Regioselective Haloaromatization of 1,2-Bis(ethynyl)benzene via Halogen Acids and PtCl2. Platinum-Catalyzed 6-π Electrocyclization of 1,2-Bis(1‘-haloethenyl)benzene Intermediates

[reaction: see text] Treatment of 1,2-bis(ethynyl)benzene (1) with aqueous HX (X = Br, I) in hot 3-pentanone (100-105 degrees C, 2 h) afforded 1,2-bis(1'-haloethenyl)benzene species 2-Br and 2-I in 98% and 95% yields, respectively. The hydrochlorination of endiyne 1 failed to proceed at elevated temperature but was implemented efficiently by PtCl2 (5 mol %) in hot 3-pentanone (100 degrees C, 2 h) to give 1,2-bis(1'-chloroethenyl)benzene 2-Cl in 80% yield. In the presence of PtCl2 (5 mol %), these halides 2-Cl,2-Br, and 2-I were subsequently converted to 1-halonaphthalenes 3-Cl, 3-Br, and 3-I in the mother solution via sequential 6-pi electrocyclization and dehalogenation reactions. PtCl2 (5 mol %) also effected direct haloaromatization of endiyne 1 with HX (X = Cl, Br, I) and gave 1-halonaphthalenes 3-Cl, 3-Br, and 3-I in 64-71% yields. This investigation reports the scope and the regioselectivity of haloaromatization of various enediynes catalyzed by PtCl2.

New Agents with Antimycobacterial Activity

In this paper, we report that a series of structurally simple a-halogenoacetamides show potent and excellent antimycobacterial activities against drug-sensitive Mycobacterium tuberculosis H(37)Rv and drug-resistant M. avium.

Synthesis of Isoxazoles via Electrophilic Cyclization

[reaction: see text] A variety of 3,5-disubstituted 4-halo(seleno)isoxazoles are readily prepared in good to excellent yields under mild reaction conditions by the reaction of 2-alkyn-1-one O-methyl oximes with ICl, I2, Br2, or PhSeBr.

Antineoplastic agents. 509: synthesis of fluorcombstatin phosphate and related 3-halostilbenes(1)

The present SAR study of combretastatin A-3 (3a) focused on replacement of the 3-hydroxyl group by a series of halogens. That approach with Z-stilbenes resulted in greatly enhanced (>10-100-fold) cancer cell growth inhibition against a panel of human cancer cell lines and the murine P388 lymphocytic leukemia cell line. Synthesis of the 3-fluoro-Z-stilbene designated fluorcombstatin (11a) and its potassium 3'-O-phosphate derivative (16c) by the route 7 --> 8a --> 11a --> 14 --> 16c illustrates the general synthetic pathway. The 3'-O-phosphoric acid ester (15) of 3-bromo-Z-stilbene 13a was also converted to representative cation salts to evaluate the potential for improved aqueous solubility, and the potassium salt (16 mg/mL in water) proved most useful. The fluoro (11a), chloro (12a), and bromo (13a) halocombstatins were nearly equivalent to combretastatin A-4 (1a) as inhibitors of tubulin polymerization and of the binding of colchicine to tubulin. The tubulin binding in cell-free systems was also retained in human umbilical vein endothelial cells. All three halocombstatins retained the powerful human cancer cell line inhibitory activity of combretastatin A-4 (1a) and proved superior to combretastatin A-3 (3a). In addition, the halocombstatins targeted Gram-positive bacteria and Cryptococcus neoformans.

1,2-Halogen migration in haloallenyl ketones: regiodivergent synthesis of halofurans

Selective 1,2-iodine, bromine, and chlorine migration in haloallenyl ketones in the presence of Au catalyst has been demonstrated. It was found that, depending on the nature of the Au catalyst used, either selective bromine migration or hydrogen shift occurs, leading to the formation of 3- or 2-bromofurans, respectively. Halirenium intermediate was proposed for the unusual 1,2-halogen migration. This cascade transformation allows for mild and efficient synthesis of various types of 3-halofurans.

The mechanisms of the Stille reaction

Eighteen years ago in Angewandte Chemie John K. Stille reviewed a novel methodology, which eventually became known by his name, for the coupling of organostannanes with organic electrophiles. Since then that seed has blossomed into a multifaceted methodology full of hidden possibilities to explore, discover, and enjoy. Very recent modifications are making synthetic wishes come true that were only dreamed of a few years ago. Moreover, as important advances are being made in the understanding of the mechanistic details of the process, it is becoming increasingly possible to apply this essential reaction and its new variants in a less empirical way. The purpose of this Review is to give a critical account of this progress.

C-25 epimeric 26-haloponasterone A: synthesis, absolute configuration and moulting activity

A convenient synthesis of inokosterone has been accomplished. Inokosterone exists as two C-25 epimers, which could be separated from each other through their diacetonide derivatives. The absolute configuration of these compounds was determined. Two C-25 epimers of 26-chloroponasterone A were synthesized from the respective C-25 epimeric inokosterone. Two epimeric 26-bromo and 26-iodoponasterone A compounds were also synthesized. Moulting activity of these compounds was evaluated using the Musca bioassay, and it was found that the (25S)-26-halo analogues were more active than the corresponding (25R)-26-halo analogues. Among the 25S series, an increase in activity with an increase in size of the halogen atom was observed, indicating that the steric factor was more important than the electronic factor in binding of these ecdysteroid analogues to the receptor. On the other hand, a decrease in activity with an increase in size of the halogen atom was noted in the 25R series, suggesting that the steric factor was less important than the electronic factor. The results indicated that the configuration at C-25 and the substituent at C-26 have significant influences on the interaction of ecdysteroids with their receptor.

