Chiral P-monodentate phosphoramidite and phosphite ligands for the enantioselective Pd-catalyzed allylic alkylation

The improved synthesis of the chiral phosphoramidite Ia, based on a biphenol backbone and bearing chiral bis(1-phenylethyl)amine group on the phosphorus atom, is described together with its Pd(II) complex. The chiral complex cis-PdCl₂L₂ (L = Ia) has been characterized by X-ray crystal structure analysis and spectroscopic data. The series of the chiral P-monodentate phosphoramidite and phosphite ligands was tested in Pd-catalyzed enantioselective allylic substitution of different substrates. In the palladium-catalyzed asymmetric allylic alkylation of 1,3-diphenylallyl acetate with dimethylmalonate, up to 79% ee was achieved with [Pd₂(dba)₃] × CHCl₃ as precatalyst.     

The Cys154-->Gly mutation in LacY causes constitutive opening of the hydrophilic periplasmic pathway

The lactose permease of Escherichia coli (LacY) is a highly dynamic membrane transport protein, while the Cys154 → Gly mutant is crippled conformationally. The mutant binds sugar with high affinity, but catalyzes very little translocation across the membrane. In order to further investigate the defect in the mutant, fluorescent maleimides were used to examine the accessibility/reactivity of single-Cys LacY in right-side-out membrane vesicles. As shown previously, sugar binding induces an increase in reactivity of single-Cys replacements in the tightly packed periplasmic domain of wild-type LacY, while decreased reactivity is observed on the cytoplasmic side. Thus, the predominant population of wild-type LacY in the membrane is in an inward-facing conformation in the absence of sugar, sugar binding induces opening of a hydrophilic pathway on the periplasmic side, and the sugar-binding site is alternatively accessible to either side of the membrane. In striking contrast, the accessibility/reactivity of periplasmic Cys replacements in the Cys154 → Gly background is very high in the absence of sugar, and sugar binding has little or no effect. The observations indicate that an open hydrophilic pathway is present on the periplasmic side of the Cys154 → Gly mutant and that this pathway is unaffected by ligand binding, a conclusion consistent with findings obtained from single-molecule fluorescence and double electron-electron resonance.     

3-Alkenyl-2-azetidinones as fatty acid amide hydrolase inhibitors

A series of novel 2-azetidinones (β-lactams) bearing short alkenyl chains at C3 and N1 have been prepared and evaluated in vitro as inhibitors of human FAAH. Compound 9c (1-(4′-pentenoyl-3-(4′-pentenyl)-2-azetidinone)) featured an IC₅₀ value of 4.5 μM and a good selectivity for FAAH versus MGL.     

Polymethylene derivatives of nucleic bases with ω-functional groups: VI. [8-(2-oxocyclohexyl)-9-oxooctyl]pyrimidines as potential inhibitors of pyrimidine phosphorylases

New polymethylene derivatives of nucleic bases with β-diketo function in ω-position were prepared by alkylation of uracil, thymine, and cytosine. Their physicochemical properties and effect on the E. coli uridine and thimidine phosphorylases were studied.     

Picomole-level mapping of protein disulfides by mass spectrometry following partial reduction and alkylation

We have deduced the disulfide bond linkage patterns, at very low protein levels (<0.5 nmol), in two cysteine-rich polypeptide domains using a new strategy involving partial reduction/alkylation of the protein, followed by peptide mapping and tanden mass spectrometry (MS/MS) sequencing on a nanoflow liquid chromatography-MS/MS system. The substrates for our work were the cysteine-rich ectodomain of human Fn14, a member of the tumor necrosis factor receptor family, and the IgV domain of murine TIM-1 (T-cell, Ig domain, and mucin domain-1). We have successfully determined the disulfide linkages for Fn14 and independently confirmed those of the IgV domain of TIM-1, whose crystal structure was published recently. The procedures that we describe here can be used to determine the disulfide structures for proteins with complex characteristics. They will also provide a means to obtain important information for structure-function studies and to ensure correct protein folding and batch-to-batch consistency in commercially produced recombinant proteins.     

An efficient synthesis of anhydrides of 2-monosubstituted succinic acid monoesters and their application to the Dakin–West reaction: Isolation of some 5-succinyloxyoxazole intermediates

Summary A rapid and versatile synthesis of 2-monosubstituted monosuccinates and their bimolecular anhydrides is described. The reaction of these anhydrides withN-Fmoc-protected dipeptides under the modified Dakin-West reaction affords mainly the corresponding 5-succinyloxyoxazoles.     

