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1.
BMC Microbiol ; 24(1): 139, 2024 Apr 24.
Artigo em Inglês | MEDLINE | ID: mdl-38658841

RESUMO

BACKGROUND: Gastric cancer is one of the global health concerns. A series of studies on the stomach have confirmed the role of the microbiome in shaping gastrointestinal diseases. Delineation of microbiome signatures to distinguish chronic gastritis from gastric cancer will provide a non-invasive preventative and treatment strategy. In this study, we performed whole metagenome shotgun sequencing of fecal samples to enhance the detection of rare bacterial species and increase genome sequence coverage. Additionally, we employed multiple bioinformatics approaches to investigate the potential targets of the microbiome as an indicator of differentiating gastric cancer from chronic gastritis. RESULTS: A total of 65 patients were enrolled, comprising 33 individuals with chronic gastritis and 32 with gastric cancer. Within each group, the chronic gastritis group was sub-grouped into intestinal metaplasia (n = 15) and non-intestinal metaplasia (n = 18); the gastric cancer group, early stage (stages 1 and 2, n = 13) and late stage (stages 3 and 4, n = 19) cancer. No significant differences in alpha and beta diversities were detected among the patient groups. However, in a two-group univariate comparison, higher Fusobacteria abundance was identified in phylum; Fusobacteria presented higher abundance in gastric cancer (LDA scored 4.27, q = 0.041 in LEfSe). Age and sex-adjusted MaAsLin and Random Forest variable of importance (VIMP) analysis in species provided meaningful features; Bacteria_caccae was the most contributing species toward gastric cancer and late-stage cancer (beta:2.43, se:0.891, p:0.008, VIMP score:2.543). In contrast, Bifidobacterium_longum significantly contributed to chronic gastritis (beta:-1.8, se:0.699, p:0.009, VIMP score:1.988). Age, sex, and BMI-adjusted MasAsLin on metabolic pathway analysis showed that GLCMANNANAUT-PWY degradation was higher in gastric cancer and one of the contributing species was Fusobacterium_varium. CONCLUSION: Microbiomes belonging to the pathogenic phylum Fusobacteria and species Bacteroides_caccae and Streptococcus_anginosus can be significant targets for monitoring the progression of gastric cancer. Whereas Bifidobacterium_longum and Lachnospiraceae_bacterium_5_1_63FAA might be protection biomarkers against gastric cancer.


Assuntos
Bactérias , Fezes , Gastrite , Metagenoma , Neoplasias Gástricas , Humanos , Neoplasias Gástricas/microbiologia , Masculino , Feminino , Pessoa de Meia-Idade , Gastrite/microbiologia , Fezes/microbiologia , Bactérias/genética , Bactérias/classificação , Bactérias/isolamento & purificação , Idoso , Microbioma Gastrointestinal/genética , Adulto
2.
Angew Chem Int Ed Engl ; 62(33): e202305571, 2023 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-37312245

RESUMO

Maximizing hole-transfer kinetics-usually a rate-determining step in semiconductor-based artificial photosynthesis-is pivotal for simultaneously enabling high-efficiency solar hydrogen production and hole utilization. However, this remains elusive yet as efforts are largely focused on optimizing the electron-involved half-reactions only by empirically employing sacrificial electron donors (SEDs) to consume the wasted holes. Using high-quality ZnSe quantum wires as models, we show that how hole-transfer processes in different SEDs affect their photocatalytic performances. We found that larger driving forces of SEDs monotonically enhance hole-transfer rates and photocatalytic performances by almost three orders of magnitude, a result conforming well with the Auger-assisted hole-transfer model in quantum-confined systems. Intriguingly, further loading Pt cocatalyts can yield either an Auger-assisted model or a Marcus inverted region for electron transfer, depending on the competing hole-transfer kinetics in SEDs.

