Analysis of the Amine Submetabolome Using Novel Isotope-Coded Pyrylium Salt Derivatization and LC-MS: Herbs and Cancer Tissues as Cases.

The amine submetabolome, including amino acids (AAs) and biogenic amines (BAs), is a class of small molecular compounds exhibiting important physiological activities. Here, a new pyrylium salt named 6,7-dimethoxy-3-methyl isochromenylium tetrafluoroborate ([d0]-DMMIC) with stable isotope-labeled reagents ([d3]-/[d6]-DMMIC) was designed and synthesized for amino compounds. [d0]-/[d3]-/[d6]-DMMIC-derivatized had a charged tag and formed a set of molecular ions with an increase of 3.02 m/z and the characteristic fragment ions of m/z 204.1:207.1:210.1. When DMMIC coupled with liquid chromatography-mass spectrometry (LC-MS), a systematic methodology evaluation for quantitation proved to have good linearity (R2 between 0.9904 and 0.9998), precision (interday: 2.2-21.9%; intraday: 1.0-19.7%), and accuracy (recovery: 71.8-108.8%) through the test AAs. Finally, the methods based on DMMIC and LC-MS demonstrated the advantaged application by the nontargeted screening of BAs in a common medicinal herb Senecio scandens and an analysis of metabolic differences among the amine submetabolomes between the carcinoma and paracarcinoma tissues of esophageal squamous cell carcinoma (ESCC). A total of 20 BA candidates were discovered in S. scandens as well as the finding of 13 amine metabolites might be the highest-potential differential metabolites in ESCC. The results showed the ability of DMMIC coupled with LC-MS to analyze the amine submetabolome in herbs and clinical tissues.

Synthesis of tetrasubstituted allenes via a 1,4-palladium migration/carbene insertion/ß-H elimination sequence.

A palladium-catalyzed synthesis of tetrasubstituted allenes from aryl bromides and aryl diazoacetates is developed. This transformation proceeded via an aryl to alkenyl 1,4-palladium migration/carbene insertion/ß-H elimination sequence under mild reaction conditions.

Multiplexed Analysis of Endogenous Guanidino Compounds via Isotope-Coded Doubly Charged Labeling: Application to Lung Cancer Tissues as a Case.

Endogenous guanidino compounds (GCs), nitrogen-containing metabolites, have very important physiological activities and participate in biochemical processes. Therefore, accurately characterizing the distribution of endogenous GCs and monitoring their concentration variations are of great significance. In this work, a new derivatization reagent, 4,4'-bis[3-(dimethylamino)propyl]benzyl (BDMAPB), with isotope-coded reagents was designed and synthesized for doubly charged labeling of GCs. BDMAPB-derivatized GCs not only promote the MS signal but also form multicharged quasimolecular ions and abundant fragment ions. With this reagent, an isotope-coded doubly charged labeling (ICDCL) strategy was developed for endogenous GCs with high-resolution liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF MS). The core of this methodology is a 4-fold multiplexed set of [d0]-/[d4]-/[d8]-/[d12]-BDMAPB that yields isotope-coded derivatized GCs. Following a methodological assessment, good linear responses in the range of 25 nM to 1 µM with correlation coefficients over 0.99 were achieved. The limit of detection and the limit of quantitation were below 5 and 25 nM, respectively. The intra- and interday precisions were less than 18%, and the accuracy was in the range of 77.3-122.0%. The percentage recovery in tissues was in the range of 85.1-113.7%. The results indicate that the developed method facilitates long-term testing and ensures accuracy and reliability. Finally, the method was applied for the simultaneous analysis of endogenous GCs in four types of lung tissues (solid adenocarcinoma, solid squamous-cell carcinoma, ground-glass carcinoma, and paracancerous tissues) for absolute quantification, nontargeted screening, and metabolic difference analysis. It is strongly believed that ICDCL combined with isotope-coded BDMAPB will benefit the analysis and study of endogenous GCs.

