The role of intramolecular H-bonds predominant effects in myricetin higher antioxidant activity

Design, Synthesis, and Biological Activity Studies of Myricetin Derivatives Containing a Diisopropanolamine Structure

A series of myricetin derivatives containing diisopropanolamine were designed and synthesized. The in vitro inhibitory effects of the target compounds on 9 fungal pathogens and 3 bacterial pathogens were also evaluated. A12 had the best inhibitory effect against Xanthomonas oryzae pv. oryzae (Xoo), with an EC50 value of 4.9 μg/mL, which was better than zinc-thiazole (ZT: EC50 = 7.3 μg/mL) and thiodiazole-copper (TC: EC50 = 65.5 μg/mL); A25 had the best inhibitory effect against Phomopsis sp. (Ps), with an EC50 value of 17.2 μg/mL, which was better than azoxystrobin (Az: EC50 = 22.3 μg/mL). In vivo inhibition tests were performed on kiwifruit for A25 and rice leaves for A12. At 200 μg/mL, the curative activity of A12 against rice leaf blight was 40.7%, which was better than that of ZT (37.2%) and TC (32.9%), and the protective activity of A12 was 44.8%, which was better than that of ZT (39.5%) and TC (34.6%). The curative activity of A25 against kiwi soft rot disease was 70.1%, which was better than that of Az (62.8%). Preliminary elucidation of the possible mechanisms of action was carried out by experiments on fluorescence microscopy, scanning electron microscopy, formation of biofilms, density functional theory calculations, and so on.

Influence of Intermolecular Interactions on Crystallite Size in Crystalline Solid Dispersions

Crystalline solid dispersions (CSDs) represent a thermodynamically stable system capable of effectively reducing the crystallite size of drugs, thereby enhancing their solubility and bioavailability. This study uses flavonoid drugs with the same core structures but varying numbers of hydroxyl groups as model drugs and poloxamer 188 as a carrier to explore the intrinsic relationships between drug-polymer interactions, crystallite size, and in vitro dissolution behavior in CSDs. Initially, we investigate the interactions between flavonoid drugs and P188 by calculating Hansen solubility parameters, determination of Flory-Huggins interaction parameters, and other methods. Subsequently, we explore the crystallization kinetics of flavonoid drugs and P188 in CSD systems using polarized optical microscopy and powder X-ray diffraction. We monitor the domain size and crystallite size of flavonoids in CSDs through powder X-ray diffraction and a laser-particle-size analyzer. Finally, we validate the relationship between crystallite size and in vitro dissolution behavior through powder dissolution. The results demonstrate that, as the number of hydroxyl groups increases, the interactions between drugs and polymers become stronger, making drug crystallization in the CSD system less likely. Consequently, reductions in crystalline domain size and crystallite size become more pronounced, leading to a more significant enhancement in drug dissolution.

Simulations on the dual effects of flavonoids as suppressors of Aβ42 fibrillogenesis and destabilizers of mature fibrils

Structural studies of the aggregation inhibition of the amyloid-β peptide (Aβ) by different natural compounds are of the utmost importance due to their great potential as neuroprotective and therapeutic agents for Alzheimer’s disease. We provided the simulation of molecular dynamics for two different states of Aβ42, including “monomeric aggregation-prone state (APS)” and “U-shaped pentamers of amyloidogenic protofilament intermediates” in the absence and presence of polyphenolic flavonoids (Flvs, myricetin and morin) in order to verify the possible mechanism of Flvs fibrillogenesis suppression. Data showed that Flvs directly bind into Aβ42 species in both states of “monomeric APS β-sheets” and “pentameric amyloidogenic intermediates”. Binding of Flvs with amyloidogenic protofilament intermediates caused the attenuation of some inter-chains H-bonds, salt bridges, van der Waals and interpeptide interaction energies without interfering with their secondary β-sheets. Therefore, Flvs redirect oligomeric amyloidogenic intermediates into unstructured aggregates by significant disruption of the "steric zipper" motif of fibrils—pairs of self-complementary β-sheets—without changing the amount of β-sheets. It is while Flvs completely destruct the disadvantageous secondary β-sheets of monomeric APS conformers by converting them into coil/helix structures. It means that Flvs suppress the fibrillogenesis process of the monomeric APS structures by converting their β-sheets into proper soluble coil/helices structures. The different actions of Flvs in contact with two different states of Aβ conformers are related to high interaction tendency of Flvs with additional H-bonds for monomeric APS β-sheet, rather than oligomeric protofilaments. Linear interaction energy (LIE) analysis confirmed the strong binding of monomeric Aβ-Flvs with more negative ∆G_binding, rather than oligomeric Aβ-Flvs system. Therefore, atomic scale computational evaluation of Flvs actions demonstrated different dual functions of Flvs, concluded from the application of two different monomeric and pentameric Aβ42 systems. The distinct dual functions of Flvs are proposed as suppressing the aggregation by converting β-sheets of monomeric APS to proper soluble structures and disrupting the "steric zipper" fibril motifs of oligomeric intermediate by converting on-pathway into off-pathway. Taken together, our data propose that Flvs exert dual and more effective functions against monomeric APS (fibrillogenesis suppression) and remodel the Aβ aggregation pathway (fibril destabilization).