3.
Food Microbiol ; 108: 104096, 2022 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-36088112

RESUMO

Microbes in pit mud play key roles in fermentation cellars for Chinese strong-flavor Baijiu (SFB) production. Pit mud, however, is frequently degraded during production, compromising the quality of the end product. In this study, a bioremediation method was used to restore degraded pit mud (DPM) using indigenous microbes derived from SFB production. Metabolomics and metagenomics were used to determine the dynamics of prokaryotes during DPM restoration and their link to SFB production. The composition of flavor compounds in SFB changed (P = 0.0001) before and after restoration of DPM. Consistent with the improved sensory quality, the ethyl caproate/ethyl lactate ratio, an SFB quality measure, increased after restoration (P < 0.001). The concentrations of humus, NH4+, available phosphorus, and available potassium in DPM increased during the restoration process (P < 0.05), which is consistent with high-quality pit mud. The relative abundance of microbes that are beneficial to SFB fermentation, such as Caproiciproducens, a bacterium that produces caproic acid, increased during the restoration process. Furthermore, a total of 18 metabolic pathways were enriched (P < 0.05) from DPM before and after restoration. This includes butanoate metabolism and pyruvate metabolism, which are related to the synthesis of key flavor esters in SFB.


Assuntos
Bebidas Alcoólicas , Bactérias , Bebidas Alcoólicas/microbiologia , Bactérias/genética , Bactérias/metabolismo , Biodegradação Ambiental , Fermentação
4.
BMC Gastroenterol ; 20(1): 380, 2020 Nov 14.
Artigo em Inglês | MEDLINE | ID: mdl-33189128

RESUMO

BACKGROUND: There is little knowledge to date about the distant metastasis of early-onset gastric signet ring cell carcinoma (SRCC) or the difference in metastasis based on age. Therefore, we conducted a comprehensive retrospective study using the Surveillance, Epidemiology, and End Results (SEER) database and data from our hospital. METHODS: Patients were collected from the SEER database and our hospital. Univariate and multivariate logistic regression analyses and propensity score matching (PSM) were used to identify risk factors for metastasis. K-M survival curves were generated to analyse patient survival. RESULTS: In total, we retrieved 2052 EOGC patients diagnosed with SRCC from the SEER database and included 403 patients from our hospital. K-M survival curves showed that late-onset SRCC patients had worse survival than early-onset patients but that late-onset SRCC patients were less likely to have distant metastasis, as validated by SEER data (OR = 0.462, 95%CI, 0.272-0.787; P = 0.004) and our data (OR = 0.301, 95%CI, 0.135-0.672; P = 0.003). Multivariate logistic regression and PSM analysis revealed that age of 45 or younger was an independent risk factor for distant metastasis. CONCLUSION: Our study showed that distant metastasis was more common in early-onset SRCC than in late-onset SRCC. However, further studies are needed to explore the potential aetiologic basis for this disparity.


Assuntos
Carcinoma de Células em Anel de Sinete , Neoplasias Gástricas , Carcinoma de Células em Anel de Sinete/epidemiologia , Humanos , Prognóstico , Estudos Retrospectivos , Fatores de Risco , Neoplasias Gástricas/epidemiologia
5.
Int J Food Microbiol ; 413: 110588, 2024 Mar 02.
Artigo em Inglês | MEDLINE | ID: mdl-38266376

RESUMO

The traditional Chinese alcoholic beverage Baijiu is produced by spontaneous fermentation of grains under anaerobic conditions. While numerous studies have used metagenomic technology to investigate the microbiome of Baijiu brewing, the microbial succession mechanism of Baijiu brewing has not been fully clarified, and metagenomic strategies for microecology surveys have not been comprehensively evaluated. Using the fermentation process of strong-flavor Baijiu as a model, we compared the data for bacterial communities based on short read 16S rRNA variable regions, V3-V4, and full-length 16S regions, V1-V9, to whole metagenomic shotgun sequencing (WMS) to measure the effect of technology selection on phylogenetic and functional profiles. The results showed differences in bacterial compositions and their relation to volatiles and physicochemical variables between sequencing methods. Furthermore, the percentage of V3-V4 sequences assigned to species level was higher than the percentage of V1-V9 sequences according to SILVA taxonomy, but lower according to NCBI taxonomy (P < 0.05). In both SILVA and NCBI taxonomies, the relative abundances of bacterial communities at both the genus and family levels were more positively correlated with WMS data in the V3-V4 dataset than in the V1-V9 dataset. The WMS identified changes in abundances of multiple metabolic pathways during fermentation (P < 0.05), including "starch and sucrose metabolism," "galactose metabolism," and "fatty acid biosynthesis." Although functional predictions derived from 16S data show similar patterns to WMS, most metabolic pathway changes are uncorrelated (P > 0.05). This study provided new technical and biological insights into Baijiu production that may assist in selection of methodologies for studies of fermentation systems.


