Studies on pyrazines. 9 . The facile synthesis of pyrazine 1-oxides substituted at C-2 with cyano,methoxycarbonyl and carboxy groups

The peroxysulfuric acid oxidation of 2-cyanopyrazine ( 1 ) gave its 1-oxide 3 (18% yield) and pyrazinecarb-oxamide (8% yield), while that of methyl pyrazinecarboxylate ( 2 ) provided the 1- and 4-oxides in 15 and 7% yields, respectively. On the other hand, pyrazinecarboxylic acid 1-oxide ( 7 ) was prepared by condensation of 2-methylpyrazine 1-oxide ( 8 ) with benzaldehyde followed by oxidative cleavage (47% overall yield).     

Recherches sur la formation et la transformation des esters LXXXI [1]. Sur la réaction d'isothiocyanates avec l'acide hydrazinoéthylphosphorique,et de l'isocyanate de phényle avec l'acide colaminephosphoreux

Hydrazinoethyl phosphoric monoester has been prepared by reacting hydrazinoethanol with polyphosphoric acid, and isolated as di-sodium salt. Sodium hydrazinoethyl phosphate reacts with phenylisothiocyanate (in H₂O+ethanol) to yield mainly the derivative thiocarbamoylated at the substituted nitrogen atom. This derivative, heated for one night at 100° in 0.5 N HCl, is cyclized to 3-amino-2-phenylimino-thiazolidine in 62% yield. Sodium hydrazinoethyl phosphate reacts with o-methoxycarbonylphenyl isothiocyanate (in H₂O+dioxane) at the unsubstituted nitrogen atom to yield mainly the corresponding quinazoline derivative (IV, X = OPO₃Na₂). This derivative, heated for one night at 100° in 0.5 N HCl, is cyclized to 2-o-carboxyphenylamino-dihydro-δ²-1, 3, 4-thiadiazine (Va) in 55% yield (hydrolysis of the lactamic function as well). Aminoethyl phosphorous monoester (colaminephosphorous acid) reacted with phenylisocyanate (in H₂0+dioxane) in slightly alkaline medium (one equivalent of NaOH) yields sodium N-phenylcarbamoylaminoethyl phosphite. Refluxed for 20 minutes in 1N NaOH, this carbamoyl derivative is not cyclized but only hydrolyzed to the open-chained N-phenyl-N′-hydroxyethylurea (VII).     

Imidazo[2,1-b]benzothiazoles. II. Synthesis and antiinflammatory activity of some imidazo[2,1-b]benzothiazoles

3-[2-[p-(Un)substituted phenyl]imidazo [2,1-b]benzothiazol-3- yl]propionic acid derivatives (2a--e) were prepared via the interaction of the corresponding 2-[p-(un)substituted phenyl]imidazo[2,1-b]benzothiazoles (1a--e) with acrylic acid in the presence of acetic anhydride and acetic acid. Esterification of 2a--e produced methyl esters (3a--e). Upon the interaction of 3a with m-chloroperbenzoic acid, the S-dioxide (4a) was obtained. Compound 5a was prepared from 4a by alkaline hydrolysis. Vilsmeier formylation for 1a--e produced novel [2-[p-(un)substituted phenyl]imidazo[2,1-b]benzothiazol-3- yl]formaldehyde derivatives (6a--e). Derivatives 6a--e reacted with ethyl bromoacetate to give ethyl 3-hydroxy-3-[2-[p-(un)substituted phenyl]imidazo[2,1-b]benzothiazol- 3-yl]propionate esters (7a--e). Compound dl-7a was resolved with l-(+)-tartaric acid. Compounds 2a--e showed weak or no activity in the carrageein-induced paw edema assay. Compound 4a significantly inhibited the leakage of pontamine-sky blue dye into the peritoneal cavity of mice, in the capillary permeability inhibition assay. Compound 5a inhibited the writhing by 62% in the acetic acid-induced writhing assay.     

Asymmetric synthesis of chiral N-sulfinyl 3-alkyl- and 3-arylpiperidines by α-alkylation of N-sulfinyl imidates with 1-chloro-3-iodopropane

α-Alkylation of N-sulfinyl imidates with 1-chloro-3-iodopropane successfully led to 2-substituted N-tert-butanesulfinyl-5-chloropentanimidates in acceptable diastereomeric ratios (dr 67/33 to 72/28) and good yields (74-86%). Subsequent reduction with NaBH(4) led to the corresponding 2-substituted N-tert-butanesulfinyl-5-chloropentylamines, which could be cyclized to a range of new chiral 3-substituted N-tert-butanesulfinylpiperidines using NaH in DMSO. Finally, the N-tert-butanesulfinylpiperidines could be efficiently deprotected to enantiomerically pure 3-alkyl- and 3-arylpiperidine hydrochlorides.     

