Studies on the 4-carbon compound needed for the formation of the O-xylene ring of riboflavin

The 4-carbon compound necessary for the formation of the o-xylene ring of riboflavin, was examined using labeled glucose and diacetyl in resting cells of Eremothecium ashbyii. The specific activity-time curves of riboflavin and lumichrome in the tracer experiments with [U-14C] glucose indicated that the specific activity of riboflavin during the incubation is much higher than that of its photolytic product, lumichrome. It is far above the level expected if the ribityl moiety of an intermediate, 4-ribitylamino-5-amino-2,6-dihydroxy-pyrimidine (RAADP), was to be utilized as the source of the 4-carbon unit on the o-xylene ring of riboflavin. It was further demonstrated that the specific activities of diacetyl and lumichrome at 10.5 h of the incubation and those of crystalline riboflavin and lumichrome at the later stage (20 h) of the incubation were identical respectively. Radioactive diacetyl furthermore proved to be likewise incorporated with a two fold dilution into riboflavin and lumichrome at 17 h of the incubation. The results reveal that it is not the ribityl fragment of RAADP bu the diacetyl that is the 4-carbon unit for the formation of the pyrazine ring of 6,7-dimethyl-8-ribityllumazine, that is, the o-xylene ring of riboflavin in the mold of Eremothecium ashbyii, although we still do not know whether the diketone requiring reaction is enzymatic or non-enzymatic.     

Possibility of 2,4,5-triamino-6-hydroxypyrimidine as an intermediate in the pathway of riboflavin biosynthesis

It was studied with resting cells of a high flavinogenic mold, Eremothecium ashbyii, whether or not 2,4,5-triamino-6-hydroxypyrimidine (THP) is an intermediate in the early pathway of riboflavin biosynthesis. A small amounts of THP strongly inhibited riboflavin formation in the resting cells, but the inhibition was effectively reversed by the added purines, except for adenine. Radioactive tracer experiments showed that the incorporation of the radioactivity from [2-14C]THP into riboflavin was negligible. The results obtained strongly suggest that THP is not an intermediate but a rigid inhibitor for riboflavin formation, and thus there is non salvage pathway of THP for the pathway of riboflavin biosynthesis in resting cells of E. ashbyii.     

Molecular features necessary for the uptake of diamines and related compounds by the polyamine receptor of rat lung slices.

The influence of 17 putrescine analogues on the uptake of putrescine and/or paraquat by rat lung slices has been determined. Most of these compounds are competitive inhibitors of putrescine and/or paraquat uptake, but three show no inhibiting activity. Apparent Ki values of the putrescine derivatives increase, and thus the inhibitory effects decrease, with increasing N-methylation. Comparison of N-methyl-1,4-diaminobutane (Ki = 8 microM) with N,N'-bis-methyl-1,4-diaminobutane (Ki = 25.5 microM) shows that a single primary amino group is desirable for high inhibiting activity. Dimethylation at one amino function does not greatly decrease inhibitory potential (thus N,N-dimethyl-1,4-diaminobutane has Ki = 11.5 microM). Increasing the size of N-alkyl substituents in putrescine derivatives, decreased their inhibitory action on the uptake of putrescine. Investigation of the effect of conformationally-restricted analogues of putrescine shows that both (E) and (Z) isomers of 1,4-diaminobut-2-ene are poor inhibitors of putrescine uptake. Analogues of putrescine with bulky substituents on the butyl chain, i.e. the meso- and rac-isomers of 1,1-dichloro-2,3-diaminomethylcyclopropane, do not inhibit putrescine uptake. Inhibiting putrescine derivatives which contain aziridine groups are competitive inhibitors of putrescine and paraquat uptake. Surprisingly, N-(4-aminobutyl)aziridine is the most effective inhibitor of putrescine uptake studied, and is a better inhibitor of paraquat uptake than the endogenous polyamine, putrescine. N-(4-Aminobutyl)aziridine binds reversibly to the polyamine transporter and its inhibitory effects do not appear to be due to any cytotoxic activity of the aziridine. The parameter A (mM)-1 defined as 1000/Ki (where Ki units are microM) was taken as a measure of the affinity of a compound for the polyamine receptor in this paper.     

4-hydroxy-3-nitro-2-quinolones and related compounds as inhibitors of allergic reactions.

The synthesis and biological activity of a number of 4-hydroxy-3-nitro-2-quinolones are discussed and compared with their related hydroaromatic analogs. Antiallergic activity has been assessed by their ability to inhibit the homocytotropic antibody-antigen induced passive cutaneous anaphylaxis reaction in the rat.     

