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1.
Front Oncol ; 14: 1304144, 2024.
Artigo em Inglês | MEDLINE | ID: mdl-38390257

RESUMO

Dogs with B-cell lymphoma typically respond well to first-line CHOP-based chemotherapy, but there is no standard of care for relapsed patients. To help veterinary oncologists select effective drugs for dogs with lymphoid malignancies such as B-cell lymphoma, we have developed multimodal machine learning models that integrate data from multiple tumor profiling modalities and predict the likelihood of a positive clinical response for 10 commonly used chemotherapy drugs. Here we report on clinical outcomes that occurred after oncologists received a prediction report generated by our models. Remarkably, we found that dogs that received drugs predicted to be effective by the models experienced better clinical outcomes by every metric we analyzed (overall response rate, complete response rate, duration of complete response, patient survival times) relative to other dogs in the study and relative to historical controls.

2.
Postgrad Med J ; 98(1163): 666-669, 2022 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-37062975

RESUMO

BACKGROUND: Subcutaneous (SC) trastuzumab is similar to intravenous trastuzumab in terms of pharmacokinetics, efficacy and tolerability. The use of dual anti-HER2 agents trastuzumab and pertuzumab has become the new standard for node-positive HER2-positive breast cancers at adjuvant setting, but the safety and tolerability of combining SC trastuzumab and intravenous pertuzumab is not well studied. METHODS: This was a prospective single-arm pilot study with locally advanced HER2-positive breast cancer who received adjuvant SC trastuzumab and intravenous pertuzumab after standard anti-HER2 treatment with chemotherapy. Primary outcomes included adverse events (AEs), severe AEs and cardiac AEs. Secondary outcome was invasive disease-free survival (iDFS). RESULTS: With a median follow-up of 21.7 months, 20 patients were enrolled. One patient (5%) developed asymptomatic drop in left ventricular ejection fraction from 69% to 53%. Two patients (10%) developed grade 1 injection site reaction related to SC trastuzumab. There were no grade 2 or above AEs. All AEs were transient. No new AEs were observed. The 1-year iDFS was 90% (95% CI 0.656 to 0.974). CONCLUSIONS: Combination of SC trastuzumab and intravenous pertuzumab for HER2-positive breast cancer is a safe and well-tolerated option in adjuvant setting.


Assuntos
Neoplasias da Mama , Humanos , Feminino , Trastuzumab/efeitos adversos , Neoplasias da Mama/tratamento farmacológico , Projetos Piloto , Volume Sistólico , Estudos Prospectivos , Receptor ErbB-2/uso terapêutico , Protocolos de Quimioterapia Combinada Antineoplásica/efeitos adversos , Função Ventricular Esquerda
3.
Vet Sci ; 8(12)2021 Dec 02.
Artigo em Inglês | MEDLINE | ID: mdl-34941828

RESUMO

First-line treatments of cancer do not always work, and even when they do, they cure the disease at unequal rates mostly owing to biological and clinical heterogeneity across patients. Accurate prediction of clinical outcome and survival following the treatment can support and expedite the process of comparing alternative treatments. We describe the methodology to dynamically determine remission probabilities for individual patients, as well as their prospects of progression-free survival (PFS). The proposed methodology utilizes the ex vivo drug sensitivity of cancer cells, their immunophenotyping results, and patient information, such as age and breed, in training machine learning (ML) models, as well as the Cox hazards model to predict the probability of clinical remission (CR) or relapse across time for a given patient. We applied the methodology using the three types of data obtained from 242 canine lymphoma patients treated by (L)-CHOP chemotherapy. The results demonstrate substantial enhancement in the predictive accuracy of the ML models by utilizing features from all the three types of data. They also highlight superior performance and utility in predicting survival compared to the conventional stratification method. We believe that the proposed methodology can contribute to improving and personalizing the care of cancer patients.

