An Easy Access to Oxime Ethers by Pd‐Catalyzed C—O Cross‐Coupling of Activated Aryl Bromides with Ketoximes and Chalcone Oximes

Oxime functionalized Chalcones: Unveiling a new class of Chalcones with potent Antiplasmodial activity against blood-stages of Plasmodium falciparum in culture

The Plasmodium falciparum parasite, which is responsible for malaria, has developed resistance to several first-line antimalarial drugs. To address this issue, researchers have been developing novel hybrid molecules that can inhibit parasite growth. In this study, a total of 38 chalcone oxime ethers, consisting of four different types, were evaluated for in vitro blood-stage antiplasmodial activity against P. falciparum (3D7) using SYBR green I assay. The four classes of oxime ethers showed promising to moderate antiplasmodial activity. At least one molecule from each class was potent, with the IC50 values of less than 5 μg/mL. Among the four classes, chalcone-chalconeoxime ethers (CCOE) were the most effective, with the IC50 values of 1.55 μg/mL and 1.4 μg/mL for CCOE-2 and CCOE-5, respectively. The most potent molecules, CKOE-13, COAE-2, CCOE-2, and CCOE-5, were tested against the chloroquine-resistant strain P. falciparum (INDO) exhibited IC50 values of less than 5 μg/mL. Notably, the most potent molecules did not induce hemolysis at concentrations up to 50 μg/mL. These findings highlight a new class of chalconeoxime ethers as potent antiplasmodial agents, warranting further exploration of their biological activities.

HFIP mediated oxime ether synthesis: a metal, base and additive free approach

Oxime ethers are extensively present as key components in numerous active pharmaceutical ingredients and many other synthetically viable organic compounds. Herein, we present a metal, base and additive free mild C-O bond formation strategy for the synthesis of oxime ethers from various oxime derivatives and tertiary and secondary aryl alcohols. The reaction is carried out in the presence of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as the green solvent at 30 °C. The reaction tolerates both aldoximes and ketoximes including ketoximes bearing heteroatoms, furnishing high yields (up to 99%). The formation of a triphenylmethyl carbocation as an intermediate is supported via UV-Vis spectroscopy. Successful gram-scale synthesis of the oxime ether, low energy input and simple reaction conditions further highlight the potential of this reaction to effectively transition from the laboratory scale to industrial production. A broad substrate scope compatibility was also observed.

Synthesis of oxime ethers via a formal reductive O-H bond insertion of oximes to α-keto esters

This study describes an efficient approach to access oxime ethers via P(III)-mediated O-H bond insertion reaction of oximes with α-keto esters. The strategy involves the protonation of in situ generated Kukhtin-Ramirez adducts, followed by SN2-type reaction. Important features include a good functional group tolerance, operational simplicity, and application to gram scale synthesis and the synthesis of an acaricide.

Oxime Ether Synthesis through O-H Functionalization of Oximes with Diazo Esters under Blue LED Irradiation

A green and sustainable oxime ether formation method via the visible-light-promoted O-H functionalization of oximes with diazo esters is described. The reaction occurs under very mild conditions (catalyst- and additive-free) with a high yield and a high functional group tolerance. When the reaction was performed with a cyclic ether as the solvent (e.g., THF, 1,4-dioxane, tetrahydropyran, ect.), an interesting photochemical three-component reaction product was obtained in good yields.

Novel Class of Chalcone Oxime Ethers as Potent Monoamine Oxidase-B and Acetylcholinesterase Inhibitors

Previously synthesized novel chalcone oxime ethers (COEs) were evaluated for inhibitory activities against monoamine oxidases (MAOs) and acetylcholinesterase (AChE). Twenty-two of the 24 COEs synthesized, except COE-17 and COE-24, had potent and/or significant selective inhibitory effects on MAO-B. COE-6 potently inhibited MAO-B with an IC₅₀ value of 0.018 µM, which was 105, 2.3, and 1.1 times more potent than clorgyline, lazabemide, and pargyline (reference drugs), respectively. COE-7, and COE-22 were also active against MAO-B, both had an IC₅₀ value of 0.028 µM, which was 67 and 1.5 times lower than those of clorgyline and lazabemide, respectively. Most of the COEs exhibited weak inhibitory effects on MAO-A and AChE. COE-13 most potently inhibited MAO-A (IC₅₀ = 0.88 µM) and also significantly inhibited MAO-B (IC₅₀ = 0.13 µM), and it could be considered as a potential nonselective MAO inhibitor. COE-19 and COE-22 inhibited AChE with IC₅₀ values of 5.35 and 4.39 µM, respectively. The selectivity index (SI) of COE-22 for MAO-B was higher than that of COE-6 (SI = 778.6 vs. 222.2), but the IC₅₀ value (0.028 µM) was slightly lower than that of COE-6 (0.018 µM). In reversibility experiments, inhibitions of MAO-B by COE-6 and COE-22 were recovered to the levels of reference reversible inhibitors and both competitively inhibited MAO-B, with K_i values of 0.0075 and 0.010 µM, respectively. Our results show that COE-6 and COE-22 are potent, selective MAO-B inhibitors, and COE-22 is a candidate of dual-targeting molecule for MAO-B and AChE.