Synthesis of robustin and related 4-hydroxy-3-phenyl coumarins and isoflavones

Robustin (31a) occurring in the roots of Derris robusta has been synthesised from mono-O-methylphloroglucinol (20) as follows. Hoesch condensation with homopiperonitrile (21) gave 2,4-dihydroxy-6-methoxyphenyl 3,4-methylenedioxybenzyl ketone (22) which on reaction with 2-hydroxy-2-methyl-3-butene in the presence of borontrifluoride-etherate afforded 5-C-(24) and 3-C-(23) prenyl derivatives. These on cyclodehydrogenation with DDQ followed by coumarin condensation with ethyl chloroformate yielded robustin (31a) and isorobustin (32) respectively. Model experiments with nuclear prenylation of 2,4-dihydroxy-6-methoxy-phenyl benzyl ketone (1), followed by oxidative cyclisation and either courmarin or isoflavone condensation have yielded new isopentenylated 4-hydroxy-3-phenylcourarins or isoflavones.     

The synthesis and properties of ferroceno[1′,2′;1″,2″]bis(1,3-dithiol-2-thione and -2-one) derivatives

The t-butyl and bis(t-butyl) derivatives of hexathia[3.3]ferrocenophane were prepared from the corresponding trithia[3]ferrocenophanes. The former was a mixture of chair-chair and chair-boat isomers, and the latter existed only chair-boat isomer. The hexathia[3.3]ferrocenophanes were led to the tetrathiols with LiAlH₄, which allowed to react with 1,1′-thiocarbonyldiimidazol to give the corresponding ferroceno[1′,2′;1″,2″]bis(1,3-dithiol-2-thione) derivatives. Mono t-butyl and unsubstituted analogs were prepared in a similar manner. The X-ray structural determination showed that these derivatives adopted the conformation in which the 1,3-dithiol-2-thione rings were heaped on top of each other. In the crystal of ferroceno[1′,2′;1″,2″]bis(1,3-dithiol-2-thione), the molecules packed so as to put the axis of molecule in order and to overlap one another above and below. The desulfurizative coupling of the ferroceno[1′,2′;1″,2″]bis(1,3-dithiol-2-thione) derivatives was unsuccessful.     

Synthesis and characterization of 6,6″′-bis(anthracen-9-yl)-2,2′;6′,2″;6″,2″′-quaterpyridine

New bianthracene-quaterpyridine ligand 6,6″′-bis(anthracen-9-yl)-2,2′;6′,2″;6″,2″′-quaterpyridine L has been obtained in a multistep synthesis using Suzuki–Miyaura and Stille-type coupling reactions. The dianthracene ligand L has four nitrogen-donor atoms and can form different supramolecular architectures with transition metal ions. Ligand L and intermediate compounds have been characterized by spectroscopic methods and elemental analyses. 2-(Anthracen-9-yl)-6-bromopyridine and 6-(anthracen-9-yl)-6′-bromo-2,2′-bipyridine have been also characterized by X-ray crystallography.     

Design and synthesis of 4″,6″-unsaturated cyclic ADP-carbocyclic ribose as a Ca-mobilizing agent

4″,6″-Didehydro-cADPcR (3), an unsaturated carbocyclic ribose analog of a Ca²⁺-mobilizing second messenger cyclic ADP-ribose (cADPR), was designed and successfully synthesized using a key intramolecular condensation reaction forming the 18-membered pyrophosphate ring structure with a S-phenyl phosphorothioate-type substrate. Biological evaluation showed that 4″,6″-didehydro-cADPcR is a potent Ca²⁺-mobilizing agent in T cells.     

Cycloalkano[1″,2″:4,5;4″,3″:4′,5′]bis(pyrrolo[2,3-c]pyrimido[5,4-e]pyridazines): synthesis, structure and mechanism of their formation

Reactions of 3-alkylamino-6,8-dimethylpyrimido[4,5-c]pyridazine-5,7(6H,8H)-diones with cyclohexyl- and cycloheptylamines in the presence of AgPy₂MnO₄ produce novel cycloalkano[1″,2″:4,5;4″,3″:4′,5′]bis(pyrrolo[2,3-c]pyrimido[5,4-e]pyridazines). Detailed information concerning the scope and mechanism of these transformations is discussed.     

