Steroidal quinoxalines

The treatment of 3β-hydroxy-16α-bromo-5α-androstan-17-one, 3β-acetoxy-16α-bromo-5-androsten-17-one and 21-bromo-5-pregnen-3β-ol-20-one with 4,5-dimethyl-o-phenylenediamine gave substituted quinoxalines. Hydrolysis of 3β-acetoxy-5-androsteno[16,17-b]-6′,7′-dimethylquinoxaline produced the corresponding 3β-hydroxy compound. 3-Oxo-4-androsteno[16,17-b]-6′,7′-dimethylquinoxaline was obtained by Oppenauer oxidation of the corresponding alcohol.     

Reaction of a 5α-bromo-6β,19-epoxysteroid with BF3·Et2O/Ac2O: An evidence of a cyclic bromonium cation

Treatment of 3β-acetoxy-5-bromo-6β,19-epoxy-5α-androstan-17-one with Ac₂O and BF₃·OEt₂, produced the cleavage of the epoxy moiety and migration of the bromine atom to afford 3β,19-diacetoxy-6α-bromo-5-hydroxy-5β-androst-17-one in high yield.     

Thermolyzed products of naphth[1,2-d]imidazo[2,1-b]-thiazole-2,3-dione

Themolysis of naphth[1,2-d]imidazo[2,1-b]thiazole-2,3-dione ( 1 ) in dimethylformamide gave an intermediate 2-isocyanatonaphtho[1,2-d]thiazole ( 2 ), which underwent [4 + 4] cyclodimerization to yield dinaphtho-[1″,2″:4,5;1′″,2′″:4′,5′]dithiazolo[3,2-a:3′,2′-e]-1,3,5,7-tetrazocine-9,19-dione ( 3 ). The possible [4 + 2] cycloadduct, 3-(2-naphtho-[1,2-d]-thiazolyl)naphtho[1′,2′:4,5]thiazolo[3,2-a]-1,3,5-triazine-2,4-dione ( 4 ), an usual dimer type of heterocyclic isocyanates was not produced. Discrimination between the two isomers was established on the basis of spectral analyses.     

Core-Modified Coelenterazine Luciferin Analogues: Synthesis and Chemiluminescence Properties

In this work on the design and studies of luciferins related to the blue-hued coelenterazine, the synthesis of heterocyclic analogues susceptible to produce a photon, possibly at a different wavelength, is undertaken. Here, the synthesis of O-acetylated derivatives of imidazo[1,2-b]pyridazin-3(5 H)-one, imidazo[2,1-f][1,2,4]triazin-7(1 H)-one, imidazo[1,2-a]pyridin-3-ol, imidazo[1,2-a]quinoxalin-1(5 H)-one, benzo[f]imidazo[1,2-a]quinoxalin-3(11 H)-one, imidazo[1′,2′:1,6]pyrazino[2,3-c]quinolin-3(11 H)-one, and 5,11-dihydro-3 H-chromeno[4,3-e]imidazo[1,2-a]pyrazin-3-one is described thanks to extensive use of the Buchwald–Hartwig N-arylation reaction. The acidic hydrolysis of these derivatives then gave solutions of the corresponding luciferin analogues, which were studied. Not too unexpectedly, even if these were “dressed” with substituents found in actual substrates of the nanoKAZ/NanoLuc luciferase, no bioluminescence was observed with these compounds. However, in a phosphate buffer, all produced a light signal, by chemiluminescence, with extensive variations in their respective intensity and this could be increased by adding a quaternary ammonium salt in the buffer. This aspect was actually instrumental to determine the emission spectra of many of these luciferin analogues.     

Reactions of α-ketohydrazidoyl halides with some heterocyclic amines. Facile synthesis of arylazo derivatives of fused heterocycles with a bridgehead nitrogen atom

Arylazo derivatives of imidazo[2,1-b]thiazoles, imidazo[1,2-b]pyrazoles, imidazo[1,2-b]-s-triazoles, imidazo[1,2-a]pyrimidines, and imidazo[1,2-a]pyridines were obtained in good yields from α-keto hydrazidoyl halides and 2-aminothiazole, 5-aminopyrazole, 5-aminotriazole, 2-aminopyrimidine, and 2-aminopyridine, respectively (cf. Tables I and II). The structures of the products were assigned and confirmed on the basis of their elemental analyses, spectra, and alternate synthesis wherever possible.     

