospholipids. We have developed a simple new method for the determination of the enzyme activity which is based on the formation of water-soluble phosphate during the enzyme reaction. This is the first assay which avoids the use of radiolabeled substrates.
1-Alkyl-2-acyl-sn-glycero-3-phosphocholine (alkyl-acyl-GPC) comprises 11% of the total phospholipids of rat alveolar macrophages. This endogenous pool of alkylacyl-GPC was prelabeled by incubating the macrophages with [1,2-3H]alkyllyso-GPC (54 Ci/mmol), which enters the cells and is acylated. The effect of various stimuli on the synthesis and release into the media of labeled alkylacetyl-GPC (platelet-activating factor) from the cells was used to establish the role of inactive alkylacyl-GPC as a precursor of the biologically active derivative. A phagocytic agent (zymosan, 100 micrograms/ml) and an ionophore (A23187, 2 microM) stimulated the release of both alkylacetyl-GPC and alkyllyso-GPC into the media at the expense of cellular alkylacyl-GPC. Phospholipase A2 activity (at pH 4.5 and in 1 mM EDTA) was also increased in the media. The stimulatory effect of zymosan and the ionophore on alkylacetyl-GPC release was prevented by mepacrine (0.1 mM), an agent that inhibits the release of fatty acids from phospholipids. These data indicate that phospholipase activity is required for the biosynthesis of alkylacetyl-GPC. However, since the inhibitory effect of mepacrine was not apparent when acetate was present, it appears that the acetylation step is rate limiting. Exposure of alveolar macrophages in culture to zymosan or A23187 stimulated acetyltransferase activity 250-300%. In contrast, phorbol myristate acetate (1.6 microM), which stimulated the accumulation of lysophospholipids but not the level of alkylacetyl-GPC in the media, did not substantially increase acetyltransferase activity. We conclude that alkylacyl-GPC serves as a precursor of alkylacetyl-GPC and that the production of this potent mediator by rat alveolar macrophages can be stimulated by agents that affect phospholipase A2 and acetyltransferase activities. The latter enzyme appears to have a regulatory function in the biosynthesis of alkylacetyl-GPC.
Phenothiazines, 10-[n-(phthalimido)alkyl-2-substituted-10H- phenothiazines, and 1-(2-chloroethyl)-3-(2-substituted-10H-phenothiazin-10-yl)alkyl-1- ureas were investigated for their effects on antibody-dependent cellular cytotoxicity (ADCC), natural killer (NK) cells and the blast transformation of human peripheral blood mononuclear cells. All of the compounds dose-dependently suppressed mitogen-stimulated T cell proliferation. In contrast, a strong enhancing effect on NK cell activity was detected mostly in the case of 1-(2-choroethyl)-3-(2-substituted-10H-phenothiazin-10-yl)alk yl-1-ureas and their related compounds. The stimulating effect directly influenced the NK cells and was demonstrated at all tested concentrations.
The mechanism of halide elimination from 2-haloethyl-5,8-dihydroxyquinazolin-4(3H)-ones was studied in aqueous buffer by means of a pH-rate profile, buffer dilution studies, isotopic labeling, and kinetic isotope effects. From the results of these studies, it is apparent that a quinazolinone tautomer, arising from a prototropic shift of the C(l') proton to the N(1) position, is formed in the rate determining step of elimination. Monobasic phosphate acts as a bifunctional catalyst for the tautomerism. The halide then eliminates from the tautomer to afford the alkene derivative. Conversely, hydroxyethyl mercaptide adds to the alkene to afford the tautomer. The significance of these studies lies in the discovery of a prototropic tautomer of quinazolinone, which is reversibly formed in aqueous buffer under mild conditions, and in the discovery of alkylation chemistry useful in the design of quinazolinone-based enzyme inhibitors.
The first examples of intramolecular Zr-catalyzed electrophilic alkylation of aryl olefins are disclosed. Substituted carbo- and heterocycles are prepared efficiently and diastereoselectively.
The activities and the expression of 3-methyladenine glycosylase (3-meAde gly) and O6-alkylguanine-DNA-alkyltransferase (O6 ATase) were investigated in ten human cancer cell lines. Both 3-meAde gly and O6 ATase activities were variable among different cell lines. mRNA levels of the O6 ATase gene, appeared to be related to the content of O6 ATase in different cell lines, whereas no apparent correlation was found between mRNA of 3-meAde gly and the enzyme activity. No correlation was found between the activity of the two enzymes and the sensitivity to alkylating agents of different structures such as CC-1065, tallimustine, dimethylsulphate (DMSO), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), cis-diamminedichloroplatinum (cDDP) and melphalan (L-PAM). The most striking finding of this study is that a correlation exists between the activity of O6 ATase and 3-meAde gly in the various cell lines investigated (P<0.01), suggesting a common mechanism of regulation of two DNA repair enzymes.
A series of 2-O-alkylated tyrosine analogues of lysine-vasopressin and desamino-lysine and arginine-vasopressin were synthesized and tested for antidiuretic activity in the water-loaded anaesthetized rat. The analogues displayed only weak antidiuretic activities. When they were infused in the rats together with lysine vasopressin it was found that 1-deamino-[2-O-ethyltyrosine]-lysine-vasopressin inhibited the vasopressin-induced antidiuretic response. The antagonistic properties were further evaluated in long-term experiments on conscious non-hydrated rats with implanted minipumps. The analogues inhibited the vasopressin-induced antidiuresis at antagonist:agonist ratios of 0.5 and 1.0.
