Is Iron Overload Associated with Worse Outcomes in Patients with Chronic Liver Disease Undergoing Liver Transplantation?

ABSTRACT Background: Iron overload is frequent in patients with chronic liver disease, associated with shorter survival after liver transplantation in patients with hereditary hemochromatosis. Its effect on patients without hereditary hemochromatosis is unclear. The aim of the study was to study the clinical impact of iron overload in patients who underwent liver transplantation at an academic tertiary referral center. Methods: We performed a retrospective cohort study including all patients without hereditary hemochromatosis who underwent liver transplantation from 2015 to 2017 at an academic tertiary referral center in Mexico City. Explant liver biopsies were reprocessed to obtain the histochemical hepatic iron index, considering a score ≥ 0.15 as iron overload. Baseline characteristics were compared between patients with and without iron overload. Survival was estimated using the Kaplan-Meier method, compared with the log-rank test and the Cox proportional hazards model. Results: Of 105 patients included, 45% had iron overload. Viral and metabolic etiologies, alcohol consumption, and obesity were more frequent in patients with iron overload than in those without iron overload (43% vs. 21%, 32% vs. 22%, p = 0.011; 34% vs. 9%, p = 0.001; and 32% vs. 12%, p = 0.013, respectively). Eight patients died within 90 days after liver transplantation (one with iron overload). Complication rate was higher in patients with iron overload versus those without iron overload (223 vs. 93 events/100 person-months; median time to any complication of 2 vs. 3 days, p = 0.043), without differences in complication type. Fatality rate was lower in patients with iron overload versus those without iron overload (0.7 vs. 4.5 deaths/100 person-months, p = 0.055). Conclusion: Detecting iron overload might identify patients at risk of early complications after liver transplantation. Further studies are required to understand the role of iron overload in survival.

Assessing greenhouse gas emissions in Cuban agricultural soils: Implications for climate change and rice (Oryza sativa L.) production.

Assessing the impact of greenhouse gas (GHG) emissions on agricultural soils is crucial for ensuring food production sustainability in the global effort to combat climate change. The present study delves to comprehensively assess GHG emissions in Cuba's agricultural soil and analyze its implications for rice production and climate change because of its rich agriculture cultivation tradition and diverse agro-ecological zones from the period of 1990-2022. In this research, based on Autoregressive Distributed Lag (ARDL) approach the empirical findings depicts that in short run, a positive and significant impact of 1.60 percent % in Cuba's rice production. The higher amount of atmospheric carbon dioxide (CO2) levels improves photosynthesis, and stimulates the growth of rice plants, resulting in greater grain yields. On the other hand, rice production index raising GHG emissions from agriculture by 0.35 % in the short run. Furthermore, a significant and positive impact on rice production is found in relation to the farm machinery i.e., 3.1 %. Conversely, an adverse and significant impact of land quality was observed on rice production i.e., -5.5 %. The reliability of models was confirmed by CUSUM and CUSUM square plot. Diagnostic tests ensure the absence of serial correlation and heteroscedasticity in the models. Additionally, the forecasting results are obtained from the three machine learning models i.e. feed forward neural network (FFNN), support vector machines (SVM) and adaptive boosting technique (Adaboost). Through the % MAPE criterion, it is evident that FFNN has achieved high precision (91 %). Based on the empirical findings, the study proposed the adoption of sustainable agricultural practices and incentives should be given to the farmers so that future generations inherit a world that is sustainable, and healthy.

Is iron overload associated with worse outcomes in patients with chronic liver disease undergoing liver transplantation?