Assuntos
Bebidas Alcoólicas , Projetos de Pesquisa , Fermentação , Filogenia , RNA Ribossômico 16S/genética , RNA Ribossômico 16S/metabolismo , Bebidas Alcoólicas/microbiologia , Bactérias
6.
Org Biomol Chem ; 11(20): 3393-9, 2013 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-23563191

RESUMO

Spirolactones, spirotetrahydrofurans, and spiropyrrolidines containing a vicinal cis-diol adjacent to the spiro-carbon center are prepared by one-pot epoxidation/spirocyclization of cyclohex-2-en-1-ols bearing an ester, alcohol, or amide functional side chain at the C(3) position of the ring.


Assuntos
Cicloexanóis/síntese química , Compostos de Epóxi/síntese química , Compostos de Espiro/síntese química , Cristalografia por Raios X , Ciclização , Cicloexanóis/química , Compostos de Epóxi/química , Modelos Moleculares , Estrutura Molecular , Compostos de Espiro/química , Estereoisomerismo
7.
Int J Food Microbiol ; 397: 110212, 2023 Jul 16.
Artigo em Inglês | MEDLINE | ID: mdl-37084618

RESUMO

The quality and composition of strong-flavor Baijiu (SFB), a type of Chinese liquor, depends on the variety of sorghum used in fermentation. However, comprehensive in situ studies measuring the effects sorghum varieties on the fermentation are lacking and the underlying microbial mechanisms remains poorly understood. We studied the in situ fermentation of SFB by using metagenomic, metaproteomic, and metabolomic techniques across four sorghum varieties. Sensory characteristics were best for SFB made from glutinous variety Luzhouhong, followed by glutinous hybrid Jinnuoliang and Jinuoliang, and those made with non-glutinous Dongzajiao. In agreement with sensory evaluations, the volatile composition of SFB samples differed between sorghum varieties (P < 0.05). Fermentation of different sorghum varieties varied in microbial diversity, structure, volatile compounds, and physicochemical properties (pH, temperature, starch, reducing sugar, and moisture) (P < 0.05), with most changes occurring within the first 21 days. Additionally, the microbial interactions and their relationship with volatiles, as well as the physicochemical factors that govern microbial succession, differed between varieties of sorghum. The number of physicochemical factors affecting bacterial communities outweighed those affecting fungal communities, suggesting that bacteria were less resilient to the brewing conditions. This correlates with the finding that bacteria play a major role in the differences in microbial communities and metabolic functions during fermentation with the different varieties of sorghum. Metagenomic function analysis revealed differences in amino acid and carbohydrate metabolism between sorghum varieties throughout most of the brewing process. Metaproteomics further indicated most differential proteins were found in these two pathways, related to differences in volatiles between sorghum varieties of Baijiu and originating from Lactobacillus. These results provide insight into the microbial principles underlying Baijiu production and can be used to improve the quality of Baijiu by selecting the appropriate raw materials and optimizing fermentation parameters.


