Enantiomeric lignans with anti-β-amyloid aggregation activity from the twigs and leaves of Pithecellobium clypearia Benth

To develop potential agents for slowing the progression of Alzheimer′s disease, two pairs of new enantiomeric lignans, including a couple of rarely 8′,9′-dinor-3′,7-epoxy-8,4′-oxyneolignanes named (7S, 8S)- and (7R, 8R)-pithecellobiumin A (1a/1b) and a pair of 2′,9′-epoxy-arylnaphthalenes named (7R, 8R, 8′R)- and (7S, 8S, 8′S)-pithecellobiumin B (2a/2b) were separated by chiral high performance liquid chromatography (HPLC). Their planar structures were elucidated by spectroscopic data analyses. The absolute configurations were determined by comparing of experimental and calculated electronic circular dichroism (ECD). The inhibitory activity on Aβ aggregation of all optical pure compounds was tested by ThT assay. Interestingly, enantiomeric inhibitors 1a (62.1%) and 1b (81.6%) exhibited different degrees of anti-Aβ aggregation activity. However, 2a (65.4%) and 2b (68.4%) showed similar inhibition rate. The different inhibition profiles were explained by molecular dynamics and docking simulation studies.     

Synthesis of oligomethylene-strapped chlorophyll derivatives and optical properties of their stereoisomers in a solution

Methyl pheophorbide-a/a′ derivatives covalently linked with oligomethylene chains at the 3-CH₂OCO– and 13²-COO– moieties in a molecule were prepared by modifying chlorophyll-a through intramolecular ring-closing metathesis of vinyl groups. At least, a C10-length between the 3³- and 13⁴-positions was necessary for the cyclization and connection of a C12-strap was the most suitable to achieve the highest closure yield. The oligomethylene chain in 13² R-epimers derived from methyl pheophorbide-a covered the α-face of the chlorin π-plane and the strap in the corresponding 13² S-epimers protected the β-face. Synthetic 13² R-epimer with a dodecamethylene chain gave a flat chlorin π-plane, while the decamethylene chain in the 13² R-epimer distorted the π-system due to its shorter linkage. The distortion by strapping in the 13² R-epimer induced a slight blue-shift of Qy peak in dichloromethane. CD spectra of the 13² R-epimers were similarly dependent on the chain length, i.e., the distortion of π-plane. Visible absorption and CD spectra of all the strapped 13² S-epimers were almost identical and only slightly different from those of the unstrapped. The strapping in the 13² S-epimers shifted the Qy peak bathochromically.     

Constrained C-terminal hexapeptide neurotensin analogues containing a 3-oxoindolizidine skeleton

Summary In order to enforce different spatial orientations in the C-terminal hexapeptide of neurotensin (NT_8–13) and to gain information about the importance of the 10–11 peptide bond for binding to NT receptors, the Pro¹⁰-Tyr¹¹ fragment has been replaced with (2R,8S,8aR)-, (2S,8S,8aR)-, (2S,8S,8aS)-, (2S,8R,8aS)- and (2R,8R,8aS)-8-amino-2-benzyl-3-oxoindolizidine-2-carboxylic acid. Molecular dynamics calculations and energy minimization studies have shown that, contrarily to the Pro-Tyr moiety, none of these indolizidines display a tendency to adopt type I and III -turns, but those having (8S,8aR) or (8R,8aS) stereochemistry essentially adopt extended conformations and the (8S,8aS) stereoisomer prefers a nonstandard folding. The four diastereomeric NT_8–13 analogues incorporating (8S,8aR) or (8R,8aS) indolizidines displayed binding affinities for the brain NT receptor similar to that of [Ala¹¹]-NT_8–13 and only five- to ninefold lower than that of the corresponding analogue, [Phe¹¹]NT_8–13. Although this slight decrease could be attributed to differences in conformational behavior between these constrained NT_8–13 analogues and [Phe¹¹]NT_8–13 or NT_8–13, it is not clear whether the -turn around Pro¹⁰-AA¹¹ (AA=Phe, Tyr) is conserved upon receptor binding. An excessive restriction in the motions of the aromatic side chain, imposed by the highly steric constraint of the indolizidine moiety, emerges as an alternative explanation. The findings reported here demonstrate the possibility of replacing the Pro¹⁰-Tyr¹¹ dipeptide in NT_8–13 with a non-peptide residue without affecting considerably the affinity for brain NT receptors.     

