Road Map Toward Computer-Guided Total Synthesis of Natural Products. The Dysiherbol A Case Study: What if Serendipity Hadn't Intervened?

We present a computational study inspired by the story of dysiherbol A, a natural product whose putative structure was found incorrect through synthesis by a completely fortuitous event. While the carbon connectivity and chemical environment between both structures remain similar, the real dysiherbol A has a different molecular weight than that reported for the natural product. Had the synthesis groups not been favored by fortune, it could be speculated that a substantial amount of time and effort would have been required to solve the structural puzzle. Within the realm of computer-guided total synthesis of natural products, the question arose whether a synthesis group could have in silico reassigned the structure before embarking on the experimental adventure. To address this query, we evaluated some state-of-the-art computational procedures based on their computational demand and ease of implementation for nonexpert users with basic skills in computational chemistry (including HOSE, CASCADE, ANN-PRA, ML-J-DP4, DP4, and DP4+). While discussing the strengths and limitations of these methods, this case study provides a roadmap of what could be done before venturing into complex and time-demanding total synthesis projects.

E/Z configurational determination of oximes and related derivatives through quantum mechanics NMR calculations: scope and limitations of the leading probabilistic methods

Oximes and related derivatives featuring a CN double bond are important in many areas of chemistry. Different methods for the determination of the E/Z configuration have been developed, each with its own scope and limitations. While some cannot be used when only one isomer is available, others require special NMR experiments. Here, three popular computational methodologies (DP4, DP4+, and ML-J-DP4) have been thoroughly studied using a challenging test set. Although DP4+ provides the best confidence, its computational cost might be high. On the other hand, ML-J-DP4 shows excellent performance in most cases in a fraction of CPU time. A detailed analysis of the structural factors affecting the NMR prediction and sense of the assignment is also provided.

Rationalizing the influence of α-cationic phospholes on π-catalysis

The physical factors behind the experimentally observed high activity of gold(I)-catalysts having an α-cationic phosphole as a ligand have been computationally explored. To this end, the gold(I)-catalysed hydroarylation reactions of phenylacetylene and mesitylene involving both neutral and cationic phosphole as well as phosphine ligands have been quantitatively analyzed in detail with the help of the activation strain model of reactivity in combination with the energy decomposition analysis method. It is found that the cationic phosphole ligands induce a dramatic change in both the geometry and the electronic structure of the initially formed π-complex which significantly enhances its electrophilicity. This results in an enhancement of the key π(mesitylene) → π*(LAu-acetylene complex) molecular orbital interaction which is the main factor responsible for the activating effect of these cationic ligands.

Influence of the CH/B replacement on the Reactivity of Boranthrene and Related Compounds

The influence of the replacement of CH groups by boron atoms on the reactivity of planar polycyclic aromatic hydrocarbons has been explored by means of computational tools. To this end, [4 + 2]-cycloaddition reactions involving anthracene and neutral boranthrene with different dienophiles such as ethylene, acetylene, and CO₂ have been compared. In addition, the influence of additional fused aromatic rings (pentacene or borapentacene) on the reactivity of these species has been also explored. It was found that the B-doped systems are systematically much more reactive than their all-carbon counterparts from both kinetic and thermodynamic points of view. The observed trends in reactivity are quantitatively analyzed in detail using state-of-the-art methods, namely, the activation strain model of reactivity and the energy decomposition analysis method. Our calculations reveal the importance of molecular orbital interactions as the key factor responsible for the enhanced reactivity of the B-doped systems.

Eco-friendly methoximation of aromatic aldehydes and ketones using MnCl2.4H2O as an easily accessible and efficient catalyst

Methoximes are important as a class of intermediates and products, among fine chemicals and specialties. The development of a new, facile and efficient method for their synthesis is reported. The methoximes were properly accessed from the corresponding aromatic aldehydes and ketones in good to excellent yields, under mild conditions, employing the inexpensive and environmentally friendly MnCl2.4H2O as a catalyst (at low loading and without the addition of ligand), in EtOH at 50°C. The scope of the process was systematically assessed.