Assuntos
Sorghum , Fermentação , Bebidas Alcoólicas/microbiologia , Metabolismo dos Carboidratos , Bactérias/genética , Bactérias/metabolismo , Grão Comestível
8.
Biomed Res Int ; 2018: 7375169, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-30539019

RESUMO

INTRODUCTION: Pretreatment platelet-to-lymphocyte ratio (PLR) has been considered a prognostic factor in various cancers. However, the application of PLR in the assessment of patients with cholangiocarcinoma remains controversial. This study aimed to evaluate the prognostic value of pretreatment PLR in cholangiocarcinoma. METHODS: A systematic search was performed in MEDLINE, EMBASE, and Cochrane Library to identify studies assessing the prognostic significance of the pretreatment PLR in cholangiocarcinoma. Three databases were searched from inception to August 5, 2018. The primary outcome was overall survival (OS), and the secondary outcomes were recurrence-free survival (RFS) and progression-free survival (PFS). Pooled hazard ratios (HRs) or odds ratios (ORs) with 95% confidence intervals (CIs) were calculated using random-effects models. RESULTS: A total of 9 studies including 2395 patients were finally enrolled in the meta-analysis based on the inclusion and exclusion criteria. All of the included studies were retrospective observational cohorts. Elevated PLR predicted poor OS (HR: 1.38, 95% CI: 1.19-1.62, P < 0.001) and RFS or PFS (HR = 1.55; 95% CI = 1.27-1.88; P < 0.001). Moreover, elevated PLR was highly associated with male sex (male versus female OR = 0.59, 95% CI: 0.44-0.80, P < 0.001) and R1 resection margin (OR = 2.09, 95% CI: 1.24-3.54, P = 0.006). CONCLUSION: The present meta-analysis demonstrated that pretreatment PLR might serve as a useful prognostic biomarker in cholangiocarcinoma.


Assuntos
Plaquetas/patologia , Colangiocarcinoma/sangue , Colangiocarcinoma/patologia , Linfócitos/patologia , Intervalo Livre de Doença , Feminino , Humanos , Contagem de Linfócitos , Masculino , Contagem de Plaquetas , Prognóstico , Intervalo Livre de Progressão
9.
Chin Med J (Engl) ; 130(2): 160-164, 2017 01 20.
Artigo em Inglês | MEDLINE | ID: mdl-28091407

RESUMO

BACKGROUND: Drug is an important cause of liver injury and accounts for up to 40% of instances of fulminant hepatic failure. Drug-induced liver injury (DILI) is increasing while the diagnosis becomes more difficult. Though many drugs may cause DILI, Chinese herbal medicines have recently emerged as a major cause due to their extensive use in China. We aimed to provide drug safety information to patients and health carers by analyzing the clinical and pathological characteristics of the DILI and the associated drug types. METHODS: A retrospective analysis was conducted in 287 patients diagnosed with DILI enrolled in our hospital from January 2011 to December 2015. The categories of causative drugs, clinical and pathological characteristics were reviewed. RESULTS: Western medicines ranked as the top cause of DILI, accounting for 163 out of the 287 DILI patients (56.79%) in our study. Among the Western medicine, antituberculosis drugs were the highest cause (18.47%, 53 patients) of DILI.   Antibiotics (18 patients, 6.27%) and antithyroid (18 patients, 6.27%) drugs also ranked among the major causes of DILI. Chinese herbal medicines are another major cause of DILI, accounting for 36.59% of cases (105 patients). Most of the causative Chinese herbal medicines were those used to treat osteopathy, arthropathy, dermatosis, gastropathy, leukotrichia, alopecia, and gynecologic diseases. Hepatocellular hepatitis was prevalent in DILI, regardless of Chinese herbal medicine or Western medicine-induced DILI. CONCLUSIONS: Risks and the rational use of medicines should be made clear to reduce the occurrence of DILI. For patients with liver injury of unknown origin, liver tissue pathological examination is recommended for further diagnosis.


