Synthesis, reactivity, electrochemical and crystallographic studies of diferrocenoyl diselenide and ferrocenoyl selenides

Diacyl diselenide (8), diacyl selenide (9) and acyl selenol esters (10-12) incorporating the ferrocenoyl substituent have been synthesized from ferrocene carboxylic acid (13). The new compounds (8-10) have been characterized by multinuclear NMR (¹H, ¹³C, ⁷⁷Se), IR spectroscopy and electrospray mass spectrometry. All compounds (8-13) undergo a one electron reversible oxidation at significantly more positive potential than ferrocene. The structures of the diselenide and selenide (8 and 10) have been confirmed by single crystal X-ray diffraction. The absolute structure parameter of 8 indicates that it crystallizes in an enantiomerically pure form. The peroxidase-like activities of the diselenide (8) and selenides (9-12) have been determined by the thiol assay.     

Photobehaviour of 2- and 3-heteroaryl substituted o-divinylbenzenes; formation of fused 2,3- and 3,2-heteroareno-benzobicyclo[3.2.1]octadienes and 3-heteroaryl benzobicyclo[2.1.1]hexenes

New β-3-thienyl (8) and β-3-furyl derivatives of o-divinylbenzene (9) have been synthesised and their photochemical behaviour compared with 2-thienyl (7) and 2-furyl derivatives (2). Whereas the β-(2-heteroaryl) substituted o-divinylbenzenes (7 or 2) give only bicyclo[3.2.1]octadiene structure (14 or 1) by 1,6-ring closure of the biradical intermediate, β-(3-heteroaryl) substituted o-divinylbenzenes (8 or 9) give bicyclo[3.2.1]octadiene structure (23 or 24) and bicyclo[2.1.1]hexene structure (25 or 26) by 1,6- and 1,4-ring closure, respectively. This photochemical approach provides a simple method to 2,3- and 3,2-fused thiophene and furan polycyclic compounds.     

Novel cyclopropyl diketones and 14-membered macrolides from the soil fungus Hamigera avellanea BCC 17816

Two novel cyclopropyl diketones, hamavellone A (1) and B (2), and two new 14-membered nonaketide macrolactones, hamigeromycin A (3) and B (4), together with six known compounds, 89-250904-F1 (radicicol analogue A, 5), pseurotin A (6), emodin (7), ω-hydroxyemodin (8), and emodin bianthrones (9 and 10) were isolated from the soil fungus Hamigera avellanea BCC 17816. The structures of the new compounds were defined by analysis of NMR and MS data. The absolute stereochemistry of 3 was addressed by chemical correlation to 5. Hamavellone B (2) exhibited antimalarial activity with an IC₅₀ of 5.2 μg/mL, whereas it also showed comparable cytotoxicity.     

Zn-promoted regio- and sequence-selective one-pot joining reactions of three components: vinylpyridines, alkyl iodides, and carbonyl compounds (or nitriles)

Addition of alkyl iodides (3) into the solution containing 2-(or 4-)vinylpyridine (1 or 2) and carbonyl compounds (6) in the presence of Zn-powder (99.9%) in acetonitrile under refluxing brought about regio- and sequence-selective joining reaction of three components to give the corresponding (2-hydroxyethyl)pyridines (7 or 8) in good to moderate yields. On the other hand, 2-(2- or 4-pyridyl)ethyl alkyl ketones (10 or 11) were obtained from the similar joining reaction of three components by addition of alkyl iodides (3) into the solution of 2-(or 4-)vinylpyridine (1 or 2), and nitriles (9) in toluene containing Zn-powder (99.9%) under the similar reaction conditions.     

Structures of enzymatic oxidation products of epigallocatechin

To understand the structures of uncharacterized black tea polyphenols, the oxidation products of (−)-epigallocatechin were investigated. Enzymatic oxidation and subsequent heating of the reaction mixture afforded four new oxidation products (6, and 9–11) along with theasinensins C (4) and E (5), dehydrotheasinensin E (12), epitheaflagallin, hydroxytheaflavin, and desgalloyl oolongtheanin. The structures of the new compounds were determined chemically and spectroscopically. Isotheasinensin E (6) is a C-2 epimer of 5, and compounds 9 and 10 are oxidation products of 12. Another new compound, 11, is a yellow pigment and presumed to be a degradation product of proepitheaflagallin. The results disclosed new oxidation mechanisms that occur during black tea production.     