First total synthesis of chromanone A, preparation of related compounds and evaluation of their antifungal activity against Candida albicans, a biofilm forming agent

A straightforward and convenient approach for the first total syntheses of chromanone A and a related 7-OMe substituted natural product is reported. These unique C-3 substituted 2-hydroxymethyl chromones were recently isolated as fungal metabolites. Chromanone A was synthesized in 25.3% overall yield from the readily available pyrocatechol, whereas the second natural product was prepared in 39.7% global yield. A small library of chromones, including both natural products and some of their synthetic heterocyclic precursors, was evaluated against Candida albicans ATCC 10231, a biofilm forming agent. It was found that 8-methoxy-3-methyl-4-oxo-4H-chromene-2-carbaldehyde, a partially oxidized form of chromanone A, exhibited a minimum inhibitory concentration of 7.8 μg mL⁻¹ and significantly inhibited the yeast's virulence factors, including the adherence to buccal epithelial cells and the secretion of phospholipases, as well as the formation of germ tubes and the generation of the hyphal pseudomycelium. In addition, despite the heterocycle exhibiting non-significant inhibition of the formation of the Candida biofilm, it completely inhibited the growth of C. albicans in preformed biofilms at 62.5 μg mL⁻¹.

Chromanone A and its 7-OMe analogue were totally synthesized. 2-Formyl chromanone A derivative inhibited C. albicans and its virulence factors.

Furo[3,2-c]coumarins carrying carbon substituents at C-2 and/or C-3. Isolation, biological activity, synthesis and reaction mechanisms

The isolation, biological activity and synthesis of natural furo[3,2-c]coumarins are presented, covering mainly the developments in the last 35 years. The most relevant approaches toward the synthesis of 2-substituted, 3-substituted and 2,3-disubstituted heterocycles are also discussed, with emphasis on the efficiency of the processes and their mechanisms.

Synthesis and evaluation of aromatic methoxime derivatives against five postharvest phytopathogenic fungi of fruits. Main structure-activity relationships

The antifungal activity of a library of twenty-four aromatic methoximes was examined against five representative postharvest phytopathogenic fungi. The panel included Penicillium digitatum, Penicillium italicum, Rhizopus stolonifer, Botrytis cinerea and Monilinia fructicola, all of which cause relevant economic losses worldwide as a result of affecting harvested fruits. The minimum inhibitory concentrations and minimum fungicidal concentrations of each compound were defined and the main structure-activity relationships were determined. Although other congeners were more potent, drug likeliness considerations pointed to the methoxime derived from 2,4-dihydroxypropiophenone as the compound with the most suitable profile. The morphology of the colonies of the fungal strains treated with the methoxime was examined microscopically and the compound was also tested in freshly harvested peaches and oranges, exhibiting promising control profiles in both fruits, similar to those of the commercial agents Imazalil and Carbendazim.

Total Synthesis and Cytotoxic Activity of 6,8-Dimethoxy-1,3-dimethylisoquinoline Isolated from Ancistrocladus tectorius: A 6π-Azaelectrocyclization Approach

A facile and convenient approach toward the total synthesis of 1,3-dimethyl-6,8-dimethoxyisoquinoline from phloroacetophenone is reported. The sequence entailed the selective 2,4-di-O-methylation and further triflation of the resulting phenolic product. This was followed by a Stille-type allylation, an allyl-to-propenyl isomerization, and the methoximation of the carbonyl moiety. A final microwave-assisted 6π-azaelectrocyclization completed the sequence. Functionalized derivatives on C-1 were also prepared. The heterocycles exhibited cytotoxic activity.

A convenient and eco-friendly cerium(III) chloride-catalysed synthesis of methoxime derivatives of aromatic aldehydes and ketones

The use of CeCl₃·7H₂O as an efficient and eco-friendly promoter for the convenient synthesis of methoximes derived from aromatic aldehydes and ketones, is reported. The transformations entail the use of equimolar amounts of MeONH₂·HCl and NaOAc in EtOH at 50°C, and no special precautions are needed with regard to the presence of oxygen. The scope and limitations of the transformation were studied and a reaction mechanism was proposed.