4.
Adv Ther ; 38(12): 5752-5762, 2021 12.
Artigo em Inglês | MEDLINE | ID: mdl-34699004

RESUMO

INTRODUCTION: Concurrent anthracycline and taxane is an effective and efficient way to deliver neoadjuvant chemotherapy for HER2-negative breast cancers. Data on efficacy and tolerance to 6 cycles of concurrent docetaxel, epirubicin, and cyclophosphamide (TEC) is limited. METHOD: All patients with HER2-negative breast cancers who received neoadjuvant TEC from January 2013 to December 2019 were reviewed. RESULTS: A total of 71 patients [57 luminal B disease; 14 triple negative breast cancer (TNBC)] received neoadjuvant TEC with prophylactic granulocyte colony-stimulating factor (G-CSF). The pathological complete response (pCR) rate was 26.3% and 28.6% for luminal B and TNBC, respectively. With median follow-up of 48.9 months, 3 years disease-free survival was 85.9%, and 3 years overall survival was 89.6%. Non-hematological toxicities were common but the majority was grade 1 or 2. The most common grade 3 or 4 toxicity were hematological, including neutropenia (26.8%) and anemia (15.5%). There was no cardiotoxicity observed. Half of the patients had at least one dose reduction but all patients completed the planned 6 cycles and had breast surgery done. CONCLUSION: Six cycles of TEC with prophylactic G-CSF is an effective and tolerable neoadjuvant regime for HER2-negative breast cancers. Hematological toxicities were the most common toxicities. Although many patients required dose reduction, all patients completed treatment and there was no observed cardiotoxicity.


Assuntos
Neoplasias da Mama , Neoplasias de Mama Triplo Negativas , Protocolos de Quimioterapia Combinada Antineoplásica/uso terapêutico , Neoplasias da Mama/tratamento farmacológico , Ciclofosfamida/uso terapêutico , Docetaxel/uso terapêutico , Epirubicina , Feminino , Humanos , Terapia Neoadjuvante , Receptor ErbB-2/uso terapêutico , Resultado do Tratamento , Neoplasias de Mama Triplo Negativas/tratamento farmacológico
5.
Adv Ther ; 38(7): 3900-3910, 2021 07.
Artigo em Inglês | MEDLINE | ID: mdl-34061324

RESUMO

BACKGROUND: Treatment of hepatocellular carcinoma (HCC) recurrences following liver transplant (LT) is challenging. Most clinical trials of systemic therapies for advanced HCC excluded patients with any history of organ transplant. We aimed to assess the outcomes in using various systemic therapies in patients with post-LT recurrence. METHODS: Consecutive patients with HCC and recurrences following LT at a large tertiary centre from 2005 to 2018 were reviewed. Overall survival (OS), response rates and adverse events (AEs) were analysed. RESULTS: Forty-three consecutive patients with a recurrence of HCC following LT were identified from 2005 to 2018. Median OS from diagnosis of recurrence was 17 months (CI 11.3, 22.7). Early recurrence within 12 months of transplant was associated with a significantly worse median survival of 10 months (CI 8.5, 11.4) compared to 26 months (CI 18.8, 33.2) when recurrences occurred after 12 months from transplant (p < 0.001) with a hazard ratio of 0.104 (log-rank test, p < 0.001). A total of 41 patients had received systemic therapies and 79.1% of them were on sorafenib as the first-line treatment. Among these patients treated with sorafenib, median OS from recurrence was 14 months (CI 7.3, 20.7). Hand-foot syndrome (34.7%) was most common among AEs followed by diarrhoea (26.7%). Overall, AEs led to dose interruptions in 8.8% of patients. Notably, 47.1% of patients received subsequent lines of systemic therapies after sorafenib. CONCLUSIONS: Early recurrence within 1 year from transplant was the most significant risk factor. Treatment efficacy and adverse events and tolerability of sorafenib were comparable with those in the setting of advanced HCC without transplant.


Assuntos
Antineoplásicos , Carcinoma Hepatocelular , Neoplasias Hepáticas , Transplante de Fígado , Antineoplásicos/uso terapêutico , Carcinoma Hepatocelular/tratamento farmacológico , Carcinoma Hepatocelular/cirurgia , Humanos , Neoplasias Hepáticas/tratamento farmacológico , Neoplasias Hepáticas/cirurgia , Recidiva Local de Neoplasia/tratamento farmacológico , Compostos de Fenilureia/uso terapêutico , Estudos Retrospectivos , Sorafenibe/uso terapêutico , Resultado do Tratamento
6.
Cancers (Basel) ; 13(9)2021 Apr 21.
Artigo em Inglês | MEDLINE | ID: mdl-33919277