Synthesis of nitrogen heterocycles underlain by application of 3-(4-Acetyl[phenyl)-2H-coumarin

3-(4-Acetylphenyl)-2H-chromen-2-one was obtained from 4-acetylphenyldiazonium chloride in the conditions of Meerwein reaction. Reactions of 3-[4-(2-bromoacetyl)phenyl]-2H-chromen-2-one with pyridine, 4-methylpyridine, quinoline, benzo[f]quinoline, and triphenylphosphine afforded quaternary salts, and with thioacetamide, thiourea, 2-aminopyridine, 2-aminopyrimidine, and 6-aminopurine provided the corresponding derivatives of thiazole, imidazo[1,2-a]pyridine, imidazo[1,2-a]pyrimidine, imidazo[2,1-i]purine. In the reaction of the same bromo derivative with thiosemicarbazide and aromatic aldehydes a thiazole ring is built and the corresponding hydrazones are formed.     

Preparation of 2-aryl and 2-aryloxymethyl imidazo[1,2-a]pyridines and related compounds

A series of substituted 2-aryl imidazo[1,2-a]pyridines has been prepared in which a variety of substituents are introduced on the 4′-position of the phenyl ring and on the 3, 5 , 6 or 7 position of the heterocyclic ring. Most examples have acetamido, bromo, cyano, or formyl substituents at the 4′-position. Analogous imidazo-[2,1-b]fhiazoles and imidazo[1,2-a]pyrimidines have also been prepared. Another series of compounds consisting of 4′-formylphenoxymethyl derivatives of imidazole, the three positional isomers of pyridine, thiazole, benzimidazole and ring-substituted imidazo[1,2-a]pyridines has been prepared. 2-(4′-Formylphenylethenyl) derivatives of imidazole and imidazo[1,2-a]pyridine were also prepared.     

Synthesis of a- and d-homoazasteroidalisoxazoles

The synthesis of the isomeric D-homoazasteroido[3,2-c]- ( 3 ) and -[2,3-d]lisoxazoles ( 4 ) and A-homoazasteroido[17,16-c]isoxazole ( 6 ) are reported by the reaction of 2-hydroxymethylene-17α-aza-D-homo-5α-androstan-3,17-dione ( 2 ) and 16-hydroxymethylene-3-aza-A-homo-4α-androsten-4,17-dione ( 5 ) correpondingly with hydroxylammonium chloride.     

Synthesis of 11-aryl-11H-indeno[1′,2′:4,5]imidazo[1,2-a]pyridines via dehydrative cyclization of aryl(2-arylimidazo[1,2-a]pyridin-3-yl)methanols

A series of 11-aryl-11H-indeno[1′,2′:4,5]imidazo[1,2-a]pyridines was obtained via AlCl₃-promoted, dehydrative cyclization of the corresponding aryl(2-arylimidazo[1,2-a]pyridin-3-yl)methanols in moderate to good yields. The synthesized compounds can be considered as conformationally restricted, privileged aza-heterocyclic scaffold bearing triarylmethane analogs.     

Efficient synthesis and antioxidant activity of coelenterazine analogues

A convenient and highly convergent method for the synthesis of new imidazo[1,2-a]pyridine-based coelenterazine analogues is reported. The imidazo[1,2-a]pyridine core was constructed through a condensation between 2-aminopyridine analogues and arylglyoxals. Additionally, a new approach to the synthesis of benzylglyoxals was introduced. The imidazo[1,2-a]pyridines display moderate antioxidant activities at a low micromolar level in 2,2-diphenyl-1-picrylhydrazyl (DPPH).     