Acute respiratory distress syndrome: evaluation and management

Acute respiratory distress syndrome (ARDS) is a life-threatening condition that affects patients admitted in the Intensive Care Units (ICUs) under mechanical ventilation. ARDS is a process of non-hydrostatic pulmonary edema and hypoxemia associated with a variety of conditions, resulting in a direct (e.g., pneumonia) or indirect (e.g., sepsis) lung injury and is associated with a significant morbidity and mortality. A large body of clinical and basic research has focused in ventilatory strategies and novel pharmacological therapies but, nowadays, treatment is mainly supportive. Mechanical ventilation is the hallmark of the management of these patients. In the last decades, the recognition that mechanical ventilation can contribute to harming the lung has changed the goals of this therapy and has driven research to focus in ventilatory strategies that mitigate lung injury. This review emphasizes clinical aspects in the evaluation and management of ARDS in the ICUs and updates the latest advances in these therapies.

Acute kidney injury in critically ill patients with 2009 influenza A (H1N1) viral pneumonia: an observational study

OBJECTIVE

To describe the incidence, risk factors, and impact on mortality of acute kidney injury (AKI) in patients with 2009 influenza A (H1N1) viral pneumonia requiring mechanical ventilation.

DESIGN

Observational cohort study.

PATIENTS AND METHODS

AKI was defined as risk, injury or failure, according to the RIFLE classification. Early and late AKI were defined as AKI occurring on intensive care unit (ICU) day 2 or before, or after ICU day 2, respectively. Demographic data and information on organ dysfunction were collected daily.

RESULTS

Of 84 patients, AKI developed in 43 patients (51%). Twenty (24%) needed renal replacement therapy. Early and late AKI were found in 28 (33%) and 15 (18%) patients, respectively. Patients with AKI, as compared with patients without AKI, had higher Acute Physiology and Chronic Health Evaluation (APACHE) II score and ICU mortality (72% versus 39%, p < 0.01) and presented on admission more marked cardiovascular, respiratory, and hematological dysfunction. Patients with early but not late AKI presented on admission higher APACHE II score and more marked organ dysfunction, as compared with patients without AKI. ICU mortality was higher in late versus early AKI (93% versus 61%, p < 0.001). On multivariate analysis, only APACHE II score and late but not early AKI [odds ratio (OR) 1.1 (95% confidence interval 1.0-1.1) and 15.1 (1.8-130.7), respectively] were associated with mortality.

CONCLUSIONS

AKI is a frequent complication of 2009 influenza A (H1N1) viral pneumonia. AKI developing after 2 days in ICU appears to be associated with different risk factors than early AKI, and is related to a higher mortality rate.

Treatment of wastewater from red and tropical fruit wine production by zeolite anaerobic fluidized bed reactor

A study of the anaerobic treatment of wastewaters derived from red (RWWW) and tropical fruit wine (TFWWW) production was carried out in four laboratory-scale fluidized bed reactors with natural zeolite as bacterial support. These reactors operated at mesophilic temperature (35 degrees C). Reactors R1 and R2 contained Chilean natural zeolite, while reactors R3 and R4 used Cuban natural zeolite as microorganism support. In addition, reactors R1 and R3 processed RWWW, while reactors R2 and R4 used TFWWW as substrate. The biomass concentration attached to zeolites in the four reactors studied was found to be in the range of 44-46 g volatile solids (VS)/L after 90 days of operation time. Both types of zeolites can be used indistinctly in the fluidized bed reactors achieving more than 80%-86% chemical oxygen demand (COD) removals for organic loading rates (OLR) of up to at least 20 g COD/L d. pH values remained within the optimal range for anaerobic microorganisms for OLR values of up to 20 and 22 g COD/L d for RWWW and TFWWW, respectively. Toxicity and inhibition levels were observed at an OLR of 20 g COD/L d in reactors R1 and R3 while processing RWWW, whereas the aforementioned inhibitory phenomena were not observed at an OLR of 24 g COD/L d in R2 and R4, treating TFWWW as a consequence of the lower phenolic compound content present in this substrate. The volatile fatty acid (VFA) levels were always lower in reactors processing TFWWW (R2 and R4) and these values (< 400 mg/L, as acetic acid) were lower than the suggested limits for digester failure. The specific methanogenic activity (SMA) was twice as high in reactors R2 and R4 than in R1 and R3 after 120 days of operation when all reactors operated at an OLR of 20 g COD/L d.

