Stereoselective Synthesis of Atropisomeric Acridinium Salts by the Catalyst-Controlled Cyclization of ortho-Quinone Methide Iminiums

Quinone methides are fundamental intermediates for a wide range of reactions in which catalyst stereocontrol is often achieved by hydrogen bonding. Herein, we describe the feasibility of an intramolecular Friedel-Crafts 6π electrocyclization through ortho-quinone methide iminiums stereocontrolled by a contact ion pair. A disulfonimide catalyst activates racemic trichloroacetimidate substrates and imparts stereocontrol in the cyclization step, providing a new avenue for selective ortho-quinone methide iminium functionalization. A highly stereospecific oxidation readily transforms the enantioenriched acridanes into rotationally restricted acridiniums. Upon ion exchange, the method selectively affords atropisomeric acridinium tetrafluoroborate salts in high yields and an enantioenrichment of up to 93 : 7 e.r. We envision that ion-pairing catalysis over ortho-quinone methide iminiums enables the selective synthesis of a diversity of heterocycles and aniline derivatives with distinct stereogenic units

Retrosynthetic polyketide disconnections for unnatural aromatics

Polyketide synthases are extraordinarily complex enzymatic machineries that govern the assembly and cyclization of poly-β-carbonyl intermediates to an enormous diversity of natural products. Captivatingly, this biosynthetic strategy is transferable to the retrosynthetic analysis of unnatural aromatics, enabling strategic biomimetic polyketide cyclizations to design an extensive range of otherwise unrelated aromatic products

Visually Adversarial Attacks and Defenses in the Physical World: A Survey

Although Deep Neural Networks (DNNs) have been widely applied in various real-world scenarios, they are vulnerable to adversarial examples. The current adversarial attacks in computer vision can be divided into digital attacks and physical attacks according to their different attack forms. Compared with digital attacks, which generate perturbations in the digital pixels, physical attacks are more practical in the real world. Owing to the serious security problem caused by physically adversarial examples, many works have been proposed to evaluate the physically adversarial robustness of DNNs in the past years. In this paper, we summarize a survey versus the current physically adversarial attacks and physically adversarial defenses in computer vision. To establish a taxonomy, we organize the current physical attacks from attack tasks, attack forms, and attack methods, respectively. Thus, readers can have a systematic knowledge of this topic from different aspects. For the physical defenses, we establish the taxonomy from pre-processing, in-processing, and post-processing for the DNN models to achieve full coverage of the adversarial defenses. Based on the above survey, we finally discuss the challenges of this research field and further outlook on the future direction

X-Ray Crystallographic Studies of Quasi-Racemates for Absolute Configuration Determinations

The determination of the absolute configuration of chiral molecular entities by means of X-ray crystallography is overall of central importance in stereochemistry. However, the growth of enantiopure single crystals often represents an unsurmountable and frustrating hurdle. Quasi-racemic crystals of biomacromolecules, for which the absolute configuration is predetermined by the chiral monomers, allowed the X-ray crystallographic analysis of systems that are difficult to crystallize as pure enantiomers, with aims other than the determination of the absolute structure. Taking advantage of the greater propensity of quasi-racemic mixtures to co-crystallize compared to growing enantiomerically pure crystals of a single compound, we herein describe the use of X-ray crystallography of quasi-racemates for the absolute configuration determination. We expect that this approach is particularly useful to establish the sense of selectivity in the development of stereoselective methods by simplified crystallizations, while confirming the consistent selectivity with a second molecular structure within the same measurement

C-F bond activation under transition-metal-free conditions

The unique properties of fluorine-containing organic compounds make fluorine substitution attractive for the development of pharmaceuticals and various specialty materials, which have inspired the evolution of diverse C-F bond activation techniques. Although many advances have been made in functionalizations of activated C-F bonds utilizing transition metal complexes, there are fewer approaches available for nonactivated C-F bonds due to the difficulty in oxidative addition of transition metals to the inert C-F bonds. In this regard, using Lewis acid to abstract the fluoride and light/radical initiator to generate the radical intermediate have emerged as powerful tools for activating those inert C-F bonds. Meanwhile, these transition-metal-free processes are greener, economical, and for the pharmaceutical industry, without heavy metal residues. This review provides an overview of recent C-F bond activations and functionalizations under transition-metal-free conditions. The key mechanisms involved are demonstrated and discussed in detail. Finally, a brief discussion on the existing limitations of this field and our perspective are presented

HiCD: Change Detection in Quality-Varied Images via Hierarchical Correlation Distillation

Advanced change detection techniques primarily target image pairs of equal and high quality. However, variations in imaging conditions and platforms frequently lead to image pairs with distinct qualities: one image being high-quality, while the other being low-quality. These disparities in image quality present significant challenges for understanding image pairs semantically and extracting change features, ultimately resulting in a notable decline in performance. To tackle this challenge, we introduce an innovative training strategy grounded in knowledge distillation. The core idea revolves around leveraging task knowledge acquired from high-quality image pairs to guide the model's learning process when dealing with image pairs that exhibit differences in quality. Additionally, we develop a hierarchical correlation distillation approach (involving self-correlation, cross-correlation, and global correlation). This approach compels the student model to replicate the correlations inherent in the teacher model, rather than focusing solely on individual features. This ensures effective knowledge transfer while maintaining the student model's training flexibility.Comment: accepted by TGR

The early design stage of a novel Solar Thermal Façade (STF) for building integration: energy performance simulation and socio-economic analysis

This paper provides a feasibility study of a new solar thermal façade (STF) concept for building integration from both technical and economic aspects in Shanghai area of China. The whole set of technical evaluation and economic analysis was investigated through simulation of a reference DOE residential building model in IES-VE software and a dedicated dynamic business model consisting of several critical financial indexes. In order to figure out the cost effectiveness of the STF concept, research work consisted of: (1) exploring the overall feasibility, i.e. energy load, energy savings, operational cost and environmental benefits, and (2) investigating the financial outputs for investment decisions within three different purchase methods. This paper presents a multidisciplinary research method that is expected to be beneficial and supportive for the strategic decision at the early design stage and it also offers a different angle to assess the economic performance of the STF application

Nanosecond pulsed electric field inhibits malignant melanoma growth by inducing the change of systemic immunity

Nanosecond pulsed electric fields (nsPEFs) showed an inhibitory effect on proliferation of malignant melanoma. In this study, the growth of melanoma were inhibited by changing the systemic immunity. C57BL/6 mice with B16 malignant were exposed to 200 pulses of 100 ns duration, 30kV/cm. The mice were executed four days later. T lymphocyte has been extracted from spleen. Cell viability was evaluated by CCK-8 assay. CD3+CD4+ T cells, CD3+CD8+ T cells, regulatory T cells (Treg) and myeloid-derived suppressor cells (MDSC) were analyzed by flow cytometry. TNF-?, IL-2, IL-10, TGF-?, IFN? ? levels in supernatants were assessed by ELISA. C57 malignant melanoma model were established successfully. After the treatment of nsPEFs(30 kV/cm 100 ns 200p), the numbers of T lymphocytes were increased.CD3+ CD4+ T cells changed from 48% to 51.2%;CD3+CD8+T lymphocytes increased from 39.6% to 40.4%.Treg cells reduced from 4.3% to 2.4%,MDSC decreased by 39.0% to 19.7% . In addition, the level of TNF-?, IL-2 were increased (P0.05). Tumor growth can be effectively inhibited by nsPEFs in vivo, which activate targets of immune respones, accumulation of inflammatory cells and immune cytokines