Pyrrolopyridazines. II. Synthesis of the novel pyrrolo[3,2-c]pyridazine ring system

The first derivatives of the pyrrolo[3,2-c]pyridazine ring system, ethyl pyrrolo[3,2-c]pyridazine-6-carboxylate 2-oxide (5) and ethyl 3-chloro-6-methylpyrrolo[3,2-c]pyridazine-7-glyoxalate 1-oxide ( 12 ), were obtained in good yields from the cyclization of 4-ethoxymethyl-eneamino-3-methylpyridazine 1-oxide (3) and 3-chloro-5-(α-ethoxyethylideneamino)-6-methylpyridazine 1-oxide (14, R ? Cl, R₁ ? OMe), respectively, with diethyl oxalate and potassium ethoxide in ether.     

Synthesis of 2H-1,4-thiazin-3(4H)-one 1-oxide and 2H-1,4-thiazin-3-(4H)-one 1,1-dioxide,structural analogs of uracil

The synthesis of 1,4-thiazine 1-oxide and 1,1-dioxide analogs of the antibiotic emimycin is described. Reaction of methylthioglycolate with 1-bromo-2,2-diethoxyethane gave methyl (2,2-diethoxyethylthio)acetate ( 2 ). Treatment of 2 with methanolic ammonia followed by cyclization furnished 2H-1,4-thiazin-3(4H)-one ( 5 ). Oxidation of 5 with m-chloroperoxybenzoic acid converted it to 2H-1,4-thiazin-3(4H)-one 1-oxide ( 6 ). Oxidation of 2 with potassium permanganate, followed by treatment with methanolic ammonia, and cyclization gave 2H-1,4-thiazin-3(4H)-one 1,1-dioxide.     

Synthesis of 4H-1,3,4-oxadiazino[5,6-b]quinoxalines from 2-substituted quinoxaline 4-oxides

The reaction of 6-chloro-2-(1-methylhydrazino)quinoxaline 4-oxide 8 with acetic anhydride resulted in the intramolecular cyclization to give 8-chloro-2,4-dimethyl-4H-1,3,4-oxadiazino[5,6-b]quinoxaline 7a , while the reaction of compound 8 with acetic anhydride/pyridine or acetic anhydride/acetic acid afforded 3-(2,2-diacetyl-1-memymydrazmo)-7-chloro-2-oxo-1,2-dihydroquinoxaline 9 , effecting no intramolecular cyclization. The reaction of 2-(2-acetyl-1-methylhydrazino)-6-chloroquinoxaline 4-oxide 10a or 6-chloro-2-(1-methyl-2-trifluoroacetylhydrazino)quinoxaline 4-oxide 10b with phosphoryl chloride provided compound 7a or 8-chloro-4-memyl-2-trifluoromethyl-4H-1,3,4-oxadiazino[5,6-b]quinoxaline 7b , respectively. The reaction of compound 7b with phosphorus pentasulfide gave 7-chloro-3-(1-methyl-2-trifluoroacetylhydrazino)-2-thioxo-1,2-dihydroquinoxaline 11 , whose dehydration with sulfuric acid in acetic acid afforded 8-chloro-4-methyl-2-trifluoromemyl-4H-1,3,4-thiadiazino[5,6-b]quinoxaline 12 .     

New derivatives of imidazoline 3-oxide and thiazoline with 2,6-dialkylphenol fragments

(2,6-Dialkyl-4-hydroxyphenyl)-2-butanones and aminooxides were used to obtain the corresponding 3-imidazoline 3-oxides. Nitrosylation of 3-imidazoline 3-oxide containing a phenol substituent proceeds either at the imidazoline ring amino group or at the phenol fragment. Intermolecular cyclization of (2,6-di-tert-butyl-4-hydroxyphenyl)-2-butanone with sulfur and ammonia gave a 3-thiazoline as two diastereomers.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 62–67, January, 1986.     

