Photoinduced electron transfer and chemical alpha-deoxygenation of D-galactono-1,4-lactone. Synthesis of 2-deoxy-D-lyxo-hexofuranosides

Two simple procedures for the synthesis of 2-deoxy-D-lyxo-hexono-1,4-lactone are described. Reductive cleavage of a 2-O-tosyl derivative of D-galactono-1,4-lactone in the presence of sodium iodide afforded the 2-deoxy derivative. On the other hand, alpha-deoxygenation of D-galactono-1,4-lactone was easily achieved by photochemical electron transfer deoxygenation of HO-2 as the 3-(trifluoromethyl)benzoate. Methyl 2-deoxy-beta-D-lyxo-hexafuranoside ('methyl 2-deoxy-beta-D-galactofuranoside') was synthesized and tested as substrate for exo beta-D-galactofuranosidase from Penicillium fellutanum. The reaction was followed by HPAEC, showing that methyl 2-deoxy-beta-D-galactofuranoside was not hydrolyzed by incubation with the enzyme. Neither the 2-deoxy lactone, nor the 2-deoxy-beta-D-galactofuranoside acted as inhibitors of the reaction with the 4-nitrophenyl beta-D-galactofuranoside. The present and our previous results show that the hydroxyl groups at C-2, C-3 and C-6 of the galactofuranoside are essential for interaction with the exo beta-D-galactofuranosidase.     

Novel 4-thiogalactofuranosyl-containing disaccharides with nitrogen in the interglycosidic linkage

The syntheses of three novel disaccharides containing a 4-thiogalactofuranosyl residue as the non-reducing unit and a nitrogen in the interglycosidic linkage are described. Acid-catalyzed condensation reactions of 4-thio-alpha/beta-D-galactofuranose with either methyl 3-amino-3-deoxy-alpha-D-mannopyranoside, methyl 2-amino-2-deoxy-alpha-D-mannopyranoside, or methyl 2-acetamido-6-amino-2,6-dideoxy-beta-D-glucopyranoside gave methyl 3-amino-3-deoxy-3-N-(4-thio-alpha/beta-D-galactofuranosyl)-alpha-D-manno pyranoside, methyl 2-amino-2-deoxy-2-N-(4-thio-alpha/beta-D-galactofuranosyl)-alpha-D-manno pyranoside, or methyl 2-acetamido-6-amino-2,6-dideoxy-6-N-(4-thio-alpha/beta-D-galactofuranosy l)-beta-D-glucopyranoside.     

A teichoic acid of Nocardioides albus VKM Ac-805T cell walls

A teichoic acid of Nocardioides albus VKM Ac-805T cell walls, a typical species of the genus Nocardioides, contains a poly(glycosylglycerol phosphate). The repeating unit of the polymer has the structure: [figure]. These units are in phosphodiester linkage at C-3 of glycerol and C-3 of beta-D-galactopyranose. beta-D-Galactopyranosyl residues are substituted at C-4 by beta-D-glucopyranose carrying a 4,6-pyruvate ketal group in S-configuration. The presence of pyruvic acid in the majority of repeating units increases the anionic properties of the polymer in comparison with most other common teichoic acids. This is the first report of the occurrence of a beta-D-galactofuranosyl residue in teichoic acids; it probably acts as a terminator of an extending chain of the polymer. The ratio of beta-D-galactopyranosyl to beta-D-galactofuranosyl units is 7:1. The polymer structure was determined by NMR spectroscopy. This type of teichoic acid structure has not been reported previously.     

Synthesis and in vitro antimicrobial and antitumor activity of some nitrogen heterocycles

5-Phenyl-2-[(3,4,5-trimethoxybenzylidene)hydrazino]-thiazole and 3-[(3,4,5-trimethoxybenzylidene)amino]-4-oxoimidazolidin-2-thione were prepared by cyclization of 1-[(3,4,5-trimethoxybenzyliden)amino]-thiourea with phenacyl bromide and ethyl chloroacetate in the presence of fused sodium acetate. Acetylation of the synthesized compounds with acetic anhydride gave corresponding N-acetyl derivatives. Condensation of the synthesized thione with aromatic aldehydes yielded two 3-substituted 5-arylidene-4oxo-imidazolidin-2-thiones. Acetylation of the latter compounds with acetic anhydride afforded the corresponding N-acetyl-4-oxo-imidazolidin-2-thiones. Some of the synthesized compounds exhibited antimicrobial activity. The cytotoxic activity of the prepared thiazole and imidazolidin-2-thione derivatives was studied on several tumor cell lines.     