Biosynthesis of pisatin: Experiments with enantiomeric precursors

Feeding experiments in cupric chloride-treated Pisum sativum pods and seedlings have demonstrated the preferential incorporation of (+)-(6aS,11aS)-[³H]maackiain over (?)-(6aR, 11aR)-[¹⁴C]maackiain into (+)-(6aR, 11aR)-pisatin, establishing that the 6a-hydroxylation of pterocarpans proceeds with retention of configuration. (+)- (6aR,11aR)-6a-hydroxymaackiain was similarly incorporated much better than (?)-(6aS,11aS)-6a- hydroxymaackiain. Where (?)-isomers were incorporated, optical activity measurements on the pisatin produced indicated significant synthesis of (?)-pisatin as well as the normal (+)-pisatin. 7,2′-Dihydroxy-4′,5′- methylenedioxyisoflav-3-ene and both enantiomers of 7,2′-dihydroxy-4′,5′-methylenedioxyisoflavan were poor precursors of pisatin.     

Characterization of chlorophyll pigments in the mutant lacking 8-vinyl reductase of green photosynthetic bacterium Chlorobaculum tepidum

The mutant lacking the enzyme BciA (renamed CT1063), which catalyzed reduction of the 8-vinyl group of a porphyrinoid-type 3,8-divinyl-(proto)chlorophyllide-a [DV-(P)Chlide-a] in the green sulfur bacterium Chlorobaculum (Cba.) tepidum, was reconstructed on the basis of the previous study reported by Chew and Bryant [J. Biol. Chem. 2007, 282, 2967–2975]. Cba. tepidum biosynthesizes the following three different types of chlorophylls (Chls) through their common precursory DV-(P)Chlide-a as its photosynthetically active pigments: bacteriochlorophyll(BChl)-c and Chl-a with the partially reduced 17,18-trans-dihydroporphyrin and BChl-a with the further reduced 7,8-trans-17,18-trans-tetrahydroporphyrin. The structures of Chls thus produced were characterized in detail by various spectroscopic techniques. In the mutant, both BChl-c and Chl-a possessing the alkyl group at the 8-position were exclusively replaced by their 8-vinylated derivatives, whereas BChl-a possessed the original 8-ethyl group. The present observations were inconsistent with the previous report. However, it was apparently confirmed that the enzyme BciA was responsible for the reduction of DV-(P)Chlide-a to produce BChl-c and Chl-a. Noteworthily, exclusive accumulation of the reduced (8-ethylated) form of BChl-a, not its 8-vinylated derivative, in the mutant indicates the presence of another enzyme catalyzing the 8-vinyl reduction as yet unidentified or any other reduction mechanism using a known enzyme to yield BChl-a.     

Repellent activity of catmint, Nepeta cataria, and iridoid nepetalactone isomers against Afro-tropical mosquitoes, ixodid ticks and red poultry mites

