Selective introduction of fluorine into molecules by the cleavage of inert C−H bonds is of central academic and synthetic interest, yet remains challenging. Given the central role of alcohols in ...organic chemistry as the most ubiquitous building blocks, a versatile and selective C(sp3)−H and C(sp2)−H fluorination of simple alcohols, enabled by novel designed exo‐directing groups, is described. C(sp2)−H bond fluorination was achieved by using a simple acetone oxime as auxiliary, whereas a new, modular and easily accessible bidentate auxiliary was developed for the efficient and site‐selective fluorination of various primary methyl, methylene, and benzylic C(sp3)−H bonds. Fluorinated alcohols can readily be accessed by the removal of auxiliaries, and significantly expands the synthetic prospect of the present procedure.
A versatile and selective C(sp3)−H and C(sp2)−H fluorination of simple alcohols, enabled by an exo‐directing group (DG) is described. C(sp2)−H bond fluorination was achieved by using simple acetone oxime as an auxiliary, whereas a new and modularly accessible bidentate auxiliary was developed for the efficient and site‐selective fluorination of C(sp3)−H bonds. The auxiliary is removable and demonstrates broad substrate scope and excellent selectivity.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Gibberellin (GA), a diterpene hormone, plays diverse roles in plant growth and development, including seed germination, stem elongation, and flowering time. Although it is known that GA accelerates ...flowering through degradation of transcription repressors, DELLAs, the underlying mechanism is poorly understood. We show here that DELLA directly binds to microRNA156 (miR156)-targeted SQUAMOSA PROMOTER BINDING-LIKE (SPL) transcription factors, which promote flowering by activating miR172 and MADS box genes. The interaction between DELLA and SPL interferes with SPL transcriptional activity and consequently delays floral transition through inactivating miR172 in leaves and MADS box genes at shoot apex under long-day conditions or through repressing MADS box genes at the shoot apex under short-day conditions. Our results elucidate the molecular mechanism by which GA controls flowering and provide the missing link between DELLA and MADS box genes.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
An efficient Pd-catalysed β-C(sp
3
)-H arylation of diverse native amides with aryl iodides was developed. This protocol overcomes the necessity of the Thorpe-Ingold effect and features broad ...substrate scope and good functional group tolerance. The potential application of this protocol is collectively demonstrated by gram-scale synthesis and the synthesis of several bioactive molecules.
A practical and concise approach for the synthesis of β-aryl amides and γ-aryl amines has been developed by utilizing the innate carbonyl of native amides as valid coordinating groups.
A detailed mechanism study on the anion ligand promoted selective C-H bond fluorination is reported. The role of the anion ligand has been clarified by experimental evidence and DFT calculations. ...Moreover, the nitrate promoted C-F bond reductive elimination enabled a selective C-H bond fluorination of various symmetric and asymmetric azobenzenes to access diverse
o
-fluoroanilines.
A detailed mechanism study on the anion ligand promoted selective C-H bond fluorination is reported.
Herein, we report a novel strategy to access CH
2
F-containing ketones through Pd-catalysed β-selective methyl C(sp
3
)-H fluorination. The reaction features high regioselectivity and a broad ...substrate scope, constituting a modular method for the late-stage transformation of the native methyl (CH
3
) into the monofluoromethyl (CH
2
F) group.
A novel strategy was developed for the modular synthesis of CH
2
F-containing ketones through palladium catalysed β-selective methyl C(sp
3
)-H fluorination.
In the current study, we developed a stable isotope labeling strategy for the absolute quantification of gibberellins (GAs) by high performance liquid chromatography–electrospray tandem mass ...spectrometry (HPLC–ESI-MS/MS). N,N-dimethyl ethylenediamine (DMED) and its deuterated counterpart d4-DMED were used to derivatize GAs extracted from plant tissue samples and GA standards respectively. The both derivatives of GAs were mixed and then subjected to HPLC–ESI-MS/MS analysis. The absolute quantification of GAs in plant tissues could be achieved by calculating the peak area ratios of DMED labeled GAs/d4-DMED labeled GAs. In the proposed strategy, the derivatization reaction of the labeling reagents with GAs could be completed rapidly (within 5min) with high efficiency (>99%) under mild conditions. The resulting derivatives could produce specific fragments in collision induced dissociation (CID), leading to high selectivity in multiple-reaction monitoring (MRM) mode, thus enhanced the reliability of the LC–MS/MS method. Furthermore, the limits of quantitation (LOQs) of GAs were considerably decreased (2–32 folds) due to incorporating easily ionized moieties into GAs, and the quantification of GAs in plant tissue could be achieved without isotopically labeled GA standards. Good linearity was obtained with correlation coefficients R2 values of >0.99. The limits of detection (LODs) and quantitation (LOQs) ranged from 0.02 to 0.74pg and 0.07 to 2.45pg, respectively. Eleven GAs could be successfully determined in spiked sample with 72–128% recoveries and the relative standard deviations (RSDs) were between 1.0% and 13.9%. Finally, the developed method was successfully applied for the detection of GAs in 50mg (fresh weight) Oryza sativa leaves.