RESUMO

(1) Background: Cabozantinib is approved in sorafenib-exposed advanced hepatocellular carcinoma (aHCC). We evaluated the real-life pattern of use, efficacy, and tolerability of cabozantinib in aHCC. (2) Methods: This territory-wide study included consecutive aHCC patients who received cabozantinib between February 2018 and September 2020 in Hong Kong. The objective response rate (ORR), disease control rate (DCR), overall survival (OS), and adverse events (AE) were assessed. (3) Results: Overall, 42 patients were included. Approximately 83.3% had Child-Pugh A cirrhosis. About 64.3% received cabozantinib as a single agent, and the remaining 35.7% received cabozantinib as an add-on to immune checkpoint inhibitors (ICIs). For single-agent patients, the median follow-up was 6.7 months. The ORR was 3.7%, DCR was 44.4%, and the median OS was 8.28 months. About 74.1% of patients experienced any AEs with 7.4% having grade ≥3 AEs. Among patients who received prior ICIs (n = 16), the ORR was 6.3%, and the median OS was 8.28 months. An exploratory analysis of patients who received cabozantinib as an add-on to ICIs showed an ORR of 6.7% and a median OS of 15.1 months, with 73.3% having any AE and 13.3% having grade ≥3 AEs. (4) Conclusions: Cabozantinib had good anti-tumor activity, survival benefits, and acceptable tolerability in real-life aHCC patients.

7.
Expert Rev Gastroenterol Hepatol ; 15(6): 589-598, 2021 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-33666530

RESUMO

INTRODUCTION: The systemic treatment of advanced, unresectable hepatocellular carcinoma (HCC) has undergone an evolution in recent years. In March 2020, a combination of nivolumab and ipilimumab was approved by the FDA for treatment of patients with advanced HCC who received prior sorafenib. This was based on the results of the phase I/II CheckMate-040 cohort 4 trials, which showed a promising overall response rate and encouraging overall survival with a manageable safety profile. AREAS COVERED: This article reviews the pharmacology, efficacy and safety of nivolumab-ipilimumab in advanced HCC with prior sorafenib. Other existing systemic treatment options for advanced HCC will be described and compared to nivolumab-ipilimumab. Impact of different dose regimes, ongoing research and future developments of nivolumab-ipilimumab will be discussed. We focus on the analysis from the aforementioned CheckMate-040 cohort 4 registration trial. EXPERT OPINION: The approval of nivolumab-ipilimumab in the second-line treatment of advanced HCC by the FDA is an important development for treatment of advanced HCC. However, further investigations are needed to optimize dosing regimens and explore the use of nivolumab-ipilimumab in other combinations and settings.


Assuntos
Protocolos de Quimioterapia Combinada Antineoplásica/uso terapêutico , Carcinoma Hepatocelular/tratamento farmacológico , Inibidores de Checkpoint Imunológico/uso terapêutico , Ipilimumab/uso terapêutico , Neoplasias Hepáticas/tratamento farmacológico , Nivolumabe/uso terapêutico , Sorafenibe/uso terapêutico , Protocolos de Quimioterapia Combinada Antineoplásica/farmacologia , Carcinoma Hepatocelular/patologia , Ensaios Clínicos como Assunto , Sinergismo Farmacológico , Humanos , Inibidores de Checkpoint Imunológico/farmacologia , Ipilimumab/farmacologia , Fígado/efeitos dos fármacos , Neoplasias Hepáticas/patologia , Gradação de Tumores , Nivolumabe/farmacologia , Inibidores de Proteínas Quinases/farmacologia , Inibidores de Proteínas Quinases/uso terapêutico , Sorafenibe/farmacologia
8.
J Immunother Cancer ; 9(2)2021 02.
Artigo em Inglês | MEDLINE | ID: mdl-33563773