Background: Iron overload is frequent in patients with chronic liver disease, associated with shorter survival after liver transplantation in patients with hereditary hemochromatosis. Its effect on patients without hereditary hemochromatosis is unclear. The aim of the study was to study the clinical impact of iron overload in patients who underwent liver transplantation at an academic tertiary referral center. Methods: We performed a retrospective cohort study including all patients without hereditary hemochromatosis who underwent liver transplantation from 2015 to 2017 at an academic tertiary referral center in Mexico City. Explant liver biopsies were reprocessed to obtain the histochemical hepatic iron index, considering a score ≥ 0.15 as iron overload. Baseline characteristics were compared between patients with and without iron overload. Survival was estimated using the Kaplan-Meier method, compared with the log-rank test and the Cox proportional hazards model. Results: Of 105 patients included, 45% had iron overload. Viral and metabolic etiologies, alcohol consumption, and obesity were more frequent in patients with iron overload than in those without iron overload (43% vs. 21%, 32% vs. 22%, p = 0.011; 34% vs. 9%, p = 0.001; and 32% vs. 12%, p = 0.013, respectively). Eight patients died within 90 days after liver transplantation (one with iron overload). Complication rate was higher in patients with iron overload versus those without iron overload (223 vs. 93 events/100 personmonths; median time to any complication of 2 vs. 3 days, p = 0.043), without differences in complication type. Fatality rate was lower in patients with iron overload versus those without iron overload (0.7 vs. 4.5 deaths/100 person-months, p = 0.055). Conclusion: Detecting iron overload might identify patients at risk of early complications after liver transplantation. Further studies are required to understand the role of iron overload in survival.

Are accessory spleen screening and resection in refractory immune cytopenia an effective strategy or a waste of resources?

Splenectomy remains an effective treatment for refractory immune cytopenia (RIC), which encompasses immune thrombocytopenia (ITP) and autoimmune hemolytic anemia (AIHA). Accessory spleens (AS) have been described without identifying specific risk factors. We retrospectively analyzed patients with RIC after splenectomy who underwent splenic scintigraphy (SS) at our institution. Seventy-one patients were included. Sixty-two patients had ITP, five had AIHA, and four had Evans syndrome. Seventy-five percent (n = 53) were women. Eleven patients (15.5%) had an AS detected by SS. A complete response (CR) to first-line steroids (odds ratio (OR) 5.75, 95% confidence interval (CI) 1.37-24.14, p = 0.017) and the absence of Howell-Jolly bodies (HJB) in peripheral blood smear (PBS) (OR 11.37, 95% CI 2.70-47.85, p = 0.001) were found to be risk factors. Patients with both elements had a higher rate of AS (83.3%) when compared to those with one or no factors (p < 0.001). Eight patients (73%) underwent an accessory splenectomy: seven (87.5%) achieved a CR, and none had perioperative complications. The presence of HJB in PBS changed from 25 to 87.5% after accessory splenectomy. We recommend the search for an AS via SS in patients with RIC due to ITP, who had a CR to corticosteroids and the absence of HJB in PBS. Accessory splenectomy is a safe and effective procedure.

Cost-effectiveness of the regimen proposed by the International Consortium on Acute Promyelocytic Leukemia for the treatment of newly diagnosed patients with Acute Promyelocytic Leukemia

ABSTRACT Introduction: We performed cost-effectiveness and cost-utility analyses of the modified International Consortium on Acute Promyelocytic Leukemia protocol in Mexico for the treatment of acute promyelocytic leukemia Acute Promyelocytic Leukemia. Methods: We performed a three-state Markov analysis: stable disease (first line complete response [CR]), disease event (relapse, second line response and CR) and death. The modified IC-APL protocol is composed of three phases: induction, consolidation and maintenance. Cost and outcomes were used to calculate incremental cost-effectiveness ratios (ICERs); quality-adjusted life-years were used to calculate incremental cost-utility ratios (ICURs). Results: The CR was achieved in 18 patients (90%), treated with the IC-APL protocol as the first-line option; one patient (5%) died in induction, another one never achieved CR (5%); of the 18 patients that achieved CR, 1 relapsed (5.5%). The median treatment cost of the IC-APL protocol was $21,523 USD. The average life-year in our study was 7.8 years, while the average quality-adjusted life-year (QALY) was 6.1 years. When comparing the ICER between the IC-APL and the all-trans retinoic acid (ATRA) plus arsenic trioxide (ATO) protocols, we found the different costs of $6497, $19,133 and $17,123 USD in Italy, the USA and Canada, respectively. In relation to the ICUR, we found the different costs to be $13,955 and $11,979 USD in the USA and Canada, respectively. Conclusion: Taking into account the similar response rates, lower cost and easy access to the modified IC-APL regimen, we consider it a cost-effective and cost-utility protocol, deeming it the treatment of choice for our population.