Photoinduced One-Electron Reduction of Alkyl Halides by Dirhodium(II,II) Tetraformamidinates and a Related Complex with Visible Light

Various substituted dirhodium tetraformamidinate complexes, Rh(2)(R-form)(4) (R = p-CF(3), p-Cl, p-OCH(3), m-OCH(3); form = N,N'-diphenylformamidinate), and the new complex Rh(2)(tpgu)(4) (tpgu = 1,2,3-triphenylguanidinate) have been investigated as potential agents for the photoremediation of saturated halogenated aliphatic compounds, RX (R = alkyl group). The synthesis and characterization of the complexes is reported, and the crystal structure of Rh(2)(tpgu)(4) is presented. The lowest energy transition of the complexes is observed at approximately 870 nm and the complexes react with alkyl chlorides and alkyl bromides under low energy irradiation (lambda(irr) > or = 795 nm), but not when kept in the dark. The metal-containing product of the photochemical reaction with RX (X = Cl, Br) is the corresponding mixed-valent Rh(2)(II,III)X (X = Cl, Br) complex, and the crystal structure of Rh(2)(p-OCH(3)-form)(4)Cl generated photochemically from the reaction of the corresponding Rh(2)(II,II) complex in CHCl(3) is presented. In addition, the product resulting from the dimerization of the alkyl fragment, R(2), is also formed during the reaction of each dirhodium complex with RX. A comparison of the dependence of the relative reaction rates on the reduction potentials of the alkyl halides and their C-X bond dissociation energies are consistent with an outer-sphere mechanism. In addition, the relative reaction rates of the metal complexes with CCl(4) decrease with the oxidation potential of the dirhodium compounds. The mechanism of the observed reactivity is discussed and compared to related systems.

Substitution of Benzylic Hydroxyl Groups with Vinyl Moieties Using Vinylboron Dihalides

[reaction: see text] Substitution of benzylic hydroxyl groups with vinyl moieties using vinylboron dihalides has been achieved. The reaction provides a novel method for preparing stereodefined alkenyl halides.

Palladium(0)-Catalyzed Tandem Cyclization of Allenenes: Direct Construction of Tricyclic Heterocycles through Aromatic CH Activation

Palladium(0)-catalyzed tandem cyclization of allenenes is described. Treatment of allenenes with an aryl halide, potassium carbonate, and catalytic [Pd(PPh(3))(4)] in dioxane afforded tri- or tetracyclic heterocycles in moderate to good yields through insertion of arylpalladium(II) halide into the allenic moiety, intramolecular carbopalladation, and aromatic C--H bond activation. The substituent on the olefin terminus has proven to be essential for the success of the tandem cyclization. The reaction with heterocyclic aryl halides such as iodopyrazine or 4-bromo-1-methylindole afforded tri- or tetracyclic heteroaromatic products in good yields.

Ionic Liquid as Reagent. A Green Procedure for the Regioselective Conversion of Epoxides to Vicinal-Halohydrins Using [AcMIm]X under Catalyst- and Solvent-Free Conditions

A variety of structurally diverse epoxides undergo facile cleavages by ionic liquid, [AcMIm]X without any catalyst and solvent to produce the corresponding vicinal halohydrins in high yields. The cleavages are considerably fast and highly regioselective.

Homogeneous catalysts supported on soluble polymers: biphasic Suzuki-Miyaura coupling of aryl chlorides using phase-tagged palladium-phosphine catalysts

The Suzuki-Miyaura coupling of aryl chlorides and PhB(OH)(2) under biphasic conditions (DMSO/heptane) can be performed in almost quantitative yields over several cycles by means of polymeric Pd catalysts with soluble polyethylene glycol phase tags. Three sterically demanding and electron-rich phosphines 1-CH(2)Br,4-CH(2)P(1-Ad)(2)-C(6)H(4), and 2-PCy(2),2'-OH-biphenyl, and 2-PtBu(2),2'-OH-biphenyl were covalently bonded to 2000 Dalton MeOPEG-OH. The catalysts, which were formed in situ from Na(2)[PdCl(4)], the respective polymeric phosphine, KF/K(3)PO(4), and PhB(OH)(2), efficiently couple aryl chlorides at 80 degrees C at 0.5 mol % loading, resulting in a >90 % yield of the respective biphenyl derivatives. The use of polar phase tags allows the efficient recovery of palladium-phosphine catalysts by simple phase separation of the catalyst-containing DMSO solution and the product-containing n-heptane phase. The high activity (TOF) of the catalyst remains almost constant over more than five reaction cycles, which involve the catalytic reaction, separation of the product phase from the catalyst phase, and addition of new reactants to initiate the next cycle. The Buchwald type biphenyl phosphines form the most active Pd catalysts, which are 1.3-2.8 times more active than catalysts derived from diadamantyl-benzylphosphine, but appear to be less robust in the recycling experiments. There is no apparent leaching of the catalyst into the heptane solution (<0.05 %), as evidenced by spectrophotometric measurements, and contamination of the product with Pd is avoided.

