Foldamers controlled by functional triamino acids: structural investigation of α/γ-hybrid oligopeptides.

Peptide-like foldamers controlled by normal amide backbone hydrogen bonding have been extensively studied, and their folding patterns largely rely on configurational and conformational constraints induced by the steric properties of backbone substituents at appropriate positions. In contrast, opportunities to influence peptide secondary structure by functional groups forming individual hydrogen bond networks have not received much attention. Here, peptide-like foldamers consisting of alternating α,β,γ-triamino acids 3-amino-4-(aminomethyl)-2-methylpyrrolidine-3-carboxylate (AAMP) and natural amino acids glycine and alanine are reported, which were obtained by solution phase peptide synthesis.

NMR crystallography of amino acids.

The development of NMR crystallography methods requires a reliable database of chemical shifts measured for systems with known crystal structure. We measured and assigned carbon and hydrogen chemical shifts of twenty solid natural amino acids of known polymorphic structure, meticulously determined using powder X-ray diffraction. We then correlated the experimental data with DFT-calculated isotropic shieldings.

Unified Total Synthesis of Diverse Meroterpenoids from .

A unified approach to meroterpenoids applanatumols B, V, W, X, and Y produced by the medicinal fungus and 2'--spiroapplanatumine O is presented. The key synthetic sequence consists of a tandem anionic ketone allylation/oxy-Cope rearrangement/α-oxygenation furnishing an α-aminoxy ketone and a persistent radical effect-based 5--trig cyclization leading to the trisubstituted cyclopentane core. The relative configuration of applanatumol V has to be revised.

Synthesis and Biological Profiling of Pyrazolo-Fused 7-Deazapurine Nucleosides.

A series of 8-substituted 1-methyl-1,4-dihydropyrazolo[3',4':4,5]pyrrolo[2,3-]pyrimidine (methylpyrazolo-fused 7-deazapurine) ribonucleosides have been designed and synthesized. Two synthetic approaches to the key heterocyclic aglycon , (i) a six-step classical heterocyclization starting from 5-chloro-1-methyl-4-nitropyrazole and (ii) a three-step cross-coupling and cyclization approach starting from the zincated 4,6-dichloropyrimidine, gave comparable total yields of 18% vs 13%. The glycosylation of was attempted by three different methods but only the Vorbrüggen silyl-base protocol was efficient and stereoselective to give desired β-anomeric nucleoside intermediate .

Towards Accurate Predictions of Proton NMR Spectroscopic Parameters in Molecular Solids.

The factors contributing to the accuracy of quantum-chemical calculations for the prediction of proton NMR chemical shifts in molecular solids are systematically investigated. Proton chemical shifts of six solid amino acids with hydrogen atoms in various bonding environments (CH, CH , CH , OH, SH and NH ) were determined experimentally using ultra-fast magic-angle spinning and proton-detected 2D NMR experiments. The standard DFT method commonly used for the calculations of NMR parameters of solids is shown to provide chemical shifts that deviate from experiment by up to 1.

Experimental and Theoretical Evidence of Spin-Orbit Heavy Atom on the Light Atom H NMR Chemical Shifts Induced through H⋅⋅⋅I Hydrogen Bond.

Invited for the cover of this issue is the group of Michal Straka and Martin Dračínský (IOCB Prague, Czech Academy of Sciences). The image depicts a neutron star, which is used to represent the relativistic effects between a heavy element and a hydrogen atom reported in this work. Read the full text of the article at 10.

Experimental and Theoretical Evidence of Spin-Orbit Heavy Atom on the Light Atom H NMR Chemical Shifts Induced through H⋅⋅⋅I Hydrogen Bond.

Spin-orbit (SO) heavy-atom on the light-atom (SO-HALA) effect is the largest relativistic effect caused by a heavy atom on its light-atom neighbors, leading, for example, to unexpected NMR chemical shifts of H, C, and N nuclei. In this study, a combined experimental and theoretical evidence for the SO-HALA effect transmitted through hydrogen bond is presented. Solid-state NMR data for a series of 4-dimethylaminopyridine salts containing I , Br and Cl counter ions were obtained experimentally and by theoretical calculations.