Expeditious syntheses of conjugated allenyl esters and oxazoles through a cascade reaction of alpha-alkynyl malonates under alkaline conditions

Diethyl alpha-alkynyl-alpha-methoxymalonates (2a--e) were smoothly hydrolyzed and then decarboxylated under alkaline conditions employing 1 N KOH in EtOH to give conjugated allenyl esters (6a--e) in high yields, and similar alkaline treatment of diethyl alpha-alkynyl-alpha-acetylaminomalonates (5a, b, d, e) furnished unexpectedly the oxazoles (7a, b, d, e) having three substituent groups in excellent yields.     

A general synthesis of substituted formylpyrroles from ketones and 4-formyloxazole

A novel two-step synthesis of substituted 2-formylpyrroles is described. Aldol adducts of ketones and 4-formyloxazole undergo a dehydration/oxazole hydrolysis/cyclization cascade on sequential treatment with MsCl/Et3N and aqueous NaOH to yield 5-substituted and 4,5-disubstituted 2-formylpyrroles. The methodology was extended to an N-benzyl thiazolium salt.     

Nitrosation of sugar oximes: preparation of 2-glycosyl-1-hydroxydiazene-2-oxides

Oximes of glucose, xylose, lactose, fructose, and mannose have been prepared. Nitrosation of the oximes of glucose, xylose, and lactose with NaNO2/HCl afforded 2-(beta-glycopyranosyl)-1-hydroxydiazene-2-oxides, which were isolated as salts 13, 22, and 28. Nitrosation of fructose oxime 29 furnished fructose, whereas nitrosation of mannose oxime 30 with NaNO2/HCl afforded the 1-hydroxy-2-(beta-D-mannopyranosyl)diazene-2-oxide 32, from which the p-anisidinium salt 31 and the sodium salt 33 were prepared. However, nitrosation of 30 with isopentyl nitrite in aqueous solutions of CsOH or KOH resulted in the formation of the 2-(alpha-D-mannofuranosyl)-1-hydroxydiazene-2-oxide salts 34 and 35, respectively. Methylation of the ammonium 2-(beta-D-glucopyranosyl)-1-hydroxydiazene-2-oxide 13 yielded the 1-methoxy compound, which was benzoylated to afford the tetra-O-benzoate 14a, the structure of which was confirmed by X-ray diffraction analysis. From the glucose O-methyloximes 15 and 16 the N-methoxy-N-nitroso-2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosylamine 18 was prepared. The structure of this compound was confirmed by X-ray diffraction analysis. Treatment of acetobromoglucose with cupferron furnished the 1-(2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyloxy)-2-phenyldiazene-2-oxide 20.     

A probable hydrogen-bonded Meisenheimer complex: an unusually high S(N)Ar reactivity of nitroaniline derivatives with hydroxide ion in aqueous media

Observations show that nitroanilines exhibit an unusually high S(N)Ar reactivity with OH(-) in aqueous media in reactions that produce nitrophenols. S(N)Ar reaction of 4-nitroaniline (2a) in aqueous NaOH for 16 h yields 4-nitrophenol (4a) quantitatively, whereas a similar reaction of 4-nitrochlorobenzene (1a) gave 4a in 2% yield together with recovered 1a in 97%, suggesting that the leaving ability of the NH(2) group far surpasses that of Cl under these conditions. An essential feature of S(N)Ar reactions of nitroanilines is probably that the NH(2) leaving group participates in a hydrogen-bonding interaction with H(2)O. Density functional theory (DFT) calculations for a set of 4-nitroaniline, OH(-), and H(2)O suggest a possible formation of a Meisenheimer complex stabilized by hydrogen-bonding interactions and a six-membered ring structure. The results obtained here contrast with conventional S(N)Ar reactivity profiles in which nitroanilines are nearly unreactive with nucleophiles in organic solvents.     

Asymmetric Michael addition of 2-alkoxyphenyl α-substituted nitroacetates to non-prochiral α,β-unsaturated carbonyl compounds catalyzed by podand-type alkali metal 2′-substituted 1,1′-binaphthalen-2-oxides

The asymmetric Michael addition of 2-alkoxyphenyl α-substituted nitroacetates to non-prochiral α,β-unsaturated carbonyl compounds catalyzed by 10 mol % of sodium 2′-[2-(2-methoxyethoxy)ethoxy]-1,1′-binaphthalen-2-oxide gave the desired adducts in high yields with up to 95% ee.     

Novel products from oxidation of the norditerpenoid alkaloid pseudaconine with HIO4.