The repellent activity of the essential oil of the catmint plant, Nepeta cataria (Lamiaceae), and the main iridoid compounds (4aS,7S,7aR) and (4aS,7S,7aS)-nepetalactone, was assessed against (i) major Afro-tropical pathogen vector mosquitoes, i.e. the malaria mosquito, Anopheles gambiae s.s. and the Southern house mosquito, Culex quinquefasciatus, using a World Health Organisation (WHO)-approved topical application bioassay (ii) the brown ear tick, Rhipicephalus appendiculatus, using a climbing repellency assay, and (iii) the red poultry mite, Dermanyssus gallinae, using field trapping experiments. Gas chromatography (GC) and coupled GC-mass spectrometry (GC-MS) analysis of two N. cataria chemotypes (A and B) used in the repellency assays showed that (4aS,7S,7aR) and (4aS,7S,7aS)-nepetalactone were present in different proportions, with one of the oils (from chemotype A) being dominated by the (4aS,7S,7aR) isomer (91.95% by GC), and the other oil (from chemotype B) containing the two (4aS,7S,7aR) and (4aS,7S,7aS) isomers in 16.98% and 69.83% (by GC), respectively. The sesquiterpene hydrocarbon (E)-(1R,9S)-caryophyllene was identified as the only other major component in the oils (8.05% and 13.19% by GC, respectively). Using the topical application bioassay, the oils showed high repellent activity (chemotype A RD₅₀ = 0.081 mg cm⁻² and chemotype B RD₅₀ = 0.091 mg cm⁻²) for An. gambiae comparable with the synthetic repellent DEET (RD₅₀ = 0.12 mg cm⁻²), whilst for Cx. quinquefasciatus, lower repellent activity was recorded (chemotype A RD₅₀ = 0.34 mg cm⁻² and chemotype B RD₅₀ = 0.074 mg cm⁻²). Further repellency testing against An. gambiae using the purified (4aS,7S,7aR) and (4aS,7S,7aS)-nepetalactone isomers revealed overall lower repellent activity, compared to the chemotype A and B oils. Testing of binary mixtures of the (4aS,7S,7aR) and (4aS,7S,7aS) isomers across a range of ratios, but all at the same overall dose (0.1 mg), revealed not only a synergistic effect between the two, but also a surprising ratio-dependent effect, with lower activity for the pure isomers and equivalent or near-equivalent mixtures, but higher activity for non-equivalent ratios. Furthermore, a binary mixture of (4aS,7S,7aR) and (4aS,7S,7aS) isomers, in a ratio equivalent to that found in chemotype B oil, was less repellent than the oil itself, when tested at two doses equivalent to 0.1 and 0.01 mg chemotype B oil. The three-component blend including (E)-(1R,9S)-caryophyllene at the level found in chemotype B oil had the same activity as chemotype B oil. In a tick climbing repellency assay using R. appendiculatus, the oils showed high repellent activity comparable with data for other repellent essential oils (chemotype A RD₅₀ = 0.005 mg and chemotype B RD₅₀ = 0.0012 mg). In field trapping assays with D. gallinae, addition of the chemotype A and B oils, and a combination of the two, to traps pre-conditioned with D. gallinae, all resulted in a significant reduction of D. gallinae trap capture. In summary, these data suggest that although the nepetalactone isomers have the potential to be used in human and livestock protection against major pathogen vectors, intact, i.e. unfractionated, Nepeta spp. oils offer potentially greater protection, due to the presence of both nepetalactone isomers and other components such as (E)-(1R,9S)-caryophyllene.     

Synthesis of (R,S)-isoproterenol,an inhibitor of tau aggregation,as an 11C-labeled PET tracer via reductive alkylation of (R,S)-norepinephrine with [2-11C]acetone

(R,S)-Isoproterenol inhibits the formation of toxic granular tau oligomers associated with neuronal loss and development of cognitive disorders, and is an attractive drug candidate for Alzheimer’s disease. To elucidate its behavior in the brain by positron emission tomography, we synthesize (R,S)-[¹¹C]isoproterenol by reductive alkylation of (R,S)-norepinephrine with [2-¹¹C]acetone, which was in turn synthesized in situ under improved conditions afforded a decay-corrected radiochemical yield of 54%. The reductive alkylation using NaBH(OAc)₃ as reducing agent in the presence of benzoic acid in DMSO/DMF (60:40 v/v) at 100 °C for 10 min gave (R,S)-[¹¹C]isoproterenol in an 87% radio-high performance liquid chromatography (HPLC) analytical yield. HPLC separation using a strong cation exchange column, followed by pharmaceutical formulation in the presence of d/l-tartaric acid, afforded (R,S)-[¹¹C]isoproterenol with a total radioactivity of 2.0 ± 0.2 GBq, a decay-corrected radiochemical yield of 19 ± 2%, chemical and radiochemical purities of 71% and >99%, respectively, and a molar activity of 100 ± 13 GBq/μmol (n = 3). The overall synthesis time from the end of the bombardment to pharmaceutical formulation was 48 min. A preliminary preclinical PET study in a rat demonstrated the potential of the radioligand for the evaluation of the penetration of (R,S)-isoproterenol in human brain.     

Afritoxinones A and B,dihydrofuropyran-2-ones produced by Diplodia africana the causal agent of branch dieback on Juniperus phoenicea