Adverse Effects Associated With the Use of Antimalarials During The COVID-19 Pandemic in a Tertiary Care Center in Mexico City.

Background: Antimalarial drugs were widely used as experimental therapies against COVID-19 in the initial stages of the pandemic. Despite multiple randomized controlled trials demonstrating unfavorable outcomes in both efficacy and adverse effects, antimalarial drugs are still prescribed in developing countries, especially in those experiencing recurrent COVID-19 crises (India and Brazil). Therefore, real-life experience and pharmacovigilance studies describing the use and side effects of antimalarials for COVID-19 in developing countries are still relevant. Objective: To describe the adverse effects associated with the use of antimalarial drugs in hospitalized patients with COVID-19 pneumonia at a reference center in Mexico City. Methods: We integrated a retrospective cohort with all adult patients hospitalized for COVID-19 pneumonia from March 13th, 2020, to May 17th, 2020. We compared the baseline characteristics (demographic and clinical) and the adverse effects between the groups of patients treated with and without antimalarial drugs. The mortality analysis was performed in 491 patients who received optimal care and were not transferred to other institutions (210 from the antimalarial group and 281 from the other group). Results: We included 626 patients from whom 38% (n = 235) received an antimalarial drug. The mean age was 51.2 ± 13.6 years, and 64% were males. At baseline, compared with the group treated with antimalarials, the group that did not receive antimalarials had more dyspnea (82 vs. 73%, p = 0.017) and cyanosis (5.3 vs. 0.9%, p = 0.009), higher respiratory rate (median of 28 vs. 24 bpm, p < 0.001), and lower oxygen saturation (median of 83 vs. 87%, p < 0.001). In the group treated with antimalarials, 120 patients had two EKG evaluations, from whom 12% (n = 16) prolonged their QTc from baseline in more than 50 ms, and six developed a ventricular arrhythmia. Regarding the trajectories of the liver function tests over time, no significant differences were found for the change in the mean value per day between the two groups. Among patients who received optimal care, the mortality was 16% (33/210) in those treated with antimalarials and 15% (41/281) in those not receiving antimalarials (RR 1.08, 95% 0.75-1.64, and adjusted RR 1.12, 95% CI 0.69-1.82). Conclusion: The adverse events in patients with COVID-19 treated with antimalarials were similar to those who did not receive antimalarials at institutions with rigorous pharmacological surveillance. However, they do not improve survival in patients who receive optimal medical care.

Cost-effectiveness of the regimen proposed by the International Consortium on Acute Promyelocytic Leukemia for the treatment of newly diagnosed patients with Acute Promyelocytic Leukemia.

INTRODUCTION: We performed cost-effectiveness and cost-utility analyses of the modified International Consortium on Acute Promyelocytic Leukemia protocol in Mexico for the treatment of acute promyelocytic leukemia Acute Promyelocytic Leukemia. METHODS: We performed a three-state Markov analysis: stable disease (first line complete response [CR]), disease event (relapse, second line response and CR) and death. The modified IC-APL protocol is composed of three phases: induction, consolidation and maintenance. Cost and outcomes were used to calculate incremental cost-effectiveness ratios (ICERs); quality-adjusted life-years were used to calculate incremental cost-utility ratios (ICURs). RESULTS: The CR was achieved in 18 patients (90%), treated with the IC-APL protocol as the first-line option; one patient (5%) died in induction, another one never achieved CR (5%); of the 18 patients that achieved CR, 1 relapsed (5.5%). The median treatment cost of the IC-APL protocol was $21,523 USD. The average life-year in our study was 7.8 years, while the average quality-adjusted life-year (QALY) was 6.1 years. When comparing the ICER between the IC-APL and the all-trans retinoic acid (ATRA) plus arsenic trioxide (ATO) protocols, we found the different costs of $6497, $19,133 and $17,123 USD in Italy, the USA and Canada, respectively. In relation to the ICUR, we found the different costs to be $13,955 and $11,979 USD in the USA and Canada, respectively. CONCLUSION: Taking into account the similar response rates, lower cost and easy access to the modified IC-APL regimen, we consider it a cost-effective and cost-utility protocol, deeming it the treatment of choice for our population.

