Structural Studies of Piperine Inclusion Complexes in Native and Derivative β-Cyclodextrins

Driving forces and large scale affinity calculations for piperine/γ-cyclodxetrin complexes: Mechanistic insights from umbrella sampling simulation and DFT calculations

Piperine (PiP), a bioactive molecule, exhibits numerous health benefits and is frequently employed as a co-delivery agent with various phytomedicines (e.g., curcumin) to enhance their bioavailability. This is attributed to PiP's inhibitory activity against drug-metabolizing proteins, notably CYP3A4. Nevertheless, PiP encounters solubility challenges addressed in this study using cyclodextrins (CDs). Specifically, γ-CD and its derivatives, Hydroxypropyl-γ-CD (HP-γ-CD), and Octakis (6-O-sulfo)-γ-CD (Octakis-S-γ-CD), were employed to form supramolecular complexes with PiP. The conformational space of the complexes was assessed through 1 μs molecular dynamics simulations and umbrella sampling. Additionally, quantum mechanical calculations using wB97X-D dispersion-corrected DFT functional and 6-311 + G(d,p) basis set were conducted on the complexes to examine the thermodynamics and kinetic stability. Results indicated that Octakis-S-γ-CD exhibits superior host capabilities for PiP, with the most favorable complexation energy (-457.05 kJ/mol), followed by HP-γ-CD (-249.16 kJ/mol). Furthermore, two conformations of the Octakis-S-γ-CD/PiP complex were explored to elucidate the optimal binding orientation of PiP within the binding pocket of Octakis-S-γ-CD. Supramolecular chemistry relies significantly on non-covalent interactions. Therefore, our investigation extensively explores the critical atoms involved in these interactions, elucidating the influence of substituted groups on the stability of inclusion complexes. This comprehensive analysis contributes to emphasizing the γ-CD derivatives with improved host capacity.

Impact of 2-hydroxypropyl-β-cyclodextrin inclusion complex formation on dopamine receptor-ligand interaction - A case study

The octanol-water distribution coefficient (logP), used as a measure of lipophilicity, plays a major role in the drug design and discovery processes. While average logP values remain unchanged in approved oral drugs since 1983, current medicinal chemistry trends towards increasingly lipophilic compounds that require adapted analytical workflows and drug delivery systems. Solubility enhancers like cyclodextrins (CDs), especially 2-hydroxypropyl-β-CD (2-HP-β-CD), have been studied in vitro and in vivo investigating their ADMET (adsorption, distribution, metabolism, excretion and toxicity)-related properties. However, data is scarce regarding the applicability of CD inclusion complexes (ICs) in vitro compared to pure compounds. In this study, dopamine receptor (DR) ligands were used as a case study, utilizing a combined in silico/in vitro workflow. Media-dependent solubility and IC stoichiometry were investigated using HPLC. NMR was used to observe IC formation-caused chemical shift deviations while in silico approaches utilizing basin hopping global minimization were used to propose putative IC binding modes. A cell-based in vitro homogeneous time-resolved fluorescence (HTRF) assay was used to quantify ligand binding affinity at the DR subtype 2 (D2R). While all ligands showed increased solubility using 2-HP-β-CD, they differed regarding IC stoichiometry and receptor binding affinity. This case study shows that IC-formation was ligand-dependent and sometimes altering in vitro binding. Therefore, IC complex formation can't be recommended as a general means of improving compound solubility for in vitro studies as they may alter ligand binding.

Isomerism of Cyclodextrin Tetramer Induced by Alkali Halide Cluster Ions Observed by Ion Mobility Spectrometry-Mass Spectrometry

Cyclodextrins (CDs) exhibit versatile self-assembly properties due to their hydrophilic and hydrophobic components, with applications such as drug delivery and selective binding. While research on CD self-assembly is extensive, limited studies have explored their aggregation behavior, particularly in interactions with small ionic guests. The present work investigates the structure of β-CD tetramers aggregated with alkali metal chloride clusters using ion mobility spectrometry-mass spectrometry (IMS-MS). The results revealed that diverse structures emerge in the tetramer depending on the alkali metal cluster size. Notably, the doubly charged tetramer exhibits distinct aggregation trends with specific numbers of MCl clusters for Na+ and K+ ions. After initially adopting a bucket-wheel structure with two internal cations, the structure transforms into a new isomer with a tetrahedral configuration upon cluster addition. The formation of the new isomer structure is closely linked to filling the cavity volume with MCl clusters and ionic interactions, which possibly compensate for the weakened hydrogen bonds between CDs. Theoretical calculations further support the structures, showing well-matched collision cross-section (CCS) values compared with the experimental CCS values. This study highlights the role of alkali metal chloride clusters as potential templates, leading to the formation of novel CD assemblies.

Enhancing solubility and stability of piperine using β-cyclodextrin derivatives: computational and experimental investigations

Piperine (PP), a natural alkaloid found in black pepper, possesses significant bioactivities. However, its use in pharmaceutical applications is hindered by low water solubility and susceptibility to UV light degradation. To overcome these challenges, we investigated the potential of β-cyclodextrin (βCD) and its derivatives with dimethyl (DMβCD), hydroxy-propyl (HPβCD) and sulfobutyl-ether (SBEβCD) substitutions to enhance the solubility and stability of PP. This study employed computational and experimental approaches to examine the complexation between PP and βCDs. The results revealed the formation of two types of inclusion complexes: the P-form and M-form involving the insertion of piperidine moiety and the methylene-di-oxy-phenyl moiety, respectively. These complexes primarily rely on van der Waals interactions. Among the three derivatives, the PP/SBEβCD complex exhibited the highest stability followed by HPβCD, as attributed to maximum atom contacts and minimal solvent accessibility. Solubility studies confirmed the formation of inclusion complexes in a 1:1 ratio. Notably, the stability constant of the inclusion complex was approximately two-fold higher with SBEβCD and HPβCD compared to βCD. The DSC thermograms provided confirmation of the formation of the inclusion complex between the host and guest. These findings highlight the potential of βCD derivatives to effectively encapsulate PP, improving its solubility and presenting new opportunities for its pharmaceutical applications.Communicated by Ramaswamy H. Sarma.