Metalated Nitriles: Organolithium, -magnesium, and -copper Exchange of α-Halonitriles

[reaction: see text] alpha-Halonitriles react with alkyllithium, organomagnesium, and lithium dimethylcuprate reagents generating reactive, metalated nitriles. The rapid halogen-metal exchange with alkyllithium and Grignard reagents allows selective exchange in the presence of reactive carbonyl electrophiles, including aldehydes, providing a high-yielding alkylation protocol. Lithiated and magnesiated nitriles react with propargyl bromide by S(N)2 displacement whereas organocopper nitriles react by S(N)2' displacement, correlating with the formation of a C-metalated nitrile.

Ring expansion-annulation strategy for the synthesis of substituted azulenes and oligoazulenes. 2. Synthesis of azulenyl halides, sulfonates, and azulenylmetal compounds and their application in transition-metal-mediated coupling reactions

A "ring expansion-annulation strategy" for the synthesis of substituted azulenes is described based on the reaction of beta'-bromo-alpha-diazo ketones with rhodium carboxylates. The key transformation involves an intramolecular Buchner reaction followed by beta-elimination of bromide, tautomerization, and in situ trapping of the resulting 1-hydroxyazulene as a carboxylate or triflate ester. Further synthetic elaboration of the azulenyl halide and sulfonate annulation products can be achieved by employing Heck, Negishi, Stille, and Suzuki coupling reactions. Reaction of the azulenyl triflate 84 with pinacolborane provides access to the azulenylboronate 91, which participates in Suzuki coupling reactions with alkenyl and aryl iodides. The application of these coupling reactions to the synthesis of biazulenes, terazulene 101, and related oligoazulenes is described, as well as the preparation of the azulenyl amino acid derivative 110.

Microwave-Promoted Heck Coupling Using Ultralow Metal Catalyst Concentrations

We show that Heck couplings can be performed in water using microwave heating and Pd catalyst concentrations as low as 500 ppb. The methodology is simple; all that is required as the catalyst is a stock solution of palladium.

The development of efficient catalysts for palladium-catalyzed coupling reactions of aryl halides

In the mid 1990s, we started a program on the development of more efficient palladium catalysts for the C-C and C-N coupling reactions of aryl halides, especially aryl chlorides. In this contribution, our investigations on new catalyst systems and their application in organic synthesis are summarized.

Optimization of CRF1R binding affinity of 2-(2,4,6-trichlorophenyl)-4-trifluoromethyl-5-aminomethylthiazoles through rapid and selective parallel synthesis

An efficient approach was developed to synthesize 2-(2,4,6-trichlorophenylamino)-4-trifluoromethyl-5-aminomethylthiazoles, corticotropin-releasing factor type 1 receptor (CRF(1)R) antagonists, by monoalkylation of amines with chloromethyl intermediate 5. The effect of variations in aminomethyl side chain of 6 on binding affinity is discussed.

Total synthesis of (+/-)-perophoramidine

The first total synthesis of racemic perophoramidine is described. The key step features the highly stereoselective introduction of the vicinial quaternary centers via base-promoted carbon-carbon bond formation between a 3-alkylindole and a 3-bromo-3-alkylindolin-2-one. This transformation presumably proceeds through a conjugate addition or Diels-Alder cycloaddition of the 3-alkylindole with a 3-alkylindol-2-one intermediate.

SNAr Iodination of 6-Chloropurine Nucleosides: Aromatic Finkelstein Reactions at Temperatures Below −40 °C1

Mesitoyl or toluoyl esters of inosine and 2'-deoxyinosine were deoxychlorinated at C6 to give the crystalline 6-chloropurine nucleoside derivatives, which underwent quantitative conversion to the 6-iodo analogues with NaI/TFA/butanone at -50 to -40 degrees C. The 6-iodo compounds were efficient substrates for SNAr, Sonogashira, and Suzuki-Miyaura reactions, in contrast with the 6-chloro analogues, and gave good to high yields of C-N and C-C coupled products.

Fragmentation of carbohydrate anomeric alkoxyl radicals: a new synthesis of 1,1-difluoro-1-iodo alditols

[reaction: see text]. The beta-fragmentation of 2,2-difluoro-saccharide anomeric alkoxyl radicals, generated under oxidative condition by treatment of the respective alcohols with (diacetoxyiodo)benzene (DIB) and iodine, afforded 1,1-difluoro-1-iodo alditols in high yield. The reactivity of the fluorinated radical generated by rupture of the C-I bond has been preliminarily assessed by reductive deiodination with tributyltin hydride/AIBN and intermolecular allylation using the Keck reaction.