RESUMO

BACKGROUND: Programmed cell death protein 1 (PD-1) pathway blockade with immune checkpoint inhibitors (ICIs) is a standard therapy in advanced hepatocellular carcinoma (HCC) nowadays. No strategies to overcome ICI resistance have been described. We aimed to evaluate the use of ipilimumab and anti-PD-1 ICIs (nivolumab or pembrolizumab) combinations in patients with advanced HCC with progression on prior ICIs. METHODS: Patients with advanced HCC with documented tumor progression on prior ICIs and subsequently received ipilimumab with nivolumab/pembrolizumab were analyzed. Objective response rate (ORR), median duration of response (DOR), time-to-progression (TTP), overall survival (OS), and treatment-related adverse events (TRAEs) were assessed. RESULTS: Twenty-five patients were included. The median age was 62 (range: 51-83). About 68% were of Child-Pugh (CP) Grade A and 48% had primary resistance to prior ICI. At median follow-up of 37.7 months, the ORR was 16% with a median DOR of 11.5 months (range: 2.76-30.3). Three patients achieved complete response. The median TTP was 2.96 months (95% CI: 1.61 to 4.31). Median OS was 10.9 months (95% CI: 3.99 to 17.8) and the 1 year, 2 year and 3 year survival rates were 42.4%, 32.3% and 21.6%, respectively. The ORR was 16.7% in primary resistance group and 15.4% in acquired resistance group (p=1.00). All responders were of CP A and Albumin-Bilirubin (ALBI) Grade 1 or 2. CP and ALBI Grades were significantly associated with OS (p=0.006 and p<0.001, respectively). Overall, 52% of patients experienced TRAEs and 12% experienced Grade 3 or above TRAEs. CONCLUSIONS: Ipilimumab and nivolumab/pembrolizumab can achieve durable antitumor activity and encouraging survival outcomes with acceptable toxicity in patients with advanced HCC who had prior treatment with ICIs.


Assuntos
Anticorpos Monoclonais Humanizados/uso terapêutico , Protocolos de Quimioterapia Combinada Antineoplásica/uso terapêutico , Carcinoma Hepatocelular/tratamento farmacológico , Inibidores de Checkpoint Imunológico/uso terapêutico , Ipilimumab/uso terapêutico , Neoplasias Hepáticas/tratamento farmacológico , Nivolumabe/uso terapêutico , Idoso , Idoso de 80 Anos ou mais , Anticorpos Monoclonais Humanizados/efeitos adversos , Protocolos de Quimioterapia Combinada Antineoplásica/efeitos adversos , Carcinoma Hepatocelular/imunologia , Carcinoma Hepatocelular/mortalidade , Carcinoma Hepatocelular/patologia , Progressão da Doença , Resistencia a Medicamentos Antineoplásicos , Feminino , Humanos , Inibidores de Checkpoint Imunológico/efeitos adversos , Ipilimumab/efeitos adversos , Neoplasias Hepáticas/imunologia , Neoplasias Hepáticas/mortalidade , Neoplasias Hepáticas/patologia , Masculino , Pessoa de Meia-Idade , Nivolumabe/efeitos adversos , Estudos Retrospectivos , Terapia de Salvação , Fatores de Tempo , Resultado do Tratamento , Microambiente Tumoral
9.
Vet Comp Oncol ; 19(1): 160-171, 2021 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-33025640

RESUMO

We report a precision medicine platform that evaluates the probability of chemotherapy drug efficacy for canine lymphoma by combining ex vivo chemosensitivity and immunophenotyping assays with computational modelling. We isolated live cancer cells from fresh fine needle aspirates of affected lymph nodes and collected post-treatment clinical responses in 261 canine lymphoma patients scheduled to receive at least 1 of 5 common chemotherapy agents (doxorubicin, vincristine, cyclophosphamide, lomustine and rabacfosadine). We used flow cytometry analysis for immunophenotyping and ex vivo chemosensitivity testing. For each drug, 70% of treated patients were randomly selected to train a random forest model to predict the probability of positive Veterinary Cooperative Oncology Group (VCOG) clinical response based on input variables including antigen expression profiles and treatment sensitivity readouts for each patient's cancer cells. The remaining 30% of patients were used to test model performance. Most models showed a test set ROC-AUC > 0.65, and all models had overall ROC-AUC > 0.95. Predicted response scores significantly distinguished (P < .001) positive responses from negative responses in B-cell and T-cell disease and newly diagnosed and relapsed patients. Patient groups with predicted response scores >50% showed a statistically significant reduction (log-rank P < .05) in time to complete response when compared to the groups with scores <50%. The computational models developed in this study enabled the conversion of ex vivo cell-based chemosensitivity assay results into a predicted probability of in vivo therapeutic efficacy, which may help improve treatment outcomes of individual canine lymphoma patients by providing predictive estimates of positive treatment response.