Studies on tertiary amine oxides—LII: Reaction of 4-nitroquinoline 1-oxide with enamines of isobutyraldehyde. A novel cyclization reaction involving participation of the nitro group

When a chloroform solution of 4-nitroquinoline 1-oxide (1) and 2 equivalents of an enamine of isobutyraldehyde (4) is kept at room temp for a prolonged time, a novel cyclization reaction occurs to produce 1-hydroxy-2-oxo-3,3-dimethylpyrrolido[4,5-c]quinoline 5-oxide (5) or/and the corresponding 1-deoxy compound (6). Their structures were established by spectral and chemical examinations. The reaction mechanisms are also discussed.     

Synthesis and applications of [1-(15)N]-labeled 4,6-dimethyl-4H-[1,2,5]oxadiazolo[3,4-d]pyrimidine-5,7-dione 1-oxide as a useful tool for mechanistic investigations

[1-(15)N]-Labeled 4,6-dimethyl-4H-[1,2,5]oxadiazolo[3,4-d]pyrimidine-5,7-dione 1-oxide (1-(15)N1) was easily prepared by nitration of commercially available 6-amino-1,3-dimethyl-1H-pyrimidine-2,4-dione using 15N-enriched nitric acid followed by an intramolecular oxidative cyclization with iodosylbenzene diacetate under mild conditions. On the basis of the experimental results using 1-(15)N1, the formation of 8-phenyltheophylline (3), the 1,3-dimethylalloxazines (4: n = 0, 1), and 1,3,7,9-tetramethyl-1H,9H-pyrimido[5,4-g]pteridine-2,4,6,8-tetraone++ + (5) in the thermal reaction of the N-oxide 1 with benzylamine, aniline, or piperidine, and the generation of NO or NO-related species in the reaction with N-acetylcysteamine were reasonably explained by considering the initial attack of the employed nucleophiles on the 3a-position of 1.     

Synthetic exploitation of the ring-opening of 3,4-dinitrothiophene. Part 4. Synthesis of 1,4-disubstituted 3-hydroximino-2-nitro-1-butenes and their cyclization to 4-nitroisoxazoles

The reduction of a single nitrovinyl moiety in 1,4-dialkyl- and 1,4-diaryl-2,3-dinitro-1,3-butadienes 1 with stannous chloride dihydrate in ethyl acetate furnishes the corresponding 3-hydroximino-2-nitro-l-butenes 4 in satisfactory yields. The oxidative cyclization of the latter compounds gives variable yields of 3,5-disubsti-tuted 4-nitroisoxazoles 5 , most likely arising from aromatization of the corresponding 4,5-dihydroisoxazoles, formed through an intramolecular Michael addition of the hydroximino group in 4 to the nitroalkene functionality. In the case of the l-naphthyl derivative 4d such oxidative cyclization mainly leads to the competitive formation of 3-[(l-naphthyl)methyl]-2-nitrobenzo[f]quinoline N-oxide 7.     

Cyclization of aryllithiums tethered to methylenecycloalkanes: stereoselective synthesis of 4a-substituted cis-hexahydrofluorenes

The cyclization of an aryllithium tethered to a methylenecycloalkane, generated from 2-(o-bromobenzyl)-1-methylenecycloalkanes 1, 2, and 3 by low-temperature lithium-bromine exchange, has been found to be a kinetically slow but thermodynamically favorable process that proceeds at a convenient rate in an exclusively 5-exo fashion when solutions of the aryllithium in n-heptane-di-n-butyl ether (9:1 v/v) are warmed to 45 degrees C. The cyclization affords stereoisomerically pure cis-fused products (7 and 8) when the methylenecycloalkane is five- or six-membered but it is less stereoselective when the methylenecycloalkane is seven-membered. The ring-closure of the aryllithium derived from 2-(o-bromobenzyl)-1-methylenecyclohexane (2) provides an experimentally convenient route to stereoisomerically pure 4a-substituted cis-hexahydrofluorenes in 60-90% isolated yield.     

A cinnoline 2-oxide from 2-nitrosobenzophenone

Base catalyzed cyclization of the 2-methylazoxybenzophenone ( 4B ) obtained by condensation of the 2-nitrosobenzophenone ( 2a ) with methylhydroxylamine led to the cinnoline 2-oxide ( 7 ) which is the major product of the peracid oxidation of the corresponding cinnoline ( 5 ).     