Two phytotoxic dihydrofuropyran-2-ones, named afritoxinones A and B, were isolated from liquid culture of Diplodia africana, a fungal pathogen responsible for branch dieback of Phoenicean juniper in Italy. Additionally, six others known metabolites were isolated and characterized: oxysporone, sphaeropsidin A, epi-sphaeropsidone, R-(−)-mellein, (3R,4R)-4-hydroxymellein and (3R,4S)-4-hydroxymellein. The structures of afritoxinones A and B were established by spectroscopic and optical methods and determined to be as (3aS¹,6R¹,7aS)-6-methoxy-3a,7a-dihydro-3H,6H-furo[2,3-b]pyran-2-one and (3aR¹,6R¹,7aS)-6-methoxy-3a,7a-dihydro-3H,6H-furo[2,3-b]pyran-2-one, respectively. The phytotoxic activity of afritoxinones A and B and oxysporone was evaluated on host (Phoenicean juniper) and non-host plant (holm oak, cork oak and tomato) by cutting and leaf puncture assay. Oxysporone proved to be the most phytotoxic compound. This study represents the first report of secondary metabolites produced by D. africana. In addition, the taxonomic implications of secondary metabolites in Botryosphaeriaceae family studies are discussed.     

Argophyllone-B,a sesquiterpene lactone from Helianthus argophyllus

The sesquiterpene lactone, 2-methyl-2-butenoic acid dodecahydro-4-(hydroxymethyl)-10a-methyl-8-methylene-3,7-dioxooxineno[5,6]cyclodeca[1,2-b]furan-9-yl ester [1aR^*-[1aS^*,4R^*,5aS^*,8aR^*,9R^*(E)]], argophyllone-B, was isolated from acetone extracts from the leaves of Helianthus argophyllus. Its structure has been determined by single crystal X-ray analysis. Complete ¹H NMR and ¹³C NMR assignments have been made.     

Substituted α-mercaptoketones,new types of specific neprilysin inhibitors

New neprilysin inhibitors containing an α-mercaptoketone HSC(R¹R²)CO group, as zinc ligand were designed. Two parameters were explored for potency optimization: the size of the inhibitor which could interact with the S₁, S₁′ or S₂′ domain of the enzyme and the nature of the substituents R¹, R² of the mercaptoketone group. Introduction of a cyclohexyl chain in R¹, R² position and a (3-thiophen)benzyl group in position R³ (compound 12n) yielded to the most potent inhibitor of this series with a Ki value of 2 ± 0.3 nM. This result suggests that this new inhibitor interacts within the S₁, S₁′ domain of NEP allowing a pentacoordination of the catalytic Zn²⁺ ion by the mercaptoketone moiety.     

Isolation and characterization of a new bacteriochlorophyll-c bearing a neopentyl substituent at the 8-position from the bciD-deletion mutant of the brown-colored green sulfur bacterium Chlorobaculum limnaeum

We recently constructed the mutant of the brown-colored green sulfur bacterium Chlorobaculum limnaeum lacking BciD which was responsible for formation of a formyl group at the 7-position in bacteriochlorophyll(BChl)-e biosynthesis. This mutant exclusively gave BChl-c, but not BChl-e, as the chlorosome pigments (Harada et al. in PLoS One 8(4):e60026, 2013). By the mutation, the homolog and epimer composition of the pigment was drastically altered. The methylation at the 8²-position in the mutant cells proceeded to create BChl-c carrying large alkyl substituents at this position. Correspondingly, the content of BChls-c having the (S)-configuration at the chiral 3¹-position remarkably increased and accounted for 80.6 % of the total BChl-c. Based on the alteration of the pigment composition in the mutant cells, a new BChl-c bearing the bulkiest, triple 8²-methylated neopentyl substituent at the 8-position ([N,E]BChl-c) was identified. The molecular structure of [N,E]BChl-c was fully determined by its NMR, mass, and circular dichroism spectra. The newly identified [N,E]BChl-c was epimerically pure at the chiral 3¹-position and its stereochemistry was determined to be an (S)-configuration by modified Mosher’s method. Further, the effects of the C8²-methylation on the optical absorption properties of monomeric BChls-c were investigated. The Soret but not Qy absorption bands shifted to longer wavelengths by the extra methylation (at most 1.4 nm). The C8²-methylation induced a slight but apparent effect on absorption properties of BChls-c in their monomeric states.     