Assuntos
Antineoplásicos/uso terapêutico , Doenças do Cão/tratamento farmacológico , Resistencia a Medicamentos Antineoplásicos , Imunofenotipagem/veterinária , Linfoma/veterinária , Animais , Doenças do Cão/patologia , Cães , Feminino , Linfonodos/patologia , Linfoma/tratamento farmacológico , Linfoma/patologia , Aprendizado de Máquina , Masculino , Modelos Biológicos , Valor Preditivo dos Testes
10.
J Pediatr Surg ; 2017 Oct 12.
Artigo em Inglês | MEDLINE | ID: mdl-29096888

RESUMO

PURPOSE: The purpose of this study is to determine the feasibility of fetal surgical repair of myelomeningocele (MMC) in a rodent model using human placental mesenchymal stromal cells (PMSCs) seeded onto extracellular matrix (ECM) and to characterize the resulting changes in spinal cord tissue. METHODS: Fetal rodents with retinoic acid (RA) induced MMC underwent surgical repair of the MMC defect using an ECM patch on embryonic age (EA) 19 and were collected via caesarean section on EA 21. Various seeding densities of PMSC-ECM and ECM only controls were evaluated. Cross-sectional compression (width/height) and apoptotic cell density of the lumbosacral spinal cord were analyzed. RESULTS: 67 dams treated with 40mg/kg of RA resulted in 352 pups with MMC defects. 121 pups underwent MMC repair, and 105 (86.8%) survived to term. Unrepaired MMC pups had significantly greater cord compression and apoptotic cell density compared to normal non-MMC pups. Pups treated with PMSC-ECM had significantly less cord compression and demonstrated a trend towards decreased apoptotic cell density compared to pups treated with ECM only. CONCLUSION: Surgical repair of MMC with a PMSC-seeded ECM disc is feasible with a postoperative survival rate of 86.8%. Fetal rodents repaired with PMSC-ECM have significantly less cord deformity and decreased histological evidence of apoptosis compared to ECM only controls.

11.
Asian Cardiovasc Thorac Ann ; 22(1): 110-4, 2014 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-24585662

RESUMO

The purpose of this review is to compare conventional endovascular procedures and the robotic endovascular approach in aortic aneurysm repair. Despite advantages over open surgery, conventional endovascular surgery has limitations. To develop an alternative, efforts have been focused on robotic endovascular systems. Two of the 3 studies comparing procedure times demonstrated reduced procedure time in the robotic group, by 6 times (p < 0.05). One study demonstrated that robotic procedures reduced fluoroscopic exposure time by 12 minute (p < 0.001). Three in-vitro studies showed that the number of movements required in robotic surgery was reduced up to 10 times (p < 0.05). One of 2 studies measuring robotic performance score showed a better performance score in the robotic endovascular group (p = 0.007). These results demonstrate that the robotic technique has multiple advantages over the conventional procedure, including improved catheter stability, a shorter learning curve, reduced procedure time, and better performance in cannulating tortuous vessels. However, robotic endovascular technology may be limited by the cost of the system, the size of the catheter, and the setup time required preoperatively. Further comparative studies between conventional and robotic approaches regarding cost-effectiveness, safety, and performance in cases involving complex anatomy and fenestrated stent grafts are essential. Nevertheless, this revolutionary technology is increasingly popular and may be the next milestone in endovascular surgery.


Assuntos
Aneurisma Aórtico/cirurgia , Implante de Prótese Vascular/métodos , Procedimentos Endovasculares/métodos , Robótica , Cirurgia Assistida por Computador , Aneurisma Aórtico/diagnóstico por imagem , Aortografia , Implante de Prótese Vascular/efeitos adversos , Procedimentos Endovasculares/efeitos adversos , Humanos , Radiografia Intervencionista , Cirurgia Assistida por Computador/efeitos adversos , Resultado do Tratamento
12.
J Am Chem Soc ; 128(50): 16398-405, 2006 Dec 20.
Artigo em Inglês | MEDLINE | ID: mdl-17165797