Synthesis,configuration, and conformation of 3-acyl derivatives of 3a,4,6,6a-tetrahydrothieno[3,4-d][1,2,3]oxathiazoline 2-oxide

3-Benzoyl-3a,4,6,6a-tetrahydrothieno[3,4-d][1,2,3]oxathiazoline 2-oxide is formed as a result of intramolecular cyclization of cis-4-benzamido-3-chlorosulfitothiophan. Only one sulfur atom — that of the sulfoxide group — is removed from the cyclization product and the analogous 3-methoxycarbonyl-3a,4,6,6a-tetrahydrothieno[3,4-d][1,2,3]oxathiazoline 2-oxide by the action of Raney nickel; the products in this case are, respectively, cis-4-benzamido-3-hydroxythiophan and 3a,4,6,6a-tetrahydrothieno]3,4-d]oxazolidone. The three-dimensional structure of 3-acyl-3a,4,4,6a-tetrahydrothieno[3,4-d][1,2,3]oxathiazoline 2-oxide was determined by ¹H and ¹³C NMR spectroscopy. A difference between the conformational state of 3-substituted 3a,4,6,6a-tetrahydrothieno[3,4-d][1,2,3]oxathiazoline 2-oxides and 3-substituted 3a,4,6,6a-tetrahydrothieno[3,4-d]oxazolidones was established.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 191–197, February, 1977.     

Azinotriazines. II Cyclizations leading to pyrido[3,4-e] - and [4,3-e]-as-triazines. Ring interconversion of a pyrido-as-triazine 1-oxide to a pyridotriazole

Treatment of 4-chloro-3-nitropyridine (I) with hydrazine hydrate followed by catalytic reduction gave 3-amino-4-hydrazinopyridine (III). Acid-catalyzed cyclizations of III and subsequent dehydrogenation gave pyrido[3,4-e]-as-triazines (V). Treatment of I with guanidine followed by base-catalyzed cyclization gave 3-aminopyrido[4,3-e]-as-triazine 1-oxide (VII). The 1-oxide function was removed by reduction and subsequent dehydrogenation gave the 3-amino derivative (IX). On treatment with hot alkali VII rearranged to a triazolo[4,5-c]pyridine (X). The ultraviolet and nmr spectra of derivatives of the title ring systems are reported.     

Reaction of 3,6-disubstituted 4-nitropyridazine 1-oxides with methanolic ammonia and liquid ammonia

Reaction of 3-chloro-6-methyW-nitropyridazine 1-oxide ( 5 ) with methanolic ammonia at 0° led to a replacement of the chlorine atom by a methoxy group as well as by an amino group. Reaction of the 3-methoxy-6-methyl-4-nitropyridazine 1-oxide ( 6 ) with the same reagent led to amino-demethoxylation; this replacement reaction was very slow. Attempts to perform these reactions with liquid ammonia failed. Pmr spectroscopy of solutions of compound 6 in methanolic ammonia revealed that no σ-adduct was present. However in liquid ammonia a 1:1 σ-adduct at C-5 i.e. 12b was formed. 3,6-Dimethoxy-4-nitropyridazine 1-oxide (7) gave with methanolic ammonia an amino-demethoxylation at C-6. No σ-adduct could be detected by pmr spectroscopy. However, in liquid ammonia convincing pmr data were obtained showing the presence of a 1:1 σ-adduct at C-5.     

Purines. LII. Synthesis and biological evaluation of 8-methylguanine 7-oxide and its 9-arylmethyl derivatives.

The synthesis of 8-methylguanine 7-oxide (3) was accomplished via a "phenacylamine route", which started from condensation of alpha-(4-methoxybenzylamino)propiophenone (6), prepared by coupling of alpha-bromopropiophenone (4) and 4-methoxybenzylamine (5), with 2-amino-6-chloro-5-nitro-4(3H)-pyrimidinone (7) and proceeded through cyclization of the resulting phenacylaminopyrimidinone (8) and removal of the 4-methoxybenzyl group. The N-oxide 3 and its 9-arylmethyl derivatives 9 and 11 showed only very weak antileukemic activity and no antimicrobial activity.     