Characterization of bio-related vanadium and zinc complexes containing tetradentate dithiolate-disulfide, -diamine and -amine-amide ligands

The reaction of [VCl₃(PMe₂Ph)₃] _{with HSS′S′SH (where the HS are thiophenolate and the S′ thioether functions, respectively), H2–1, yields [VCl(μ-SS′S′S)]2 (3) with one of the thiolate groups of each of the two ligands in the bridging mode. Reaction of Na2–1 with [VOCl2(thf)2] leads to a polymeric product of composition [VO(SS′S′S)]x (4). The products obtained from the reaction between [VOCl2(thf)2] and NaSNNSNa, Na2–2, (S is thiophenolate, N the amine function) depend on subtle changes in the diamine backbone of this ligand: If the amine functions are linked by -CH2CH2– (2a), the tetranuclear V^IV complex [V(SNNS)μ-O]4 (5) is formed alongside the V^III complex [VCl(SNNS)]. If the backbone is -CH(Me)CH(Me)- (2b), [VO(SNNS)] (7) and the dinuclear, asymmetrically oxo-bridged V^IV complex [{(SNN ^– S)(thf)V}μ-O{V(SNN ^– S)}] (8) are obtained. In 8, one amine of each of the two ligands is deprotonated to the amide group. In either case, the complexation is accompanied by oxidation of the thiolates to disulfides, leading to the generation of teraazatetrathio-cycloeicosanes (6a/b). Compounds 5 and 8·2THF have been structurally characterized by X-ray analyses. The connectivities have further been established for 3·2CH2Cl2 and for 6b, which exhibits the same conformation as formally characterized 6a. The cluster compound 5 is stabilized by an extended intramolecular N-H...O and N-H...S) hydrogen-bonding network. In 7·2THF, one of the THFs of crystallization is hydrogen-bonded to the NH of the penta-coordinated {VO(SNN ^– S)} moiety; further, there is an intramolecular hydrogen bond between one of the thiolates of this tetragonal-pyramidal half of the molecule and the NH of the octahedral {VO(SNN ^– S)thf} half. The generation of the ligand 2b from its precursor compound, the zinc complex [Zn(SNNS)] (9) leads to the structural characterization of 9·CH3OH with a large SZnS bite angle and a strong hydrogen bond between the methanolic OH and one of the thiolate sulfurs. The relevance of these compounds in biological systems is discussed.}     

Flavonoids from Millettia pulchra

Chemical examination of Millettia pulchra yielded (?)-maackiain, (?)-pterocarpin, (?)-sophoranone and the new compounds (6S, 6aS, 11aR)-6α-methoxypterocarpin, (6S, 6aS,11aR)-6α-methoxyhomopterocarpin, (2S)5,7,4′-trihydroxy-8,3′,5′-triprenylflavanone, (2R,3R)7,4′-dihydroxy-8,3′,5′-triprenyldihydroflavanol, 5,7,2′,4′-tetrahydroxy-6,3′-diprenylisoflavone and 5,7,4′-trihydroxy-2′-methoxy-6,3′-diprenylisoflavone.     

Neolignans from an Aniba species

A benzene extract of the trunk of an Aniba species (Lauraceae) contained benzyl benzoate, benzyl salicylate, sitosterol and the neolignans (2S,3S,3aR)-3a-allyl-5-methoxy-3-methyl-2-piperonyl-2,3,3a,6-tetrahydro-6-oxobenzofuran (burchellin); (2S,3S,3aR)-3a-allyl-5-methoxy-3-methyl-2-veratryl-2,3,3a,6-tetrahydro-6-oxobenzofuran; (2S,3S,3aR)-3a-allyl-5,7-dimethoxy-3-methyl-2-veratryl-2,3,3a,6-tetrahydro-6-oxobenzofuran; (2S,3S,5S)-5-allyl-5-methoxy-3-methyl-2-veratryl-2,3,5,6-tetrahydro-6-oxo-benzofuran; (2R,3R)-7-methoxy-3-methyl-5-propenyl-2-veratryl-2,3-dihydrobenzofuran; rel-(1R,5R,6R,7R,8S)-1-allyl-8-hydroxy-3-methoxy-7-methyl-4-oxo-6-piperonylbicyclo[3,2,1]oct-2-ene (guianin); rel-(1S,5S,6S,7R,8R)-1-allyl-8-hydroxy-3,5-dimethoxy-7-methyl-4-oxo-6-piperonylbicyclo[3,2,1]oct-2-ene; rel-(1S,5S,6S,7R,8R)-8-acetoxy-1-allyl-3-hydroxy-5-methoxy-7-methyl-4-oxo-6-piperonyl-bicyclo[3,2,1]oct-2-ene; rel-1S,5S,6S,7R,8R)-8-acetoxy-3,5-dimethoxy-7-methyl-4-oxo-6-piperonylbicyclo[3,2,1]oct-2-ene; rel-(1R,5S,6R,7R)-1-allyl-3-methoxy-7-methyl-4,8-dioxo-6-piperonylbicyclo[3,2,1]oct-2-ene.     