Prognostic Factors and Outcomes in Adults With Secondary Hemophagocytic Lymphohistiocytosis: A Single-center Experience.

INTRODUCTION: Hemophagocytic lymphohistiocytosis (HLH) is a disorder caused by severe immune activation. There are no specific criteria to establish the diagnosis in adults; however, the HLH-04 criteria are among the most commonly used. The HScore is a non-validated tool that can also be useful for HLH diagnosis. PATIENTS AND METHODS: We describe the prognostic factors and outcomes of 64 adults diagnosed with HLH in a reference medical center in Mexico City. We included patients ≥ 18 years with HLH, diagnosed and treated at our institution from 1998 to 2016. RESULTS: The median age was 35 years (range, 18-77 years). The underlying cause of HLH was lymphoma in 33 (51.56%) patients (MA-HLH). Cutaneous involvement was more frequent in MA-HLH (33.33%), when compared with patients with non-malignancy associated HLH (NM-HLH) (9.68%) (P = .022). Neurologic symptoms were more frequent in NM-HLH (25.81%) versus MA-HLH (6.06%) (P = .032). After a median follow-up of 14 months (range, 0-216 months), 30-day mortality was 26.56%. Three-year overall survival (OS) was higher for patients with MA-HLH compared with patients with NM-HLH (41% vs. 22.5%; P = .046). Multivariate analysis showed that the presence of nosocomial infection and neurologic symptoms were statistically significant predictors of inferior OS (P = .034 and P = .033, respectively). CONCLUSION: In this series of adults with HLH, patients with nosocomial infections and neurologic symptoms had a statistically significant worse OS. In the largest series in Latin America, the most common cause of HLH was T-cell lymphoma. In our population, NM-HLH presented a higher mortality.

Survival analysis of adult patients with ALL in Mexico City: first report from the Acute Leukemia Workgroup (ALWG) (GTLA).

Acute lymphoblastic leukemia (ALL) is a hematologic malignancy characterized by the clonal expansion of hematopoietic lymphoid progenitors. With new target therapies, the survival of adults with ALL has improved in the past few decades. Unfortunately, there are no large ALL patient series in many Latin American countries. Data from the Acute Leukemia Workgroup that includes five Mexico City referral centers were used. Survival was estimated for adult patients with ALL during 2009-2015. In total, 559 adults with ALL were included. The median age was 28 years; 67% were classified into the adolescent and young adult group. Cytogenetic information was available in 54.5% of cases. Of the 305 analyzed cases, most had a normal caryotype (70.5%) and Philadelphia-positive was present in 16.7%. The most commonly used treatment regimen was hyper-CVAD. In approximately 20% of cases, there was considerable delay in the administration of chemotherapy. Primarily refractory cases accounted for 13.1% of patients. At the time of analysis, 26.7% of cases had survived. The 3-year overall survival was 22.1%. The main cause of death was disease progression in 228 (55.6%). Clinical and public health strategies are needed to improve diagnosis, treatment and survivorship care for adult with ALL. This multicentric report represents the largest series in Mexico of adult ALL patients in which a survival analysis and risk identification were obtained.

Splenic myeloid metaplasia in warm autoimmune hemolytic anemia (wAIHA): a retrospective study.