Assuntos
Doença Hepática Induzida por Substâncias e Drogas/diagnóstico , Fígado/efeitos dos fármacos , Adolescente , Adulto , Idoso , Idoso de 80 Anos ou mais , Antibacterianos/efeitos adversos , Antitireóideos/efeitos adversos , Antituberculosos/efeitos adversos , Doença Hepática Induzida por Substâncias e Drogas/etiologia , Criança , China , Medicamentos de Ervas Chinesas/efeitos adversos , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Estudos Retrospectivos , Adulto Jovem
10.
J Med Chem ; 49(16): 4971-80, 2006 Aug 10.
Artigo em Inglês | MEDLINE | ID: mdl-16884309

RESUMO

A potent SARS coronavirus (CoV) 3CL protease inhibitor (TG-0205221, Ki = 53 nM) has been developed. TG-0205221 showed remarkable activity against SARS CoV and human coronavirus (HCoV) 229E replications by reducing the viral titer by 4.7 log (at 5 microM) for SARS CoV and 5.2 log (at 1.25 microM) for HCoV 229E. The crystal structure of TG-0205221 (resolution = 1.93 A) has revealed a unique binding mode comprising a covalent bond, hydrogen bonds, and numerous hydrophobic interactions. Structural comparisons between TG-0205221 and a natural peptide substrate were also discussed. This information may be applied toward the design of other 3CL protease inhibitors.


Assuntos
Antivirais/síntese química , Carbamatos/síntese química , Cisteína Endopeptidases/química , Dipeptídeos/síntese química , Proteínas Virais/antagonistas & inibidores , Proteínas Virais/química , Animais , Antivirais/química , Antivirais/farmacologia , Carbamatos/química , Carbamatos/farmacologia , Linhagem Celular , Chlorocebus aethiops , Coronavirus Humano 229E/efeitos dos fármacos , Proteases 3C de Coronavírus , Cristalografia por Raios X , Dipeptídeos/química , Dipeptídeos/farmacologia , Estabilidade de Medicamentos , Humanos , Ligação de Hidrogênio , Interações Hidrofóbicas e Hidrofílicas , Camundongos , Modelos Moleculares , Estrutura Molecular , Ratos , Coronavírus Relacionado à Síndrome Respiratória Aguda Grave/efeitos dos fármacos , Relação Estrutura-Atividade , Replicação Viral/efeitos dos fármacos
11.
Chem Commun (Camb) ; 51(96): 17104-7, 2015 Dec 14.
Artigo em Inglês | MEDLINE | ID: mdl-26451893

RESUMO

para-CH activation of pyridine with allylbenzene is described by Ni/Al cooperative catalysis in combination with a bulkier NHC ligand and a Lewis acid, leading to linear hydroheteroarylation products. Interestingly, the branch selectivity can be achieved by using the combination of a less sterically hindered amino-NHC ligand and AlMe3 through tandem reaction of facile alkene isomerization followed by a slow CH bond activation process.

12.
Biomicrofluidics ; 8(5): 052105, 2014 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-25332733

RESUMO

In this report, we describe in detail a microfluidic analyzer, which is able to conduct blood coagulation tests using whole blood samples. Sample preparation steps, such as whole blood aliquoting and metering, plasma separation, decanting, and mixing with reagents were performed in sequence through microfluidic functions integrated on a disk. Both prothrombin time (PT) and activated partial thromboplastin time (aPTT) were carried out on the same platform and the test results can be reported in 5 min. Fifty clinical samples were tested for both PT and aPTT utilizing the microfluidic disk analyzer and the instrument used in hospitals. The test results showed good correlation and agreement between the two instruments.