22,23-Epoxides of Sitosterol and Related 7-Oxygenated Δ5-Sterols

(22S,23S)-22,23-Epoxysitosterol, (22R,23R)-22,23-epoxysitosterol, (22S, 23S)-22,23-epoxy-7-ketositosterol, (22R,23R)-22,23-epoxy-7-ketositosterol, (22S, 23S)-22,23-epoxy-7α-hydroxysitosterol, (22S,23S)-22,23-epoxy-7β-hydroxysitosterol, and (22R, 23R)-22,23-epoxy-7β-hydroxysitosterol were synthesized. Their ¹H and ¹³C NMR and the mass spectra of their trimethylsilyl derivatives were studied.     

Use of isotopically chiral [4′-13C]penciclovir and 13C NMR to determine the specificity and absolute configuration of penciclovir phosphate esters formed in HSV-1- and HSV-2-infected cells and by HSV-1-encoded thymidine kinase

Penciclovir is a potent antiherpesvirus agent which is highly selective due to its phosphorylation only in virus infected cells. Phosphorylation of one of the hydroxymethyl groups of penciclovir (PCV) creates a chiral centre leading to the possible formation of (R)- and (S)-enantiomers. The absolute configuration and stereospecificity of the PCV-phosphates produced in cells infected with herpes simplex viruses types 1 and 2 (HSV-1 and HSV-2), as well as by HSV-1-encoded thymidine kinase, were determined using isotopically chiral [4′-¹³C]PCV precursors and ¹³C NMR spectroscopy of the isolated metabolites. The absolute configuration of penciclovir-triphosphate (PCV-TP) produced in HSV-1-infected cells was shown to be S with an enantiomeric purity of greater than 95%. However, in contrast to HSV-1-infected cells in which none of the (R) enantiomer was detected, about 10% of (R)-PCV-TP was produced in HSV-2-infected cells. Phosphorylation of PCV by HSV-1-encoded thymidine kinase was found to give 75% (S)- and 25% (R)-PCV-monophosphate. The proportion of the (S)-isomer appears to be amplified in the subsequent phosphorylations leading to the triphosphate. © 1993 Wiley-Liss, Inc.     

Methylenecyclopropane Analogues of Nucleosides: Synthesis,Absolute Configuration,and Enantioselectivity of Antiviral Effect of (R)-(-)- and (S)-(+)-Synadenol

Abstract

Synthesis, absolute configuration and antiviral activity of enantiomeric antiviral agents (R)-(-)- and (S)-(+)-synadenol (2 and 3a) are described.     

Synthesis of hydroxyeicosatetraenoic (HETEs) and epoxyeicosatrienoic acids (EETs) by cultured bovine coronary artery endothelial cells

Endothelial cells release several factors which influence vascular tone, leukocyte function and platelet aggregation. Some of these factors are metabolites of arachidonic acid, most notably prostacyclin. However, many of the endothelial metabolites of arachidonic acid have not been positively identified. The purpose of these studies is to identify the arachidonic acid metabolites synthesized by bovine coronary endothelial cells. Cultured bovine coronary artery endothelial cells were incubated with [ ¹⁴C]arachidonic acid. The incubation media was extracted and the radioactive metabolites resolved by a combination of reverse phase- and normal phase-high pressure liquid chromatography (HPLC). The cells synthesized 6-keto prostaglandin (PG)F_1α, PGE₂, 12-hydroxyheptadecatrienoic acid (HHT), 12-, 15-, and 11- hydroxyeicosatetraenoic acids (HETE), and 14,15-, 11,12-, 8,9-, and 5,6-epoxyeicosatrienoic acids (EET). Several of the HETEs were further analyzed by chiral-phase HPLC. The cells synthesized predominately 12(S)-, 15(S)-, and 11(R)-HETE. The synthesis of the S optical isomers of 12- and 15-HETE suggested that the 12- and 15-lipoxygenases were present in these cells. 11(R)-HETE is probably derived from cyclooxygenase. They also synthesized smaller amounts of 9-, 8- and 5-HETEs. The structures of the HETEs and EETs were confirmed by mass spectrometry. The release of 6-keto PGF_1α and 15-HETE was measured by specific radioimmunoassays. Melittin, thrombin, arachidonic acid and A23187 stimulated the release of both eicosanoids in a concentration-related matter. Under all conditions, the release of 6-keto PGF_1α exceed the release of 15-HETE. Therefore, cultured bovine coronary artery endothelial cells synthesize cyclooxygenase, lipoxygenase and cytochrome P-450 metabolites of arachidonic acid.     