BACKGROUND: Splenic myeloid metaplasia (SMM) is a kind of extramedullary hematopoiesis, whereas its clinical significance in wAIHA remains unclear. The aim of this study is evaluating the frequency and clinical characteristics of SMM, compared with splenic-congestion (SC). METHODS: We included patients with wAIHA treated in a Mexican tertiary hospital between January 1992 and December 2015. All patients received steroids as first-line treatment and splenectomy as second-line treatment. RESULTS: Among the thirty-six splenectomized patients, 15 (41.6%) and 21 (58.4%) were diagnosed as SMM and SC, respectively. No differences were found in clinical characteristics between two groups. SMM patients showed lower platelet count (147×109/L vs. 240×109/L, P=0.02) and higher presence of anti-dsDNA antibodies (40% vs. 4.7%, P=0.01) than SC patients. Although the complete response (CR) rate with first-line treatment was lower in SMM patients (13.3% vs. 47.6%; P=0.04), post-splenectomy median disease-free-survival (DFS) was longer (16.2 mo vs. 5.1 mo; P=0.19). Univariate/multivariate analysis showed that achieving CR during first-line treatment (OR 0.3, 95% CI: 0.03-0.94, P=0.03) and higher platelet count (OR 0.99, 95% CI: 0.98-0.99, P=0.03) were protective factors for SMM; and anti-dsDNA titer higher than 9.6 IU/dL was a risk factor for SMM (OR 2.76, 95% CI: 1.48-5.14, P<0.001). CONCLUSION: The wAIHA patients with SMM have different biological profiles with those without SMM. This study is the first trial evaluating the significance of histopathological spleen findings and their association with rheumatologic profile.

Importance of CD117 in the Assignation of a Myeloid Lineage in Acute Leukemias.

The correct classification of acute leukemias (AL) is an essential part in the evaluation of any patient with this disease. Historically, CD117 has been an important asset in the diagnosis of patients with mixed-phenotype acute leukemia (MPAL). In an attempt to simplify the diagnosis of MPAL with fewer and more lineage specific markers, the World Health Organization (WHO) proposed in 2008 a new criteria for the diagnosis of this type of AL, which excluded CD117 from the myeloid markers that are utilized to diagnose MPAL. In order to assess whether CD117 is necessary in the diagnosis of MPAL, we evaluated the sensitivity and specificity of CD117 for acute myeloid leukemia (AML) in 331 patients with AL. The calculated sensitivity of CD117 for AML was 85.88% (103/120), while the specificity was 83.9% (177/211). Besides myeloperoxidase (MPO), which was used as the gold standard in differentiating AML from other type of ALs, the most specific markers for AML in our study were CD14 and CD64 (99.5 and 95.6%). Although the specificity of CD117 in this study is not as high as CD14 and CD64, markers concomitantly used in this this study and in the WHO classification, based on the results of other researches (i.e. the specificity of CD117 for AML was 100% in one study) and due to the fact that its specificity for AML in this study is relatively high, we recommend the use CD117 in assigning a myeloid lineage in MPAL.

Warm autoimmune hemolytic anemia: experience from a single referral center in Mexico City

BACKGROUND: Autoimmune hemolytic anemia (AIHA) is characterized by an autoimmune-mediated destruction of red blood cells. Warm AIHA (wAIHA) represents 60% of AIHA cases and is associated with the positive detection of IgG and C3d in the direct antiglobulin test (DAT). This study aimed to assess the clinical and laboratorial differences between primary and secondary wAIHA patients from a referral center in Mexico City. METHODS: All patients diagnosed with wAIHA in our institution from January 1992 to December 2015 were included and received corticosteroids as the first-line treatment. We analyzed the response to the first-line treatment, relapse-free survival, and time to splenectomy. RESULTS: Eighty-nine patients were included. Secondary wAIHA represented 55.1% of the cases. At diagnosis, secondary wAIHA patients showed a DAT mixed pattern more frequently than primary wAIHA patients (36.7 vs. 17.5%, P<0.001). In the survival analysis, patients with secondary wAIHA had a lower time to response (18 vs. 37 days, P=0.05), median disease-free survival (28.51 vs. 50.95 weeks, P=0.018), and time to splenectomy (43.5 vs. 61 wks, P=0.029) than those with primary wAIHA. Due to economic constraints, rituximab was considered as the third-line treatment in only two patients. CONCLUSION: Secondary wAIHA may benefit from a longer low-dose steroid maintenance period mainly due to its shorter time to relapse and time to splenectomy than primary wAIHA.