Novel halo-oxo-allenic fatty ester derivatives from epoxidized methyl santalbate (methyl trans-11-octadecen-9-ynoate)

Methyl santalbate (methyl trans-11-octadecen-9-ynoate) from Sandal wood seed oil, Santalbum alum) was epoxidized to methyl trans-11,12-epoxy-octadec-9-ynoate (1). Treatment of compound 1 with tetrabutylammonium dihydrogentrifluoride, and boron trifluoride etherate gave the corresponding anti- (2a) (57%) and syn- (2b) (35%) fluorohydrin derivatives, respectively. These reactions were regio- and stereoselective in nature. The structures of the anti- and syn- isomers were confirmed by NMR spectroscopy. Ring opening of the epoxy system of compound 1 with lithium chloride gave the anti-chlorohydrin derivative (3) (89%). Oxidation of either compound 2a or 2b gave the same fluoro-keto acetylenic fatty ester (4) (75%), and compound 3 on chromic acid oxidation yielded the corresponding chloro-keto acetylene (5) (73%). Isomerization of compounds 4 and 5 with potassium carbonate in dichloromethane furnished the requisite fluoro-allenic (6) (63%, methyl 11-fluoro-12-oxo-9,10-octadecadienoate) and chloro-allenic (7) (80%, methyl 11-chloro-12-oxo-9,10-octadecadienoate) C(18) fatty esters. All products were confirmed by a combination of spectrometric and spectroscopic techniques.

A Convenient Synthesis of 7-Halo-1-indanones and 8-Halo-1-tetralones

A regioselective oxidation of N-indan-4-yl-acetamide or N-(5,6,7,8-tetrahydronaphthalen-1-yl)acetamide with potassium permanganate followed by acidic hydrolysis gave 7-aminoindan-1-one or 8-aminotetral-1-one in good yield. The amino ketones were converted to the corresponding 7-haloindanone or the 8-halotetralone. Another method to prepare 7-haloindan-1-ones was completed by a cyclization of 3-chloro-1-(2-halophenyl)propan-1-one under Friedel-Crafts conditions to produce the product in gram quantity.

Syntheses of Regioisomerically Pure 5- or 6-Halogenated Fluoresceins

Three routes to regioisomerically pure 5- and 6-iodofluoresceins or 5- and 6-bromofluoresceins are described. The first, shown in Scheme 1, involves diazotization/iodination of the corresponding aminofluoresceins. In the second approach (Scheme 2) a mixture of regioisomeric fluoresceins was prepared, and the 5-bromo isomers were isolated as the ring closed diacetates 9b and 11 by fractional crystallization. Scheme 3 shows an approach to sulfonic acid derivatives 3 and 4 of 5-iodofluorescein. This is the most convenient procedure of the three, and it is particularly useful as sulfofluoresceins have more favorable water solubility characteristics than fluoresceins that lack the sulfonic acid group.

Allylic halogenation of unsaturated amino acids

A range of dehydro amino acid derivatives has been prepared and subjected to halogenation using either molecular bromine or chlorine, or NBS. Allylic halogenation of the unsaturated amino acid side chains occurs through radical bromination with NBS. The procedure is complementary to treatment with chlorine, which also affords allyl halides. This latter and unusual reaction is shown through a deuterium labelling study to proceed via an ionic mechanism. The choice of NBS or chlorine for allyl halide synthesis is shown to depend on the potential to avoid competing reactions, such as halolactonization of leucine derivatives with chlorine, and hydrogen abstraction and bromine incorporation at multiple sites on treatment of isoleucine derivatives with NBS. The synthetic utility of the allyl halides prepared in this study is indicated through the synthesis of a cyclopropyl amino acid derivative and the extension of the carbon skeleton of an amino acid side chain.

Convergent synthesis of polyhalogenated quinoline C-nucleosides as potential antiviral agents

2,5,6-Trichloro-1-(beta-d-ribofuranosyl)benzimidazole (TCRB) and 2-bromo-5,6-dichloro-1-(beta-d-ribofuranosyl)benzimidazole (BDCRB) are benzimidazole nucleosides that exhibit strong and selective anti-HCMV activity. We proposed to synthesize 2-halo-6,7-dichloro-4-(beta-d-ribofuranosyl)quinolines as 6 + 6 bicyclic analogues of TCRB. The synthesis used Wittig reactions in two key steps. The first Wittig reaction coupled a fully functionalized benzene with a ribofuranose derivative to provide (Z)-6-O-(tert-butyldimethylsilyl)-1-(4,5-dichloro-2-nitrophenyl)-1,2-dideoxy-3,4-O-isopropylidene-d-allo-1-enitol (5) as the basic skeleton for the target compounds. The following electrophile-mediated intramolecular cyclization of the cis-alkene (5) was found to afford (1S,2S)-2,5-anhydro-1-bromo-6-O-(tert-butyldimethylsilyl)-1-deoxy-1-(4,5-dichloro-2-nitrophenyl)-3,4-O-isopropylidene-d-allitol (8) as the major product. This alpha-stereoselectivity was contrary to the literature precedence. A double-bond isomerization was established to be the cause of the unexpected stereochemistry. The bromo group of 8 was displaced by a hydroxyl group. Oxidation of the hydroxy group and the reduction of a phenylnitro group provided (2S)-1-(2-amino-4,5-dichlorophenyl)-2,5-anhydro-6-O-(tert-butyldimethylsilyl)-3,4-O-isopropylidene-d-allose (11), which was subjected to the second Wittig reaction with a phosphacumulene to construct 4-[5-O-(tert-butyldimethylsilyl)-2,3-O-isopropylidene-alpha-d-ribofuranosyl]-6,7-dichloroquinolin-2-one (13). Halogenation followed by deprotection of 13 and led to the synthesis of 4-(alpha-d-ribofuranosyl)-2,6,7-trichloroquinoline (17) as the major product. The 2-aminophenone alpha-nucleoside (11) was successfully anomerized to the beta-anomer (19), which led to the synthesis of the targeted 2-chloro- and 2-bromo-6,7-dichloro-4-(beta-d-ribofuranosyl)quinolines (18and 21, respectively).