Enantioselective synthesis of 3-aryl-phthalides through a nickel-catalyzed stereoconvergent cross-coupling reaction.

A nickel-catalyzed asymmetric Suzuki-Miyaura cross-coupling of racemic 3-bromo-phthalides and arylboronic acids was realized for the synthesis of diverse chiral 3-aryl-phthalides in moderate to excellent reaction yields. The reaction proceeded in a stereoconvergent manner and high enantioselectivities were observed for most examined examples. A number of functional groups like aldehyde, ester and bromide were well tolerated. Heteroaromatic boronic acids were also competent coupling partners in this reaction.

Non-targeted screening of pyranosides in Rhodiola crenulata using an all ion fragmentation-exact neutral loss strategy combined with liquid chromatography-quadrupole time-of-flight mass spectrometry.

INTRODUCTION: Pyranosides as one kind of natural glycosides contain a pyran ring linked to an aglycone in the structure. They occur widely in plants and possess diverse biological activities. The discovery of new pyranosides not only contributes to research on natural products but also may promote pharmaceutical development. OBJECTIVES: A non-targeted liquid chromatography-quadrupole time-of-flight mass spectrometry method coupled with an all ion fragmentation-exact neutral loss (AIF-ENL) strategy was developed for the screening of pyranosides in plants. METHODS: Pyranosides in various types were collected as a model. The AIF-ENL strategy comprised three steps: AIF spectrum acquisition and generation, ENL-based searching and identification, and confirmation of structural type using target second-stage mass spectrometry (MS/MS). The strategy was systematically evaluated based on the matrix effects, fragmentation stability, scan rate and screening efficiency and finally applied to Rhodiola crenulata (Hook. f. et Thoms) H. Ohba. RESULTS: The method was proved to be an efficient tool for the screening of pyranosides. When it was applied to R. crenulata, a total of 24 pyranoside candidates were detected. Among them, six were tentatively identified on the basis of the agreement of their elemental composition with the reported. The other 18 were detected in R. crenulata for the first time. CONCLUSION: The method offers a new platform for discovering pyranosides. In addition, the developed non-targeted strategy can also be used for other natural products, such as flavonoids and coumarins, as long as there is a common fragmentation behaviour in their MS/MS to generate characteristic neutral losses or fragments.

Regio- and Diastereoselective Access to 4-Imidazolidinones via an Aza-Mannich Initiated Cyclization of Sulfamate-Derived Cyclic Imines with α-Halo Hydroxamates.

An efficient regio- and diastereoselective cyclization of sulfamate-derived cyclic imines with unsubstituted or monosubstituted α-halo hydroxamates is developed under mild conditions. This reaction proceeds smoothly under transition-metal-free conditions via a domino aza-Mannich addition/intramolecular nucleophilic substitution sequence, providing a convenient route to access 2-monosubstituted and 2,5-disubstituted 4-imidazolidinones. Notably, the products were obtained with single trans-isomers in moderate to excellent yields.

Sequential Cross-Coupling/Annulation of ortho-Vinyl Bromobenzenes with Aromatic Bromides for the Synthesis of Polycyclic Aromatic Compounds.

A sequential cross-coupling/annulation of ortho-vinyl bromobenzenes with aromatic bromides was realized, providing a direct and modular approach to access polycyclic aromatic compounds. A vinyl-coordinated palladacycle was proposed as the key intermediate for this sequential process. Excellent chemoselectivity and regioselectivity were observed in this transformation. The practicability of this method is highlighted by its broad substrate scope, excellent functional group tolerance, and rich transformations associated with the obtained products.

Asymmetric Alkenylation of Enones and Imines Enabled by A Highly Efficient Aryl to Vinyl 1,4-Rhodium Migration.

The asymmetric rhodium-catalyzed alkenylation of enones and imines with arylboronic acids has been developed. A highly controllable aryl to vinyl 1,4-rhodium migration is the key step. Stereodefined vinyl moieties were installed in excellent enantioselectivies for most examined examples. DFT calculations reveal that the driving force of this rhodium migration is a kinetically favored process.