Expression of HER2/Neu in B-Cell Acute Lymphoblastic Leukemia.

BACKGROUND: The expression of HER2/neu in B-cell acute lymphoblastic leukemia has been reported in previous studies. OBJECTIVE: The objective of this research was to study the expression of HER2/neu on the blasts of patients with acute leukemia from the Instituto Nacional de Ciencias Medicas y Nutricion Salvador Zubiran. METHODS: From June 2015 to February 2016, a HER2/neu monoclonal antibody was added to the panel of antibodies that we routinely use in patients with acute leukemia. An expression of ≥ 30% was considered positive. RESULTS: We studied 33 patients: 19 had de novo leukemia (57.6%), three (9.1%) were in relapse, and in 11 (33.3%) their status could not be specified. Seventeen patients (51.5%) were classified as B-cell acute lymphoblastic leukemia with a median expression of HER2/neu of 0.3% (range 0-90.2). Three patients with B-cell acute lymphoblastic leukemia were positive for HER2/neu: 89.4%, 90.9%, and 62.4%. The first and third patient had de novo B-cell acute lymphoblastic leukemia. The second patient was in second relapse after allogeneic stem cell transplant. All three patients were categorized as high-risk at the time of diagnosis. CONCLUSIONS: In the studied Mexican population, we found a positive expression of HER2/neu in 17% of the B-cell acute lymphoblastic leukemia patients, similar to previous studies in which the expression was found in 15-50%.

Atypical Proliferating Trichilemmal Cyst with Malignant Breast Skin Transformation: A Case Report and Review of the Literature.

Proliferating trichilemmal tumors (PTTs) are benign adnexal skin neoplasms that arise from the outer root sheath of the hair follicle. These tumors are most commonly observed on the scalp and occur, most of the time, in elderly women. Malignant transformation of these neoplasms is a rare event; less than 50 cases have been reported in the English medical literature. We present the case of a 39-year-old Hispanic woman with a tumor located on the skin of one of her breasts that in her third surgical procedure the histologic examination revealed the presence of a malignant proliferating trichilemmal tumor (MPTT). Furthermore, a review of the medical literature and a discussion of the clinical and pathologic features of this rare entity are provided.

Mixed-phenotype acute leukemia: suboptimal treatment when the 2008/2016 WHO classification is used.

BACKGROUND: Different criteria have been used to diagnose mixed-phenotype acute leukemia (MPAL), which has impacted the number of individuals diagnosed with this pathology. Better outcomes have been reported when using acute lymphoblastic leukemia (ALL)-type chemotherapy in the treatment of MPAL. METHODS: We compared the outcome of 4 groups of patients with MPAL. Group 1 included patients diagnosed using the 2008/2016 World Health Organization (WHO) classification; group 2 included patients diagnosed using the European Group for the Immunological Characterization of Leukemias (EGIL) criteria; group 3 included patients diagnosed using either the EGIL or the 2008/2016 WHO criteria; and group 4 was comprised of patients diagnosed with MPAL using the EGIL classification only. RESULTS: We found a significantly worse disease-free survival (groups 1-4) and overall survival (OS) (groups 2 and 3) when comparing MPAL patients to other acute leukemia (AL) patients. A significantly better OS was obtained in patients (groups 2-4) treated with ALL-type chemotherapy compared to acute myeloid leukemia (AML)-type regimens. CONCLUSION: In light of these results, and because a trend (P=0.06) was found with regard to a better OS in group 4 when compared to other AL patients, an argument can be made that the 2008/2016 WHO classification is underpowered to diagnose all MPAL cases, potentially resulting in the suboptimal treatment of some individuals with AL.

Impact of Aberrant Antigens in the Outcome of Patients with Acute Leukemia at a Referral Institution in Mexico City.