13.
J Gastroenterol ; 49(8): 1274-84, 2014 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-24129885

RESUMO

BACKGROUND: It is known that malignant transformation to hepatocellular carcinoma (HCC) occurs at a higher frequency in hepatocellular adenoma (HCA) from type I glycogen storage disease (GSD I) compared to HCA from other etiologies. In this study, we aimed to identify differentially expressed miRNAs in GSD Ia HCA as candidates that could serve as putative biomarkers for detection of GSD Ia HCA and/or risk assessment of malignant transformation. METHODS: Utilizing massively parallel sequencing, the miRNA profiling was performed for paired adenomas and normal liver tissues from seven GSD Ia patients. Differentially expressed miRNAs were validated in liver tumor tissues, HCC cell lines and serum using quantitative RT-PCR. RESULTS: miR-34a, miR-34a, miR-224, miR-224, miR-424, miR-452 and miR-455-5p were found to be commonly deregulated in GSD Ia HCA, general population HCA, and HCC cell lines at compatible levels. In comparison with GSD Ia HCA, the upregulation of miR-130b and downregulation of miR-199a-5p, miR-199b-5p, and miR-214 were more significant in HCC cell lines. Furthermore, serum level of miR-130b in GSD Ia patients with HCA was moderately higher than that in either GSD Ia patients without HCA or healthy individuals. CONCLUSION: We make the first observation of distinct miRNA deregulation in HCA associated with GSD Ia. We also provide evidence that miR-130b could serve as a circulating biomarker for detection of GSD Ia HCA. This work provides prominent candidate miRNAs worth evaluating as biomarkers for monitoring the development and progress of liver tumors in GSD Ia patients in the future.


Assuntos
Adenoma de Células Hepáticas/genética , Doença de Depósito de Glicogênio Tipo I/complicações , Neoplasias Hepáticas/genética , MicroRNAs/genética , Adenoma de Células Hepáticas/etiologia , Adenoma de Células Hepáticas/patologia , Biomarcadores Tumorais/genética , Estudos de Casos e Controles , Linhagem Celular Tumoral , Regulação para Baixo , Doença de Depósito de Glicogênio Tipo I/genética , Humanos , Neoplasias Hepáticas/etiologia , Neoplasias Hepáticas/patologia , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Regulação para Cima
14.
PLoS One ; 5(9)2010 Sep 20.
Artigo em Inglês | MEDLINE | ID: mdl-20862214

RESUMO

Virus-encoded microRNAs (miRNAs) have been shown to regulate a variety of biological processes involved in viral infection and viral-associated pathogenesis. Epstein-Barr virus (EBV) is a herpesvirus implicated in nasopharyngeal carcinoma (NPC) and other human malignancies. EBV-encoded miRNAs were among the first group of viral miRNAs identified. To understand the roles of EBV miRNAs in the pathogenesis of NPC, we utilized deep sequencing technology to characterize the EBV miRNA transcriptome in clinical NPC tissues. We obtained more than 110,000 sequence reads in NPC samples and identified 44 EBV BART miRNAs, including four new mature miRNAs derived from previously identified BART miRNA precursor hairpins. Further analysis revealed extensive sequence variations (isomiRs) of EBV miRNAs, including terminal isomiRs at both the 5' and 3' ends and nucleotide variants. Analysis of EBV genomic sequences indicated that the majority of EBV miRNA nucleotide variants resulted from post-transcriptional modifications. Read counts of individual EBV miRNA in NPC tissue spanned from a few reads to approximately 18,000 reads, confirming the wide expression range of EBV miRNAs. Several EBV miRNAs were expressed at levels similar to highly abundant human miRNAs. Sequence analysis revealed that most of the highly abundant EBV miRNAs share their seed sequences (nucleotides 2-7) with human miRNAs, suggesting that seed sequence content may be an important factor underlying the differential accumulation of BART miRNAs. Interestingly, many of these human miRNAs have been found to be dysregulated in human malignancies, including NPC. These observations not only provide a potential linkage between EBV miRNAs and human malignancy but also suggest a highly coordinated mechanism through which EBV miRNAs may mimic or compete with human miRNAs to affect cellular functions.


Assuntos
Carcinoma/virologia , Herpesvirus Humano 4/genética , MicroRNAs/genética , Neoplasias Nasofaríngeas/virologia , RNA Viral/genética , Sequência de Bases , Linhagem Celular Tumoral , Herpesvirus Humano 4/metabolismo , Sequenciamento de Nucleotídeos em Larga Escala , Humanos , MicroRNAs/metabolismo , Dados de Sequência Molecular , RNA Viral/metabolismo
15.
J Org Chem ; 72(22): 8175-85, 2007 Oct 26.
Artigo em Inglês | MEDLINE | ID: mdl-17915919