The identification of 1,3-oxazolidine-2-thiones and 1,3-thiazolidine-2-thiones from the reaction of glucose with benzyl isothiocyanate

The structure of interaction products resulting from the reaction of unmodified glucose with benzyl isothiocyanate is reported. Prior to their identification, the main products of this reaction were isolated using solid-phase extraction (SPE) as well as preparative HPLC. They were then identified by NMR and MS as 3-benzyl-4-hydroxy-5-(D-arabino-1,2,3,4-tetrahydroxybutyl)-1,3-oxazolidine-2-thione, 3-benzyl-4-hydroxy-4-hydroxymethyl-5-(D-erythro-1,2,3-trihydroxypropyl)-1,3-oxazolidine-2-thione, N-benzyl-(D-gluco-4,5-dihydroxy-6-hydroxymethyl-tetrahydropyrano)[2,3-b]oxazolidine-2-thione and 3-benzyl-4-(N-benzyl amino)-5-(D-arabino-1,2,3,4-tetrahydroxybutyl)-1,3-thiazolidine-2-thione. The identity of the last compound was secured by X-ray crystal structure data.     

Synthesis of 4-nitrophenyl beta-D-fucofuranoside and beta-D-fucofuranosyl-(1-->3)-D-mannopyranose: modified substrates for studies on catalytic requirements of beta-D-galactofuranosidase

Syntheses of 4-nitrophenyl beta-D-fucofuranoside (6) and beta-D-fucofuranosyl-(1-->3)-D-mannopyranose (10) are reported. These compounds, as analogues of galactofuranosides, were used for studying the influence of the hydroxyl group at C-6 in the interaction of the substrate with beta-D-galactofuranosidase. For the synthesis of the fucofuranosides, 2,3,5-tri-O-benzoyl-6-bromo-6-deoxy-D-galactono-1,4-lactone (1) was the key intermediate, which upon reduction of the lactone group with diisoamylborane, acetylation of the anomeric hydroxyl group, and catalytic hydrogenolysis of the bromine at C-6, led to 1-O-acetyl-2,3,5-tri-O-benzoyl-alpha,beta-D-fucofuranose (4), a convenient derivative for the preparation of fucofuranosides. Compound 4 was glycosylated in the presence of SnCl4, either with 4-nitrophenol for the preparation of 6, or with 2,5,6-tri-O-benzoyl-D-mannono-1,4-lactone (7), for the synthesis of disaccharide 10, via the glycosyl-aldonolactone approach. The synthetic route developed for the beta-D-fucofuranosides is simple and efficient. Compound 6 was not hydrolyzed by incubation with the exo beta-D-galactofuranosidase from Penicillium fellutanum, showing that HO-6 is essential for interaction of the substrate with the enzyme.     

Mechanism-based inhibition of lactoperoxidase by thiocarbamide goitrogens. Identification of turnover and inactivation pathways

Direct evidence is presented in support of mechanism-based (suicide) inactivation of lactoperoxidase by thiocarbamide thyroid inhibitors. The turnover of 1-methylbenzimidazolidine-2-thione was demonstrated by identifying the inhibitor-derived products 1-methylbenzimidazole and bisulfite ion that are formed concurrent to enzyme inactivation. The turnover of a hydroperoxide cosubstrate, 5-phenyl-4-pentenyl hydroperoxide, was quantitated from formation of the corresponding alcohol during enzyme inactivation. A specific inactivation pathway is suggested by the covalent binding of 1 mol of 14C- and 35S-labeled benzimidazolidine-2-thione and 1-methylbenzimidazolidine-2-thione per mole of inactivated lactoperoxidase. These results are explained by partitioning of inhibitor-derived S-oxygenated intermediates between turnover and inactivation pathways. The properties of the inactivation process are unique among thiono-sulfur compounds and suggest that benzimidazolinesulfenic acids are the reactive intermediates.     

A new route to the imidazole-2-thiones from 2-thiohydantoins. Implications in the study of ergothioneine

1. 2-Thiohydantoins are reduced by borohydrides to 4(5)-hydroxyimidazolidine-2-thiones, which eliminate water in acid to form imidazole-2-thiones. Both steps take place in mild conditions, in high yield. A number of imidazole-2-thiones have been synthesized by this sequence of steps, with one, two or three substituents in the 1-, 3- and 4(5)-positions. 2. 4(5)-Hydroxyimidazolidine-2-thiones are ammonium pseudo-bases, giving rise to an equilibrium mixture of amino aldehyde, carbinolamine and mesomeric ammonium cationic forms. The elimination of water is suggested to be a property of the mesomeric ammonium cation. 3. The mild conditions in which imidazole-2-thiones are formed from 4(5)-hydroxyimidazolidine-2-thiones are similar to those in which ergothioneine, a naturally occurring imidazole-2-thione of uncertain function, is normally released and measured. It is suggested that the occurrence in vivo of a precursor to ergothioneine, in the form of a 4(5)-hydroxyimidazolidine-2-thione, would explain many otherwise conflicting published data.     

