N-Heterocyclic carbene-catalyzed aerobic oxidation of aryl alkyl alcohols to carboxylic acids

Aerobic Oxidation of PMB Ethers to Carboxylic Acids

The first aerobic protocol of direct transformation of p-methoxybenzyl (PMB) ethers to carboxylic acids efficiently with Fe(NO3)3 ⋅ 9H2O and TEMPO as catalysts at room temperature has been developed. The reaction accommodates C-Br bond, terminal/non-terminal C-C triple bond, amide, cyano, nitro, ester, and trifluoromethyl groups. Even highly selective oxidative deprotection of different benzylic PMB ethers has been realized. The reaction has been successfully applied to the total synthesis of natural product, (R)-6-hydroxy-7,9-octadecadiynoic acid, demonstrating the practicality of the method. Based on experimental studies, a possible mechanism involving oxygen-stabilized benzylic cation has been proposed.

Metal-Free Visible-Light Induced Oxidative Cleavage of C(sp3 )-C, and C(sp3 )-N Bonds of Nitriles, Alcohols, and Amines

Selective cleavage of unstrained (sp3 ) C-C/ C-N bonds under mild conditions is highly challenging due to the higher bond dissociation energy. A visible light mediated metal-free oxidative dehomologation of aryl acetonitriles, primary alcohols and diols to carboxylic acids via organophotocatalyzed C(sp3 )-CN, C(sp3 )-C(OH) bond cleavage is reported. Notably, this methodology was further extended towards selective synthesis of aldehydes via deamination of both primary as well as secondary amines. This mild protocol features wide array of substrate variation with excellent functional group tolerance, preparative-scale synthesis, and operational simplicity. Possible mechanisms for these transformations were demonstrated through a series of control experiments.

MOF-Zn-NHC as an efficient N-heterocyclic carbene catalyst for aerobic oxidation of aldehydes to their corresponding carboxylic acids via a cooperative geminal anomeric based oxidation

As an efficient heterogenous N-heterocyclic carbene (NHC) catalyst, MOF-Zn-NHC was used in the aerobic oxidation of aryl aldehydes to their corresponding carbocyclic acids via an anomeric based oxidation. Features such as mild reaction conditions and no need for a co-catalyst or oxidative reagent can be considered as the major advantages of the presented method in this study.

As an efficient heterogenous N-heterocyclic carbene (NHC) catalyst, MOF-Zn-NHC was used in the aerobic oxidation of aryl aldehydes to their corresponding carbocyclic acids via an anomeric based oxidation.

Chemical Constituents with GNMT-Promoter-Enhancing and NRF2-Reduction Activities from Taiwan Agarwood Excoecaria formosana

Hepatocellular carcinoma (HCC) is considered to be a silent killer, and was the fourth leading global cause of cancer deaths in 2018. For now, sorafenib is the only approved drug for advanced HCC treatment. The introduction of additional chemopreventive agents and/or adjuvant therapies may be helpful for the treatment of HCC. After screening 3000 methanolic extracts from the Formosan plant extract bank, Excoecaria formosana showed glycine N-methyltransferase (GNMT)-promoter-enhancing and nuclear factor erythroid 2-related factor 2 (NRF2)-suppressing activities. Further, the investigation of the whole plant of E. formosana led to the isolation of a new steroid, 7α-hydroperoxysitosterol-3-O-β-d-(6-O-palmitoyl)glucopyranoside (1); two new coumarinolignans, excoecoumarin A (2) and excoecoumarin B (3); a new diterpene, excoeterpenol A (4); and 40 known compounds (5-44). Among them, Compounds 38 and 40-44 at a 100 μM concentration showed a 2.97 ± 0.27-, 3.17 ± 1.03-, 2.73 ± 0.23-, 2.63 ± 0.14-, 6.57 ± 0.13-, and 2.62 ± 0.05-fold increase in GNMT promoter activity, respectively. In addition, Compounds 40 and 43 could reduce NRF2 activity, a transcription factor associated with drug resistance, in Huh7 cells with relative activity of 33.1 ± 0.2% and 45.2 ± 2.5%. These results provided the basis for the utilization of Taiwan agarwood for the development of anti-HCC agents.