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1.
Am J Bot ; 109(10): 1652-1671, 2022 10.
Artigo em Inglês | MEDLINE | ID: mdl-36164832

RESUMO

PREMISE: Understanding evolutionary history and classifying discrete units of organisms remain overwhelming tasks, and lags in this workload concomitantly impede an accurate documentation of biodiversity and conservation management. Rapid advances and improved accessibility of sensitive high-throughput sequencing tools are fortunately quickening the resolution of morphological complexes and   thereby improving the estimation of species diversity. The recently described and critically endangered Banksia vincentia is morphologically similar to the hairpin banksia complex (B. spinulosa s.l.), a group of eastern Australian flowering shrubs whose continuum of morphological diversity has been responsible for taxonomic controversy and possibly questionable conservation initiatives. METHODS: To assist conservation while testing the current taxonomy of this group, we used high-throughput sequencing to infer a population-scale evolutionary scenario for a sample set that is comprehensive in its representation of morphological diversity and a 2500-km distribution. RESULTS: Banksia spinulosa s.l. represents two clades, each with an internal genetic structure shaped through historical separation by biogeographic barriers. This structure conflicts with the existing taxonomy for the group. Corroboration between phylogeny and population statistics aligns with the hypothesis that B. collina, B. neoanglica, and B. vincentia should not be classified as species. CONCLUSIONS: The pattern here supports how morphological diversity can be indicative of a locally expressed suite of traits rather than relationship. Oversplitting in the hairpin banksias is atypical since genomic analyses often reveal that species diversity is underestimated. However, we show that erring on overestimation can yield negative consequences, such as the disproportionate prioritization of a geographically anomalous population.


Assuntos
Proteaceae , Austrália , Filogenia , Proteaceae/genética , Evolução Biológica , Biodiversidade
2.
Evolution ; 76(6): 1209-1228, 2022 06.
Artigo em Inglês | MEDLINE | ID: mdl-35304742

RESUMO

The expansions and contractions of a species' range in response to temporal changes in selective filters leave genetic signatures that can inform a more accurate reconstruction of their evolutionary history across the landscape. After a long period of continental decline, Australian rainforests settled into localized patterns of contraction or expansion during the climatic fluctuations of the Quaternary. The environmental impacts of recurring glacial and interglacial periods also intensified the arrival of new lineages from the Sunda shelf, and it can be expected that immigrant versus locally persistent taxa responded to environmental challenges in quantifiably different manner. To investigate how such differences impact on species' distribution, we contrast landscape genomic patterns and changes in habitat availability between a species with a long continental history on Doryphora sassafras and a Sunda-derived species (Toona ciliata), across a distributional overlap. Extensive landscape-level homogeneity across chloroplast and nuclear genomes for the Sunda-derived T. ciliata, characterize the genetic signature of a very recent invasion and a rapid southern "exploratory" expansion that had not been previously recorded in the Australian flora (i.e., of Gondwanan origin or Sahul-derived). In contrast, D. sassafras is consistent with other Sahul-derived species characterized by strong geographical divergence and regional differentiation. Interestingly, our findings suggest that admixture between genetically divergent populations during expansion events might be a contributing factor to the successful colonization of novel habitats. Overall, this study identifies some of the mechanisms regulating the rearrangements in species distributions and assemblage composition that follow major environmental shifts, and reminds us how a species' current range might not necessarily define species' habitat preference, with the consequence that estimates of past or future range might not always be reliable.