Oxidation of pseudaconine 8, a norditerpenoid alkaloid, with HIO4 led to a series of novel interesting products, depending greatly on reaction medium and work-up conditions. Treatment of 8 in MeOH-H2O (1:1) with NaIO4 gave compounds 10 and 11, but compound 12 was obtained quantitatively when the final reaction solution was alkalized with conc. NH4OH. The imine 12 was also obtained in 100% yield by treating 8 in 5% HCl solution with NaIO4 followed by alkalizing the reaction products to pH>9 with conc. NH4OH. When the work up pH was 7-8, only N,O-mixed acetal-ketal 13 was formed in 96% yield, which was converted quantitatively to 12 by further alkalizing. When the reaction mixture was alkalized to pH 7-8 with Na2CO3, a hemiacetalketal 14 was afforded quantitatively, which was converted to 15 in 87% yield by further treatment with Na2CO3 or 5% NaOH methanol. Compound 15 could be converted back to 14 by treatment with 10% HCl solution. Acetylation of the imine 12 gave the compounds 16 and 17 in 15% and 19% yields, respectively. All of the new compounds were isolated and fully characterized.     

Reaktionen von N-alkoxycyclimoniumsalzen—II. Heterocyclen aus ringöffnungsreaktionen von N-methoxypyridiniumsalzen

Rearrangement of 3-substituted N-methoxypyridinium-salts (R= COOH, COOCH₃, CONH₂) in aqueous solution by alkali resp. ammonia yields 3 - methoxyiminomethylpyridone - (2). Under the same conditions, 5 - hydroxy - 3′- (2′- methoxyiminoethylidene) - pyrrolidone - (2) is formed from N - Methoxypyridinium - 4 - carbonitrile.     

Addition of trifluoromethyltrimethylsilane to acyl phosphonates: synthesis of TMS-protected 1-alkyl-1-trifluoromethyl-1-hydroxyphosphonates and 1-aryldifluoroethenyl phosphates

Addition reactions of nucleophilic CF3TMS to acyl phosphonates were investigated. Various acyl phosphonates reacted readily with CF3TMS in the presence of K2CO3 in DMF at rt to give 1-alkyl-2,2,2-trifluoro-1-trimethylsilyloxyethylphosphonate in 70-90% yields. When benzoyl phosphonates were used as starting material, after addition of CF3, the formed alcoholate undergoes phosphonate-phosphate rearrangement to form the acyl anion, followed by elimination of F- to give 1-aryldifluoroethenyl phosphates in 87-97% yields. As a representative example, vinylphosphate 6a was converted into 2,2-difluoro-1-phenylethanone 7 with 6 N HCl/EtOH/reflux or CAN/NaOH/MeOH/0 degrees C in 82-90% yields.     

Studies on tertiary amine oxides. LXVIII. . Reactions of aromatic N-oxides with 2-substituted 2-oxazolin-5-ones in the presence of acetic anhydride

Quinoline l-oxides 1a-f readily react with 2-phenyl- and 2-methyl-2-oxazolin-5-ones, 2a and 2b , in the presence of acetic anhydride to afford 2-substituted 4-(2-quinolyl)-2-oxazolin-5-ones 3a-h in good yields. Hydrolysis of 3a-f with 10% hydrochloric acid under refluxing conditions gives the corresponding 2-amino-methylquinoline dihydrochlorides 5a-e or monohydrochloride 5f also in good yields. Similar results are obtained from reactions of isoquinoline 2-oxide 9 with 2a,b under the same conditions.     

An efficient enzymatic synthesis of benzocispentacin and its new six- and seven-membered homologues

A very efficient enzymatic method was developed for the synthesis of new enantiomeric benzocispentacin and its six- and seven-membered homologues through the Lipolase (lipase B from Candida antarctica) catalyzed enantioselective (E > 200) ring opening of 3,4-benzo-6-azabicyclo[3.2.0]heptan-7-one, 4,5-benzo-7-azabicyclo[4.2.0]octan-8-one, and 5,6-benzo-8-azabicyclo[5.2.0]nonan-9-one with H2O in iPr2O at 60 degrees C. The (1R,2R)-beta-amino acids (ee > or = 96%, yields > or = 40%) and (1S,6S)-, (1S,7S)-, and (1S,8S)-beta-lactams (ee > 99%, yields > or = 44%) produced could be easily separated. The ring opening of racemic and enantiomeric beta-lactams with 18% HCl afforded the corresponding beta-amino acid hydrochlorides.     