Omega-halonitriles: domino cyclizations to oxa- and carbocyclic nitriles

t-BuOK-induced deprotonation of omega-haloalkylnitriles generates remarkably stable potassiated nitriles. In situ deprotonation and alkylation of omega-chloroalkylnitriles with aldehyde electrophiles trigger sequential nucleophilic-electrophilic alkylations generating substituted tetrahydrofuranyl and tetrahydropyranyl nitriles. Redirecting the cyclization manifold with 5-iodopentanenitrile and a ketone causes a complementary electrophilic-nucleophilic cyclization to the corresponding carbonitrile. Collectively these cyclizations provide rapid assembly of five- and six-membered oxa- and carbocyclic nitriles demonstrating the utility of omega-halonitriles in domino alkylations.

Synthesis of new N-substituted cyclic imides with potential anxiolytic activity. XXV. Derivatives of halogenodibenzo[e.h]bicyclo[2.2.2]octane-2.3-dicarboximide

The preparation of a number of derivatives of dibenzo[e.h]bicyclo[2.2.2]octane-2.3-dicarboximide with an expected anxiolytic activity.

An approach to the total synthesis of the marine ascidian metabolite perophoramidine via a halogen-selective tandem Heck/carbonylation strategy

A halogen-selective tandem intramolecular Heck/carbonylation reaction has been developed for the construction of the C,E,F-ring system and the C20 quaternary center found in perophoramidine (1). This process can be effected in good yields in the presence of both the chlorine and bromine atoms found in the natural product. In addition, it is possible to introduce the quaternary center at C4 in a stereoselective manner by a lactone enolate alkylation, using NaH and allyl bromide. [reaction: see text]

Stereoselective halogenation of the 16-hydroxymethyl-3-methoxy-13alpha-estra-1,3,5(10)-trien-17-ols and their solvolytic investigation

The primary hydroxy functions of 16alpha-hydroxymethyl-3-methoxy-13alpha-estra-1,3,5(10)-trien-17beta-ol (3a) and 16beta-hydroxymethyl-3-methoxy-13alpha-estra-1,3,5(10)-trien-17alpha-ol (4a) were stereoselectively transformed into good leaving groups. On alkaline methanolysis of the 16-halomethyl or 16-tolylsulfonyloxymethyl derivatives, a new D-seco-13alpha-estrone derivative was obtained in high yield.

A mild, convenient, and inexpensive procedure for conversion of vinyl halides to alpha-haloketones

Treatment of a vinyl chloride with commercially available aqueous sodium hypochlorite solution in a 2:5 mixture of acetic acid/acetone at 0 degrees C for about 1 h cleanly leads to the corresponding alpha-chloroketone. Similarly, if a vinyl bromide is exposed to sodium hypobromite (freshly prepared from bromine and sodium hydroxide) at 0 degrees C in 2:5 acetic acid/acetone as solvent, an alpha-bromoketone is produced. This methodology has been applied to a number of vinyl chlorides and vinyl bromides, and the transformations generally proceed in high yields. The mild reaction conditions are compatible with a variety of functional groups including amides, esters, and imines.

ortho-Halogen naphthaleins as specific inhibitors of Lactobacillus casei thymidylate synthase. Conformational properties and biological activity

Thymidylate synthase (TS) (EC 2.1.1.45), an enzyme involved in the DNA synthesis of both prokaryotic and eukaryotic cells, is a potential target for the development of anticancer and antinfective agents. Recently, we described a series of phthalein and naphthalein derivatives as TS inhibitors. These compounds have structures unrelated to the folate (Non-Analogue Antifolate Inhibitors, NAAIs) and were selective for the bacterial versus the human TS (hTS). In particular, halogen-substituted molecules were the most interesting. In the present paper the halogen derivatives of variously substituted 3,3-bis(4-hydroxyphenyl)-1H,3H-naphtho[2,3-c]furan-1-one (1-5) and 3,3-bis(4-hydroxyphenyl)-1H,3H-naphtho[1,8-c,d]pyran-1-one (6-14) were synthesized to investigate the biological effect of halogen substitution on the inhibition and selectivity for the TS enzymes. Conformational properties of the naphthalein series were explored in order to highlight possible differences between molecules that show species-specific biological profile with respect to non species-specific ones. With this aim, the conformational properties of the synthesized compounds were investigated by NMR, in various solvents and at different temperatures, and by computational analysis. The apparent inhibition constants (K(i)) for Lactobacillus casei TS (LcTS) were found to range from 0.7 to 7.0 microM, with the exception of the weakly active iodo-derivatives (4, 10, 13); all] the compounds were poorly active against hTS. The di-halogenated compounds 7, 8, 14 showed the highest specificity towards LcTS, their specificity index (SI) ranging between 40 and >558. The di-halogenated 1,8-naphthalein derivatives (7-10) exhibited different conformational properties with respect to the tetra-haloderivatives. Though a clear explanation for the observed specificity by means of conformational analysis is difficult to find, some interesting conformational effects are discussed in the context of selective recognition of the compounds investigated by the LcTS enzyme.