Efficient and regioselective chromium(0)-catalyzed reaction of 2-substituted furans with diazo compounds: stereoselective synthesis of (2E,4Z)-2-aryl-hexadienedioic acid diesters

Pentacarbonyl(η²-cis-cyclooctene)chromium(0) (1) catalyzes efficiently reactions of diazo compounds with electron-rich furans. The reaction of 2-methoxyfuran (2) with alkyl α-diazoarylacetate (3a-g) furnishes the (2E,4Z)-2-aryl-hexadienedioic acid diesters (4a-g) in excellent yields. These reactions are highly regioselective. The cyclopropanation intermediates formed from 1 and diazo compounds 3a-g always arise from a carbene addition to the less substituted CC bond of 2. The resulting cyclopropanation product undergoes a ring opening reaction to form the corresponding (2E,4Z)-2-aryl-hexadienedioic acid diesters (4a-g). The pentacarbonylchromium(0)-catalyzed reactions of 2-alkylfuran (5a-b) with ethyl α-diazophenylacetate (3a) and 9-diazo-9H-fluorene (3h) produce the 1(E),3(E)-butadienes (6a-d) in very good yields.     

Synthesis and electrochemical studies of ferrocene-dithiafulvalenes (Fc-DTF) and 1,1′-bis(dithiafulvalenyl)ferrocene (DTF-Fc-DTF). An approach towards new conducting organic materials

Novel π-conjugated donor compounds based on the strong electron-donating ferrocene moiety and dithiafulvalene donors exhibited increased electron donor ability. The ferrocenylketones 4a,b, 5, 8 and 9 were synthesized via described methods, and allowed to react with 2-dimethoxyphosphinyl-1,3-benzodithiole (13) in the presence of n-BuLi at −78°C in dry THF to afford the corresponding ferrocene-dithiafulvalenes 14a,b, 18, 19 and 1,1′-bis(benzo-1,3-dithiol-2-ylidene)ethyl]ferrocene (15). Electrochemical properties of these new donor compounds were studied using cyclic voltammetry (CV) and UV-Vis spectra. CV and absorption spectra of the new compounds were studied in comparison with ferrocene (6) and dibenzo-tetrathiafulvalene DB-TTF 3. Two-electron and three-electron redox behaviors were observed as two waves. The absorption spectra showed a red-shift with a slight increase in the absorption intensities.     

Further studies on the constituents of the gorgonian octocoral Pseudopterogorgia elisabethae collected in San Andrés and Providencia islands, Colombian Caribbean: isolation of a putative biosynthetic intermediate leading to erogorgiaene

Chemical investigations of the MeOH-CH₂Cl₂ extract of Pseudopterogorgia elisabethae specimens collected in the islands of San Andrés and Providencia, Colombian Caribbean, yielded four new diterpenes (1, 3, 5, 7) along with seco-pseudopterosin J (8), and amphilectosins A (9) and B (10). The structures of the new compounds were established through spectral studies as an elisabethatriene analog named elisabethatrienol (1), 10-acetoxy-9-hydroxy- and 9-acetoxy-10-hydroxy-amphilecta-8,10,12,14-tetraenes (isolated as an interconverting mixture) (3), amphilecta-8(13),11,14-triene-9,10-dione (5), and a seco-pseudopterosin 7-O-α-l-fucopyranoside named seco-pseudopterosin K (7). Elisabethatrienol can be regarded as a biosynthetic intermediate leading to erogorgiaene.     

The high-temperature alicyclic ring contraction of 1,1-dichloroperfluorotetralin and the alicyclic ring opening of 1,1-dichloroperfluorobenzocyclobutene

The pyrolysis of 1,1-dichloroperfluorotetralin (4) in a stream of argon gives a mixture contained perfluoro-1-methyleneindan (1), perfluoro-3-methylindene (6), 1,1-dichloroperfluoroindan (2) and perfluoroindene (7), while copyrolysis of tetralin 4 with CHClF₂ gives a mixture of compounds 1, 6 in the absence of compounds 2 and 7. 1-Chloro-2-(1-chloro-2,2-difluorovinyl)-3,4,5,6-tetrafluorobenzene (12) is formed in the pyrolysis of 1,1-dichloroperfluorobenzocyclobutene (5) in a stream of argon as well as in a stream of CHClF₂.     