Highly Stereoselective Synthesis of 1,3-Dienes through an Aryl to Vinyl 1,4-Palladium Migration/Heck Sequence.

An efficient aryl to vinyl 1,4-palladium migration/Heck sequence was developed for the stereoselective synthesis of 1,3-dienes. High stereoselectivity was observed not only for 1,3-dienes bearing two similar aryl groups at terminal positions, but also for those with configurations shown to be unfavorable with previous methods.

Ir-SpinPHOX Catalyzed Enantioselective Hydrogenation of 3-Ylidenephthalides.

The first asymmetric hydrogenation of 3-ylidenephthalides has been developed using the IrI complex of a spiro[4,4]-1,6-nonadiene-based phosphine-oxazoline ligand (SpinPHOX) as the catalyst, affording a wide variety of chiral 3-substituted phthalides in excellent enantiomeric excesses (up to 98 % ee). The utility of the protocol has been demonstrated in the asymmetric synthesis of chiral drugs NBP and BZP precursor, as well as the natural products chuangxinol and typhaphthalide.

Borylation of Olefin C-H Bond via Aryl to Vinyl Palladium 1,4-Migration.

The aryl to vinyl palladium 1,4-migration was realized for the first time. The generated alkenyl palladium species was trapped by diboron reagents under Miyaura borylation conditions, providing a new method to synthesize ß,ß-disubstituted vinylboronates. The excellent regioselectivity and broad substrate scope were observed for this novel transformation.

Ligand-enabled γ-C-H olefination and carbonylation: construction of ß-quaternary carbon centers.

Monoselective γ-C-H olefination and carbonylation of aliphatic acids has been accomplished by using a combination of a quinoline-based ligand and a weakly coordinating amide directing group. The reaction provides a new route for constructing richly functionalized all-carbon quaternary carbon centers at the ß-position of aliphatic acids.

Achyranthes bidentata polysaccharides improve cyclophosphamide-induced adverse reactions by regulating the balance of cytokines in helper T cells.

The manuscript aimed to study the immune function maintenance effect of Achyranthes bidentata polysaccharides (ABPs). The mice were divided into the control group, cyclophosphamide-induced (CTX) group, and ABPs-treated (ABP) group. The results showed that, compared with the CTX group, ABPs could significantly improve the spleen index and alleviate the pathological changes in immune organs. Ex vivo study of whole spleen cells, the levels of interleukin-2 (IL-2), interleukin-6 (IL-6), interferon-γ (IFN-γ), and tumor necrosis factor-α (TNF-α) were increased. The proliferation of lymphocytes and the proportion of CD3+CD4+ Th cells in peripheral blood mononuclear cells were increased. The transcription of GATA-3, Foxp3, and ROR γ t were decreased, while the transcription of T-bet was increased. The transcriptome sequencing analysis showed that the differentially expressed genes (DEGs) caused by ABPs-treated were mostly downregulated in CTX-induced mice. The Th2-related genes were significantly enriched in DEGs, with representative genes, including Il4, II13, Il9, etc., while increasing the expression of immune effector genes simultaneously, including Ccl3, Ccr5, and Il12rb2. It was suggested that ABPs possibly regulated the balance of cytokines in helper T cells to ameliorate the immune function of CTX-induced mice.

Pd(II)-catalyzed phosphorylation of aryl C-H bonds.

A Pd(II)-catalyzed C-H phosphorylation reaction has been developed using heterocycle-directed ortho-palladation. Both H-phosphonates and diaryl phosphine oxides are suitable coupling partners for this reaction.

Pd-catalyzed intermolecular consecutive double Heck reaction "on water" under air: facile synthesis of substituted indenes.

An efficient and environmentally benign method for the preparation of substituted indene derivatives has been developed by using water as the sole solvent. This reaction proceeded under air, tolerated a wide range of functional-groups and was easily scaled up. Bioactive natural products like indriline were synthesized via the developed protocol. Preliminary results demonstrate that the enantioselective variant can also be achieved.