(Z)-alpha-haloacrylates: an exceptionally stereoselective preparation via Cr(II)-mediated olefination of aldehydes with trihaloacetates

(Z)-alpha-Fluoro-, (Z)-alpha-chloro-, and (Z)-alpha-bromoacrylates were obtained with unprecedented yield and stereocontrol (>99%) via addition of the corresponding commercial trihaloacetates to aldehydes at room temperature using stoichiometric Cr(II) salts or catalytic Cr(II) with a regeneration system. The intermediate 2,2-dihalo-3-hydroxy adducts could be isolated in good yields under conditions of limited reagent at 0 degrees C.

C10-substituted camphors and fenchones by electrophilic treatment of 2-methylenenorbornan-1-ols: enantiospecificity, scope, and limitations

Valuable chiral sources of C(10)-substituted camphors and C(10)-substituted fenchones can be straightforwardly obtained by treatment of an appropriate, easily obtainable, camphor- or fenchone-derived 2-methylenenorbornan-1-ol with an electrophilic reagent. The process takes place via a tandem regioselective carbon-carbon double-bond addition/stereocontrolled Wagner-Meerwein rearrangement. A complete study of the enantiospecificity, scope, and limitations of this process, as well as about the role played by the hydroxyl group attached at the C(1) bridgehead position of the starting 2-methylenenorbornan-1-ols, has been realized. The feasibility of the described methodology has been exemplified by the highly efficient enantiospecific preparation of several interesting C(10)-halogen-, C(10)-O-, C(10)-S-, C(10)-Se-, or C(10)-C-substituted camphors and fenchones.

Multifunctional palladium catalysis. 2. Tandem haloallylation followed by Wacker-Tsuji oxidation or sonogashira cross-coupling

[reaction: see text] Multifunctional palladium catalysis is utilized in the one-pot stereocontrolled synthesis of tetrasubstituted methyl ketones and enynes. The homogeneous palladium dihalide catalyst utilized for the bromo-/chloroallylation of alkynes is reused in situ for subsequent Wacker-Tsuji oxidation or Sonogashira cross-coupling.

Synthesis of radioiodinated aryl iodides via boronate precursors

Arylboronate esters are converted to iodine-123 labeled aryl iodides using no-carrier-added iodine-123 labeled sodium iodide in the presence of chloramine-T. High yields of radiochemically pure products are obtained.

Halo-enediynes: probing the electronic and stereoelectronic contributions to the Bergman cycloaromatization

A series of halogen-substituted cyclic enediynes were prepared with use of carbenoid coupling strategy. DFT analysis, initially used to identify synthesis candidates, was also employed to rationalize the propensity for cycloaromatization of the compounds. In all cases studied the halogen atom had a strongly retardative effect on the thermal Bergman cycloaromatization reaction. The isolation of the first C-9 monochloroenediyne is noteworthy, and may find application in prodrug design.

Study of alpha-crustacyanin utilizing halogenated canthaxanthins

[structure: see text] The preparations and spectroscopic characteristics of five all-trans halogenated canthaxanthins are described in this letter. The air/light-sensitive halogenated canthaxanthins were used to study alpha-crustacyanin, a blue astaxanthin-protein complex, which is isolated from the carapace of the lobster. Steric and electronegative effects of the halogen substituents on the noncovalent interaction between astaxanthin and the protein in alpha-crustacyanin were observed.

Formation of vinyl halides via a ruthenium-catalyzed three-component coupling

The ruthenium-catalyzed three-component coupling of an alkyne, an enone, and halide ion to form E- or Z-vinyl halides has been investigated. Through systematic optimization experiments, the conditions effecting the olefin selectivity were examined. In general, more polar solvents such as DMF favored the formation of the E-isomer, and less polar solvents such as acetone favored formation of the Z-isomer. The optimized conditions for the formation of E-vinyl chlorides were found to be the use of cyclopentadienyl ruthenium (II) cyclooctadiene chloride, stannic chloride pentahydrate as a cocatalyst, and for a chloride source, either ammonium chloride in DMF/water mixtures or tetramethylammonium chloride in DMF. A range of several other ruthenium (II) catalysts was also shown to be effective. A wide variety of vinyl chlorides could be formed under these conditions. Substrates with tethered alcohols or ketones either five or six carbons from the alkyne portion gave instead diketone or cyclohexenone products. For formation of vinyl bromides, a catalyst system involving the use of cyclopentadienylruthenium (II) tris(acetonitrile) hexafluorophosphate with stannic bromide as a cocatalyst was found to be most effective. The use of ammonium bromide in DMF/acetone mixtures was optimal for the synthesis of E-vinyl bromides, and the use of lithium bromide in acetone was optimal for formation of the corresponding Z-isomer. Under either set of conditions, a wide range of vinyl bromides could be formed. When alkynes with propargylic substituents are used, enhanced selectivity for formation of the Z-isomer is observed. When aryl acetylenes are used as the coupling partners, complete selectivity for the Z-isomer is obtained. A mechanism involving a cis or trans halometalation is invoked to explain formation of the observed products. The vinyl halides have been shown to be precursors to alpha-hydroxy ketones and cyclopentenones, and as coupling partners in Suzuki-type reactions.