Preparation of a series of novel fluorophores, N-substituted 6-amino and 6,6″-diamino-2,2′:6′,2″-terpyridine by palladium-catalyzed amination

A new series of N-substituted 6-amino- and 6,6″-diamino-2,2′:6′,2″-terpyridine (6-amino- and 6,6″-diamino-tpy) was conveniently synthesized in one-step by Pd-catalyzed amination of bromo-substituted tpys with various amines. For highly coordinating tpy substrates, use of appropriate chelating phosphine ligand was critical to achieve moderate to satisfactory yield. The prepared N-substituted 6-amino- and 6,6″-diamino-tpys exhibited moderate to intense fluorescence in dichloromethane with fine-tuned fluorescence maxima ranging from 385 to 455 nm.     

Rapid atropisomerization of 1,1′:5′,1″-ternaphthalene-2,2′,6′,2″-tetrol (TERNOL) and its inhibition by tethering at positions 7 and 7″

Atropisomerization of 1,1′:5′,1″-ternaphthalene-2,2′,6′,2″-tetrol (TERNOL) is very fast under basic conditions. The stereochemical instability is attributed to the nature of oxide anion of the central 2,6-naphthodiol moiety. Ring-closing metathesis of 7,7″-diallyloxy TERNOL results in intramolecular tethering in a high yield, which intrinsically inhibits the rapid isomerization. Bidentate sites in the tethered TERNOL are proved to have enough structural flexibility as an axial chiral ligand.     

Towards the preparation of 2″-deoxy-2″-fluoro-adenophostin A. Study of the glycosylation reaction

The synthesis of 2″-deoxy-2″-fluoro-adenophostin A framework starting from tri-O-acetylglucal and adenosine is described. The key steps are the formation of the 2-deoxy-2-fluoroglycosyl donor by electrophilic fluorination of tri-O-acetylglucal and the stereoselective glycosylation of a suitable adenosine derivative. The glycosylation reaction was optimized affording the desired 2″-deoxy-2″-fluoroglycoside with excellent α-stereoselectivity and in good yields, taking into account that glycosylations using nucleosides as glycosyl acceptors do not usually give excellent results. In that sense, an improvement of the glycosylation step with respect to that of the reported adenophostin synthesis, using adenosine derivatives as glycosyl donors, has been made.     

Design and synthesis of 4″,6″-unsaturated cyclic ADP-carbocyclic-ribose, a Ca-mobilizing agent selectively active in T cells

We previously developed cyclic ADP-carbocyclic-ribose (cADPcR, 3a) as a stable mimic of cyclic ADP-ribose (cADPR, 1), a Ca²⁺-mobilizing second messenger. The unsaturated carbocyclic-ribose analogs of cADPR, i.e., 4″,6″-didehydro-cADPcR (8a) and its inosine congener 4″,6″-didehydro-cIDPcR (8b) were newly designed and successfully synthesized using the key intramolecular condensation reaction with S-phenyl phosphorothioate-type substrates. The Ca²⁺-mobilizing potency of the compounds was examined in sea urchin egg homogenates, NG108-15 neuronal cells, and permeabilized Jurkat T-lymphocytes, which may indicate that 4″,6″-didehydro-cADPcR is the first cADPR analog selectively active in T cells. Acid-base behavior and conformation of 8a were also investigated and compared with those of cADPcR.     

Synthesis of a novel ditopic ligand incorporating directly bonded 1,10-phenanthroline and 2,2′:6′,2″-terpyridine units

The synthesis of a rigid ditopic ligand incorporating a 1,10-phenanthroline directly connected through its 3-position to the 5-position of a 2,2′:6′,2″-terpyridine is described. The synthesis is based on a series of palladium(0)-catalyzed cross-coupling reactions (Stille and Suzuki couplings) starting from 1,10-phenanthroline and bromo-substituted pyridines.     

The Thorpe-Ziegler-type reaction of 3-cyanopyridine-2(1H)-thiones with Biginelli 6-bromomethyl-3,4-dihydropyrimidin-2(1H)-ones: cascade assembling of tetra- and pentacyclic heterocyclic scaffolds

3-Cyanopyridine-2(1H)-thiones have been shown to react with Biginelli-type ethyl 4-aryl-6-(bromomethyl)-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylates upon heating in DMF giving rise to ethyl 4-aryl-6-{[(3-cyanopyridin-2-yl)thio]methyl}-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylates. The latter upon treatment with an excess of NaH or t-BuOK in boiling DMF undergo a tandem Thorpe-Ziegler-type heterocyclization to give pyrido[3″,2″:4′,5′]thieno[2′,3′:5,6]pyrido[4,3-d]pyrimidine derivatives in good yields. Selected compounds were tested for antibacterial and antifungal activity.     