Synthesis and structure of dichloropalladium(II) complexes of heteroleptic N,S- and N,Se-donor ligands based on the 2-organochalcogenomethylpyridine motif, and Mizoroki-Heck catalysis mediated by complexes of N,S-donor ligands

Ligands containing the 2-organochalcogenomethylpyridine motif with substituents in the 4- or 6-position of the pyridyl ring, R⁴,R⁶-pyCH₂ER¹ [R⁴ = R⁶ = H, ER¹ = SMe (1), SeMe (2), SPh (6), SePh (7); R⁴ = Me, R⁶ = H, ER¹ = SMe (3), SPh (8), SePh (9); R⁴ = H, R⁶ = Me, ER¹ = SMe (4), SPh (10), SePh (11); R⁴ = H, R⁶ = Ph, ER¹ = SMe (5), SPh (12), SePh (13)] are obtained on the reaction of R⁴,R⁶-pyMe with LiBuⁿ followed by R¹EER¹. On reaction with PdCl₂(NCMe)₂, the ligands with a 6-phenyl substituent form cyclopalladated species PdCl{6-(o-C₆H₄)pyCH₂ER¹-C,N,E} (5a, 12a, 13a) with the structure of 13a (ER¹ = SePh) confirmed by X-ray crystallography; other ligands form complexes of stoichiometry PdCl₂(R⁴,R⁶-pyCH₂ER¹). Complexes with R⁶ = H are monomeric with N,E-bidentate configurations, confirmed by structural analysis for 3a (R⁴ = Me, ER¹ = SMe), 7a (R⁴ = H, ER¹ = SePh) and 9a (R⁴ = Me, ER¹ = SePh). Two of the 6-methyl substituted complexes examined by X-ray crystallography are oligomeric with trans-PdCl₂(N,E) motifs and bridging ligands, trimeric [PdCl₂(μ-6-MepyCH₂SPh-N,S)]₃ (10a) and dimeric [PdCl₂(μ-6-MepyCH₂SePh-N,Se)]₂ (11a). This behaviour is attributed to avoidance of the Me···Cl interaction that would occur in the cis-bidentate configuration if the pyridyl plane had the same orientation with respect to the coordination plane as observed for 3a, 7a and 9a [dihedral angles 8.0(2)-16.8(2)°]. When examined as precatalysts for the Mizoroki-Heck reaction of n-butyl acrylate with aryl halides in N,N-dimethylacetamide at 120 °C, the complexes exhibit the anticipated trends in yield (ArI > ArBr > ArCl, higher yield for electron withdrawing substituents in 4-RC₆H₄Br and 4-RC₆H₄Cl). The most active precatalysts are PdCl₂(R⁴-pyCH₂SMe-N,S) (R = H (1a), Me (3a)); complexes of the selenium containing ligands exhibit very low activity. For closely related ligands, the changes SMe to SPh, 6-H to 6-Me, and 6-H to 6-Ph lead to lower activity, consistent with involvement of both the pyridyl and chalcogen donors in reactions involving aryl bromides. The precatalyst PdCl₂(pyCH₂SMe-N,S) (1a) exhibits higher activity for the reaction of aryl chlorides in Buⁿ₄NCl at 120 °C as a solvent under non-aqueous ionic liquid (NAIL) conditions.     

Absolute configuration and stereochemical analysis of 3α,6β-dibenzoyloxytropane

Both enantiomers of 3α,6β-dibenzoyloxytropane (1) have been prepared from optical active 6β-hydroxyhyoscyamines establishing their absolute configurations as (?)-(3R,6R) and (+)-(3S,6S)-dibenzoyloxytropane. Independent stereochemical confirmation was obtained by vibrational circular dichroism measurements, since bands characteristic of (3R,6R) and (3S,6S) configurations of tropanediols derivatives were observed. In addition, a chiral HPLC method was developed for determining absolute configurations of tropane-related natural substances at the microgram (μg) level. The complete ¹H NMR characterization of the scaffold of 1 is also reported.