Synthesis and antimicrobial activity of some novel 2-(p-substituted-phenyl)-5-substituted-carbonylaminobenzoxazoles

A series of 2-(p-substituted-phenyl)-5-substituted-carbonylamino benzoxazole derivatives (5-22) was synthesized and their antimicrobial activities determined in comparison to several control drugs. The synthesized compounds were tested in vitro against Staphylococcus aureus, Streptococcus faecalis and Bacillus subtilis as Gram-positive, Pseudomonas aeruginosa and Escherichia coli as Gram-negative bacteria and the yeast Candida albicans. Microbiological results showed that the compounds possessed a diffuse spectrum of antibacterial activity against these microorganisms. Compound 9 which bears a phenylacetamido moiety at position 5 and a 4-fluorophenyl group at the 2-position of benzoxazole ring was the most active derivative against S. aureus, S. faecalis and P. aeruginosa with a MIC value of 12.5 microg/ml. Compound 11 provided higher potency than the other tested compounds against B. subtilis at a MIC value of 12.5 microg/ml. Compounds 5-22 showed antifungal activity against C. albicans with MIC values between 50 and 12.5 microg/ml.

Palladium-catalyzed arylation of malonates and cyanoesters using sterically hindered trialkyl- and ferrocenyldialkylphosphine ligands

Palladium-catalyzed reactions of aryl bromides and chlorides with two common stabilized carbanions-enolates of dialkyl malonates and alkyl cyanoesters-are reported. An exploration of the scope of these reactions was conducted, and the processes were shown to occur in a general fashion. Using P(t-Bu)(3) (1), the pentaphenylferrocenyl ligand (Ph(5)C(5))Fe(C(5)H(4))P(t-Bu)(2) (2), or the adamantyl ligand (1-Ad)P(t-Bu)(2) (3), reactions of electron-poor and electron-rich, sterically hindered and unhindered aryl bromides and chlorides were shown to react with diethyl malonate, di-tert-butyl malonate, diethyl fluoromalonate, ethyl cyanoacetate, and ethyl phenylcyanoacetate. Although alkyl malonates and ethyl alkylcyanoacetates did not react with aryl halides using these catalysts, the same products were formed conveniently in one pot from diethylmalonate by cross-coupling of an aryl halide in the presence of excess base and subsequent alkylation.

Radiocarbon content of synthetic and natural semi-volatile halogenated organic compounds

Some halogenated organic compounds, such as polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs) and polybrominated diphenyl ethers (PBDEs), have been suggested to have natural sources but separating these compounds from their commercially synthesized counterparts is difficult. Molecular-level 14C analysis may be beneficial since most synthetic compounds are manufactured from petrochemicals (14C-free) and natural compounds should have "modern" or "contemporary" 14C levels. As a baseline study, we measured, for the first time, the 14C abundance in commercial PCB and PBDE mixtures, a number of organochlorine pesticides, as well as one natural product 2-(3',5'-dibromo-2'-methoxyphenoxy)-3,5-dibromoanisole. The latter compound was isolated from a marine sponge and is similar in structure to a PBDE. All of the synthetic compounds were 14C-free except for the pesticide toxaphene. which had a modern 14C abundance, as did the brominated natural compound. The result for toxaphene was not surprising since it was commercially synthesized by the chlorination of camphene derived from pine trees. These results suggest that measuring the 14C content of halogenated organic compounds may be quite useful in establishing whether organic compounds encountered in the environment have natural or synthetic origins (or both) provided that any synthetic counterparts derive from petrochemical feedstock.

Synthesis of some halogen-containing 1,2,4-triazolo-1,3,4-thiadiazines and their antibacterial and anticancer screening studies--part I

A series of 7-arylidene-6-(2,4-dichloro-5-fluorophenyl)-3-substituted-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazines (3) were prepared by the condensation of 4-amino-5-mercapto-3-substituted-1,2,4-triazoles (1) and 3-aryl-1-(2,4-dichloro-5-fluorophenyl)-2-bromo-2-propen-1-one (2). An alternative route for the synthesis of the title compound 3 has been described. The newly synthesised compounds were characterised on the basis of N-analyses, IR, 1H NMR and mass spectral data. Some of the newly synthesised compounds were tested for their antibacterial activities against Gram + ve and Gram - ve bacteria. Among the tested compounds 3n showed the highest degree of antibacterial activity against S. aureus and evaluation of the LD50 value of this compound was carried out. Some of the newly synthesised compounds were also screened for their anticancer activities. Among these, compounds 3b, 3g, 3n and 3p are found to be active against NCI-H460 (lung), MCF7 (breast), SF 268 (CNS) in the preliminary anticancer screening studies. Further, 60-cell-line anticancer studies of these compounds were carried out. The results of such studies are discussed in this paper.