Syntheses and bioactivities of tricyclic pyrones

In search of compounds that ameliorate the toxicity of amyloid-β (Aβ) peptides, new derivatives of tricyclic pyrones (1-7) were synthesized and their biological activities evaluated. The carboxylic ester and amide derivatives 1-4 were synthesized from a selective carboxylation of C3 methyl of (5aS,7S)-{7-Isopropenyl-3-methyl-1H,7H-5a,6,8,9-tetrahydro-1-oxopyrano[4,3-b][1]benzopyran (8) with LDA followed by benzyl chloroformate or carbon dioxide to provide ester 1 and carboxylic acid 9, respectively. Three isomeric tricyclic pyrone, 5-7, containing adenine moiety at C7 side chain were synthesized from the alkylation of mesylate 13 with adenine, and displacement of chloropurine 15 with amine 14. Although C3-benzyloxycarbonylmethyl analogs 1-3 have marginal ACAT and CETP activities, their modified aspartate analog 4 and C3-methyl-C7-(N3-adeninyl)-2-propyl analog 6 show a significant effect in protecting against neuron-cell death from the toxicity of intracellular accumulation of Aβ or Aβ-containing C-terminal fragments (CTF) of amyloid β precursor protein (APP). N9-Adenine analog 5 is 20-fold less effective than N3-adenine derivative 6 in the protection of neuron-cell death induced by Aβ, while N10-adenine analog 7 was inactive. As a result of this study, compounds 4 and 6 will well serve as lead compounds for further studies of the mechanism of action of Aβ-and CTF-induced neuron-cell death, studies which should enhance the future development of new drugs for the prevention and treatment of AD.     

Fluorinated molecules relevant to conducting polymer research

The synthesis of versatile fluorine compounds for conducting polymer research on fluorinated materials is presented. 1,2,4,5-Tetrafluorobenzene was converted to 1,2,4,5-tetrafluorobenzaldehyde (1) and protected as an acetal. This gave the acetals 1,2,4,5-tetrafluoro-3-(1,3-dioxol-2-yl)benzene (2a) and 1,2,4,5-tetrafluoro-3-(5,5-dimethyl-1,3-dioxan-2-yl)benzene (2b). Compounds 2a and 2b were converted into the semiprotected 2,3,5,6-tetrafluoroterephthaldehydes: 1,2,4,5-tetrafluoro-3-(1,3-dioxol-2-yl)-6-formylbenzene (3a) and 1,2,4,5-tetrafluoro-3-(5,5-dimethyl-1,3-dioxan-2-yl)-6-formylbenzene (3b). While 3a was easily deprotected to give 2,3,5,6-tetrafluoroterephthaldehyde (4) compound 3b proved very resilient to hydrolysis and gave a 1:1 mixture of 4 and 1,2,4,5-tetrafluoro-3,6-bis(5,5-dimethyl-1,3-dioxan-2-yl)benzene (5). Compound 4 was reduced to 1,2,4,5-tetrafluoro-3,6-dihydroxymethylbenzene (6) and converted into 1,2,4,5-tetrafluoro-3,6-dibromomethylbenzene (7). Compound 7 was finally converted into 1,2,4,5-tetrafluoro-3,6-bis(diethylphosponylmethyl)benzene (8). Compounds 4 and 8 are versatile fluorinated molecules that can be used to replace their hydrogen counterparts in many molecules and materials. To illustrate this compounds 4 and 8 were oligomerised to give partially fluorinated polyphenylenevinylene (9).     

New C21 Δ pregnanes, inhibitors of mitochondrial respiratory chain, from Indopacific octocoral Carijoa sp.

Two new compounds, pregnanes 1 and 2, the known pregnane 3 and a series of known chlorinated prostanoids (4-9) have been isolated from the Indian octocoral Carijoa sp. Their structures have been elucidated by spectroscopic methods, mainly by 1D and 2D NMR. The new compounds were potent inhibitors of the mitochondrial respiratory chain.     

Aigialomycins and related polyketide metabolites from the mangrove fungus Aigialus parvus BCC 5311

Reinvestigation of the secondary metabolites from the marine mangrove fungus Aigialus parvus BCC 5311 led to the isolation of six new nonaketide metabolites, aigialomycins F (4) and G (5a/5b), 7′,8′-dihydroaigialospirol (7), 4′-deoxy-7′,8′-dihydroaigialospirol (8), and rearranged macrolides 9 and 10, along with six previously described compounds, hypothemycin (1), aigialomycins A (2) and B (3), aigialospirol (6), 4-O-demethylhypothemycin (11), and aigialone (12). The structures of the new compounds were elucidated by analyses of the NMR spectroscopic and mass spectrometry data in combination with chemical means.     

