Conformationally Biased Ketones React Diastereoselectively with Allylmagnesium Halides.

The addition of the highly reactive reagent allylmagnesium halide to α-substituted acyclic chiral ketones proceeded with high stereoselectivity. The stereoselectivity cannot be analyzed by conventional stereochemical models because these reactions do not conform to the requirements of those models. Instead, the stereoselectivity arises from the approach of the nucleophile to the most accessible diastereofaces of the lowest-energy conformations of the ketones. High stereoselectivity is expected, and the stereochemical outcome can be predicted, with conformationally biased ketones that have sterically distinguishable diastereofaces wherein only one face is accessible for nucleophilic addition. The conformations of the ketones can be determined by a combination of computational modeling and, in some cases, structure determination by X-ray crystallography.

Diastereoselective Additions of Allylmagnesium Reagents to α-Substituted Ketones When Stereochemical Models Cannot Be Used.

The stereoselectivities of reactions of allylmagnesium reagents with chiral ketones cannot be easily explained by stereochemical models. Competition experiments indicate that the complexation step is not reversible, so nucleophiles cannot access the widest range of possible encounter complexes and therefore cannot be analyzed easily using available models. Nevertheless, additions of allylmagnesium reagents to a ketone can still be stereoselective provided that the carbonyl group adopts a conformation that leads to one face being completely blocked from the approach of the allylmagnesium reagent.

SARS-CoV-2 diagnostic diary: from rumors to the first case. Early reports of molecular tests from the military research and diagnostic institute of Rio de Janeiro.

Corona virus disease (COVID-19) presents a serious threat to global health. A historical timeline of early molecular diagnostics from government alert (January 22) (D) was presented. After in silico analysis, Brazilian Army Institute of Biology (IBEx-RJ) tested samples in house using real-time reverse transcriptase polymerase chain reaction (RT-PCR) (fast mode) based on Centers for Disease Control and Prevention (CDC) recommendations. First cases from Brazil, Rio de Janeiro, IBEx, and diagnosis team were reported in D36, D44, D66, and D74 respectively. Therefore, after 1300 tests, we recommend N1/N2 primer sets (CDC) for preliminary and Charité protocol confirmation in case of positive results. Moreover, every professional should be tested before starting work, in addition to weekly tests for everyone involved.

Heritable nanosilver resistance in priority pathogen: a unique genetic adaptation and comparison with ionic silver and antibiotics.

The past decade has seen the incorporation of antimicrobial nanosilver (NAg) into medical devices, and, increasingly, in everyday 'antibacterial' products. With the continued rise of antibiotic resistant bacteria, there are concerns that these priority pathogens will also develop resistance to the extensively commercialized nanoparticle antimicrobials. Herein, this work reports the emergence of stable resistance traits to NAg in the WHO-listed priority pathogen Staphylococcus aureus, which has previously been suggested to have no, or very low, capacity for silver resistance. With no native presence of genetically encoded silver defence mechanisms, the work showed that the bacterium is dependent on mutation of physiologically essential genes, including those involved in nucleotide synthesis and oxidative stress defence. While some mutations were uniquely associated with resistance to NAg, the study also found common mutations that could be protective against both NAg and ionic silver. This is consistent with the observation of NAg/ionic silver cross-resistance. These mutations were detected following withdrawal of the silver exposure, denoting heritable characteristics that allow for spread of the resistance traits even with discontinued silver use. Heritable silver resistance in priority pathogen cautions that these nanoparticle antimicrobials should only be used as needed, to preserve their efficacy for treating infections.

Reactions of Allylmagnesium Reagents with Carbonyl Compounds and Compounds with C═N Double Bonds: Their Diastereoselectivities Generally Cannot Be Analyzed Using the Felkin-Anh and Chelation-Control Models.

This review describes the additions of allylmagnesium reagents to carbonyl compounds and to imines, focusing on the differences in reactivity between allylmagnesium halides and other Grignard reagents. In many cases, allylmagnesium reagents either react with low stereoselectivity when other Grignard reagents react with high selectivity, or allylmagnesium reagents react with the opposite stereoselectivity. This review collects hundreds of examples, discusses the origins of stereoselectivities or the lack of stereoselectivity, and evaluates why selectivity may not occur and when it will likely occur.

SARS-CoV-2 diagnostic diary: from rumors to the first case. Early reports of molecular tests from the military research and diagnostic institute of Rio de Janeiro

Corona virus disease (COVID-19) presents a serious threat to global health. A historical timeline of early molecular diagnostics from government alert (January 22) (D) was presented. After in silico analysis, Brazilian Army Institute of Biology (IBEx-RJ) tested samples in house using real-time reverse transcriptase polymerase chain reaction (RT-PCR) (fast mode) based on Centers for Disease Control and Prevention (CDC) recommendations. First cases from Brazil, Rio de Janeiro, IBEx, and diagnosis team were reported in D36, D44, D66, and D74 respectively. Therefore, after 1300 tests, we recommend N1/N2 primer sets (CDC) for preliminary and Charité protocol confirmation in case of positive results. Moreover, every professional should be tested before starting work, in addition to weekly tests for everyone involved.

Reiterative epoxide-based strategies for the synthesis of stereo-n-ads and application to polypropionate synthesis. A Personal Account.

The enantioselective synthesis of polypropionates continues to be an attractive realm for the synthetic chemists mostly due to the challenges presented by the number of consecutive stereogenic centers contained within the aliphatic chain. Over the years, our laboratory has developed an epoxide-based three-step reiterative methodology for the construction of these targets, with the ultimate goal that the approach could be extended to the synthesis of polypropionate-containing natural products. The key steps include the diastereoselective epoxidation of allylic and homoallylic alcohols, and the regioselective cleavage of 2-methyl-3,4-epoxy alcohols. The choice of the organometallic reagent, and the cis/trans geometry of the chiral epoxide can be used to control both the relative and absolute configuration of the resulting propionate unit, allowing our approach to be applied in the synthesis of advanced fragments. Additionally, the combination of our first- and second-generation methodologies permits the incorporation of different variations at the methyl moiety.

Solvent effects in the nucleophilic substitutions of tetrahydropyran acetals promoted by trimethylsilyl trifluoromethanesulfonate: trichloroethylene as solvent for stereoselective C- and O-glycosylations.

The selectivities of nucleophilic substitution reactions of tetrahydropyran acetals promoted by trimethylsilyl trifluoromethanesulfonate depend upon the reaction solvent. Polar solvents favor the formation of S(N)1 products, while nonpolar solvents favor S(N)2 products. Trichloroethylene was identified as the solvent most likely to give S(N)2 products in both C- and O-glycosylation reactions.

Concise epoxide-based synthesis of the C14-C25 bafilomycin A(1) polypropionate chain.

An efficient non-aldol convergent synthesis of the C14-C25 polyketide fragment of bafilomycin A(1) was completed in 16% overall yield and 8 steps in its longest linear sequence. This synthesis highlights the formation of the key fragments using a three-step sequence of epoxide cleavage, alkyne reduction, and epoxidation developed in our laboratory; starting from suitably protected enantiomeric epoxides of trans-2,3-epoxybutanol. This chemistry represents a quick asymmetric and diastereoselective construction of the polyketide chain of bafilomycin A(1), in which every stereogenic center was constructed using solely epoxide chemistry.