Methemoglobin formation and binding to blood constituents as indicators for the formation,availability and reactivity of activated metabolites derived from trans-4-aminostilbene and related aromatic amines

trans-4-Aminostilbene derivatives exhibit higher acute and chronic toxicity than 4-aminobibenzyl derivatives. Yet, trans-4-aminostilbene produced less methemoglobin in female Wistar rats than 4-aminobibenzyl. This cannot be explained by differences in N-oxidation since trans-4-nitrosostilbene was also less efficient than 4-nitrosobibenzyl.The fate of intravenously injected, highly and specifically ³H-labeled trans-4- aminostilbene, cis-4-aminostilbene, 4-aminobibenzyl, trans-4-nitrosostilbene and 4-nitrosobibenzyl was investigated. The results indicate that trans-4-aminostilbene and 4-aminobibenzyl are N-oxidized to a similar extent and primary activation products of trans-4-aminostilbene appear even faster in the blood. However, intermediates originating during methemoglobin formation are more reactive and covalently bind to hemoglobin 2–3 times as much with trans-stilbene as compared to bibenzyl derivatives. As a consequence the availability of these intermediates in the cyclic process and thus methemoglobin formation is reduced.Therefore, binding to hemoglobin rather than levels of methemoglobin appears to be an indicator for the availability and reactivity of some activated aromatic amine metabolites.A preliminary account of part of this work has been published (Neumann and Wieland, 1973)     

Evidence for various tryptamines and related compounds acting as substrates of the platelet 5-hydroxytryptamine transporter

Summary The aim of the present study was to answer the question whether amines other than 5-hydroxytryptamine (5-HT) and tryptamine act as substrates of the platelet 5-HT transporter. To this end, a large number of tryptamines, 5-HT receptor agonists and phenethylamines (which had IC₅₀ values for ³H-5-HT uptake inhibition of 145–24500 nmol l^–1) was examined in rabbit platelets in order to determine their ability to induce an outward transport of ³H-5-HT Platelets (the MAO of which was blocked) from reserpine-pretreated animals were loaded with ³H-5-HT and then exposed for 5 min to various concentrations (ranging from 0.25 to 40 times the IC₅₀) of each compound. The concentration-effect curves for the drug-induced increase in ³H-5-HT efflux served to determine values of E_max (maximum increase in efflux expressed in % of the ³H-5-HT content of cells) and EC₅₀ (drug concentration producing E_max/2).For the 24 compounds studied here (which included the 5-HT uptake inhibitors imipramine, citalopram, fluoxetine and cocaine) a linear correlation between EC₅₀ and IC₅₀ (r = 0.975) and a mean ratio of EC₅₀/IC₅₀ of 2.4 was found. Most of the compounds [e.g., (±)8-hy-ydroxy-2-(N,N-dipropylamino)tetralin, S(+)-methyl-5-HT, 5-carboxamidotryptamine and 5-methoxytryptamine] gave rise to E_max values (15.8–32.5%) that exceeded that brought about by imipramine (6.6%), indicating that they act as substrates of the 5-HT transporter; the ³H-5-HT outward transport observed in response to these substances was abolished in the presence of imipramine. Others (e.g., 2-methyl-5-HT and 5-methylurapidil) produced Emax values (3.4–14.3%) not significantly different from that of imipramine and, therefore, can be classified either as poor substrates or as inhibitors of the 5-HT transporter.Hence, many tryptamines and 5-HT receptor agonists are substrates of the platelet 5-HT transporter. The property of being substrates gives them the latent capacity to bring about release of endogenous 5-HT and, as a result, to cause indirect 5-HT receptor-mediated effects.Abbreviations MAO monoamine oxidase - 5-HT 5-hydroxytryptamine - 2-M-5-HT 2-methyl-5-HT - N-M-5-HT N-methyl-5-HT - N,N-DM-5-HT N,N-dimethyl-5-HT - S(+)-M-5-HT S(+)-methyl-5-HT - 5-CT 5-carboxamidotryptamine - 5-M-tryptamine 5-methyltryptamine - 5-MO-tryptamine 5-methoxytryptamine - 7-M-tryptamine 7-methyltryptamine - N-M-tryptamine N-methyltryptamine - N,N-DM-tryptamine N,N-dimethyltryptamine - N,N-DM-5-MO-tryptamine N,N-dimethyl-5-methoxytryptamine - (±)8-OH-DPAT (±)8-hydroxy-2-2-(N,N-dipropylamino)tetralin - 5-M-urapidil 5-methyl-urapidil Send offprint requests to R. Wölfel at the above address     

Chemical fate and mutagenic formation potentials of phenothiazine and related compounds during water chlorination

The reactions of hetero-tricyclic aromatic hydrocarbons (H-TCAHs) with hypochlorite in an aqueous solution were investigated under conditions that simulate wastewater disinfection. H-TCAH-hypochlorite reaction products were determined by gas chromatographic-mass spectrometric (GC-MS) analyses. For 20 μM, 10H-phenothiazine, 10H-phenoxazine, and phenoxathiin reacted rapidly with active chlorine in neutral pH (7.0), but no phenazine-hypochlorite reaction was observed over pH values of 5-9 for 1 hr. The 10H-phenothiazine-hypochlorite reaction began by oxidation with active chlorine to form its dioxides, followed by chloro-substitution in water. The extent of the reactions depended on the chlorine dose, solution pH and compound structures. Ames assays for the chlorination byproducts of 10H-phenothiazine and 10H-phenoxazine also showed to be weak mutagenicity in TA98 and TA100 strains without S9 mix, but no chlorination byproducts of phenoxathiin exhibited any mutagenicity in both tester strains with and without S9 mix.     