Highly enantioselective synthesis and potential biological activity of chiral novel nucleoside analogues containing adenine and naturally phenol derivatives

This paper described an efficient synthetic strategy for chiral acyclic nucleoside analogues containing both the phenoxy components of some bioactive natural compounds and a heterocyclic base. The phenoxy components with adenine moiety were incorporated into the chiral acyclic nucleoside analogues through two key synthetic tactics. Chiron 5-(R)-menthyloxy-2(5H)-furanone 5 was obtained in good yield from the cheap starting material furfural via a valuable synthetic route. The asymmetric Michael addition of 5 with adenine and the subsequent reduction reaction afforded the key chiral intermediate, 2-(R)-(9′-adeninyl)-1,4-butanediol 8. The absolute configuration of 8 was established by X-ray crystallography. The intermolecular dehydration reaction between 2-(9′-adeninyl)-1,4-butanediol 8 and phenoxy components 9 on treatment with diethyl azodicarboxylate and triphenylphosphine was carried out to give the chiral acyclic nucleoside analogues 1a-1e. The regioselectivity of the reaction was established by NMR methods, especially through ¹³C NMR shifts and NOE effect observed in the target molecule 1c, as well as by HMBC/HMQC experiments. The target compounds were tested for inhibition of cytopathogenicity against different cancer cells and exhibited potential anticancer activity.     

Cobalt(II), nickel(II) and zinc(II) coordination compounds derived from aromatic amines

The structural and spectroscopic characterization of coordination compounds of four aromatic amines derived from benzimidazole, 2-aminobenzimidazole (L1), 1-(S-methylcarbodithioate)-2-aminobenzimidazole (L2), 2-(2-aminophenyl)-1H-benzimidazole (L3) and 6,6-dimethyl-5H-benzimidazolyl[1,2-c]quinazoline (L4) are reported. Cobalt(II) [Co(L1)₂(CH₃COO)₂] (1) and nickel(II) [Ni(L1)₂(CH₃COO)₂] (2) acetate coordination compounds of L1 are discussed. The synthesis and the X-ray crystal structure of the new 1-(S-methylcarbodithioate)-2-aminobenzimidazole (L2) is informed, together with its cobalt(II) [Co(L2)₂Cl₂] (3), [Co(L2)₂Br₂] (4) and zinc(II) [Co(L2)₂Cl₂] (5), [Zn(L2)₂Br₂] (6) coordination compounds. In these compounds the imidazolic nitrogen is coordinated to the metal center, while the ArNH₂ and the S-methylcarbodithioate groups do not participate as coordination sites. A co-crystal of L1 and L2 is analyzed. Structural analyses of the coordination compounds of L3 showed that this ligand behaves as a bidentate ligand through the aniline and the imidazole groups forming six membered rings in the cobalt(II) [Co(L3)Cl₂] (7) and zinc(II) [Zn(L3)Cl₂] (8) compounds, as well as the nickel(II) nitrate [Ni(L3)₂(H₂O)₂](NO₃)₂ (9). The quinazoline L4 was produced by insertion of one acetone molecule and water elimination in L3, its X-ray crystal diffraction analysis, as well as that of its zinc(II) coordination compound [Zn(L4)₂Cl₂] (10), are discussed.     

Highly stereoselective synthesis of para-substituted (E)-N-styrylcarbazoles via sequential silylative coupling-Hiyama coupling reaction

A series of new para-substituted (E)-(N)-styrylcarbazoles, i.e., eight (E)-9-[2-(aryl)ethenyl]-9H-carbazoles (5-12) and 1,4-bis[(E)-2-(9H-carbazol-9-yl)vinyl]benzene (13), have been synthesized in high yield and stereoselectively by a sequential silylative coupling-Hiyama coupling reaction, i.e., coupling of commercially available 9-vinylcarbazole with vinyltriethoxysilane or divinyltetramethyldisiloxane in the presence of [RuHCl(CO)(PCy₃)₂] (I), followed by Pd (II) catalyzed cross-coupling with para-substituted iodobenzenes.The tandem procedure has facilitated the synthesis of 13. X-ray structures of the intermediate silylvinylcarbazole (4), as well as products 12 and 13 have been obtained.     