Spectroscopic quantitation of organic isothiocyanates by cyclocondensation with vicinal dithiols.

Organic isothiocyanates are widely distributed in plants and are responsible for a variety of beneficial and toxic biological effects. No direct and generic method for quantitating isothiocyanates has been described. Under mild conditions nearly all organic isothiocyanates (R-NCS) react quantitatively with an excess of vicinal dithiols to give rise to five-membered cyclic condensation products with release of the corresponding free amines (R-NH2). The products of the condensation of propyl-NCS with 1,2-ethanedithiol, 2,3-dimercaptopropanol, and 1,2-benzenedithiol have been isolated and identified as 1,3-dithiolane-2-thione, 4-hydroxymethyl-1,3-dithiolane-2-thione, and 1,3-benzodithiole-2-thione, respectively. Since 1,3-benzodithiole-2-thione (lambda max 365 nm and alpha m 23,000 M-1 cm-1) can be sensitively measured spectroscopically, the reaction of organic isothiocyanates with 1,2-benzenedithiol has been developed for analytical purposes. All aliphatic and aromatic isothiocyanates tested (except tert-butyl and other tertiary isothiocyanates) reacted quantitatively with an excess of 1,2-benzenedithiol. Thiocyanates, cyanates, isocyanates, cyanides, or related compounds did not interfere with this reaction under assay conditions. The method can be used to measure 1 nmol or less of pure isothiocyanates or isothiocyanates in crude mixtures. It can also be used to measure isothiocyanates in chromatographic fractions obtained from plant extracts and for the assay of the rate of cleavage of glucosinolates by myrosinase (thioglucoside glucohydrolase; EC 3.2.3.1).     

High-pressure liquid chromatographic analysis for identification of in vitro and in vivo metabolites of 4-phenethyl-5-[4-(1-(2-hydroxyethyl)-3,5-dimethyl-4-pyrazolylazo)phenyl]-2,4-dihydro-3H-1,2,4-triazole-3-thione in rats

All azo colorants whose metabolism can liberate a carcinogenic arylamine, are suspected of having carcinogenic potential. Therefore, a new azo compound 4-phenethyl-5-[4-(1-(2-hydroxyethyl)-3,5-dimethyl-4-pyrazolylazo)phenyl]-2,4-dihydro-3H-1,2,4-triazole-3-thione (substrate) was prepared to investigate its in vitro and in vivo biotransformation in rats by HPLC. Chromatographic separation of substrate and its metabolites was performed using a Chromasil C(18) column. The mobile phase consisted of acetonitrile and water in a linear gradient system. From the biotransformation of this compound, the reduction metabolite 4-(2-phenethyl)-5-(4-aminophenyl)-2,4-dihydro-3H-1,2,4-triazole-3-thione was identified by comparing it to reference standard by HPLC-DAD. In the in vivo study, identification of the unknown peak which was the N-acetylation metabolite was confirmed by LC-MS spectrometry. Besides this, the azo compound was reduced to its corresponding amine in intestinal and cytosolic parts. In addition, oxidation of the methyl group and the phenyl ring, and reduction of azo group to hydrazo were identified in the cytosolic part using LC-MS.     

Thiosugar nucleosides. Synthesis and biological activity of 1,3,4-thiadiazole, thiazoline and thiourea derivatives of 5-thio-D-glucose

New acylated 5-thio-beta-D-glucopyranosylimino-disusbstituted 1,3,4-thiadiazols 8, and 11 were prepared, via spontaneous rearrangements, by cycloaddition of the glycosyl isothiocyanate 2 with the reactive intermediates 1-aza-2-azoniaallene hexachloroantimonates 4 and 6, respectively. Reaction of 2 with aminoacetone or chloroethylamine afforded the acylated 5-thio-beta-D-glucopyranosyl-4-imidazoline-2-thione nucleoside 16 and glucopyranosylamino-2-thiazoline derivative 18, respectively. Deblocking of 8, 11, 17 and 19 furnished the free nucleoside analogues 9, 12, 18 and 20, respectively. Analogously, treatment of 2 with chloroethylamine in the 1:2 ratio afforded the thioureylendisaccharide 21. No in vitro antiviral activity against HIV-1, HIV-2, human cytomegallovirus (HMCV), has been found for the new synthesized compounds.     