AN UNUSUAL ADDITION AND RING-CLOSURE REACTION OF 1-(2-BROMOETHYL)-2,3-DIHYDRO- 3-PROPYL-1,3,2-BENZO-DIAZAPHOSPHORIN-4(1H)-ONE 2-OXIDE WITH CARBON DISULFIDE FOR A NEW AND CONVENIENT SYNTHESIS OF THE FUSED PHOSPHORUS HETEROCYCLIC COMPOUND

ABSTRACT

The reaction of 1-(2-bromoethyl)-2,3-dihydro-3-propyl-1,3,2-benzodiazaphosphorin-4(1H)-one 2-oxide with carbon disulfide takes an alternative pathway in the use of different bases. The sodium hydride mediated reaction leads to the formation of the tricyclic fused 1,2,3,4,4a,4b,5,6-octahydro-6-oxo-5-propyl-4-thia-3,4b,4a-thiazphosphaphenanthridine 4a-oxide via addition of H-P bond across the double bond of carbon disulfide followed by intramolecular cyclization. In the presence of triethylamine, refluxing a mixture of 1-(2-bromoethyl)-2,3-dihydro-3-propyl-1,3,2-benzodiazaphosphorin-4(1H)-one 2-oxide with carbon disulfide in benzene takes an unusual course with formation in excellent yield of the first example of fused phosphorus heterocyclic 4-[1′-(β-bromoethyl)-4′-oxo- 3′-propyl-1′,2′,3′,4′-tetrahydro-1,3,2-benzodiazaphosphorin-2′- sulfide]-1,2,3,4,4a,4b,5,6-octahydro-6-oxo-5-propyl-3,4b, 4a-thiazphosphaphenanthridine 4a,2′-dioxide, which was confirmed by spectroscopic methods, microanalyses and single crystal X-ray structure determination.     

Kinetic results implicating a polar radical reaction pathway in the rearrangement catalyzed by alpha-methyleneglutarate mutase

alpha-Methyleneglutarate mutase (MGM) catalyzes the rearrangement of 2-methyleneglutarate to 3-methylitaconate (2-methylene-3-methylsuccinate). A putative mechanism for the MGM-catalyzed reaction involves 3-exo cyclization of the 2-methyleneglutaric acid-4-yl radical to a cyclopropylcarbinyl radical intermediate that ring opens to the 3-hydroxycarbonyl-2-methylenebutanoic acid-4-yl radical (3-methylitaconic acid radical). Model reactions for this mechanism were studied by laser flash photolysis kinetic methods. alpha-Ester radicals were produced by 266 nm photolysis of alpha-phenylselenyl ester derivatives. Rate constants for cyclizations of the (Z)-1-ethoxycarbonyl-4-(2,2-diphenylcyclopropyl)-3-buten-1-yl radical ((Z)-8a) and (E)- and (Z)-1,3-di(ethoxycarbonyl)-4-(2,2-diphenylcyclopropyl)-3-buten-1-yl radicals ((E)- and (Z)-8b) were determined. The ester group in (Z)-8a accelerates the 3-exo cyclization in comparison to the parent radical lacking an ester group by a factor of 3, an effect ascribed to a polarized transition state. The ester groups at C3 in radicals 8b slow the 3-exo cyclization reaction by a factor of 50. The rate constant for cyclization of the 2-methyleneglutaric acid-4-yl radical is estimated to be k approximately 2000 s(-1) at ambient temperature. When coupled with the estimated partitioning of the intermediate cyclopropylcarbinyl radical, the overall rate constant for the conversion is estimated to be k approximately equal to 1 x 10(-3) s(-1), which is much too small for any radical reaction and several orders of magnitude too small for kinetic competence for the MGM-catalyzed process. The possibility that the radical reaction in nature involves an unusual mechanism in which polar effects are important is discussed.     