RESUMO

The catalytic ability of a dinuclear Zn2+ complex of 1,3-bis-N1-(1,5,9-triazacyclododecyl)propane (3) in promoting the cleavage of an RNA model, 2-hydroxypropyl-p-nitrophenyl phosphate (HPNPP, 1), and a DNA model, methyl p-nitrophenyl phosphate (MNPP, 4), was studied in methanol solution in the presence of added CH3O- at 25 degrees C. The di-Zn2+ complex (Zn2 :3), in the presence of 1 equiv of added methoxide, exhibits a second-order rate constant of (2.75 +/- 0.10) x 10(5) M(-1) s(-1) for the reaction with 1 at s(s)pH 9.5, this being 10(8)-fold larger than the k2 value for the CH3O- promoted reaction (kOCH3 = (2.56 +/- 0.16) x 10(-3) M(-1) s(-1)). The complex is also active toward the DNA model 4, exhibiting Michaelis-Menten kinetics with a KM and kmax of 0.37 +/- 0.07 mM and (4.1 +/- 0.3) x 10(-2) s(-1), respectively. Relative to the background reactions at s(s)pH 9.5, Zn2 :3 accelerates cleavage of each phosphate diester by a remarkable factor of 1012-fold. A kinetic scheme common to both substrates is discussed. The study shows that a simple model system comprising a dinuclear Zn2+ complex and a medium effect of the alcohol solvent achieves a catalytic reactivity that approaches enzymatic rates and is well beyond anything seen to date in water for the cleavage of these phosphate diesters.


Assuntos
DNA/química , Modelos Biológicos , RNA/química , Zinco/química , Cátions Bivalentes/química , Ciclização , Cinética , Metano/química , Estrutura Molecular
13.
Org Biomol Chem ; 3(8): 1525-33, 2005 Apr 21.
Artigo em Inglês | MEDLINE | ID: mdl-15827652

RESUMO

The methanolyses of a series of O,O-diethyl O-aryl phosphates (2,5) and O,O-diethyl S-aryl phosphorothioates (6) promoted by methoxide and two metal ion systems, (La3+)2(-OCH3)2 and 4:Zn2+:-OCH3 (4 = 1,5,9-triazacyclododecane) has been studied in methanol at 25 degrees C. Brønsted plots of the logk2 values vs. pKa for the phenol leaving groups give beta(lg) values of -0.70, -1.43 and -1.12 for the methanolysis of the phosphates and -0.63, -0.87 and -0.74 for the methanolysis of the phosphorothioates promoted by the methoxide, La3+ and Zn2+ systems respectively. The kinetic data for the metal-catalyzed reactions are analyzed in terms of a common mechanism where there is extensive cleavage of the P-XAr bond in the rate-limiting transition state. The relevance of these findings to the mechanism of action of the phosphotriesterase enzyme is discussed.


Assuntos
Lantânio/química , Metanol/química , Organofosfatos/química , Compostos Organotiofosforados/química , Hidrolases de Triester Fosfórico/metabolismo , Zinco/química , Catálise , Cátions/química , Esterificação , Estrutura Molecular
14.
Org Biomol Chem ; 2(23): 3457-63, 2004 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-15565237

RESUMO

The La3+-catalyzed methanolysis of two phosphorothioate derivatives, O,O-diethyl S-(p-nitrophenyl) phosphorothioate (4a) and O,O-diethyl S-phenyl phosphorothioate (4b) were studied as a function of [La3+] and pH in methanol solvent. In both cases the kinetics of catalyzed methanolysis maximize at pH 9.1 and a detailed analysis indicates that the dominant species responsible for catalysis are dimers formulated as La3+(2)(-OCH3)2 and La3+(2)(-OCH3)4. The catalysis is compared with that seen for the corresponding phosphate esters, namely paraoxon (3a) and O,O-diethyl phenyl phosphate (3b) for which La3+ catalysis is slightly better and markedly worse than for 4a and 4b respectively. Overall, at s(s)pH 9.1, a 2 mmol dm-3 solution of La(OTf)3 with equimolar NaOCH3 provides accelerations of 2.2x10(8)-fold, 9.7x10(6)-fold and 9.3x10(6)-fold for methanolysis of 3a, 4a and 4b, relative to the background reaction of methoxide reacting with the three substrates. In each case, the P-containing product of the reactions is exclusively diethyl methyl phosphate. Turnover experiments with 6-fold and 100-fold excesses of 4a and 4b respectively, methanolyzed in the presence of approximately 10 mmol dm-3 La3+ and equimolar NaOCH3, indicate that the reactions are essentially complete within 103 s and 70 min respectively. The latter turnover experiment with 4b corresponded to 100 turnovers in 70 min and an overall reaction t1/2 of 8 min. A common mechanism of reaction is postulated for each of the substrates which involves Lewis acid coordination of one of the La3+ to the P=O unit, followed by nucleophilic attack by the second La3+-(-)OCH3.

