Highly enantioselective synthesis of γ-, δ-, and ε-chiral 1-alkanols via Zr-catalyzed asymmetric carboalumination of alkenes (ZACA)-Cu- or Pd-catalyzed cross-coupling

Total synthesis of (6R,12R)-6,12-dimethylpentadecan-2-one, the sex pheromone of Diabrotica balteata LeConte

Diabrotica balteata LeConte is one of the most important polyphagous agricultural pests. The sex pheromone of this pest was synthesized using Evans asymmetric alkylation, ring-opening reaction of (R)-2-methyloxirane, SN 2 alkylation of secondary tosylate, and coupling of chiral tosylate with Grignard reagent as central strategies. The sex pheromone prepared herein would be useful to control D. balteata.

PHLDA3 activated by BARX2 transcription, suppresses the malignant development of esophageal squamous cell carcinoma by downregulating PI3K/AKT levels

BACKGROUND

Low pleckstrin homology-like domain family A, member 3 (PHLDA3) expression has been reported to be associated with cancer specificity and disease-free survival in esophageal squamous cell carcinoma (ESCC), and was an independent predictor of postoperative recurrence. However, the specific mechanisms involved are still unclear. This paper aimed to explore the role and its mechanisms of PHLDA3 in ESCC.

MATERIALS AND METHODS

PHLDA3 and BarH-like homeobox 2 (BARX2) expressions in ESCC were predicted by Gene Expression Profiling Interactive Analysis (GEPIA) analysis and determined by quantitative real-time polymerase chain reaction (qRT-PCR) and western Blot. Western blot detected the expression of proteins associated with migration, angiogenesis and phosphoinositide 3-kinase (PI3K)/protein kinase B (PKB/AKT) signaling pathway. The University of California Santa Cruz Genomics Institute (UCSC) database predicted that the relationship of BARX2 and PHLDA3 promoter and JASPAR identified the possible binding sites. Dual luciferase gene reporter verified PHLDA3 promoter activity, and the relationship of both was determined by chromatin immunoprecipitation (CHIP). Cell counting kit (CCK)-8, 5-ethynyl-2'-deoxyuridine (EDU) and colony formation were used to assess cell proliferation. Wound healing and transwell were used to detect cell migration and invasion ability. Tube formation assay was applied to assess angiogenesis. Mice were injected with transfected KYSE30 cells under the right axilla. Body weight and tumor volume and mass were recorded for each group of mice. Immunohistochemistry was performed to detect KI67 level in tumor tissues.

RESULTS

Both PHLDA3 and BARX2 were downregulated in ESCC. The upregulated PHLDA3 suppressed PI3K/AKT expression. In addition, BARX2 bound to the PHLDA3 promoter and transcriptionally activated PHLDA3. PHLDA3 overexpression inhibited ESCC cell proliferation, migration, invasion and angiogenesis, but this effect was reversed by BARX2 knockdown. In addition, BARX2 overexpression inhibited ESCC cell proliferation, migration, invasion and angiogenesis, but this effect was reversed by PHLDA3 knockdown.

CONCLUSION

PHLDA3 was transcriptionally activated by BARX2 and inhibited malignant progression of ESCC by downregulating PI3K/AKT levels.

Synthesis and evaluation of ent-Conduramine C-1 derivatives as α-glucosidase inhibitors via CSI-mediated amination reaction

Concise synthesis of ent-conduramine C-1 and its derivatives has been achieved by using commercially available d-ribose. The key steps in the synthesis are regioselective and diastereoselective amination of polybenzyl ethers by chlorosulfonyl isocyanate (CSI), chelation-controlled carbonyl addition, and intramolecular olefin metathesis. All of the synthesized compounds were evaluated for inhibitory activity against α-glucosidase. The derivatives 18 (IC₅₀ = 0.65 ± 0.03 mM) and 19 (IC₅₀ = 0.26 ± 0.01 mM) were identified to be more potent than well-known α-glucosidase inhibitor acarbose (IC₅₀ = 1.05 ± 0.17 mM) as a positive control.

Chiral 2-phenyl-3-hydroxypropyl esters as PKC-alpha modulators: HPLC enantioseparation, NMR absolute configuration assignment, and molecular docking studies

Protein kinase C (PKC) isoforms play a pivotal role in the regulation of numerous cellular functions, making them extensively studied and highly attractive drug targets. In our previous work, we identified in racemate 1-2, based on the 2-benzyl-3-hydroxypropyl ester scaffold, two new potent and promising PKCα and PKCδ ligands, targeting the C1 domain of these two kinases. Herein, we report the resolution of the racemates by enantioselective semi-preparative HPLC. The attribution of the absolute configuration (AC) of homochirals 1 was performed by NMR, via methoxy-α-trifluoromethyl-α-phenylacetic acid derivatization (MTPA or Mosher's acid). Moreover, the match between the experimental and predicted electronic circular dichroism (ECD) spectra confirmed the assigned AC. These results proved that Mosher's esters can be properly exploited for the determination of the AC also for chiral primary alcohols. Lastly, homochiral 1 and 2 were assessed for binding affinity and functional activity against PKCα. No significative differences in the K_i of the enantiopure compounds was observed, thus suggesting that chirality does not seem to play a significant role in targeting PKC C1 domain. These results are in accordance with the molecular docking studies performed using a new homology model for the human PKCαC1B domain.

A bioinspired microreactor with interfacial regulation for maximizing selectivity in a catalytic reaction

We report a bioinspired emulsion microreactor composed of an electrical double layer to mimic the functions of cell membranes. This "artificial cell" can modulate the phase-oriented transport of reagents at the oil-liquid interface via the electrical double layer, affording a powerful tool to optimize the selectivity in a catalytic reaction.