Palladium-catalyzed disilylation of ortho-halophenylethylenes enabled by 2-pyridone ligand.

A palladium-catalyzed disilylation reaction applicable for a variety of non-, α-, or ß-substituted and α,ß-disubstituted ortho-halophenylethylenes has been developed. This reaction proceeds with high yields and very low catalyst loadings. The two C-Si bonds of the disilylated products could be well-differentiated chemoselectively in the reaction with various electrophiles.

DMMIC derivatization-assisted liquid chromatography-mass spectrometry method for metabolite profiling of the glutathione anabolic pathway in esophageal cancer tissues and cells.

In this work, a new pyrylium derivatization-assisted liquid chromatography-mass spectrometry (LC-MS) method was developed for metabolite profiling of the glutathione anabolic pathway (GAP) in cancer tissues and cells. The pyrylium salt of 6,7-dimethoxy-3-methyl isochromenylium tetrafluoroborate (DMMIC) was used to label the amino group of metabolites, and a reductant of dithiothreitol (DTT) was employed to stabilize the thiol group. By combining DMMIC derivatization with LC-MS, it was feasible to quantify the 13 main metabolites on the GAP in complex biological samples, which had good linearity (R2 = 0.9981-0.9999), precision (interday precision of 1.6%-19.0% and intraday precision of 1.4%-19.8%) and accuracy (83.4%-115.7%). Moreover, the recovery assessments in tissues (82.5%-107.3%) and in cells (98.1%-118.9%) with GSH-13C2, 15N, and Cys-15N demonstrated the reliability of the method in detecting tissues and cells. Following a methodological evaluation, the method was applied successfully to investigate difference in the GAP between the carcinoma and para-carcinoma tissues of esophageal squamous cell carcinoma (ESCC) and the effect of p-hydroxycinnamaldehyde (CMSP) on the GAP in KYSE-150 esophageal cancer cells. The results demonstrate that the developed method provides a promising new tool to elucidate the roles of GAP in physiological and pathological processes, which can contribute to research on drugs and diseases.

Tandem Reactions involving 1,4-Palladium Migrations.

Transition-metal-catalyzed tandem reactions have become a mainstay in organic chemistry owing to their high atom- and step-economies. Metal-migration-based tandem reactions allow the engagement of simple starting materials for incorporating functional groups into certain positions and constructing complex scaffolds, which provide novel means that are complementary to traditional cross-coupling or C-H activation processes. In light of the broad utility of the 1,4-Pd migration reaction, this paper reviews its progress in the past two decades, summarizing the tandem process and classifying it based on insertion, elimination, transmetalation, and C-H bond activation. Special emphasis is placed on the driving force of Pd migration and different migration mechanisms. Moreover, this review also attempts to summarize common strategies for improving the regio- and site-selectivities of the migration process.

Palladium-catalyzed cross-coupling of unreactive C(sp3)-H bonds with azole C(sp2)-H bonds by using bromide as a traceless directing group.

A palladium-catalyzed intermolecular cross-coupling of unreactive C(sp3)-H bonds and azole C(sp2)-H bonds with bromide as a traceless directing group is described. The judicious selection of the bulky and electron-rich phosphine ligand is the key for the success of this cascade process. The protocol features a broad substrate scope, excellent regioselectivity, and good functional group tolerance.

Phosphorylation of C(sp3)-H Bonds via 1,4-Palladium Migration.

1,4-Palladium migration has emerged as a reliable method for directed C-H functionalization. In contrast to coupling with carbon nucleophiles, limited examples with heteroatom nucleophiles have been reported. Herein we report a palladium-catalyzed intermolecular C(sp3)-H phosphorylation reaction via 1,4-palladium migration, which is often difficult because of the strong coordination of phosphorus reagents to palladium catalysts. Phosphorylation of C(sp3)-H bonds is accomplished in good reaction yields with excellent regioselectivity. The judicious selection of the phosphine ligand proved to be the key to the success of this cascade process.