Assuntos
Ecossistema , Variação Genética , Austrália , Evolução Biológica , Mudança Climática , Geografia
3.
Heredity (Edinb) ; 123(4): 532-548, 2019 10.
Artigo em Inglês | MEDLINE | ID: mdl-31243348

RESUMO

Niche partitioning can lead to differences in the range dynamics of plant species through its impacts on habitat availability, dispersal, or selection for traits that affect colonization and persistence. We investigated whether niche partitioning into upland and riparian habitats differentiates the range dynamics of two closely related and sympatric eastern Australian trees: the mountain water gum (Tristaniopsis collina) and the water gum (T. laurina). Using genomic data from SNP genotyping of 480 samples, we assessed the impact of biogeographic barriers and tested for signals of range expansion. Circuit theory was used to model isolation-by-resistance across three palaeo-environment scenarios: the Last Glacial Maximum, the Holocene Climate Optimum and present-day (1950-2014). Both trees showed similar genetic structure across historically dry barriers, despite evidence of significant environmental niche differentiation and different post-glacial habitat shifts. Tristaniopsis collina exhibits the signature of serial founder effects consistent with recent or rapid range expansion, whilst T. laurina has genetic patterns consistent with long-term persistence in geographically isolated populations despite occupying a broader bioclimatic niche. We found the minor influence of isolation-by-resistance on both species, though other unknown factors appear to shape genetic variation. We postulate that specialized recruitment traits (adapted to flood-disturbance regimes) rather than habitat availability limited post-glacial range expansion in T. laurina. Our findings indicate that niche breadth does not always facilitate range expansion through colonization and migration across barriers, though it can promote long-term persistence in situ.


Assuntos
Genética Populacional , Myrtaceae/genética , Simpatria/genética , Árvores/genética , Austrália , Mudança Climática , Ecossistema , Variação Genética/genética , Genótipo , Myrtaceae/crescimento & desenvolvimento , Polimorfismo de Nucleotídeo Único/genética , Árvores/crescimento & desenvolvimento , Água
4.
J Lipid Res ; 60(1): 85-97, 2019 01.
Artigo em Inglês | MEDLINE | ID: mdl-30416103

RESUMO

Bile acid imbalance causes progressive familial intrahepatic cholestasis type 2 (PFIC2) or type 3 (PFIC3), severe liver diseases associated with genetic defects in the biliary bile acid transporter bile salt export pump (BSEP; ABCB11) or phosphatidylcholine transporter multidrug resistance protein 3 (MDR3; ABCB4), respectively. Mdr2-/- mice (a PFIC3 model) develop progressive cholangitis, ductular proliferation, periportal fibrosis, and hepatocellular carcinoma (HCC) because the nonmicelle-bound bile acids in the bile of these mice are toxic. We asked whether the highly hydrophilic bile acids generated by Bsep-/- mice could protect Mdr2-/- mice from progressive liver damage. We generated double-KO (DKO: Bsep-/- and Mdr2-/- ) mice. Their bile acid composition resembles that of Bsep-/- mice, with increased hydrophilic muricholic acids, tetrahydroxylated bile acids (THBAs), and reduced hydrophobic cholic acid. These mice lack the liver pathology of their Mdr2-/- littermates. The livers of DKO mice have gene expression profiles very similar to Bsep-/- mice, with 4,410 of 6,134 gene expression changes associated with the Mdr2-/- mutation being suppressed. Feeding with THBAs partially alleviates liver damage in the Mdr2-/- mice. Hydrophilic changes to biliary bile acid composition, including introduction of THBA, can prevent the progressive liver pathology associated with the Mdr2-/- (PFIC3) mutation.


Assuntos
Subfamília B de Transportador de Cassetes de Ligação de ATP/deficiência , Ácidos e Sais Biliares/farmacologia , Sistema Biliar/metabolismo , Citoproteção/efeitos dos fármacos , Interações Hidrofóbicas e Hidrofílicas , Fígado/lesões , Fosfolipídeos/metabolismo , Subfamília B de Transportador de Cassetes de Ligação de ATP/genética , Membro 11 da Subfamília B de Transportadores de Cassetes de Ligação de ATP/deficiência , Membro 11 da Subfamília B de Transportadores de Cassetes de Ligação de ATP/genética , Animais , Ácidos e Sais Biliares/química , Sistema Biliar/efeitos dos fármacos , Técnicas de Inativação de Genes , Hidroxilação , Fígado/citologia , Fígado/efeitos dos fármacos , Fígado/metabolismo , Masculino , Camundongos , Mutação , Membro 4 da Subfamília B de Transportadores de Cassetes de Ligação de ATP
5.
J Ultrasound Med ; 37(12): 2829-2839, 2018 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-29675869