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•A stable isotope labeling strategy for quantification of gibberellins by LC–MS.•Rapid derivatization reaction with high efficiency under mild conditions.•High selectivity for LC–MS analysis with specific fragments of the derivates.•Decreased LOQs of GAs (2–32) folds upon derivatization.•Accurate quantification without individual isotopically labeled internal standards.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A palladium catalyzed selective C(sp
3
)-H arylation and acetoxylation of alcohols using a practical bidentate auxiliary were developed. Masked alcohols were selectively arylated at the β-position ...with diverse aryl iodides for the first time. Moreover, an efficient and site-selective acetoxylation of various primary methyl, methylene, and benzylic C(sp
3
)-H bonds was performed by using cheap K
2
S
2
O
8
as the external oxidant.
A palladium catalyzed selective C(sp
3
)-H arylation and acetoxylation of alcohols using a practical bidentate auxiliary were developed.
Thermal deposition and temperature distribution on the interface of explosive welding composites affect the formation of molten regions and the interface morphology. This study is primarily devoted ...to discussing the effect of thermal conduction on the distribution of interfacial temperature. Two-dimensional models with thermal conductivity coefficient were established based on the
Johnson-Cook
constitutive equation and
Grüneisen
state equation by using the smooth-particle hydrodynamics (SPH) method in Fortran. The simulation results show that the melting of interface metals occurred in all the case even it was too small to observe, which verified the interface melting metal has similar characteristics of incompressible fluid during the welding process. Furthermore, the temperature distribution was significantly different from the adiabatic model with the help of high cooling rate when the plate thickness is less than 1 mm, which suggested the thermal conduction cannot be neglected in the analysis of temperature and melting under this condition.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
A nitrate-promoted Pd-catalysed mild cross-dehydrogenative C(sp
2
)-H bond oxidation of oximes or azobenzenes with diverse carboxylic acids has been developed. In contrast to the previous catalytic ...systems, this protocol features mild conditions (close to room temperature for most cases) and a broad substrate scope (up to 64 examples), thus constituting a versatile method to directly prepare diverse
O
-aryl esters. Moreover, the superiority of the nitrate additive in this mild transformation was further determined by experimental and computational evidence.
A nitrate-promoted Pd-catalysed cross-dehydrogenative C(sp
2
)-H oxidation of oximes or azobenzenes with diverse aromatic and aliphatic acids was developed, allowing the versatile formation of
O
-aryl esters under mild reaction conditions.
Preoperative prediction of lymph node metastases has a major impact on prognosis and recurrence for patients with papillary thyroid carcinoma (PTC). Thyroid ultrasonography is the preferred ...inspection to guide the appropriate diagnostic procedure.
To investigate the relationship between PTC and cervical lymph node metastasis (CLNM, including central and lateral LNM) using both conventional ultrasound (US) and contrast-enhanced ultrasound (CEUS).
Our study retrospectively analyzed 379 patients diagnosed with PTC confirmed by surgical pathology at our hospital who underwent US and CEUS examinations from October 2016 to March 2021. Individuals were divided into two groups: the lymph node metastasis group and the nonmetastasis group. The relationship between US and CEUS characteristics of PTC and CLNM was analyzed. Univariate and multivariable logistic regression methods were used to identify the high-risk factors and established a nomogram to predict CLNM in PTC. Furthermore, we explore the frequency of CLNM at each nodal level in PTC patients.
Univariate analysis indicated that there were significant differences in gender, age, tumor size, microcalcification, contact with the adjacent capsule, multifocality, capsule integrity and enhancement patterns in CEUS between the lymph node metastasis group and the nonmetastasis group (all
<0.05). Multivariate regression analysis showed that tumor size ≥1 cm, age ≤45 years, multifocality, and contact range of the adjacent capsule >50% were independent risk factors for CLNM in PTC, which determined the nomogram. The diagnostic model had an area under the curve (AUC) of 0.756 (95% confidence interval, 0.707-0.805). And calibration plot analysis shown that clinical utility of the nomogram. In 162 PTC patients, the metastatic rates of cervical lymph nodes at levels I-VI were 1.9%, 15.4%, 35.2%, 34.6%, 15.4%, 82.1%, and the difference was statistically significant (
<0.001).
Our study indicated that the characteristics of PTC on ultrasonography and CEUS can be used to predict CLNM as a useful tool. Preoperative analysis of ultrasonographical features has important value for predicting CLNM in PTCs. The risk of CLNM is greater when tumor size ≥1 cm, age ≤45 years, multifocality, contact range of the adjacent capsule >50% are present.
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