Identification and synthesis of volatiles released by the myxobacterium Chondromyces crocatus

Cultures of the myxobacterium Chondromyces crocatus on agar plates were analysed by closed-loop-stripping analysis or solid phase micro extraction. The odour profiles consist mainly of pyrazines, sesquiterpenoids and some aromatic compounds, summing up to more than 50 components. Several new pyrazines as 2-(1-hydroxy-1-methylethyl)-3-methoxypyrazine (9), 2-(1-hydroxy-1-methylpropyl)-3-methoxypyrazine (10), and 2-(1-hydroxy-2-methylpropyl)-3-methoxypyrazine (11) were identified besides several known pyrazines. A major pyrazine occurring in most samples was 2,5-bis-(1-methylethyl)pyrazine (3). While the well known sesquiterpenoid geosmin (1) was present in low amounts, the related compound (1(10)E,5E)-germacradien-11-ol (21) was identified in most samples in larger quantities. Other prominent sesquiterpenoids not reported before from microorganisms were (6S,10S)-6,10-dimethylbicyclo[4.4.0]dec-1-en-3-one (16), which was accompanied by smaller amounts of several derivatives. The biosynthesis of these compounds is discussed in relation to the recently proposed biosynthetic pathways to 1 and 21.     

Selective lithiation of 1,6-dihalohex-1-enes and 1,6-dihalohex-1-ynes

The lithiation of 1-choro- and 1-bromo-6-chlorohex-1-yne (2, 3) with lithium naphthalene in the presence of benzaldehyde in THF at −78 °C leads after hydrolysis with water to the corresponding chloroalkynol (5) resulting from a regioselective lithiation at the alkynylic position. However, the lithiation of 1-chloro-6-iodohex-1-yne (4) under the same reaction conditions and using pentan-3-one as electrophile leads to the corresponding chloroalcohol (6) from the exclusive lithiation at the aliphatic carbon-iodine bond. Double lithiation of compounds 2 and 3 under Barbier conditions allows the isolation of diols (9), whereas the two-step process leads to differently substituted diols 13. The monolithiation of (E)-1-bromo-6-chlorohex-1-ene (14) under the above conditions and using pentan-3-one as electrophile affords a mixture of chloroalcohols 15 and 16, the process being not stereospecific. However, the lithiation of the same starting material with t-BuLi leads exclusively to a bromine-lithium exchange with retention of the configuration, so after treatment with pentan-3-one only compound 16 was isolated. Finally, whereas double lithiation of compound 14 under the conditions for compounds 9 gives the mixture of compounds 18 and 19, the tandem process involving the t-BuLi-promoted bromine-lithium exchange as the first step followed by lithiation under DTBB-catalysed conditions allows the isolation of (E)-diols 19 as the only reaction products isolated.     

Pelseneeriol-1 and -2: new furanosesquiterpene alcohols from porostome nudibranch Doriopsilla pelseneeri

The paper reports the first chemical study of the porostome nudibranch Doriopsilla pelseneeri collected off the Portuguese coast (Atlantic Ocean). Two new furanosesquiterpene alcohols, pelseneeriol-1 (1) and pelseneeriol-2 (2), have been isolated together with known compounds, 15-acetoxy-ent-pallescensin-A (5), and dendocarbin-A (6), from the mantle of the nudibranch, whereas euryfuran (3) and drimane ester mixture 4 were identified in the extract of the internal glands. The structures of 1 and 2 have been determined by extensive spectroscopic studies as well as by comparison with literature model compounds. In order to assess the relative stereochemistry of 1 and 2, full NMR assignment of related sponge metabolite microcionin-2 (8) and of co-occurring sesquiterpenes 9-11, that have been re-isolated from the Mediterranean sponge Fasciospongia cavernosa, has been also conducted. In particular, the relative stereochemistry of tricyclic sesquiterpene microcionin-1 (9) has now been rigorously assigned by detailed analysis of NOE difference experiments.     

[60]Fullerene adducts with 9-substituted anthracenes: mechanochemical preparation and retro Diels-Alder reaction

Three 9-substituted anthracene derivatives, that is, 9-hydroxymethylanthracene (2), 9-methoxymethylanthracene (3) and bis(9-anthrylmethyl) adipate (6), were chosen as the model compounds to evaluate the reactivity in their Diels-Alder reactions with [60]fullerene and in retro Diels-Alder reactions of the formed cycloadducts. Corresponding adducts 4, 5 and 7 were prepared in high yields under solvent-free conditions using high-speed vibration milling technique. In order to determine thermal stabilities of adducts 4, 5 and 7, their dissociations in the temperature range of 40-65 °C were investigated. Fitting the dissociation rates and temperatures to the Arrhenius equation gives the activation energies of 25.8, 21.8 and 24.9 kcal/mol for compounds 4, 5 and 7, respectively.