RESUMO

OBJECTIVES: This study aimed to ascertain the association between levator avulsion and pelvic organ prolapse (POP). METHODS: This was a cross-sectional study involving 195 women enrolled in a longitudinal cohort study and seen 20 years after an index birth. All had a standardized patient-administered questionnaire, the International Continence Society Pelvic Organ Prolapse Quantification assessment and 4D translabial ultrasound. Main outcome measures were objective POP clinically and on translabial ultrasound. Postimaging assessment of levator integrity and sonographically determined pelvic organ descent was done blinded against other data. RESULTS: Of 195 women who were seen a mean of 23 (range, 19.4-46.2) years after their first birth, one declined ultrasound assessment and was excluded, leaving 194. Mean age was 50.2 (range 36.9-66.5) years with a mean body mass index (BMI) of 27.6 (range, 18.3-54.3) kg/m2 . Median parity was 3 (range 1-14). Ninety-one percent (n = 176) had delivered vaginally. Eighteen percent (n = 34) were symptomatic of prolapse. Clinically, 36% (n = 69) had significant POP. Levator avulsion was diagnosed in 16% (n = 31). Mean levator avulsion defect score was 2.2 (range, 0-12). On univariate analysis, levator avulsion and levator avulsion defect score were associated with clinically and sonographically significant POP, that is, odds ratio 2.6 (1.2-5.7), P = .01; and odds ratio 3.3 (1.4-7.7); P = .003, respectively; Ba (P < .001); bladder (P < .001); uterine (P < .001) and rectal ampulla (P = .009) descent, but not POP symptoms, C, and Bp. Multivariate analysis controlling for potential confounders confirmed our findings. CONCLUSIONS: Levator avulsion is associated with female pelvic organ prolapse, especially of the anterior and central compartments. This association may become stronger with aging.


Assuntos
Diafragma da Pelve/lesões , Prolapso de Órgão Pélvico/diagnóstico por imagem , Adulto , Estudos de Coortes , Estudos Transversais , Feminino , Humanos , Imageamento Tridimensional/métodos , Estudos Longitudinais , Pessoa de Meia-Idade , Tempo , Ultrassonografia/métodos , Adulto Jovem
6.
PLoS One ; 12(11): e0186663, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-29117184

RESUMO

BACKGROUND: Prehistoric human activities have contributed to the dispersal of many culturally important plants. The study of these traditional interactions can alter the way we perceive the natural distribution and dynamics of species and communities. Comprehensive research on native crops combining evolutionary and anthropological data is revealing how ancient human populations influenced their distribution. Although traditional diets also included a suite of non-cultivated plants that in some cases necessitated the development of culturally important technical advances such as the treatment of toxic seed, empirical evidence for their deliberate dispersal by prehistoric peoples remains limited. Here we integrate historic and biocultural research involving Aboriginal people, with chloroplast and nuclear genomic data to demonstrate Aboriginal-mediated dispersal of a non-cultivated rainforest tree. RESULTS: We assembled new anthropological evidence of use and deliberate dispersal of Castanospermum australe (Fabaceae), a non-cultivated culturally important riparian tree that produces toxic but highly nutritious water-dispersed seed. We validated cultural evidence of recent human-mediated dispersal by revealing genomic homogeneity across extensively dissected habitat, multiple catchments and uneven topography in the southern range of this species. We excluded the potential contribution of other dispersal mechanisms based on the absence of suitable vectors and current distributional patterns at higher elevations and away from water courses, and by analyzing a comparative sample from northern Australia. CONCLUSIONS: Innovative studies integrating evolutionary and anthropological data will continue to reveal the unexpected impact that prehistoric people have had on current vegetation patterns. A better understanding of how traditional practices shaped species' distribution and assembly will directly inform cultural heritage management strategies, challenge "natural" species distribution assumptions, and provide innovative baseline data for pro-active biodiversity management.