Mechanistic Insights into Stereospecific Bioactivity and Dissipation of Chiral Fungicide Triticonazole in Agricultural Management

Research interest in chiral pesticides has increased probably because enantiomers often exhibit different environmental fate and toxicity. An investigation into the enantiomer-specific bioactivity of chiral triticonazole enantiomers in agricultural systems revealed intriguing experimental and theoretical evidence. For nine of the phytopathogens studied ( Rhizoctonia solani, Fusarium verticillioide, Botrytis cinerea (strawberry and tomato), Rhizoctonia cereali, Alternaria solani, Gibberella zeae, Sclerotinia sclerotiorum, and Pyricularia grisea), the fungicidal activity data showed ( R)-triticonazole was 3.11-82.89 times more potent than the ( S) enantiomer. Furthermore, ( R)-triticonazole inhibited ergosterol biosynthesis and cell membrane synthesis 1.80-7.34 times higher than its antipode. Homology modeling and molecular docking studies suggested the distinct bioactivities of the enantiomers of triticonazole were probably due to their different binding modes and affinities to CYP51b. However, field studies demonstrated that ( S)-triticonazole was more persistent than ( R)-triticonazole in fruits and vegetables. The results showed that application of pure ( R)-triticonazole, with its high bioactivity and relatively low resistance risk, instead of the racemate in agricultural management would reduce the application dosage required to eliminate carcinogenic mycotoxins and any environmental risks associated with this fungicide, yielding benefits in food safety and environmental protection.

Indenylmetal Catalysis in Organic Synthesis

Synthetic organic chemists have a long-standing appreciation for transition metal cyclopentadienyl complexes, of which many have been used as catalysts for organic transformations. Much less well known are the contributions of the benzo-fused relative of the cyclopentadienyl ligand, the indenyl ligand, whose unique properties have in many cases imparted differential reactivity in catalytic processes toward the synthesis of small molecules. In this Review, we present examples of indenylmetal complexes in catalysis and compare their reactivity to their cyclopentadienyl analogues, wherever possible.

Zirconium-Catalyzed Asymmetric Carboalumination of Unactivated Terminal Alkenes

Carbometalation of alkenes with stereocontrol offers an important opportunity for asymmetric C-C bond formation. However, the scope of catalytic stereoselective carbometalation of alkenes had until recently been limited to electronically biased alkenes or those with the presence of directing groups or other auxiliary functionalities to overcome the challenge associated with regio- and stereoselectivity. Catalytic asymmetric carbometalation of unactivated alkenes on the other hand remained as a formidable challenge. To address this long-standing problem, we sought to develop Zr-catalyzed asymmetric carboalumination of alkenes (namely, ZACA reaction) encouraged by our discovery of Zr-catalyzed alkyne carboalumination in 1978. Zr-catalyzed methylalumination of alkynes (ZMA) shows high regioselectivity and nearly perfect stereoselectivity. Its mechanistic studies have revealed that the ZMA reaction involves acyclic carbometalation with "superacidic" bimetallic reagents generated by interaction between two Lewis acids, i.e., alkylalanes and 16-electron zirconocene derivatives through dynamic polarization and ate complexation, affectionately termed as the "two-is-better-than-one" principle. With the encouraging results of Zr-catalyzed carboalumination of alkynes in hand, we sought to develop its alkene version for discovering a catalytic asymmetric C-C bond-forming reaction by using alkylalanes and suitable chiral zirconocene derivatives, which would generate "superacidic" bimetallic species to promote the desired carbometalation of alkenes. However, this proved to be quite challenging. Three major competing side reactions occur, i.e., (i) β-H transfer hydrometalation, (ii) bimetallic cyclic carbometalation, and (iii) Ziegler-Natta polymerization. The ZACA reaction was finally discovered by employing Erker's (-)-(NMI)₂ZrCl₂ as the catalyst and chlorinated hydrocarbon as solvent to suppress the undesired side reactions mentioned above. The ZACA reaction has evolved as a powerful tool for the efficient preparation of a wide range of chiral natural products through the following methodological developments: (1) three mutually complementary protocols for methyl-branched chiral alkanols; (2) water, MAO, and IBAO as promoters to accelerate otherwise sluggish carboaluminations; (3) one-step homologation synthesis of deoxypropionates based on one-pot ZACA-Pd-catalyzed vinylation tandem process; (4) ZACA-lipase-catalyzed acetylation-transition-metal-catalyzed cross-coupling processes for preparing various virtually enantiopure chiral alcohols; (5) the chemoselective ZMA and ZACA reactions as well as alkyne elementometalation-Pd-catalyzed cross-coupling for constructing a variety of chiral compounds containing regio- and stereodefined substituted alkenes; (6) the ZACA reaction of dienes to generate chiral organocyclic compounds including those with all-carbon quaternary stereocenters.

Catalytic enantioselective synthesis of chiral organic compounds of ultra-high purity of >99% ee

Shortly after the discovery of Zr-catalyzed carboalumination of alkynes in 1978, we sought expansion of the scope of this reaction so as to develop its alkene version for catalytic asymmetric C-C bond formation, namely the ZACA (Zr-catalyzed asymmetric carboalumination of alkenes). However, this seemingly easy task proved to be quite challenging. The ZACA reaction was finally discovered in 1995 by suppressing three competitive side reactions, i.e., (i) cyclic carbometalation, (ii) β-H transfer hydrometalation, and (iii) alkene polymerization. The ZACA reaction has been used to significantly modernize and improve syntheses of various natural products including deoxypolypropionates and isoprenoids. This review focuses on our recent progress on the development of ZACA-lipase-catalyzed acetylation-transition metal-catalyzed cross-coupling processes for highly efficient and enantioselective syntheses of a wide range of chiral organic compounds with ultra-high enantiomeric purities.