Silver(I) complexes with heterocyclic thiones and tertiary phosphines as ligands. Part 4. Dinuclear complexes of silver(I) bromide: the crystal structure of bis[bromo-(pyrimidine-2-thione)(triphenylphosphine)silver(I)]

Mixed-ligand complexes of the formula [Ag(PPh₃)(L)Br]₂ were obtained by treatment of various heterocyclic thiones L {L=pyridine-2-thione (py2SH), pyrimidine-2-thione (pymtH), benz-1,3-imidazoline-2-thione (bzimtH₂), benz-1,3-thiazoline-2-thione (bztztH), 1-methyl-1,3-imidazoline-2-thione (meimtH) and 5-methoxy-benz-1,3-imidazoline-2-thione (5MeObzimtH₂)} with equivalent quantities of silver(I) bromide and triphenylphosphine in dry acetone. The compounds were characterized by their IR, far-IR, UV–Vis and ¹H NMR spectroscopic data. The crystal structure of [Ag(PPh₃)(pymtH)Br]₂ was determined by single-crystal X-ray diffraction methods. The complex exhibits a planar Ag₂Br₂ moiety in which each of the doubly bromine-bridged Ag(I) centres is further bonded to one phosphine P and one thione S atom.     

Improved synthesis methods of standards used for quantitative determination of total isothiocyanates from broccoli in human urine

A well-known method for quantification of isothiocyanates (ITCs) and their metabolites is the condensation reaction with 1,2-benzenedithiole to produce 1,3-benzodithiole-2-thione, which can be quantified by high-performance liquid chromatography. Standards of an ITC metabolite and 1,3-benzodithiole-2-thione are required for this assay but are not commercially available. In the present study, we report on an improved synthesis of the ITC metabolite N-acetyl-S-(N-4-methylsulfinylbutylthiocarbamoyl)-L-cysteine and 1,3-benzodithiole-2-thione. The standards were used to quantify the urinary excretion of ITCs from 10 healthy subjects who consumed 350 g broccoli. The excretion was investigated throughout 48 h showing a cumulative urinary ITC excretion of 49.1+/-25.2% of the dose.     

Design, synthesis, and in vitro antitumor activity of new 1,4-diarylimidazole-2-ones and their 2-thione analogues

A series of new 1,4-diarylimidazol-2(3H)-one derivatives and their 2-thione analogues has been prepared and evaluated in vitro for antitumor activity against the NCI human cancer cell panel. Compounds bearing a 3,4,5-trimethoxyphenyl ring linked to either N-1 or C-4 position of the imidazole core demonstrated an interesting profile of cytotoxicity with preferential activity against leukemic cell lines. Compound 13 exhibited a potent antitumor activity against MOLT-4 (GI(50)=20 nM) and SR (GI(50)=32 nM) cell lines.     

Photolysis of N-hydroxpyridinethiones: a new source of hydroxyl radicals for the direct damage of cell-free and cellular DNA.

N-Hydroxypyridine-2-thione (2-HPT), known to release hydroxyl radicals on irradiation with visible light, and two related compounds, viz. N-hydroxypyridine-4-thione (4-HPT) and N-hydroxyacridine-9-thione (HAT), were tested for their potency to induce DNA damage in L1210 mouse leukemia cells and in isolated DNA from bacteriophage PM2. DNA single-strand breaks and modifications sensitive to various repair endonucleases (Fpg protein, endonuclease III, exonuclease III, T4 endonuclease V) were quantified. Illumination of cell-free DNA in the presence of 2-HPT and 4-HPT gave rise to damage profiles characteristic for hydroxyl radicals, i.e. single-strand breaks and the various endonuclease-sensitive modifications were formed in the same ratios as after exposure to established hydroxyl radical sources. In contrast, HAT plus light gave rise to a completely different DNA damage profile, namely that characteristic for singlet oxygen. Experiments with various scavengers (t-butanol, catalase, superoxide dismutase) and in D2O as solvent confirmed that hydroxyl radicals are directly responsible for the DNA damage caused by photoexcited 2-HPT and 4-HPT, while the damage by HAT plus light is mediated by singlet oxygen and type I reactions. The type of DNA damage characteristic of hydroxyl radicals was also observed in L1210 mouse leukemia cells when treated with 2-HPT plus light or with H2O2 at 0 degrees C. t-Butanol (2%) inhibited the cellular DNA damage by approximately 50%. A dose of 2-HPT plus light that generated single-strand breaks at a frequency of 5 x 10(-7)/bp was associated with 50% cell survival. No DNA damage and cytotoxicity was observed after treatment with 2-HPT in the dark. We propose that 2-HTP and 4-HTP may serve as new agents to study the consequences of DNA damage induced by hydroxyl radicals in cells. In addition, the data provide direct evidence that hydroxyl radicals are ultimately responsible for the genotoxic effects caused by H2O2 in the dark.     