Assuntos
Antropologia , Conservação dos Recursos Naturais , Fabaceae , Havaiano Nativo ou Outro Ilhéu do Pacífico/genética , Austrália , Produtos Agrícolas , Ecossistema , História Antiga , Humanos , Havaiano Nativo ou Outro Ilhéu do Pacífico/história , Floresta Úmida , Árvores , Clima Tropical
7.
Curr Opin Obstet Gynecol ; 28(5): 441-8, 2016 10.
Artigo em Inglês | MEDLINE | ID: mdl-27454848

RESUMO

PURPOSE OF REVIEW: There is increasing awareness of the importance of intrapartum events for future pelvic floor morbidity in women. In this review, we summarize recent evidence and potential consequences for clinical practice. RECENT FINDINGS: Both epidemiological evidence and data from perinatal imaging studies have greatly improved our understanding of the link between childbirth and later morbidity. The main consequences of traumatic childbirth are pelvic organ prolapse (POP) and anal incontinence. In both instances the primary etiological pathways have been identified: levator trauma in the case of POP and anal sphincter tears in the case of anal incontinence. As most such trauma is occult, imaging is required for diagnosis. SUMMARY: Childbirth-related major maternal trauma is much more common than generally assumed, and it is the primary etiological factor in POP and anal incontinence. Both sphincter and levator trauma can now be identified on imaging. This is crucial not only for clinical care and audit, but also for research. Postnatally diagnosed trauma can serve as intermediate outcome measure in intervention trials, opening up multiple opportunities for clinical research aimed at primary and secondary prevention.


Assuntos
Parto Obstétrico/efeitos adversos , Prolapso de Órgão Pélvico/prevenção & controle , Prolapso de Órgão Pélvico/cirurgia , Canal Anal/lesões , Incontinência Fecal/etiologia , Feminino , Humanos , Lacerações , Complicações do Trabalho de Parto , Forceps Obstétrico/efeitos adversos , Parto , Diafragma da Pelve/lesões , Prolapso de Órgão Pélvico/complicações , Gravidez , Incontinência Urinária/etiologia
8.
EuroIntervention ; 10(10): 1239-46, 2015 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-25701511

RESUMO

AIMS: A bipolar multi-electrode 7 Fr-compatible balloon-catheter radiofrequency (RF) renal denervation system (Vessix™ Renal Denervation System; Boston Scientific, Marlborough, MA, USA) was evaluated for safety in domestic swine. METHODS AND RESULTS: Renal arteries of 27 swine received overlapping treatments proximally/single treatments distally to mimic balloon overlap clinically. Each histopathology cohort (30, 90, 180 days) had four RF-treated and three sham-treated (no RF energy delivered) animals, with the response of artery/surrounding nerves to bilateral treatment examined (42 arteries). Scanning electron microscopy of the renal artery flow surface for endothelialisation was performed in six additional pigs (three at each of 30 and 90 days: 12 arteries) following unilateral whole artery treatment with proximal overlap: RF one side, sham the other side. Power was ~1 watt, treatment duration 30 seconds, target temperature 68°C. Renal histology and assessment for off-target injury was performed in all 27 swine. Renal artery thermal injury was transmural and segmental involving <10% to >90% of the circumference (typically 30-60%) with segmental neointimal hyperplasia exceeding shams but haemodynamically trivial (maximum stenosis 17.7%). Healing of necrotic arterial media was by replacement fibrosis. Overlying nerves also became fibrotic. Endothelialisation was focally incomplete at 30 days but confluent at 90 days. No off-target injury occurred outside the renal arteries. CONCLUSIONS: Safety was demonstrated.