Heterocyclic analogs of 5,12-naphthacenequinone. 2. Synthesis of 4,11-dihydroxynaphtho[2,3-f]indazole-5,10-dione and its n-methyl derivatives

On methylating 4,11-dimethoxynaphtho[2,3-f]indazole-5,10-dione with methyl iodide in the presence of base a mixture is formed of its 1-and 2-methyl derivatives. Demethylation of the methoxy groups of the starting material and of the products of its alkylation leads to the formation of 4,11-dihydroxynaphtho[2,3-f]indazole-5,10-dione (pyrazoloquinizarine) and its 1-and 2-methyl derivatives. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 691–696, May, 2006.     

An efficient route to 5,5″-diaryl-2,2′:6′,2″-terpyridines through 2,6-bis(1,2,4-triazin-3-yl)pyridines

A new route to substituted 2,2′:6′,2″-terpyridines based on a new method for the synthesis of substituted 2,6-bis(1,2,4-triazin-3-yl)pyridines and their inverse electron demand Diels-Alder reaction is shown to be an efficient strategy for the synthesis of structurally diverse terpyridine ligands.     

Synthesis of N-vinyl derivatives of 2-methyl- and 4(5)-methylimidazoles

Conclusions The reaction of 2-methyl and 4(5)-methylimidazoles with acetylene in the presence of Gu₂Cl₂ leads to the corresponding N-vinyl derivatives. 1-Vinyl-4(5)-methylimidazole is formed as a mixture of two isomers differing in the position of the methyl group.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2122–2124, September, 1987.     

Synthesis of 4″-alkoxy avermectin derivatives using rhodium carbenoid-mediated O-H insertion reaction

4″-Alkoxy avermectin derivatives have been synthesized using O-H insertion reaction with ethyl diazoacetate in the presence of Rh₂(OAc)₄ as a catalyst.     

Ring transformation of 6-methyl-3,4-dihydro-2H-1,3-oxazine-2,4-diones

Ring transformation of 6-methyl-3,4-dihydro-2H-1,3-oxazine-2,4-dione (Ia) and its N-sub-stituted derivatives, such as 3-methyl (Ib), 3-ethyl (Ic), and 3-benzyl (Id) derivatives is described. Reaction of Ia with hydrazine hydrate gave 1-amino-6-methyluracil (II), while Id reacted with hydrazine hydrate to give 3-hydroxy-5-methylpyrazole (III). Reaction of Ia,b,d with ethyl acetoacetate in ethanol in the presence of sodium ethoxide afforded ethyl 3-acetyl-6-hydroxy-4-methyl-2(1H) pyridone-5-carboxylate derivatives (IVa,b,d). On the other hand, reaction of Ib,c,d with ethyl acetoacetate in tetrahydrofuran in the presence of sodium hydride did not give IV, but gave 3-acetyl-1-alkyl-5-(N-alkylcarbamoyl)-6-hydroxy4-methyl-2(1H) pyridone (VIb,c,d). Mechanisms for the formation of compounds IV and VI are discussed.     

A convenient synthesis of substituted 2,2′:6′,2″-terpyridines

The 2,2′:6′,2″-terpyridines 7a-c were prepared in good yield by reacting α-acetoxy-α-chloro-β-keto-esters 3a-c with bis-amidrazone 4 and 2,5-norbornadiene 6 in ethanol at reflux. Compounds 3a and 3b gave the 2,2′:6′,2″-terpyridines 9a and 9b, respectively, in moderate yield when treated with compound 4 and enamine 8.     

2-Amino-6-phenyl-7,8-dihydroindazolo[4,5-d]thiazoles

Treatment of 4-oxo-l -phenyl-4,5,6,7-tetrahydroindazole and its 3-methyl, 6-phenyl, and 3-methyl-6 phenyl substituted derivatives with pyridinium bromide-perbromide and subsequent reaction of the 5-brorno derivatives obtained with thiourea gave 2-amino-6 phenyl-7, 8-dihydroindazolo[4,5-d]thiazole and its corresponding substituted derivatives. The condensation of these products with 2 formyldimedone led to their 4, 4-dimethyl-2, 6-dioxocyclohexylidene derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 497–500. April, 1966.     

Functionalization at C-5 and at the C-6 methyl group of 4-methoxy-6-methyl-2-pyrone

A new entry to C-5 substituted 4-hydroxy-6-methyl-2-pyrones has been achieved. The best conditions to prepare the monobromo and the dibromo derivatives at C-3 and the C-6 methyl group of the title pyrone have been defined. The synthetic applicability of the phosphonium salts at CH₃-C-6 of both 4-methoxy-6-methyl-2-pyrone, 5 , and dehydroacetic acid, 2 , has also been evaluated.