One-pot synthesis of imidazo[1,2-b]pyrazole,imidazo[1,2-b]-1,2,4-triazole,imidazo[1,2-a]pyridine,imidazo[1,2-a]pyrimidine,imidazo[1,2-a]benzimidazole,and 1,2,4-triazolo[4,3-a]benzimidazole derivatives

Hydrazonoyl bromides 1a-c react with 5-amino-3-phenyl-1H-pyrazole, 5-amino-1H-1,2,4-triazole, 2-aminopyridine, and 2-aminobenzimidazole to afford the corresponding imidazol[1,2-b]pyrazoles 10, imidazo[1,2-b]-1,2,4-triazoles 11, imidazo[1,2-a]pyridines 16, imidazo[1,2-a]pyrimidines 17, and imidazo[1,2-a]benzimidazoles 20, respectively. Compounds 1a-c reacted also with 2-methylthiobenzimidazole to give 1,2,4-triazolo[4,3-a]benzimidazole derivatives 21. © 1997 John Wiley & Sons, Inc.     

K2S2O8-Mediated halogenation of 2-arylimidazo[1,2-a]pyridines using sodium halides as the halogen sources

A convenient halogenation of 2-arylimidazo[1,2-a]pyridines using sodium chloride/bromide/iodide as the halogen sources in the presence of K₂S₂O₈ as an easy-to-handle oxidizing agent was developed. The present work offers an efficient and rapid access to 3-chloro-, 3-bromo- and 3-iodo-2-arylimidazo[1,2-a]pyridines which can be readily converted to C3-substituted imidazo[1,2-a]pyridines by cross-coupling reactions.     

Synthese von 4-[3β, 14-Dihydroxy-5β, 14β-androstan-17β-yl]-3-pyrrolin-2-on (Hothesimogenin). Partialsynthetische Versuche in der Reihe der Herzgifte, 11. Mitteilung

Synthesis of 4-[3β, 14-Dihydroxy-5β, 14β-androstan-17β-yl]-3-pyrrolin-2-one (hothesimogenin) We describe the synthesis of 4-[3β, 14-Dihydroxy-5β, 14β-androstan-17β-yl]-3-pyrrolin-2-one (24-aza-24-desoxa-digitoxigenin) (7) , starting from 3-O-acetyl-digitoxigenin (1) .     

Some novel heterocyclic systems derived from 7-amino-2,3-dihydro-8-nitro-1H-pyrrolo[1,2-α]benzimidazole and the corresponding diamine

The preparation of 7-amino-2,3-dihydro-8-nitro-1H-pyrrolo[1,2-a]benzimidazole from 1,4-diacetamido-2,3-dinitrobenzene is described. Reaction of this compound with 2,5-dimethoxytetrahydrofuran produces 2,3-dihydro-8-nitro-7-N-pyrrolo-1H-pyrrolo[1,2-a]benzimidazole, which can be cyclised to produce two new heterocyclic ring systems, 9,10-dihydro-8H-pyrrolo[1,2-a]pyrrolo(1′,2′:1,2]imidazo[5,4-f]quinoxaline and 9,10-dihydro-8H-pyrrolo[2,1-c]pyrrolo[1′,2′:1,2]imidazo[4,5-h][1,2,4]benzotriazine. The corresponding diamine, 7,8-diamino-2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole undergoes a variety of condensation reactions to produce several new heterocyclic systems, for example, with formic acid, 1,7,8,9-tetrahydroimidazo-[4,5-e]pyrrolo[2,1-6]benzimidazole is formed and with diacetyl, 9,10-dihydro-2,3-dimethyl-8H-pyrrolo-[1′,2′:1,2]imidazo[5,4-y]quinoxaline is obtained.     

Carbon-nitrogen bond formation in cyclisation by deoxygenation,thermolysis or photolysis of phenylimidazo[1,2-a][1,8]naphthyridines

Triethyl phosphite deoxygenation of 2-(2-nitrophenyl)imidazo[1,2-a][1,8]naphthyridine (3) led to the C-insertion to give the indoloimidazonaphthyridine 5. Our attempt to promote the N-insertion by blocking the C-3 position failed. Triethyl phosphite deoxygenation of 1-nitroso-2-(4-fluorophenyl)imidazo[1,2-a][1,8]-naphthyridine (12) led to the corresponding amine structure (15). Thermolysis and photolysis of 6,8-dimethyl-2-(2-azidophenyl)imidazo[1,2-a][1,8]naphthyridine (17) are also reported.     