Assuntos
Ablação por Cateter/instrumentação , Hipertensão/cirurgia , Artéria Renal/cirurgia , Simpatectomia/instrumentação , Animais , Microscopia Eletrônica de Varredura , Modelos Anatômicos , Neointima/patologia , Artéria Renal/inervação , Artéria Renal/patologia , Sus scrofa
9.
ACS Chem Biol ; 9(10): 2412-20, 2014 Oct 17.
Artigo em Inglês | MEDLINE | ID: mdl-25101481

RESUMO

Because RNA lacks strong intrinsic fluorescence, it has proven challenging to track RNA molecules in real time. To address this problem and to allow the purification of fluorescently tagged RNA complexes, we have selected a high affinity RNA aptamer called RNA Mango. This aptamer binds a series of thiazole orange (fluorophore) derivatives with nanomolar affinity, while increasing fluorophore fluorescence by up to 1,100-fold. Visualization of RNA Mango by single-molecule fluorescence microscopy, together with injection and imaging of RNA Mango/fluorophore complex in C. elegans gonads demonstrates the potential for live-cell RNA imaging with this system. By inserting RNA Mango into a stem loop of the bacterial 6S RNA and biotinylating the fluorophore, we demonstrate that the aptamer can be used to simultaneously fluorescently label and purify biologically important RNAs. The high affinity and fluorescent properties of RNA Mango are therefore expected to simplify the study of RNA complexes.


Assuntos
Aptâmeros de Nucleotídeos/metabolismo , Caenorhabditis elegans/genética , Corantes Fluorescentes/química , Microscopia de Fluorescência , RNA Bacteriano/química , RNA não Traduzido/química , RNA/isolamento & purificação , RNA/metabolismo , Animais , Aptâmeros de Nucleotídeos/química , Benzotiazóis/química , Biotina/metabolismo , Caenorhabditis elegans/metabolismo , Gônadas/metabolismo , Proteínas de Fluorescência Verde/química , Proteínas de Fluorescência Verde/metabolismo , Mangifera/química , Quinolinas/química , RNA/química , RNA Bacteriano/metabolismo , RNA não Traduzido/metabolismo , Spinacia oleracea/química
10.
Cancer ; 120(11): 1639-46, 2014 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-24668504

RESUMO

BACKGROUND: The management of brain metastases in patients with germ cell tumors remains controversial. The authors assessed the outcome in this patient group after the introduction of GAMEC chemotherapy (14-day cisplatin, high-dose methotrexate, etoposide, and actinomycin-D with filgrastim support) and cessation of the routine use of cranial irradiation. METHODS: Data were recorded prospectively from 39 patients with germ cell tumors and concurrent brain metastases who received treatment before and after the advent of GAMEC after they relapsed on conventional cisplatin-based chemotherapy. Neurosurgery was offered to selected patients. Radiotherapy generally was used only as a salvage therapy after chemotherapy failure. The primary outcome measure was overall survival and was depicted using a Kaplan-Meier plot. RESULTS: The 3-year overall survival rates were 38% for the whole cohort, 69% for those who presented with brain metastases at diagnosis (group 1), and 21% and 0% for those who developed metastases after initial chemotherapy (group 2) and while receiving chemotherapy (group 3), respectively. For the whole cohort, the median overall survival was 10.6 months (range, 5.5 months to not evaluable); and, for groups 1, 2, and 3 individually, the overall survival was not yet reached (range, from 7.4 months to not evaluable), 6.2 months (range, 2.1-15.3 months), and 2.7 months (range, from 0.6 months to not evaluable), respectively. The 3-year survival rate for those who received GAMEC chemotherapy was 56% compared with 27% for those who received chemotherapy pre-GAMEC. CONCLUSIONS: The prognosis for patients with germ cell tumors and brain metastases seems less bleak than previously thought. It is possible to achieve long-term survival with chemotherapy alone.


