Highly sensitive determination of multiple pesticide residues in foods by supercritical fluid chromatography coupled with ion mobility quadrupole time-of-flight mass spectrometry.

This experiment aimed to establish a green, simple and highly sensitive method (supercritical fluid chromatography (SFC) coupled with ion mobility quadrupole time-of-flight mass spectrometry (IM-Q-TOF/MS)) for the detection of multiple pesticides in foods. During the experiments, several important SFC parameters, such as stationary phase, modifier, make-up solution, back-temperature and back-pressure were optimized. Here, single-field collision cross section (CCS) values and multifield CCS values of 20 pesticides were examined by IM-Q-TOF/MS as highly specific parameters with excellent experimental precision. In addition, based on accurate mass matching and fragment ion comparison, mass fragments were obtained by IM-Q-TOF/MS, which elucidated the regularities of compound structure and characteristic fragment ions. Under the optimized conditions, satisfactory linearity (R2 ≥ 0.9989) and recoveries (79.60 % to 112.97 %) were obtained. The intra- and interday precisions were favorable, with RSDs lower than 4.91 and 7.65 %, respectively. Additionally, the method showed low limits of detection (0.1-8.8 ng/mL). The proposed method has been successfully applied to the highly sensitive detection of phenylurea herbicide, triazine herbicides, organophosphorus pesticide, pyrethroid insecticide and acaricide in yam and potato.

Gold-Catalyzed [4 + 1] Heterocyclization of Hydroxamic Acid and Nonactivated Alkyne: A Protocol to Construct 5-Methyl-1,4,2-dioxazole.

A novel gold-catalyzed [4 + 1] heterocyclization of nonactivated alkyne and hydroxamic acid is developed for the regiospecific synthesis of 5-methyl-1,4,2-dioxazole, which is an important structural motif in various bioactive molecules. The current methodology is characterized by high efficiency, simple operation, mild reaction conditions, and good functional group compatibility. Moreover, gram-scale synthesis and synthetic application toward bioactive molecular skeletons have been realized.

Synthesis of heterocyclic ring-fused analogs of HMG499 as novel degraders of HMG-CoA reductase that lower cholesterol.

HMG-CoA reductase (HMGCR) is the rate-limiting enzyme in cholesterol de novo biosynthesis and its degradation may bring therapeutic benefits for the treatment of cardiovascular disease (CVD) and nonalcoholic steatohepatitis (NASH). Before, we disclosed compound HMG499 as a potent HMGCR degrader, which could be a promising agent for treating CVD, however its side-effect of promoting cholesterol accumulation in cells should be eliminated before progression. Herein, a series of novel heterocyclic ring-fused analogs of HMG499 were synthesized and investigated for their activities of stimulating HMGCR degradation using a HMGCR (TM1-8)-GFP reporting system. Among them, the most active compound 29 (QH536) showed an EC50 of 0.22 µΜ in promoting HMGCR degradation, which was about 2 times more potent than HMG499 (EC50 = 0.43 µM). Interestingly, 29 was different from HMG499, it had no side-effect of inducing cholesterol accumulation in cells. Mechanistic studies disclosed that 29 could significantly decrease statin-induced accumulation of HMGCR protein via ubiquitination and degradation of HMGCR through ubiquitin-proteasome pathway and inhibit the cholesterol biosynthesis in cells. Therefore, these heterocyclic ring-fused analogs could be used as promising leads for the development of new types of agents against CVD. Furthermore, 29 also lowered cholesterol levels and suppressed TGFß1-induced proliferation of LX-2 hepatic stellate cells in a dose-dependent manner. In particular, 29 not only decreased the NASH associated fibrotic mRNA and protein expression of α-SMA, COL1A1, TIMP1 and TGFß1 but also suppressed cholesterol levels and inflammatory genes of TNF-α, IL-6 an IL-1ß in RAW264.7 macrophage cells, indicating that 29 may bring therapeutic benefit to treat NASH.

Genetic structure of Culex tritaeniorhynchus (Diptera: Culicidae) based on COI DNA barcodes.

Culex tritaeniorhynchus Gile is a major vector of Japanese encephalitis in China. The population genetics study is crucial as it helps understanding the epidemiological aspects of mosquito-brone diseases and improving vector control measures. Here, the genetic population structure of C. tritaeniorhynchus in the mainland China were estimated using the cytochrome c oxidase subunit 1 (COI) DNA barcodes region. 485 individuals of C. tritaeniorhynchus were collected from 38 sampling sites in 21 geographic populations in the mainland China. In total, 485 sequences were used to explore the population structure and genetic diversity. The results showed that the populations of C. tritaeniorhynchus had high haplotype diversity (Hd = 0.98, with 303 haplotypes), low nucleotide diversity (p = 0.02245) and high gene flow (Nm = 47.11) with two maternal lineages and four groups. An AMOVA indicated that 98.8% of the total variation originated from variation within populations. In addition, the population genetic structure exhibited by C. tritaeniorhynchus filling the vacant of the genetic structure in the mainland China. Human activities may also assist mosquito movement and migration. Gene flow among the populations of C. tritaeniorhynchus can facilitate the spread of insecticide resistance genes over geographical areas, and it will be a challenging for controlling the populations.