BACKGROUND: Patients with acute leukemia can express aberrant markers, defined as antigens that are normally restricted to a different lineage. The reported significance and frequency of these markers is inconclusive. We assessed the frequency and impact of aberrant markers in patients with acute leukemia in a referral institution in Mexico City. METHODS: We included 433 patients, diagnosed and treated between 2005 and 2015 in our institution. RESULTS: Aberrant markers were expressed in 128 patients (29.6%); CD13 and CD33 were the most frequent aberrant markers in patients with acute lymphoblastic leukemia, while CD7 and CD19 were the most frequent in patients with acute myeloid leukemia. In the univariate analysis, the group with aberrant markers had a lower disease-free survival when compared with the aberrant-free group (8 vs. 13 months) (p = 0.03). Aberrant expression of CD10, CD20, and CD33 correlated with a worse outcome in a statistically significant manner. In the multivariate analysis, male gender, lymphoid lineage, secondary leukemia, high risk at diagnosis, and the presence of aberrant markers had a significantly negative impact on disease-free survival. CONCLUSION: The use of more aggressive treatment strategies could be considered in patients with acute leukemia and an aberrant expression of CD10, CD20, and CD33.

Stereochemical outcome of copper-catalyzed C-H insertion reactions. An experimental and theoretical study.

The combination of chiral preparative HPLC separation, VCD measurements, and theoretical calculations allows the unambiguous determination of the absolute configuration of the conformationally flexible products of copper-catalyzed carbene insertion reactions. DFT calculations were used to predict the stereochemical outcome of the copper-bis(oxazoline)-catalyzed C-H insertion reaction between methyl diazophenylacetate and tetrahydrofuran and also to predict the absolute configuration of the major stereoisomers derived from the same reaction with different cyclic ethers. These predictions were verified experimentally through NMR and VCD spectroscopy and allowed rationalization of the stereochemical outcome of these reactions without further derivatization of the products, which can be prblematic under certain conditions as described herein.

Metal-free dehydration of glucose to 5-(hydroxymethyl)furfural in ionic liquids with boric acid as a promoter.

The dehydration of glucose and other hexose carbohydrates to 5-(hydroxymethyl)furfural (HMF) was investigated in imidazolium-based ionic liquids with boric acid as a promoter. A yield of up to 42% from glucose and as much as 66% from sucrose was obtained. The yield of HMF decreased as the concentration of boric acid exceeded one equivalent, most likely as a consequence of stronger fructose-borate chelate complexes being formed. Computational modeling with DFT calculations confirmed that the formation of 1:1 glucose-borate complexes facilitated the conversion pathway from glucose to fructose. Deuterium-labeling studies elucidated that the isomerization proceeded via an ene-diol mechanism, which is different to that of the enzyme-catalyzed isomerization of glucose to fructose. The introduced non-metal system containing boric acid provides a new direction in the search for catalyst systems allowing efficient HMF formation from biorenewable sources.

Theoretical insights into enantioselective catalysis: the mechanism of the Kharasch-Sosnovsky reaction.

The mechanism of the Kharasch-Sosnovsky reaction has been investigated using B3 LYP/6-31G* calculations on a chiral reaction model [cyclohexene+tert-butyl perbenzoate-->cyclohex-2-enyl benzoate+tert-butyl alcohol, catalyzed by a chiral bisoxazoline-copper(I) complex]. Although two previous reaction mechanisms have been considered, the results are consistent with a new mechanistic pathway. This path involves ligand exchange between the catalyst-cyclohexene complex with tert-butyl perbenzoate to give a catalyst-perester complex, which undergoes an (either one- or two-step) oxidative addition reaction to yield a copper(III) complex. The limiting step of the Kharasch-Sosnovsky reaction consists of an intramolecular step involving the abstraction of an allylic hydrogen from cyclohexene [which is pi-bound to the copper(III) complex]. The resulting allyl-copper(III) complex (subsequent to the loss of tert-butanol) can undergo a haptotropic rearrangement by means of an eta1-allyl/eta3-allyl equilibrium, leading to scrambling between vinylic and allylic positions when an isotopically labeled substrate is used. The allyl-copper(III) ion undergoes a stereospecific reductive elimination involving the pi-bond migration to yield a reaction product-catalyst complex, which can regenerate the alkene-copper(I) complex by ligand exchange. The proposed reaction mechanism is consistent with all known experimental results (including enantioselectivity data).