[The role of halogenation in the electro-oxidation of halogenated anilines in acetonitrile as the solvent]

The 4-halogeno-, 2,4-dihalogeno- and 2,4,6-trihalogenoanilines were the model substances of the research described. Acetonitrile being one of the most popular aprotic solvent was used. The halogeno monomers were chloro and bromoanilines. The electrodimerised substrate is stabilised by rejecting halogenide ion and protons. The rejected halogenide ions are oxidisable more easier compared to the substrate therefore the halogene formed substitutes both the substrate, and the dimer as well. The protons formed during the oxidation bind by the strong base monomer primary amine. Because of these not only a simple electrodimerisation will take place, but protonised monomers, higher halogenated monomers, and the corresponding dimer molecules are formed in the solution.

Pd(DIPHOS)2-catalyzed cross-coupling reactions of organoborons with free or polymer-bound aryl halides

Bis[1,2-bis(diphenylphosphino)ethane]palladium(0) [Pd(DIPHOS)2] catalyzes cross-coupling reactions of free or polymer-bound aryl halides with organoboron compounds to produce biaryls in overall yields of 60-96%.

Relationships between reduction properties and cancer cell growth inhibitory activities of cis-dichloro- and cis-diiodo-Pt(IV)-ethylenediamines

The chemical reactivities and cancer cell growth inhibitory activities of a new series of cis-diiodo-Pt(IV)-ethylenediamines were compared and contrasted with their cis-dichloro-Pt(IV)-counterparts, cis-Diiodo-Pt(IV)-ethylenediamines bearing various axial ligands (i.e., OH, OAc, OCOCF3, OSO2CH3) were prepared by oxidizing [PtI2(en)] with 30% H2O2 to yield trans,cis-[PtOH2I2(en)], which was then reacted with either Ac2O, (CF3CO)2O, or (SO2CH3)2O in CH2Cl2. The cis-diiodo-Pt(IV) complexes were readily reduced by biological thiols such as L-cysteine, glutathione (GSH), and bovine serum albumin (BSA) at pH 6.9 and 37 degrees C; the kinetics of reduction were second-order with respect to thiol concentration. In contrast, the cis-dichloro analogues were stable in the presence of GSH. The reduction potentials estimated by means of cyclovoltammetry for the Pt(IV) complexes are useful for obtaining a ranking order of reactivity towards biological thiols; however, the reduction potentials alone cannot be used to predict whether a Pt(IV) complex will be reduced by GSH at biologically relevant concentrations. GSH greatly facilitated the platination of calf thymus DNA by the diiodo-Pt(IV) complexes, which was > 90% complete after 24 h at 37 degrees C when the ratio of GSH to Pt(IV) was 2:1. DNA-platination by trans,cis-[Pt(OH)2I2(en)] and trans,cis-[Pt(OAc)2I2(en)] were dependent on the presence of GSH while trans,cis-[Pt(OSO2CH3)2I2(en)] showed 23% DNA platination after 24 h in the absence of GSH. In contrast, the dichloro analogues trans,cis-[Pt(OH)2Cl2(en)] and trans,cis-[Pt(OAc)2Cl2(en)] failed to react with DNA in the presence of either low (0.015 mM) to high (3.0 mM) concentrations of GSH. Cell culture experiments with four human cancer cell lines showed that the maximal growth inhibitory activity of the cis-diiodo-Pt(IV)-ethylenediamines was reached within a 24 h exposure to platinum complex, while the dichloro-Pt(IV) analogues required a much longer drug-exposure time (i.e., 96 h) to reach maximal activity.

Synthesis and characterization of bay region halohydrins derived from Benzo[a]pyrene diol epoxide and their role as intermediates in halide-catalyzed cis adduct formation

The bay region epoxide of benzo[a]pyrene (anti-BPDE) alkylates DNA to form adducts with >98% trans stereochemistry. Halide ions catalyze this reaction; however, this pathway is characterized by the formation of adducts with altered cis stereochemistry. Bay region halohydrins are possible intermediates in these reactions, but are too unstable to be isolated from aqueous solutions. However, we successfully synthesized halohydrins in tetrahydrofuran (THF) by treatment of anti-BPDE with the corresponding lithium halide salt in the presence of acetic acid. Absorbance and CD spectroscopy clearly indicated the formation of chloro-, bromo-, and iodohydrins. The structure and stereochemistry of the chlorohydrin was established by NMR. Chloride addition is exclusively at the benzylic position of the epoxide, and the stereochemistry of the C-9 and -10 positions is trans. The long-wavelength absorbance band in the chloro-, bromo-, and iodohydrin is red-shifted 7, 13, and 22 nm, respectively, relative to the hydrolysis product of anti-BPDE. The ellipticity of the same absorbance band in CD spectra of enantiomerically pure halohydrins is opposite in sign compared to that of the corresponding anti-BPDE enantiomer. The relative stability of these derivatives is chlorohydrin > bromohydrin > iodohydrin. The chloro- and bromohydrins were isolated, but the iodohydrin decomposed during this manipulation. The addition of 500 mM chloride decreased the hydrolysis rate of the chlorohydrin 4-fold in 50% THF/buffer. Direct evidence for the transient formation of the iodohydrin in aqueous buffer/acetone mixtures was obtained by absorbance spectroscopy. At 1 M chloride, bromide, and iodide, alkylation of deoxyadenosine by anti-BPDE in aqueous buffer yields 85, 91, and 92% cis adducts, respectively. In the absence of halide, alkylation of deoxyadenosine in buffer by anti-BPDE, the chlorohydrin, and the bromohydrin yields 32, 65, and 83% cis adducts, respectively.