Syntheses and applications of enantiopure δ-amino acids and their precursors

Enantiopure unnatural homologated amino acids, whereby there is?>?1 carbon atom between the C- and N- termini have found great utility in a number of applications. The enantiopure syntheses of β-amino acids are well documented, as increasingly are those of γ-amino acids. δ-Amino acids on the other hand are much less well-studied despite reports of their potential utility. This review attempts to summarise strategies that have been adopted towards the enantioselective synthesis of δ-amino acids and their precursors (e.g. nitrile/nitro/azido/ester/alcohol etc) and where appropriate demonstrate their utility. Only systems which are all carbon between the two termini are considered and only those where the shortest route between any given C-termini and any given N-termini is four carbons long (i.e. lysine derivatives are not considered).     

Accelerated Chemical Reactions and Organic Synthesis in Leidenfrost Droplets

Leidenfrost levitated droplets can be used to accelerate chemical reactions in processes that appear similar to reaction acceleration in charged microdroplets produced by electrospray ionization. Reaction acceleration in Leidenfrost droplets is demonstrated for a base‐catalyzed Claisen–Schmidt condensation, hydrazone formation from precharged and neutral ketones, and for the Katritzky pyrylium into pyridinium conversion under various reaction conditions. Comparisons with bulk reactions gave intermediate acceleration factors (2–50). By keeping the volume of the Leidenfrost droplets constant, it was shown that interfacial effects contribute to acceleration; this was confirmed by decreased reaction rates in the presence of a surfactant. The ability to multiplex Leidenfrost microreactors, to extract product into an immiscible solvent during reaction, and to use Leidenfrost droplets as reaction vessels to synthesize milligram quantities of product is also demonstrated.     

Mapping a Noncovalent Protein–Peptide Interface by Top-Down FTICR Mass Spectrometry Using Electron Capture Dissociation

Noncovalent protein–ligand and protein–protein complexes are readily detected using electrospray ionization mass spectrometry (ESI MS). Furthermore, recent reports have demonstrated that careful use of electron capture dissociation (ECD) fragmentation allows covalent backbone bonds of protein complexes to be dissociated without disruption of noncovalent protein–ligand interactions. In this way the site of protein–ligand interfaces can be identified. To date, protein–ligand complexes, which have proven tractable to this technique, have been mediated by ionic electrostatic interactions, i.e., ion pair interactions or salt bridging. Here we extend this methodology by applying ECD to study a protein–peptide complex that contains no electrostatics interactions. We analyzed the complex between the 21 kDa p53-inhibitor protein anterior gradient-2 and its hexapeptide binding ligand (PTTIYY). ECD fragmentation of the 1:1 complex occurs with retention of protein–peptide binding and analysis of the resulting fragments allows the binding interface to be localized to a C-terminal region between residues 109 and 175. These finding are supported by a solution-phase competition assay, which implicates the region between residues 108 and 122 within AGR2 as the PTTIYY binding interface. Our study expands previous findings by demonstrating that top-down ECD mass spectrometry can be used to determine directly the sites of peptide–protein interfaces. This highlights the growing potential of using ECD and related top-down fragmentation techniques for interrogation of protein–protein interfaces.     

A model for the etching of silicon in SF6/O2 plasmas

A model has been developed to describe the chemistry which occurs in SF₆/O₂ plasmas and the etching of silicon in these plasmas. Emphasis is placed nn the gas-phase free radical reactions, and the predictions n( the model are compared with experimental results. Forty-seven reactions are included, although a subset of 18 reactions describes the chemistry equally well. Agreement between the calculated and measured concentrations of stable products downstream of the plasma is better than a factor of 2. The need for additional kinetic data and fàr well-characterized diagnostic studies of SF₆/O₂ plasmas is discussed.     

Vacuum ultraviolet spark emission spectra of fluorine and some polyatomic fluorides in noble gases

Spark emission spectra in the vacuum ultraviolet are reported for several polyatomic fluorides in He + Ar mixtures, and for pure fluorine. These results are discussed in terms of the potential of a given fluorine compound for ArF formation. The 158 nm emission in fluorine is tentatively assigned to the ³Π_g → ³Π_u.     

Heteropoly acids in the determination of phosphorus by neutron activation analysis

Phosphorus is selectively extracted as molybdovanadophosphoric acid (MVPA) and determined indirectly using⁵²V. Silicon, germanium, arsenic, fluoride and tannic acid do not interfere. The sensitivity for phosphorus was 1421±13 counts⁵²V per ng P ml^–1 with a detection limit of 0.2 ng P ml^–1. The precision is ±10% over the range 0.7±70 ng P ml^–1. The sensitivity is four orders of magnitude greater than for conventional neutron activation analysis (NAA) using the³¹P(n, )²⁸ Al reaction and a SLOWPOKE II reactor. Greater selectivity for phosphorus is obtained than by direct measurement of³²P by beta ray spectroscopy.     

Synthesis of 1,5-disubstituted tetrazoles via Suzuki-Miyaura cross-coupling of 5-chloro-1-phenyltetrazole

Suzuki-Miyaura coupling reactions of 5-chloro-1-phenyl-tetrazole with various functionalized arylboronic acids were investigated. In the presence of catalytic amounts of SPhos/Pd(OAc)₂ or RuPhos/Pd(OAc)₂, the reaction proceeded smoothly to afford 1,5-diaryltetrazoles in good to excellent yields.     

Strategies in boosting photosensitization for biomedical applications

Science China Chemistry -     

A Universal DNA Aptamer that Recognizes Spike Proteins of Diverse SARS-CoV-2 Variants of Concern

We report on a unique DNA aptamer, denoted MSA52, that displays universally high affinity for the spike proteins of wildtype SARS-CoV-2 as well as the Alpha, Beta, Gamma, Epsilon, Kappa, Delta and Omicron variants. Using an aptamer pool produced from round 13 of selection against the S1 domain of the wildtype spike protein, we carried out one-round SELEX experiments using five different trimeric spike proteins from variants, followed by high-throughput sequencing and sequence alignment analysis of aptamers that formed complexes with all proteins. A previously unidentified aptamer, MSA52, showed K_d values ranging from 2 to 10 nM for all variant spike proteins, and also bound similarly to variants not present in the reselection experiments. This aptamer also recognized pseudotyped lentiviruses (PL) expressing eight different spike proteins of SARS-CoV-2 with K_d values between 20 and 50 pM, and was integrated into a simple colorimetric assay for detection of multiple PL variants. This discovery provides evidence that aptamers can be generated with high affinity to multiple variants of a single protein, including emerging variants, making it well-suited for molecular recognition of rapidly evolving targets such as those found in SARS-CoV-2.