Reactions of 3-Aroylpyrrolo[1,2-<Emphasis Type="Italic">a</Emphasis>]quinoxaline-1,2,4(5<Emphasis Type="Italic">H</Emphasis>)-triones with 2,3-Dihydrofuran and 3,4-Dihydro-2<Emphasis Type="Italic">H</Emphasis>-pyran

3-Aroylpyrrolo[1,2-a]quinoxaline-1,2,4(5H)-triones reacted with 2,3-dihydrofuran and 3,4-dihydro-2H-pyran to give mixtures of the corresponding hetero-Diels–Alder (furo- and pyrano[3″,2″: 5′,6′]pyrano- [4′,3′: 2,3]pyrrolo[1,2-a]quinoxalines) and Michael adducts (furyl- and pyranylpyrrolo[1,2-a]quinoxalines).     

Environmentally friendly and efficient method for the synthesis of the new α,α′-diimine ligands with benzimidazole moiety

The new α,α′-diimine ligands with benzimidazole moiety were synthesized based on the rearrangement of 3-aroylquinoxalin-2(1H)-ones when exposed to 4,5-diamino-2,1,3-benzoxadiazole, 4,5-diamino-2,1,3-benzothiadiazole and 5,6-diaminoquinoxaline. Among them, we report the first examples of the new heterocyclic system namely benzo[4′,5′]imidazo[1′,2′:1,2]quinolino[3,4-b and 4,3-b][1,2,5]oxadiazolo[3,4-f]quinoxalines, which exhibits an interesting electrochemical behavior. All compounds were fully characterized by IR, ¹H and ¹³C NMR spectroscopies, and mass spectrometry.     

Copper-catalyzed four-component synthesis of imidazo[1,2-a]pyridines via sequential reductive amination,condensation, and cyclization

A novel and efficient four-component approach for the synthesis of 2,3-disubstituted imidazo[1,2-a]pyridines is described. The copper-catalyzed reductive amination of 2-bromopyridine by sodium azide followed by sequential condensation and cyclization with aldehydes and isocyanides afforded the corresponding imidazo[1,2-a]pyridines in good yields.     

Action of 1,2-diamines and o-aminophenols on 1-alkyl-3-carboxyindole-2-acetic acid anhydrides. Preparation of new ring systems

1-Alkyl-3-carboxyindole-2-acetic acid anhydrides (I) react with ethylenediamine and with o-phenylenediamine to give directly 10-alkylimidazo[3,2:1′,2′]pyrido[4,5-b]indol-5(1H)-ones (II) and 5,6-dihydro-5-alkyl-13H-indolo[2′,3′:4,5]pyrido[1,2-a]benzimidazol-13-one (V), respectively. However, anhydrides I react with o-aminophenol and with o-aminothiophenol to give carboxyindole-acetanilide derivatives IX, which can be cyclised to indolo[2′,3′:4,5]pyrido[2,1-b]benzoxazolone and indolo[2′,3′:4,5]pyrido[2,1-b]benzthiazolone (XI). Some derivatives of II and V were prepared to help in elucidating the structures.     

5α-androstano [3,2-b]pyridines, 5α-androstano[17,16-b]pyridines and androst-4 and 5-eno[17,16-b]pyridines

A new synthesis of 5α-androstano[3,2-b]pyridin-17β-ol acetate (VIa) and 17-methyl-5α-androstano[3,2-b]pyridin-17β-ol (VIb), first reported by Shimizu, Ohta, Ueno, and Takegoshi, was achieved. The analogous 5α - androstano[17,16-b]pyridin-3β-ol (XII), 5α-androstano[17,16-b]pyridin-3-one (XIVa), and androst-4-eno[17,16-b]pyridin-3-one (XIVb) were also prepared. An illustration of the method follows. Condensation of 3β-hydroxy-5α-androstan-17-one (VIIa) with 3-(2-furyl)acrolein afforded 16-[3-(2-furyl)-2-propenylidene]-3β-hydroxy-5α-androstan-17-one (VIIIa), the oxime (IXa) of which was thermally cyclized to 5α-androstano[17,16-b]-6′-(2-furyl)pyridin-3β-ol (Xa). 3β-Hydroxy-5α-androstano[17,16-b]pyridine-6′-carboxylic acid (XI) was obtained by ozonolysis of Xa. Thermal decarboxylation of XI gave XII. Cinnamaldehyde was used in place of 3-(2-furyl)acrolein to give the corresponding phenylpyridines.