Synthesis and antiviral evaluation of some new pyrazole and fused pyrazolopyrimidine derivatives

Some novel substituted pyrazole and pyrazolo[3,4-d]pyrimidine derivatives 2, 4, 8, and 9 were synthesized. Also, some acyclic S-nucleosides of pyrazolo[3,4-d]pyrimidine derivatives 10-13 were prepared via reaction of pyrazolo[3,4-d]pyrimidine-4(3H)-thione derivative 9 with some acyclic sugars. Moreover, the N-nucleoside derivative 14 was prepared via reaction of compound 8 with glucosamine hydrochloride. The antiviral evaluation of some selected new products showed that they have promising antiviral activity against hepatitis-A virus (HAV) and herpes simplex virus type-1 (HSV-1).     

Facile synthesis of (R)-4-mercaptopyrrolidine-2-thione from L-aspartic acid

An SN2-type of substitution of (S)-bromide 4, which had been prepared from L-aspartic acid, with potassium thiobenzoate provided (R)-benzoylthio derivative 5 with complete inversion of the configuration. Compound 5 was converted, via iodide 6c, to (R)-4-amino-3-benzoylthiobutyric acid 8b. (R)-4-Mercapto pyrrolidine-2-thione 1 was readily obtained from 8b through cyclization with acetic anhydride, thionation with Lawesson's reagent and facile removal of the S-benzoyl group with sodium methoxide.     

Preparation of 1,3,5-thiadiazine-2-thione derivatives of chitosan and their potential antioxidant activity in vitro

Three new kinds of 1,3,5-thiadiazine-2-thione derivatives of chitosan with two different molecular weight (SATTCS1, SATTCS2, TITTCS1, TITTCS2, CITTCS1 and CITTCS2) have been prepared. Their structures were characterized by IR spectroscopy. The substitution degree of derivatives calculated by elemental analyses was 0.47, 0.42, 0.41, 0.38, 0.41 and 0.36, respectively. The result shows that substitution degree of derivatives was higher with lower molecular weight. The antioxidant activity was studied using an established system, such as hydroxyl radical scavenging, superoxide radical scavenging and reducing power. Antioxidant activity of the 1,3,5-thiadiazine-2-thione derivatives of chitosan were stronger than that of chitosans and antioxidant activity of low molecular weight derivatives were stronger than that of high molecular weight derivatives. It is a potential antioxidant in vitro.     

Structure of a teichoic acid from Nocardioides luteus VKM Ac-1246T cell wall

A teichoic acid from the cell walls of Nocardioides luteus VKM Ac-1246T, a validly described species of the Nocardioides genus, is a 1,5-poly(ribitol phosphate) completely substituted at C-4 by alpha-D-galactopyranosyl residues carrying a 4,6-pyruvate ketal group in R-configuration. The structure of the repeating unit of the polymer is as follows: [figure]. The chain consists of approximately 18 repeating units and six beta-D-galactofuranosyl residues linked in the oligomer by 1,6-glycosidic bonds. The oligomer probably terminates the growing end of the teichoic acid. The structure of the polymer was determined by chemical methods and NMR spectroscopy. This teichoic acid has not been described so far.     

A simple spectrophotometric determination of solid supported amino groups

A simple spectrophotometric method for the quantitative determination of solid phase supported amino groups is described. The method involves reacting the solid support with an excess of activated acylating agent, N-succinimidyl-3-(2-pyridyldithio)propionate (SPDP) and an efficient acylation catalyst, 4-dimethylaminopyridine, and after thoroughly removing the unreacted SPDP, the solid support is reacted with an excess of dithiothreitol to quantitatively release pyridine-2-thione from the solid support to the solution. After an appropriate dilution, the released pyridine-2-thione which has a strong absorbance at 343 nm, is quantified by reading its absorbance in a spectrophotometer at 343 nm.