An efficient procedure for the preparation of natural products bearing the 2-(2-phenylethyl)chromone skeleton

Iodine-PEG as a unique combination for the metal-free synthesis of flavonoids through iodonium-triiodide ion-pair complexation

An efficient metal-free single-step protocol has been developed for the direct synthesis of flavones from 2-hydroxyacetophenone and substituted benzaldehydes. This chemical transformation is exclusively promoted by the iodonium-triiodide ion couple formed through iodine and PEG-400 complexation. The triiodide anion not only helps in the abstraction of a proton from the acetophenone but also promotes the cyclization of intermediate chalcone to the corresponding flavones. The flavones were obtained in very high yields without using any toxic metal catalysts or harsh reaction conditions. The reaction mechanism was established through a series of test reactions and entrapping of reaction intermediates. The developed protocol provides direct access to flavones in high yields under milder reaction conditions with great substrate compatibility, including hydroxylated derivatives.

Comprehensive Comparisons between Grafted Kynam Agarwood and Normal Agarwood on Traits, Composition, and In Vitro Activation of AMPK

Agarwood, a highly valuable resin/wood combination with diverse pharmacological activities but scarce supply, has a long history of being used as a medicine in several medical systems. Grafted Kynam agarwood (GKA) has been cultivated successfully recently and has the qualities meeting the definition of premium Kynam agarwood. However, there are few comprehensive comparisons between GKA and normal agarwood in terms of traits, global composition, and activity, and some key issues for GKA to be adopted into the traditional Chinese medical (TCM) system have not been elaborated. The two types of agarwood samples were evaluated in terms of trait characteristics, physicochemical indicators, key component groups, and global compositional profile. Furthermore, a molecular docking was performed to investigate the active ingredients. In vitro activity assays were performed to evaluate the activation of adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) by GKA and normal agarwood. The results revealed that, overall, the traits, microscopic characteristics, chemical composition types, and bioactivity between GKA and normal agarwood were similar. The main differences were the content of resin (ethanolic extract content), the content of key component groups, and the composition of the different parent structural groups of 2-(2-phenethyl) chromones (PECs). The contents of total PEC and ethanol extract content of GKA were significantly higher than those of normal agarwood. The MS-based high-throughput analysis revealed that GKA has higher concentrations of sesquiterpenes and flindersia-type 2-(2-phenylethyl) chromones (FTPECs) (m/z 250-312) than normal agarwood. Molecular docking revealed that parent structural groups of FTPECs activated multiple signaling pathways, including the AMPK pathway, suggesting that FTPECs are major active components in GKA. The aim of this paper is to describe the intrinsic reasons for GKA as a high-quality agarwood and a potential source for novel drug development. We combined high-throughput mass spectrometry and multivariate statistical analysis to infer the different components of the two types of agarwood. Then we combined virtual screening and in vitro activity to construct a component/pharmacodynamic relationship to explore the causes of the activity differences between agarwood with different levels of quality and to identify potentially valuable lead compounds. This strategy can also be used for the comprehensive study of other TCMs with different qualities.

Iodine-Mediated Synthesis of 2-(Methylthio)-4H-chromen-4-ones and Study of Their Halogenation Reactions

An efficient iodine-mediated method is developed for the synthesis of functionalized 2-(methylthio)-4H-chromen-4-ones by intramolecular cyclization of easily accessible 1-(2-benzyloxy-aryl)-3,3-bis-methylsulfanyl-propenones. The synthesized chromen-4-ones turn out to be a key precursor for various kinds of chemical reactions. Mechanistically, we observed that iodine-mediated intramolecular cyclization of ketene dithioacetal proceeded through a radical pathway. 3-Halo-2-(methylthio)-4H-chromen-4-ones were achieved via various two- or one-pot halogenation approaches.

