A novel chiral spirocyclic amide (SPA)-derived triazolium organocatalyst has been designed and demonstrated to effect asymmetric homo- and heterodialkylations of various bisoxindoles, enabling enantioselective construction of vicinal all-carbon quaternary stereocenters. These reactions feature excellent enantio- and diastereoselectivities (up to 99% ee and >20:1 dr) as well as good to high yields (up to 89% over two steps). As an application of this methodology, the first asymmetric total synthesis of (-)-chimonanthidine has been achieved.
The specificity and predictability of hybridization make
oligonucleotides
a powerful platform to program assemblies and networks with logic-gated
responses, an area of research which has grown into a field of its
own. While the field has capitalized on the commercial availability
of DNA oligomers with its four canonical nucleobases, there are opportunities
to extend the capabilities of the hardware with unnatural nucleobases
and other backbones. This Topical Review highlights nucleobases that
favor hybridizations that are empowering for assemblies and networks
as well as two chiral XNAs than enable orthogonal hybridization networks.
Dark-field microscopy (DFM) based on localized surface plasmon resonance (LSPR) was used for observation of experimental phenomena, which is a hopeful nondamaging and nonphotobleaching biological imaging technique. In this strategy, plasma nanoaggregates with stronger scattering efficiency were formed in the presence of the target, causing a "turn-on" phenomenon, when asymmetry modified AuNPs were introduced as probes with zero LSPR background. First, Au 1 −N 3 probe and Au 2 −CC probe were designed for the cycloaddition between azide and alkyne to form AuNP dimers under catalytic action by Cu + , which was obtained from the reduction of Cu 2+ by sodium ascorbate. The two kinds of probes were successfully used for the detection of Cu 2+ in rat serum. Then, to apply this concept to protein on cells, DNA and antibody were modified on the probes. DNA1/Au 1 −N 3 probe and anti-HER2/Au 2 −CC probe were proposed for HER2 protein DFM on cells. By designing an aptamer sequence in primer, the rolling circle amplification (RCA) was introduced in HER2 DFM on cells, and the image signal was much brighter than that from no-RCA. The unique design made it easier to discriminate the target signal from background noise in cell DFM. This method might be used in the fields of molecular diagnostics and cell imaging.
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