A cascade involving p85, Cdc42 and septin 2 regulates cytokinesis

Mitosis, the final phase of cell division, includes the processes of nuclear division and cytosolic division (cytokinesis). Cytokinesis occurs when DNA separation terminates, and involves a number of proteins that induce furrowing at the region of cell separation, formation of new membrane, and abscission. This process is remarkably complex, and the list of proteins that regulate it is long. Our understanding is limited as to how these players are organized in space and time to ensure that the cytosol divides equally, and only after nuclear division. Class I(A) PI3K (phosphoinositide 3-kinase) is an enzyme activated by growth factor receptor stimulation, but it is re-activated in early mitosis and regulates mitosis entry. By the end of mitosis, PI3K activity is low; at this point, the class I(A) PI3K regulatory subunit p85 contributes to co-ordination of the cytoskeletal changes required for cytokinesis. The impact of these observations on current models of cytokinesis execution is discussed here.

Anaerobic fluidized bed reactor application to tropical fruit wine effluent

The influence of the organic loading rate (OLR), the fluidization level (FL) and the particle diameter of natural zeolite used as support (D(p)), was evaluated at a laboratory scale anaerobic fluidized bed reactor (AFBR), treating tropical fruit wine effluent (vinasse). The experiment was carried out at an OLR from 2-5 kg COD/m3 d, FL of 20 and 40% and D(p) from 0.25 to 0.80 mm. It was demonstrated that OLR and FL had a slight influence on chemical oxygen demand removal and strong influence on the methane production rate. The COD removal was slightly higher for the higher particle diameter used. Additionally using the scanning electron microscope (SEM), it was observed that natural zeolites have excellent physical characteristics as a support medium in AFBR.

[Antioxidative state and lipid peroxidation in erectile dysfunction: preliminary study]

OBJECTIVE

The aims of this study were to analyze the cavernosal tissue metabolic status of patients with vascular and psychogenic impotence and attempt to establish metabolic differences between these types of erectile dysfunction.

METHODS

103 patients were classified according to the type of erectile dysfunction into group A (vascular) and group B (psychogenic). Diagnosis was based on clinical history, physical examination, intracavernosal injection test, penile echo-doppler assessment, cavernosography-cavernosometry and nocturnal penile test. Cavernosal and peripheral venous blood samples were obtained from each patient and the lipoperoxide (LPO) levels and total antioxidant status (TAS) were determined. SPSS V9.0 was used for the statistical analysis.

RESULTS

The mean age was 62 years (range 32-73). Cavernosal blood lipoperoxide levels were statistically higher (p < 0.05) in patients with vascular impotence (2.45 mumol/L) than in those with psychogenic impotence (1.47 mumol/L). Cavernosal blood total antioxidant status was statistically higher (p < 0.05) in patients with psychogenic (1.40 mmol/L) than those with vascular impotence (1.10 mmol/L). The lipoperoxide levels and total antioxidant status for peripheral blood were 1.68 mumol/L vs 1.60 mumol/L and 1.29 mmol/L vs 1.35 mmol/L, respectively, with no statistically significant differences between both groups.

CONCLUSIONS

Cavernosal blood lipoperoxide levels and total antioxidant status can be an indicator of cavernosal tissue metabolic status and function.