15.
J Am Chem Soc ; 125(25): 7602-7, 2003 Jun 25.
Artigo em Inglês | MEDLINE | ID: mdl-12812502

RESUMO

The methanolysis of the insecticide paraoxon (2) was investigated in methanol solution containing varying [La(OTf)(3)] (OTf = (-)OS(O)(2)CF(3)) as a function of at 25 degrees C. Plots of the pseudo-first-order rate constants (k(obs)) for methanolysis as a function of [La(OTf)(3)](total) were obtained under buffered conditions from 5.15 to 10.97, and the slopes of the linear parts of these were used to determine the second-order rate constants (k(2)(obs)) for the La(3+)-catalyzed methanolysis of 2. Detailed analysis of the potentiometric titration data of La(OTf)(3) in methanol through fits to a multicomponent equilibrium mixture of dimers of general stoichiometry La(3+)(2)((-)OCH3)n, where n assumes values of 1-5, gives the equilibrium distribution of each as a function of. These data, when fit to a second expression describing k(2)(obs) in terms of a linear combination of individual rate constants k(2)(2:1), k(2)(2:2).k(2)(2:)n for the dimers, allow one to describe the overall catalytic profile in terms of the individual contributions. The most catalytically important species are the three dimers La(3+)(2)((-)OCH3)1, La(3+)(2)((-)OCH3)2, and La(3+)(2)((-)OCH3)3. The catalysis of the methanolysis of 2 is spectacular: a 2 x 10(-3) M solution of [La(3+)](total), at neutral, affords a 10(9)-fold acceleration relative to the base reaction (t(1/2) approximately 20 s at 8.2) with excellent turnover. A mechanism of the catalyzed reaction involving the La(3+)(2)((-)OCH3)2 species is proposed.


Assuntos
Substâncias para a Guerra Química/química , Inseticidas/química , Lantânio/química , Mesilatos/química , Metanol/química , Paraoxon/química , Cinética , Espectroscopia de Ressonância Magnética
16.
J Am Chem Soc ; 125(6): 1559-66, 2003 Feb 12.
Artigo em Inglês | MEDLINE | ID: mdl-12568616

RESUMO

The methanolysis of hydroxypropyl-p-nitrophenyl phosphate (HPNPP, 1) promoted by La(OTf)(3) under buffered conditions was studied in methanol as a function of pH at 25 degrees C. (31)P NMR studies at -90 degrees C indicate that there are at least three La/1 complexes formed at pH approximately 5.3 of 1:1, 2:2, and 1:2 stoichiometry. Kinetic studies of the observed pseudo-first-order rate constants for the methanolysis of 1 as a function of [La(3+)] at 4.5 < pH < 10.5 indicate there are two general pH regimes. In the low pH regime between 4.5 and 7.6, the plots of k(obs) versus [La(3+)] exhibit saturation behavior with very strong 1:1 binding, with a plateau rate constant that depends on [OCH(3)(-)]. The catalytically productive species is shown to be a 2:2 complex of La(3+) and 1, where the phosphate is proposed to be doubly activated, thereby promoting the methoxide reaction by some 4.6 x 10(10)-fold. In the high pH regime from 7.9 to 10.5, 1:1, 2:2, and 2:1 La(3+)/1 complexes are formed with the La(3+) coordinated in the form of [La(3+)(OCH(3)(-))](1,2). Throughout this pH regime at high [La(3+)], a saturation complex, (La(3+)OCH(3)(-))(2)/1, is formed that spontaneously decomposes with a rate constant of (5-10) x 10(-)(3) s(-)(1), leading to an acceleration of 10(9)-fold at pH 8.0.


Assuntos
Lantânio/química , Compostos Organofosforados/química , RNA/química , Catálise , Cátions , Esterificação , Concentração de Íons de Hidrogênio , Cinética , Espectroscopia de Ressonância Magnética/métodos , Metanol/química , Organofosfatos , Fósforo , Prótons , RNA/metabolismo
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