Assuntos
Neoplasias Encefálicas/tratamento farmacológico , Neoplasias Encefálicas/secundário , Neoplasias Embrionárias de Células Germinativas/tratamento farmacológico , Adulto , Neoplasias Encefálicas/mortalidade , Feminino , Humanos , Pessoa de Meia-Idade , Neoplasias Embrionárias de Células Germinativas/mortalidade , Neoplasias Embrionárias de Células Germinativas/secundário , Estudos Prospectivos
11.
PLoS One ; 7(11): e49737, 2012.
Artigo em Inglês | MEDLINE | ID: mdl-23185420

RESUMO

Microbial pathogens are ancient selective agents that have driven many aspects of multicellular evolution, including genetic, behavioural, chemical and immune defence systems. It appears that fungi specialised to attack insects were already present in the environments in which social insects first evolved and we hypothesise that if the early stages of social evolution required antifungal defences, then covariance between levels of sociality and antifungal defences might be evident in extant lineages, the defences becoming stronger with group size and increasing social organisation. Thus, we compared the activity of cuticular antifungal compounds in thrips species (Insecta: Thysanoptera) representing a gradient of increasing group size and sociality: solitary, communal, social and eusocial, against the entomopathogen Cordyceps bassiana. Solitary and communal species showed little or no activity. In contrast, the social and eusocial species killed this fungus, suggesting that the evolution of sociality has been accompanied by sharp increases in the effectiveness of antifungal compounds. The antiquity of fungal entomopathogens, demonstrated by fossil finds, coupled with the unequivocal response of thrips colonies to them shown here, suggests two new insights into the evolution of thrips sociality: First, traits that enabled nascent colonies to defend themselves against microbial pathogens should be added to those considered essential for social evolution. Second, limits to the strength of antimicrobials, through resource constraints or self-antibiosis, may have been overcome by increase in the numbers of individuals secreting them, thus driving increases in colony size. If this is the case for social thrips, then we may ask: did antimicrobial traits and microbes such as fungal entomopathogens play an integral part in the evolution of insect sociality in general?


Assuntos
Cordyceps/patogenicidade , Fungos/patogenicidade , Tisanópteros/microbiologia , Animais , Antifúngicos/metabolismo , Comportamento Animal , Evolução Biológica , Cordyceps/fisiologia , Feminino , Fungos/fisiologia , Insetos , Modelos Lineares , Masculino
12.
PLoS One ; 6(7): e21763, 2011.
Artigo em Inglês | MEDLINE | ID: mdl-21754998

RESUMO

Microbial diseases are important selective agents in social insects and one major defense mechanism is the secretion of cuticular antimicrobial compounds. We hypothesized that given differences in group size, social complexity, and nest type the secretions of these antimicrobials will be under different selective pressures. To test this we extracted secretions from nine wasp species of varying social complexity and nesting habits and assayed their antimicrobial compounds against cultures of Staphylococcus aureus. These data were then combined with phylogenetic data to provide an evolutionary context. Social species showed significantly higher (18x) antimicrobial activity than solitary species and species with paper nests showed significantly higher (11x) antimicrobial activity than those which excavated burrows. Mud-nest species showed no antimicrobial activity. Solitary, burrow-provisioning wasps diverged at more basal nodes of the phylogenetic trees, while social wasps diverged from the most recent nodes. These data suggest that antimicrobial defences may have evolved in response to ground-dwelling pathogens but the most important variable leading to increased antimicrobial strength was increase in group size and social complexity.