Structure activity relationship exploration of 5-hydroxy-2-(3-phenylpropyl)chromones as a unique 5-HT2B receptor antagonist scaffold

Antagonists for the serotonin receptor 2B (5-HT_2B) have clinical applications towards migraine, anxiety, irritable bowl syndrome, and MDMA abuse; however, few selective 5-HT_2B antagonists have been identified. Previous studies from these labs identified a natural product, 5-hydroxy-2-(2-phenylethyl)chromone (5-HPEC, 2) as the first non-nitrogenous ligand for the 5-HT_2B receptor. Studies on 5-HPEC optimization led to the identification of 5-hydroxy-2-(3-phenylpropyl)chromone (5-HPPC, 3), which showed a tenfold improvement in binding affinity over 2 at 5-HT_2B. This study aimed to further improve receptor pharmacology of this unique scaffold. Guided by molecular modeling studies modifications at the C-3' and C-4' positions of 3 were made to probe their effects on ligand binding affinity and efficacy. Among the derivatives synthesized 5-hydroxy-2-(3-(3-cyanophenyl)propyl)chromone (5-HCPC, 3d) showed the most promise with a multifold improvement in binding affinity (pK_i = 7.1 ± 0.07) over 3 with retained antagonism.

Soft-enolization Baker-Venkataraman Rearrangement Enabled Total Synthesis of Dirchromones and Related 2-Substituted Chromones

A seven-step total synthesis of the original scaffold of cytotoxic dirchromones involving an unprecedented soft-enolization Baker-Venkataraman rearrangement was designed. The methodology enabled access to naturally occurring dirchromone 1 (21% overall yield) at gram-scale, which was screened for cytotoxicity against 13 cancer cell lines. The scope of the soft-enolization Baker-Venkataraman rearrangement encompasses diversely substituted dirchromones, including flavonoids, 2-styrylchromones, and 2-phenylethylchromones.

Synthesis and Characterization of 5-Hydroxy-2-(2-phenylethyl)chromone (5-HPEC) and Its Analogues as Non-nitrogenous 5-HT2B Ligands

The involvement of the neurotransmitter serotonin (5-HT) in numerous physiological functions is often attributed to the diversity of receptors with which it interacts. Ligands targeting serotonin receptor 2B (5-HT2B) have received renewed interest for their potential to help understand the role of 5-HT2B in migraines, drug abuse, neurodegenerative diseases, and irritable bowel syndrome. To date, most of the ligands targeting 5-HT2B have been nitrogen-containing compounds. The natural product 5-hydroxy-2-(2-phenylethyl)chromone (5-HPEC, 5) has been shown previously to act as a non-nitrogenous antagonist for the 5-HT2B receptor (pKi = 5.6). This report describes further progress on the study of the structure-activity relationship of both naturally occurring and synthetic compounds bearing the 2-(2-phenylethyl)chromone scaffold at the 5-HT2B receptor. The inhibitory activity of the newly synthesized compounds (at 10 μM) was tested against each of the 5-HT2 receptors. Following this assay, the binding affinity and antagonism of the most promising compounds were then evaluated at 5-HT2B. Among all the analogues, 5-hydroxy-2-(2-phenylpropyl)chromone (5-HPPC, 22h) emerged as a new lead compound, showing a 10-fold improvement in affinity (pKi = 6.6) over 5-HPEC with reasonable antagonist properties at 5-HT2B. Additionally, ligand docking studies have identified a putative binding pocket for 5-HPPC and have helped understand its improved affinity.

5-Hydroxy-2-(2-phenylethyl)chromone (5-HPEC): a novel non-nitrogenous ligand for 5-HT2B receptor

Chromones are a class of natural products found in almost every known terrestrial plant with over 4000 naturally occurring derivatives having been isolated and structurally elucidated. Recently, 5-hydroxy-2-(2-phenylethyl)chromone (5-HPEC), isolated from Imperata cylindrical, showed neuroprotective activity against glutamate induced excitotoxicity in primary cultures of rat cortical cells. In comparison to other naturally occurring neuroprotective chromones, 5-HPEC contains fewer hydroxyl groups. Here we report our most recent characterization on this interesting natural product against a number of CNS receptors for the purpose to identify the potential molecular targets that may be related to its biological activity. Based on our studies, including radiobinding assays, calcium flux functional assays and molecular modeling studies, 5-HPEC may represent a type of novel nonnitrogenous ligands to the 5-HT2B receptor.