Linearly fused isoquinolines. Part II. The synthesis of the s-triazolo[4,3-b]isoquinoline system

3-Hydrazinoisoquinoline ( 2 ) was synthesized via its N-oxide derivative by removal of the N-oxide funçtion with titanium trichloride. Acylation of the hydrazino compound ( 2 ) led to suitable starting materials ( 4 and 6 ) for cyclization to the novel, linearly fused ring system: tri-azolo[4,3-b]isoquinoline, which was more stable in the form of its perchlorate salt. The structure of the first representatives of the new ring system was proved by ir, nmr and ms spectroscopy.     

Generation of oxodiazonium ions 6. Unexpected formation of tetrazole 1-oxides

(E)-2-[2,2-Bis(tert-butyl-NNO-azoxy)-1-(methylsulfinyl)vinyl]-1-isopropoxydiazene 1-oxide reacts with boron trifluoride etherate (BF₃?Et₂O) producing 2-tert-butyl-N-nitro-2H-tetrazolo-5-carboxamide 4-oxide and 2-tert-butyl-2H-tetrazolo-5-carbonitrile 4-oxide but not the expected 1,2,3,4-tetrazine 1,3-dioxide derivative. This reaction direction can be explained by cationic domino cyclization, the key stage of which is coupling of the oxodiazonium ion with the geminal MeS(O) group. Structure of N-nitrocarboxamide was confirmed by X-ray diffraction analysis.     

Synthesis of 3-substituted 4-imino-4,5-dihydro-1,2,3-triazole 1-oxides and 4-amino-1,2,3-triazole 1-oxides. Crystal and molecular structure of 4-imino-5,5-dimethyl-3-phenyl-4,5-dihydro-1,2,3-triazole 1-oxide

A new procedure for the synthesis of triazole N-oxides, based on base-induced intramolecular cyclization of 1-(-cyanoalkyl)-3-aryl(hetaryl)triazen-1-oxides, is proposed. An X-ray study of 4-imino-5,5-dimethyl-3-phenyl-4,5-dihydro-1,2,3-triazole 1-oxide was carried out.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 746–751, April, 1993.     

Reaction progress of chromophore biogenesis in green fluorescent protein

The mature form of green fluorescent protein (GFP) is generated by a spontaneous self-modification process that is essentially irreversible. A key step in chromophore biosynthesis involves slow air oxidation of an intermediate species, in which the backbone atoms of residues 65-67 have condensed to form a five-membered heterocycle. We have investigated the kinetics of hydrogen peroxide evolution during in vitro GFP maturation and found that the H2O2 coproduct is generated prior to the acquisition of green fluorescence at a stoichiometry of 1:1 (peroxide/chromophore). The experimental progress curves were computer-fitted to a three-step mechanism, in which the first step proceeds with a time constant of 1.5 (+/-1.1) min and includes protein folding and peptide cyclization. Kinetic data obtained by HPLC analysis support a rapid cyclization reaction that can be reversed upon acid denaturation. The second step proceeds with a time constant of 34.0 (+/-1.5) min and entails rate-limiting protein oxidation, as supported by a mass loss of 2 Da observed for tryptic peptides derived from species that accumulate during the reaction. The final step in GFP maturation proceeds with a time constant of 10.6 (+/-1.2) min, suggesting that this step may contribute to overall rate retardation. We propose that under highly aerobic conditions, the dominant reaction path follows a cyclization-oxidation-dehydration mechanism, in which dehydration of the heterocycle is facilitated by slow proton abstraction from the Tyr66 beta-carbon. In combination, the results presented here suggest a role for molecular oxygen in trapping the cyclized form of GFP.     

Sulfur-containing heterocycles 14. New synthesis of cyclic anhydrides of 3-sulfinocarboxylic acids

3-Chlorosulfinylalkanoyl chlorides undergo cyclization into the corresponding five-membered mixed anhydrides (1,2-oxathiolan-5-one 2-oxides) under the action of sodium or mercury acetates. 2-Chlorosulfinylbenzoyl chloride gives 3H-2,1-benzoxathiol-3-one 1-oxide in high yield.