Highly enantioselective Michael addition of 2-alkoxyphenyl esters of α-substituted β-keto acids to non-prochiral α,β-unsaturated carbonyl compounds catalyzed by sodium 2′-[2-(2-methoxyethoxy)ethoxy]-1,1′-binaphthalen-2-oxide

The enantioselective Michael addition of 2-alkoxyphenyl esters of α-substituted β-keto acids to non-prochiral α,β-unsaturated carbonyl compounds catalyzed by 5–10 mol % of sodium 2′-[2-(2-methoxyethoxy)ethoxy]-1,1′-binaphthalen-2-oxide afforded the desired adducts in high yields with up to 97% ee.     

Radioiodinated phenoxyacetic acid derivatives as potential brain imaging agents. I. Efficient synthesis via trimethylsilyl intermediates

The usefulness of radioiodination via demetallation of aryltrimethylsilanes was demonstrated. The radioiodination reaction was found to be very rapid and the regiospecific incorporation of radioiodine could be carried out with high radiochemical yields and high radiospecific activity. 125I-Labeled dimethylaminoethyl iodophenoxyacetate derivatives (5a--e), dimethylaminoethyl iodophenoxyacetamide derivatives (7a--c), iodophenoxyethyl ethylenediamine derivatives (9,14) and an iodophenoxyethylpiperazine derivative (18) were efficiently synthesized from the corresponding aryltrimethylsilyl intermediates (4a--e, 6a--c, 8, 13, 17) by this method.     

A facile method for the synthesis of 3,1-benzooxazines from N-acyl-2-(alk-2-enyl)anilines

Electrophilic addition of HCl or Br₂ to N-acyl-2-(alk-2-enyl)anilines is accompanied by intramolecular cyclization of these amides to give 3,1-benzooxazine hydrochlorides or hydrobromides in high yields.     

Note sur la préparation et la scission de l'acide (diméthyl-3, 3-butyl)-phosphorique

3,3-Dimethylbutanol treated with polyphosphoric acid or with an equimolecular amount of POCl₃ gives rise to 3,3-dimethylbutyl phosphoric acid, isolated as baryum salt (yield 20 to 30%) or as sodium salt (yield 15%). Stable in NaOH 1N at 100°C, this monoester is split at pH 4.5 and in HCl 1N much slower than choline phosphate.     

The deoxydative substitution reactions of nicotinamide and nicotinic acid N-oxides by 1-adamantanethiol in acetic anhydride

The reaction of nicotinamide N-oxide with 1-adamantanethiol in acetic anhydride yielded a mixture of 2-and 6-(1-adamantylthio)nicotinamides (49%, in the ratio of 24:1) and 2-, 5-, and 6-(1-adamantylthio)nicotino-nitriles (18%, in the ratio of 79:1:20). From a reaction of nicotinic acid N-oxide with 1-adamantanethiol, there was isolated 2-(1-adamantylthio)nicotinic acid as the only sulfide in 23% yield. Carbon? sulfur bond cleavage took place when 2-(1-adamantylthio)nicotinic acid, or the corresponding amide or nitrile, were boiled with concentrated hydrochloric acid to furnish 2-mercaptonicotinic acid and 1-chloroadamantane, quantitatively. The reaction of nicotinamide N-oxide alone in acetic anhydride at 135° formed N-acetyl-2-hydroxynicotinamide (61%), 2-hydroxynicotinonitrile (0.5%) and N,N-diacetyl-2-acetoxynicotinamide (0.8%).     

Colorimetric method for the quantitative determination of the antibilharzial drug praziquantel and its application to pharmaceutical preparations.

A method for the colorimetric assay of praziquantel has been developed. For the colorimetric assay, it was necessary to hydrolyse praziquantel with 3 mol dm-3 NaOH, 6 mol dm-3 HCl and 85% phosphoric acid separately. 4-Chloro-7-nitro-2,1,3-benzoxadiazole (NBD-Cl) reacts with the basic hydrolysis product in methanolic aqueous phosphate buffer (pH 7.4), resulting in the formation of an orange product with a characteristic absorption maximum at 478 nm. The red-orange product of the interaction between the hydrochloric acid hydrolysis product and NBD-Cl showed an absorption maximum at 486 nm. The colours obtained were stable for 24 h. The colour system obeyed Beer's law in the concentration range 2-15 and 2-18 micrograms ml-1 for the basic hydrolysis product and the acid hydrolysis product, respectively. The results obtained showed good recoveries with relative standard deviations of 0.378 and 0.47% for the basic and the acid hydrolysis product, respectively. The determination limit was found to be 0.124 and 0.150 micrograms ml-1 for the praziquantel basic hydrolysis product and the acid hydrolysis product, respectively. The coloured reaction products obtained with the proposed method were synthesized. The structures of these products were studied and the compounds identified.