We describe a fully stereodivergent synthesis of a range of α,α-disubstituted α-amino acids via an Ir/Cu-catalyzed α-allylation of readily available imine esters. The introduction of a Cu-Phox complex-activated imine ester into the chiral iridium-catalyzed allylic allylation process is crucial for its high reactivity and excellent enantio- and diastereoselectivity (up to>99% ee and >20:1 dr). Importantly, the two chiral catalysts allow for full control over the configuration of the stereocenters, affording all stereoisomers of the desired products. The utility of this methodology was demonstrated by synthesizing dipeptides and analogues of bioactive molecules in a stereodivergent manner.
Although the Transformer translation model (Vaswani et al., 2017) has achieved state-ofthe-art performance in a variety of translation tasks, how to use document-level context to deal with discourse phenomena problematic for Transformer still remains a challenge. In this work, we extend the Transformer model with a new context encoder to represent document-level context, which is then incorporated into the original encoder and decoder. As large-scale document-level parallel corpora are usually not available, we introduce a two-step training method to take full advantage of abundant sentence-level parallel corpora and limited document-level parallel corpora. Experiments on the NIST Chinese-English datasets and the IWSLT French-English datasets show that our approach improves over Transformer significantly. 1
Electronic materials and devices that can mimic biological systems featured with elasticity, toughness, self-healing, degradability, and environmental friendliness drive the technological developments in fields spanning from bioelectronics, biomedical diagnosis and therapy, electronic skin, and soft robotics to Internetof-Things with "green" electronics. Among them, ionic devices based on gel electrolytes have emerged as attractive candidates for biomimetic systems. Herein, we presented a straightforward approach to demonstrate soft ionic microdevices based on a versatile organohydrogel platform acting as both a free-standing, stretchable, adhesive, healable, and entirely degradable support and a highly conductive, dehydration-and freezing-tolerant electrolyte. This is achieved by forming a gelatin/ferric-ion-cross-linked polyacrylic acid (GEL/PAA) dual dynamic supramolecular network followed by soaking into a NaCl glycerol/water solution to further toughen the gelatin network via solvent displacement, thus obtaining a high toughness of 1.34 MJ•cm −3 and a high ionic conductivity (>7 mS•cm −1 ). Highly stretchable and multifunctional ionic microdevices are then fabricated based on the organohydrogel electrolytes by simple transfer printing of carbon-based microelectrodes onto the prestretched gel surface. Proof-of-concept microdevices including resistive strain sensors and microsupercapacitors are demonstrated, which displayed outstanding stretchability to 300% strain, resistance to dehydration for >6 months, autonomous self-healing, and rapid room-temperature degradation within hours. The present material design and fabrication approach for the organohydrogel-based ionic microdevices will provide promising scope for life-like and sustainable electronic systems.
Double-network
tough hydrogels have raised increasing interest
in stretchable electronic applications as well as electronic skin
(e-skin) owing to their excellent mechanical properties and functionalities.
While hydrogels have been extensively explored as solid-state electrolytes,
stretchable energy storage devices based on tough hydrogel electrolytes
are still limited despite their high stretchability and strength.
A key challenge remains in the robust electrode/electrolyte interface
under large mechanical strains. Inspired by the skin structure that
involves the microstructured interface for the tight connection between
the dermis and epidermis, we demonstrated that a surface-microstructured
tough hydrogel electrolyte composed of agar/polyacrylamide/LiCl (AG/PAAm/LiCl)
could be exploited to allow stretchable supercapacitors with enhanced
mechanical and electrochemical performance. The prestretched tough
hydrogel electrolyte was treated to generate surface microstructures
with a roughness of tens of micrometers simply via mechanical rubbing
followed by the attachment of activated carbon electrodes on both
sides to realize the fabrication of the stretchable supercapacitor.
Through investigating the properties of the tough hydrogel electrolyte
and the electrochemical performance of the as-fabricated supercapacitors
under varied strains, the surface-microstructured hydrogel electrolyte
was shown to enable robust adhesion to electrodes, improving electrochemical
behavior and capacitance, as well as having better performance retention
under repeated stretching cycles, which surpassed the pristine hydrogel
with smooth surfaces. Our approach could provide an alternative and
general strategy to improve the interfacial properties between the
electrode and the hydrogel electrolyte, driving new directions for
functional stretchable devices based on tough hydrogels.
We report a stereoselective and site-specific allylic alkylation of Schiff base activated amino acids and small peptides via a Pd/Cu dual catalysis. A range of noncoded α,α-dialkyl α-amino acids were easily synthesized in high yields and with excellent enantioselectivities (up to >99% ee). Furthermore, a direct and highly stereoselective synthesis of small peptides with enantiopure α-alkyl or α,α-dialkyl α-amino acids residues incorporated at specific sites was accomplished using this dual catalyst system.
In contrast to the widely explored
methods for the asymmetric synthesis
of molecules bearing a single stereocenter or adjacent stereocenters,
the concurrent construction of 1,3-stereogenic centers in an enantio-
and diastereoselective manner remains a challenge, especially in acyclic
systems. Herein, we report an enantio- and diastereodivergent construction
of 1,3-nonadjacent stereocenters bearing allenyl axial and central
chirality through synergistic Pd/Cu-catalyzed dynamic kinetic asymmetric
allenylation with racemic allenylic esters. The protocol is suitable
for a wide range of substrates including the challenging allenylic
esters with less sterically bulky substituents and provided chiral
allenylic products bearing 1,3-nonadjacent stereocenters with high
levels of enantio- and diastereoselectivities (up to >20:1 dr and
>99% ee). Furthermore, several representative transformations involving
axial-to-central chirality transfer were conducted, affording useful
structural motifs containing nonadjacent stereocenters in a diastereodivergent
manner.
Castration resistant-prostate cancer is largely impervious to feather hormonal therapy and hence the outlook for patients is grim. Here we use an approach to attach the recently discovered Achilles heel. The experimental treatment established in this study is based on the recent discovery that it is the FABP5-PPARγ-VEGF signalling axis, rather than the androgen receptor pathway, played a dominant role in promoting the malignant progression of castration resistant prostate cancer cells. Treatments have been established in mice by suppressing the biological activity of FABP5 using a chemical inhibitor SBFI26. The inhibitor significantly suppressed the proliferation, migration, invasiveness and colony formation of PC3-M cells in vitro. It also produced a highly significant suppression of both the metastases and the primary tumours developed from cancer cells implanted orthotopically into the prostate glands of the mice. The inhibitor SBFI26 interferes with the FABP5-PPARγ- signalling pathway at the initial stage of the signal transduction by binding competitively to FABP5 to inhibit cellular fatty acid uptake. This avoids the fatty-acid stimulation of PPARγ and prevents it activating the down-stream regulated cancer-promoting genes. This entirely novel experimental approach to treating castration- resistant prostate cancer is completely different from current treatments that are based on androgen-blockade therapy.
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