Chemistry and pharmacology of compounds related to 4-(4-hydroxy-4-phenyl-piperidino)-butyrophenone

Summary Haloperidol (R 1625) is 50 to 100 times more active than chlorpromazine as an inhibitor of exploratory motor behaviour in rats. Emotional defaecation in rats is inhibited by both drugs at similar dose levels.Thanks are due to Mr. Remi Frederickx for his technical assistance.     

Phenothiazines and structurally related compounds as modulators of cancer multidrug resistance

Phenothiazines and structurally related compounds alongside their other biological activities are able to modulate multidrug resistance (MDR) in tumor cells. The extensive investigations on their MDR modulation effects consist part of the efforts to overcome MDR - the major obstacle in cancer chemotherapy. In this article we try to systematize the results collected in the last two decades in two main aspects. The first one comprises the mechanism of modulation by phenothiazine-type MDR modulators. Two main possible mechanisms of MDR reversal are reviewed: (i) direct interaction with Pgp; (ii) interactions with membrane phospholipids. The second aspect relates to the structural properties of phenothiazines and related compounds responsible for their MDR reversing effect. The structural alerts and physicochemical properties influencing anti-MDR activity are considered as identified by structure--activity (SAR) or quantitative structure--activity relationship (QSAR) studies. Results discussed in the article point to MDR modulation by phenothiazines and related compounds as a complex process in which more than one mechanism are certainly involved. Further investigations in this direction should contribute to elucidation of the possible mechanisms of MDR modulation by these compounds. On the basis of the studies discussed the potential use of phenothiazine-type MDR modulators as a model system in the further investigations of the MDR phenomenon is outlined.     

SAR study of a novel triene-ansamycin group compound, quinotrierixin, and related compounds, as inhibitors of ER stress-induced XBP1 activation

Four novel triene-ansamycin group compounds, quinotrierixin, demethyltrienomycin A, demethyltrienomycin B and demethyltrienomycinol, were isolated from the culture broth of Streptomyces sp. PAE37 as inhibitors of ER stress-induced XBP1 activation. The structures of quinotrierixin, demethyltrienomycin A, demethyltrienomycin B and demethyltrienomycinol were determined on the basis of their spectroscopical and chemical properties. All of four possessed 21-membered macrocyclic lactams including triene moieties.     

Spiro[1,2,4-benzotriazine-3(4H),4'-(1'-substituted)piperidines] and related compounds as ligands for sigma receptors

As analogues of some conformationally restricted spiropiperidine derivatives which are endowed with high affinity for sigma1 receptor, a set of 16 spiro[1,2,4-benzotriazine-3(4H),4'-(1'-substituted)piperidines] and congeneric compounds was prepared and tested for affinity to sigma1 receptor subtype. All N-arylalkyl substituted derivatives exhibited high affinity for the relevant receptor, with Ki in the low nanomolar range. Affinity for sigma2 subtype (assayed only for a few representative compounds) was from one to three order of magnitude lower. Spiro[1,2,4-benzotriazine-3(4H),4'-(1'-benzyl)piperidine] (2), with a ratio Ki sigma2/Ki sigma1 = 7000 should represent the most selective sigma1 ligand so far described.     

Antitumor agents. 113. New 4 beta-arylamino derivatives of 4'-O-demethylepipodophyllotoxin and related compounds as potent inhibitors of human DNA topoisomerase II

A number of 4'-O-demethylepipodophyllotoxin derivatives possessing various 4 beta-N-, 4 beta-O- or 4 beta-S-aromatic rings have been synthesized and evaluated for their inhibitory activity against the human DNA topoisomerase II as well as for their activity in causing cellular protein-linked DNA breakage. The results indicated, that for DNA topoisomerase II, a basic unsubstituted 4 beta-anilino moiety is structurally required for the enhanced activity. Substitution on this moiety with CN, COOCH3, COOC2H5, OH and COOCH3, OCH3, COCH3, CH2OH, OCH2O, OCH2CH2O, phenoxy, morpholino, NO2, and NH2 either at the para and/or the meta position yielded compounds which are as potent or more potent than etoposide. Substitution with COOC2H5 and OH at the ortho position afforded inactive compounds. Replacement of the aryl nitrogen with oxygen or sulfur gave compounds which are much less active or inactive. However, replacement of the phenyl ring with a pyridine nucleus furnished compounds which are as active or slightly more active than etoposide. There is a lack of correlation between the ability of these compounds in inhibiting DNA topoisomerase II and in causing protein-linked DNA breaks.