Synthesis and Quantitative Analysis of Diastereomeric Linked Ester Conjugates With Remote Stereocenters Using High‐Field NMR and Chiral HPLC

A stereochemically safe high‐yielding procedure for linking unprotected as well as protected hydroxycarboxylic acids to chiral secondary alcohols via glycolic acid linker is proposed. L‐menthol has been linked with both enantiomers of mandelic, malic, and methoxyphenylacetic acid using bromo‐ or iodoacetyl group as a precursor of the glycolic acid linker. High‐field nuclear magnetic resonance (NMR) and chiral high‐performance liquid chromatography (HPLC) determination of high diastereomeric ratio (dr) (>99%) of the products bearing remote stereocenters was explored. Chiral HPLC allowed quantitation of the diastereomers up to dr 99.9/0.1. High‐field NMR quantitation of the diastereomeric and parent alcoholic impurities in esters was demonstrated at the molar 0.3% and 0.03% levels, respectively. These analyses were done via comparison of integral intensities from major component ¹³C satellites in ¹H or even in ¹³C spectra to the ¹H or ¹³C signals of impurities. Despite lower sensitivity, the last option generally has much better selectivity. In this way the dynamic resolution is brought down by two orders. Chirality 25:793–798, 2013. © 2013 Wiley Periodicals, Inc.     

Catalytic asymmetric total synthesis of (S)-(−)-zearalenone,a novel lipoxygenase inhibitor

A catalytic asymmetric synthesis of (S)-(?)-zearalenone is reported using asymmetric allylic alkylation for the introduction of the stereocenter. (S)-(?)-Zearalenone turned out to be a novel lipoxygenase inhibitor.     

Effect O6‐guanine alkylation on DNA flexibility studied by comparative molecular dynamics simulations

Alkylation of guanine at the O6 atom is a highly mutagenic DNA lesion because it alters the coding specificity of the base causing G:C to A:T transversion mutations. Specific DNA repair enzymes, e.g. O⁶‐alkylguanin‐DNA‐Transferases (AGT), recognize and repair such damage after looping out the damaged base to transfer it into the enzyme active site. The exact mechanism how the repair enzyme identifies a damaged site within a large surplus of undamaged DNA is not fully understood. The O⁶‐alkylation of guanine may change the deformability of DNA which may facilitate the initial binding of a repair enzyme at the damaged site. In order to characterize the effect of O⁶‐methyl‐guanine (O⁶‐MeG) containing base pairs on the DNA deformability extensive comparative molecular dynamics (MD) simulations on duplex DNA with central G:C, O⁶‐MeG:C or O⁶‐MeG:T base pairs were performed. The simulations indicate significant differences in the helical deformability due to the presence of O⁶‐MeG compared to regular undamaged DNA. This includes enhanced base pair opening, shear and stagger motions and alterations in the backbone fine structure caused in part by transient rupture of the base pairing at the damaged site and transient insertion of water molecules. It is likely that the increased opening motions of O⁶‐MeG:C or O⁶‐MeG:T base pairs play a decisive role for the induced fit recognition or for the looping out of the damaged base by repair enzymes. © 2014 Wiley Periodicals, Inc. Biopolymers 103: 23–32, 2015.     

Ethyl Methanesulfonate as Inductor of Somaclonal Variants in Different Crops

Ethyl methanesulfonate is a chemical mutagen, which is currently being used in plant breeding, to increase genetic variability in genes of agronomic interest, of species useful in agriculture. It primarily causes single base point mutations by inducing guanine alkylation, resulting in GC to AT transitions. Its effect is different between clones of a genotype and between genotypes of the same species. This review presents the results obtained in recent research, where its effect on plant tissues, callus, and cells in suspension has been evaluated. Changes in the phenotypic expression of somaclonal variants were reported, involving morphology, production of secondary metabolites, changes in metabolic routes of resistance, tolerance to stress, increased seed yield, among others. In addition, this review compiles the doses and guidelines to consider before using this mutagen, which can serve as a guide for future trials in deciding the response variables, the type of plant explants and the selection of the study model. Mutant lines have allowed plant breeders to have a collection of plants with different characteristics, in places where the cultivar does not have its center of origin. It is important to note that it is still necessary to continue evaluating the heritability of mutations and their behaviour in the environment where they will be established, in order to obtain new varieties of plants that can be cultivated with uniformity in their genetic response.