Assuntos
Anti-Infecciosos/imunologia , Evolução Biológica , Comportamento de Nidação/fisiologia , Comportamento Social , Vespas/imunologia , Vespas/microbiologia , Animais , Anti-Infecciosos/farmacologia , Testes de Sensibilidade Microbiana , Comportamento de Nidação/efeitos dos fármacos , Filogenia , Staphylococcus aureus/efeitos dos fármacos , Vespas/efeitos dos fármacos
13.
Sci Prog ; 93(Pt 4): 335-59, 2010.
Artigo em Inglês | MEDLINE | ID: mdl-21180342

RESUMO

The technical principles and practices of the civil nuclear industry are described with particular reference to fission and its products, natural and artificial radioactivity elements principally concerned and their relationships, main types of reactor, safety issues, the fuel cycle, waste management, issues related to weapon proliferation, environmental considerations and possible future developments.

14.
J Microbiol Methods ; 72(1): 103-6, 2008 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-18054097

RESUMO

Bioprospecting for novel antimicrobials increasingly relies on extremely small samples unsuitable for conventional bulk extraction and assay. We developed a microtitre plate assay for minimal amounts of test materials which is rapid, extremely sensitive, allows time-course analysis and reduces false negatives. Developed for the analyses of antimicrobial sensitivity and resistance, the technique is appropriate for assays where source materials are scarce.


Assuntos
Antibacterianos/análise , Antibacterianos/farmacologia , Escherichia coli/efeitos dos fármacos , Testes de Sensibilidade Microbiana/métodos , Ampicilina/farmacologia , Animais , Farmacorresistência Bacteriana/genética , Escherichia coli/genética , Escherichia coli/crescimento & desenvolvimento , Proteínas de Escherichia coli/genética , Proteínas de Escherichia coli/metabolismo , Concentração Inibidora 50 , Insetos/química , Plasmídeos , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Estreptomicina/farmacologia
15.
Org Lett ; 8(7): 1427-9, 2006 Mar 30.
Artigo em Inglês | MEDLINE | ID: mdl-16562908

RESUMO

[reaction: see text] The first total synthesis of the C(3)-symmetric and biologically active natural product, (-)-xyloketal A, has been accomplished in one step from phloroglucinol (1,3,5-trihydroxybenzene) and (4R)-3-hydroxymethyl-2,4-dimethyl-4,5-dihydrofuran. This remarkably direct process involved an exceedingly facile and diastereoselective boron trifluoride diethyl etherate-promoted triple electrophilic aromatic substitution reaction that was coupled to three bicyclic acetal formation reactions.


Assuntos
Produtos Biológicos/síntese química , Piranos/síntese química , Produtos Biológicos/química , Catálise , Estrutura Molecular , Piranos/química , Estereoisomerismo , Xylariales/química
16.
Org Biomol Chem ; 4(5): 877-85, 2006 Mar 07.
Artigo em Inglês | MEDLINE | ID: mdl-16493472

RESUMO

The synthesis of a series of chiral nonracemic and C2-symmetric 2,2'-bipyridyl ligands (R = Me, i-Pr and Ph) as well as the syntheses of the corresponding unsymmetric 2,2'-bipyridyl ligands (R = Me and Ph) is described. These bipyridyl ligands were prepared, in a notably direct and modular fashion, from the readily available and corresponding 2-chloropyridine acetals (R = Me, i-Pr and Ph). The bipyridyl ligands were evaluated in copper(I)-catalyzed cyclopropanation reactions of styrene with the ethyl and t-butyl esters of diazoacetic acid. The stereoselectivities, as well as the yields of the cyclopropanation reactions, were dependant on the ratio of the bipyridyl ligands and copper triflate that was employed. The best result was obtained in the asymmetric cyclopropanation reaction of styrene and tert-butyl diazoacetate with the C2-symmetric bipyridyl ligand (R = i-Pr). This afforded the corresponding trans-cyclopropane in good diastereoselectivity (4 : 1) and in moderate enantioselectivity (44% ee). The X-ray structure determination of a complex formed between the C2-symmetric 2,2'-bipyridyl ligand (R = Ph) and copper(I) chloride showed that two bipyridyl ligands had coordinated to the copper(I) ion. This information, along with the results of a series of cyclopropanation reactions and NMR data, led to the conclusion that the 2,2'-bipyridyl ligands had the propensity to form catalytically inactive bis-ligated copper(I) species in solution that were in equilibrium with catalytically active copper(i) triflate and the desired mono-ligated copper(I) species. Moreover, it was observed that the complex of the bipyridyl ligand (R = Ph) and copper(I) chloride had a particularly large optical rotation (sodium D-line). The maximum positive optical rotation was subsequently found to be +1.1 x 10(4) at 304 nm and the maximum negative optical rotation was -1.3 x 10(4) at 329 nm.