Tandem Anionic oxy-Cope Rearrangement/Oxygenation Reactions as a Versatile Method for Approaching Diverse Scaffolds.

Tandem anionic oxy-Cope rearrangement/radical oxygenation reactions provide δ,ϵ-unsaturated α-(aminoxy) carbonyl compounds, which serve as convenient precursors to diverse compound classes. Functionalized carbocycles are accessible by very rare all-carbon 5-endo-trig cyclizations, but also common 5-exo-trig radical cyclizations, based on the persistent radical effect. The tandem reactions can be further extended by highly diastereoselective allylation or reduction steps to give complex scaffolds.

Determination of nucleobase-pairing free energies from rotamer equilibria of 2-(methylamino)pyrimidines.

A fast straightforward method for the determination of free energies of modified nucleobase pairing is proposed. The method is based on the nuclear magnetic resonance (NMR) spectroscopy monitoring of conformational changes of 2-(methylamino)-pyrimidines upon intermolecular binding.

Two immunoassays for the detection of 2C-B and related hallucinogenic phenethylamines.

Introduction: The use of new psychoactive substances as drugs of abuse has dramatically increased over the last years. Hallucinogenic phenethylamines gained particular popularity as they have both stimulating and psychedelic effects. Although generally perceived as safe, these illicit drugs pose a serious health risk; they have been linked to cases of severe poisoning or even deaths.

Synthesis of Dihydroxyalkynyl and Dihydroxyalkyl Nucleotides as Building Blocks or Precursors for Introduction of Diol or Aldehyde Groups to DNA for Bioconjugations.

(3,4-Dihydroxybut-1-ynyl)uracil, -cytosine and -7-deazaadenine 2'-deoxyribonucleoside triphosphates (dNTPs) were prepared by direct aqueous Sonogashira cross-coupling of halogenated dNTPs with dihydroxybut-1-yne and converted to 3,4-dihydroxybutyl dNTPs through catalytic hydrogenation. Sodium periodate oxidative cleavage of dihydroxybutyl-dUTP gave the desired aliphatic aldehyde-linked dUTP, whereas the oxidative cleavage of the corresponding deazaadenine dNTP gave a cyclic aminal. All dihydroxyalkyl or -alkynyl dNTPs and the formylethyl-dUTP were good substrates for DNA polymerases and were used for synthesis of diol- or aldehyde-linked DNA.

Influence of Intramolecular Charge Transfer and Nuclear Quantum Effects on Intramolecular Hydrogen Bonds in Azopyrimidines.

Intramolecular hydrogen bonds (IMHBs) in 5-azopyrimidines are investigated by NMR spectroscopy and DFT computations that involve nuclear quantum effects. A series of substituted 5-phenylazopyrimidines with one or two hydrogen bond donors able to form IMHBs with the azo group is prepared by azo coupling. The barrier of interconversion between two rotamers of the compounds with two possible IMHBs is determined by variable temperature NMR spectroscopy and it is demonstrated that the barrier is significantly affected by intramolecular charge transfer.

Short communication: Pasteurization as a means of inactivating staphylococcal enterotoxins A, B, and C in milk.

Our aim was to assess the effect of pasteurization temperature on inactivation of staphylococcal enterotoxins (SE). Milk samples were inoculated with log 4.38 to 5.

Effects of microcystin and complex cyanobacterial samples on the growth and oxidative stress parameters in green alga Pseudokirchneriella subcapitata and comparison with the model oxidative stressor--herbicide paraquat.

Oxidative stress is one of the biochemical mechanisms involved in toxicity of cyanobacterial toxins microcystins (MC), but its role in the effects of complex water blooms is elusive. The aim of this study was to investigate effects of pure MCs and different complex mixtures of cyanobacterial metabolites on the growth and biochemical markers of oxidative stress and detoxification in green alga Pseudokirchneriella subcapitata. Pure MCs at high concentrations (300 μg/L) had no effects on the growth of P.