RESUMO

A series of chiral vanadyl(V) methoxides bearing 3-t-butyl-5-substituted N-salicylene-L-valinate and L-t-leucinate as chiral auxiliaries has been prepared. In all cases except the 3,5-di-t-butyl analogue, they exist as monomers both in solution and in the single crystal state. In the case of the 3,5-di-t-butyl analogue, the architectural nature of the vanadyl(V) complex highly depends on the base used during the complex formation event. A pentanuclear C4-symmetric complex was formed when potassium salts were employed instead of the corresponding sodium salts. A central vanadate(V) unit serves to grip four identical chiral monomeric vanadyl(V) units together, by which a potassium ion sits on top of the four flanking units through carbonyl coordinations and serves to hold the whole cluster by cooperation with the central vanadate(V) unit. In comparison with the corresponding monomeric vanadyl(V) methoxide complex, the cluster complex was utilized to facilitate the asymmetric aerobic oxidations of various racemic alpha-hydroxyesters, -amides, and -thioesters with excellent selectivity factors (krel 40 to >500).


Assuntos
Hidroxiácidos/síntese química , Compostos Organometálicos/química , Vanadatos/química , Cristalografia por Raios X , Hidroxiácidos/química , Leucina/química , Modelos Moleculares , Estrutura Molecular , Oxirredução , Estereoisomerismo
16.
J Org Chem ; 70(4): 1328-39, 2005 Feb 18.
Artigo em Inglês | MEDLINE | ID: mdl-15704967

RESUMO

[reaction: see text] A diverse array of oxometallic species were examined as catalysts in nucleophilic acyl substitution (NAS) reactions of methyl (or ethyl) esters with protic nucleophiles. Among them, oxotitanium acetylacetonate (TiO(acac)(2)) and vanadyl chloride (VOCl(2)-(THF)(x)()) served as the most efficient and water-tolerant catalysts. Transesterifications of methyl and/or ethyl esters with functionalized (including acid- or base-sensitive) 1 degrees and 2 degrees alcohols can be carried out chemoselectively in refluxed toluene or xylene in a 1:1 substrate stoichiometry using 1 mol % catalyst loading. The resultant products were furnished in 85-100% yields by simple aqueous workup to remove water-soluble catalysts. The new NAS protocol is also amenable to amines and thiols in 74-91% yields, albeit with higher loading (2.5 equiv) of protic nucleophiles. Representative examples of commercial interests such as Padimate O and antioxidant additives for plastics were also examined to demonstrate their practical applications. A 1:1 adduct between TiO(acac)(2) and a given 1-octadecanol was identified as (C(18)H(37)O)(2)Ti(acac)(2) and was responsible for its subsequent NAS of methyl esters.

17.
J Org Chem ; 70(4): 1188-97, 2005 Feb 18.
Artigo em Inglês | MEDLINE | ID: mdl-15704950

RESUMO

[reaction: see text] Among six different group VIb oxometallic species examined, dioxomolybdenum dichloride and oxomolybdenum tetrachloride were the most efficient catalysts to facilitate nucleophilic acyl substitution (NAS) of anhydrides with a myriad array of alcohols, amines, and thiols in high yields and high chemoselectivity. In contrast to the well-recognized redox chemical behaviors associated with oxomolybdenum(VI) species, the catalytic NAS was unprecedented and tolerates virtually all kinds of functional groups. By using benzoic anhydride as a mediator for in situ generation of an incipient mixed anhydride-MoO(2)Cl(2) adduct with a given functional alkanoic acid, one can achieve oleate, dipeptide, diphenylmethyl, N-Fmoc-alpha-amino, pyruvic, and tert-butylthio ester, N-tert-butylamide, and trityl methacrylate syntheses with appropriate protic nucleophiles. The amphoteric character of the Mo=O unit in oxomolybdenum chlorides was found to be responsible for the catalytic NAS profile as supported by a control NAS reaction of using an authentic adduct-MoOCl(2)(O(2)CBu(t)())(2) between pivalic anhydride and MoO(2)Cl(2) as the catalyst.

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