17.
J Org Chem ; 71(4): 1620-5, 2006 Feb 17.
Artigo em Inglês | MEDLINE | ID: mdl-16468815

RESUMO

A series of demethyl analogues of the natural products xyloketal A, B, C, D, and G have been prepared in a notably direct manner from 3-hydroxymethyl-2-methyl-4,5-dihydrofuran and a series of corresponding phenols. These syntheses featured a boron trifluoride diethyl etherate-promoted electrophilic aromatic substitution reaction as a key step. In the case of the synthesis of analogues of xyloketal A, the process was found to be highly efficient (up to 93% yield). The optimized isolated yield of these reaction products is remarkable in view of the fact that this transformation involves, minimally, six individual reactions. Moreover, these synthetic studies provide significant insight into the possible biogenic origin of the xyloketal natural products.


Assuntos
Piranos/síntese química , Produtos Biológicos/síntese química , Catálise , Furanos/química , Fenóis/química
18.
Org Biomol Chem ; 4(1): 41-3, 2006 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-16357993

RESUMO

The evaluation of a chiral, nonracemic and C2-symmetric 2,2'-bipyridyl ligand in copper(I)-catalyzed asymmetric allylic oxidation reactions of a series of cyclic alkenes with tert-butyl peroxybenzoate is reported (up to 91% ee, the highest reported enantioselectivity for a bipyridyl ligand copper(I) complex to date).

19.
Org Lett ; 7(5): 901-4, 2005 Mar 03.
Artigo em Inglês | MEDLINE | ID: mdl-15727470

RESUMO

Enantioselective Friedel-Crafts alkylation reactions of a series of substituted indoles with methyl trifluoropyruvate, catalyzed by a chiral nonracemic C(2)-symmetric 2,2'-bipyridyl copper(II) triflate complex, are described. The corresponding 3,3,3-trifluoro-2-hydroxy-2-indole-3-yl-propionic acid methyl esters were formed in good yield and in high enantiomeric excess (up to 90%). This is the first report of the use of a chiral nonracemic 2,2'-bipyridyl ligand in catalytic and enantioselective Friedel-Crafts alkylation reactions. The structural characterization of a copper(II) chloride complex of the chiral 2,2'-bipyridyl ligand by X-ray crystallography is also presented. [reaction: see text]

20.
Org Lett ; 7(3): 467-70, 2005 Feb 03.
Artigo em Inglês | MEDLINE | ID: mdl-15673266

RESUMO

[reaction: see text] A remarkable phenylboronic acid mediated triple condensation reaction of phloroglucinol (1,3,5-trihydroxybenzene) with a series of alpha,beta-unsaturated carbonyl compounds is reported. This experimentally simple reaction afforded novel C3-symmetric 2H-chromene derivatives. These derivatives represent structural analogues of the natural product xyloketal A, which has been reported to be a potent inhibitor of acetylcholine esterase.


Assuntos
Ácidos Borônicos/química , Floroglucinol/síntese química , Acetilcolinesterase/metabolismo , Benzopiranos/química , Catálise , Inibidores da Colinesterase/síntese química , Inibidores da Colinesterase/farmacologia , Floroglucinol/farmacologia , Piranos/química
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