Anionic micelles of sodium lauryl sulfate, NaLS, catalyze the monoalkylation of Hg2+ in dilute acid by alkyl aquobis-(dimethyl glyoximato) cobalt (III), RCo(DH)2(H2O) degrees and the related propane derivatives RCo(DOH) DOpn (H2O)+, where R = Me, Et, n-C5H11. Nonionic micelles of Igepal do not catalyze the reaction. In the absence of micelles RCo(DH)2(H2O) degrees is considerably more reactive than RCo(DOH)DOpn(H2O)+, but this higher reactivity is offset in part by its higher basicity. Anionic micelles markedly increase the basicity of RCo(DOH)DOpn(H2O)+ and slightly increase that of RCo(DH)2(H2O) degrees. For reactions of the unprotonated Co(III) complexes the maximum rate enhancements by micelles of NaLS are: R = Me, 19(131); Et, 58 (65); n-C5H11, 46 (32). (The values in parentheses are for RCo(DOH)DOpn(H2O)+.)
Chlorambucil derivatives involving alkyl 2-aminodeoxy sugars have been synthesized in good yield by coupling the chlorambucil moiety to positions C-2 or C-3 of the sugar, directly or via a spacer. The starting material was easily available from 2-acetamido-2-deoxy-D-glucose. The final compounds were tested for cytotoxicity, and some of those that presented the best results were studied for inhibition of cell proliferation.
The affinity alkylating progesterone analogue 17-(bromoacetoxy)progesterone has been used to label the active site of a microsomal cytochrome P-450 enzyme from neonatal pig testis. The enzyme causes removal of the C20 and C21 side chains from the substrates progesterone and pregnenolone by catalyzing both 17-hydroxylase and C17,20-lyase reactions, which produce the corresponding C19 steroidal precursors of testosterone. The progesterone analogue causes simultaneous inactivation of the two catalytic activities of the enzyme by a first-order kinetic process that obeys saturation kinetics. Progesterone and 17-hydroxyprogesterone each protect the enzyme against inactivation. The progesterone and analogue is a competitive inhibitor of the enzyme with Ki values of 8.4 microM and 7.8 microM for progesterone and 17-hydroxyprogesterone, respectively. The enzyme inactivation and kinetic data are consistent with a theory proposing that the analogue and the two substrates compete for the same active site. The radioactive analogue 17-[( 14C]bromoacetoxy)progesterone causes inactivation of the enzyme with incorporation of 1.5-2.2 mol of the analogue per mole of inactivated enzyme. When this experiment is carried out in the presence of a substrate, then 0.9-1.2 mol of radioactive analogue is incorporated per mole of inactivated enzyme. The data suggest that the analogue can bind to two different sites, one of which is related to the catalytic site. Radiolabeled enzyme samples, from reactions of the 14C-labeled analogue with the enzyme alone or with enzyme in the presence of a substrate, were subjected to amino acid analysis and also to tryptic digestion and peptide mapping.(ABSTRACT TRUNCATED AT 250 WORDS)
Cytochrome P450(BM3)-F87G reacts with aromatic aldehydes and hydrogen peroxide to generate covalent heme adducts in a reaction that may involve the formation of a stable isoporphyrin intermediate [Raner, G. M., Hatchell, A. J., Morton, P. E., Ballou, D. P., and Coon, M. J. (2000) J. Inorg. Biochem. 81, 153-160]. Electron paramagnetic resonance spectra for the proposed isoporphyrin intermediates generated using two different aromatic aldehydes suggest that, in each case, the heme remained coordinated to the apoenzyme via the cysteine thiolate, the metal center remained ferric low spin, and a slight distortion in the geometry of the pyrrole nitrogens occurred. Characterization of the resulting heme adducts via 1D and 2D NMR showed conclusively that the heme was modified at the gamma-meso position alone, and mass spectral analysis indicated loss of formate from the aldehyde prior to alkylation. The enzyme derivatives in which the hemes were covalently altered retained the characteristic UV/vis and EPR spectral properties of a P450, indicating that the heme was properly ligated in the active site. The modified enzymes were able to accept electrons from NADPH in the presence of lauric acid at a rate comparable to that of the unmodified forms, although oxidation of the lauric acid was not observed with either modified enzyme. Oxidation of 4-nitrophenol and 4-nitrocatechol was observed for both derivatives. However, 4-nitrocatechol oxidation was completely quenched in the presence of superoxide dismutase. The results are consistent with heme modification occurring through a peroxo-dependent pathway and also suggest that modification results in altered catalytic activity, rather than complete inactivation of the P450.
A method for enantioselective Cu-catalyzed allylic substitution between various alkylzincs and alpha,beta-unsaturated carboxylic esters that bear a gamma-phosphate is reported. These transformations afford alpha-alkyl-beta,gamma-unsaturated carbonyls with regioselectivities of 7:1 to >20:1 (S(N)2':S(N)2) and in 87-97% ee. The utility of the method is illustrated by a convergent total synthesis of topoisomerse II inhibitor (R)-elenic acid.
1,3-Dipolar cycloaddition of benzyl azide or peracetylated glucopyranosyl azides to propargyl halides or 1,4-dihalobutynes yielded 1-benzyl- or 1-glycosyl(halomethyl)-1,2,3-triazoles. Alkylating chloromethyl- bromomethyl- and iodomethyl-1,2,3-triazoles were also obtained from the corresponding hydroxymethyl derivatives by treatment with (C6H5)3P/CCl4, (C6H5O)3P/Br2, and (C6H5O)3P/I2, respectively. 1-Benzyl-4-(fluoromethyl)-1,2,3-triazole was obtained from 1-benzyl-4-(bromomethyl)-1,2,3-triazole by treatment with KF and 18-crown-6. Chloromethyl-, bromomethyl-, and iodomethyl-1,2,3-triazole derivatives inhibited the "in vitro" growth of HeLa cells. Some of these compounds increased the life span of mice bearing tumors.