Lipophilicity of vinpocetine and related compounds characterized by reversed-phase thin-layer chromatography

Synthesis and pharmacological activity of vinpocetine derivatives

Vinpocetine and its derivatives were extensively employed in the treatment of ischemic stroke, serving as effective cerebrovascular vasodilators. They could also be utilized for neuroprotection, anti-inflammatory purposes, anti-aging interventions, insomnia treatment, and antidepressant effects. However, due to issues such as hepatic first-pass effect, low bioavailability, and poor patient compliance with multiple dosing, the secondary development of Vinpocetine to address these limitations became a prominent area of research. Five primary methodologies were employed for the synthesis of Vinpocetine derivatives. These included substitution on the A ring to modify the 14-ester group, alteration of the 16-ethyl group, simplification of the D and E rings, and modification of the conformation of Vinpocetine. This paper summarized the current synthesis and activity studies of Vinpocetine and its derivatives, with the aim of providing a reference for the discovery of more potent derivatives of Vinpocetine.

Vinpocetine (A comprehensive profile)

Vinpocetine (VIN) is a herbal supplement extracted from the periwinkle plant. It is a multi-action agent, which is used to treat various neurological disorders such as Alzheimer's and Parkinson's disease. Vinpocetine has also anti-inflammatory, analgesic, antioxidant property and treats various thinking and memory problems. Currently, vinpocetine is also available in the market as a dietary supplement to enhance cognition and memory. This profile explains the physicochemical properties, methods of preparation, content of related impurities and different spectroscopical behavior of vinpocetine. It also discusses the reported methods of analysis of the drug, which include Compendial Methods, Electrochemical Methods, Spectrophotometric Methods and Chromatographic Methods of analysis. Furthermore, this profile explains the stability of the drug subjected to stress conditions of acid, alkaline and photolytic degradation. In addition, the clinical applications of the drug, its uses, side effects, dosing information, pharmacokinetics and mechanism of action are also discussed.

Neuroprotective effects of novel nanosystems simultaneously loaded with vinpocetine and piracetam after intranasal administration

AIMS

The study aim was to test the efficacy of a novel created hybrid nanosystem compared to other nanosystems in treatment of scopolamine induced memory impairment.

MAIN METHODS

The fabrication and characterization of nanoformulations (microemulsion, liposomes, ethosomes, transfersomes and transethosomes) coencapsulating two cognitive enhancers; piracetam and vinpocetine delivered intranasally, in addition to a novel nanocomposite microemulsion/vesicular nanoformulation was described.

KEY FINDINGS

Formulations delivered the drugs across sheep nasal mucosa, with cumulative percentage reaching 29.99% for vinpocetine and 57.78% for piracetam. While the solution form of the drugs was totally ineffective, the selected transethosomal, microemulsion and nanocomposite formulations reversed the scopolamine induced effect on the step through latency of passive avoidance test and the spontaneous alternation behavior in Y maze test, further confirmed by histopathlogical examination. All three nanoformulations significantly decreased the acetylcholinesterase activity and the extent of lipid peroxidation by 32-42%. The nanocomposite formulation was superior to the microemulsion and transethosomal formulations in its anti-inflammatory and antiapoptotic effects, delineated by higher extent of inhibition of COX-2 and caspase 3 expression respectively.

SIGNIFICANCE

Results support the hypothesis that the novel microemulsion/vesicular nanocomposite system is a promising neuroprotective modality for intranasal brain targeting which is worthy of exploitation in other brain diseases.

Physico-chemical profiling of semisynthetic opioids

Species-specific acid-base and partition equilibrium constants were experimentally determined for the therapeutically important semisynthetic opioid receptor agonist hydromorphone, dihydromorphine, and mixed agonist-antagonist nalorphine and nalbuphine. The acid-base microequilibria were characterized by combining pH-potentiometry and deductive methods using synthesized auxiliary compounds. Independent of the pH, there are approximately 4.8 times as many zwitterionic microspecies than non-charged ones in nalbuphine solutions, while for nalorphine it is the non-charged form that predominates by the same ratio. The non-charged microspecies is the dominant one also in the case of hydromorphone, although its concentration exceeds only 1.3 times that of its zwitterionic protonation isomer. The pH-independent partition coefficients of the individual microspecies were determined by a combination of experimentally measured, pH-dependent, conditional distribution constants and a custom-tailored evaluation method, using highly similar auxiliary compounds. The pH-independent contribution of the zwitterionic microspecies to the distribution constant is 1380, 1070, 3160 and 72,440 times smaller than that of the inherently more lipophilic non-charged one for hydromorphone, dihydromorphine, nalbuphine and nalorphine, respectively.

A structural framework of biologically active coumarin derivatives: crystal structure and Hirshfeld surface analysis

The relation between the lipophilicity parameter (log P) and the contribution of C–H⋯π interactions to the Hirshfeld surface has been investigated.

Brain targeted solid lipid nanoparticles for brain ischemia: preparation and in vitro characterization

This study aims at formulating solid lipid nanoparticles (SLNs) of Vinpocetine (VIN) to be used as a brain targeted sustained drug-delivery system. VIN is a derivative of vincamine alkaloid, used for chronic cerebral vascular ischemia. However, it suffers from low bioavailability and short half-life. Its oral bioavailability is recorded to be between 7 and 55%. Its elimination half-life is 1-2 h so it would be a good candidate for a sustained drug-delivery system. VIN SLNs were prepared using modified high shear homogenization followed by ultrasonication technique. The effect of incorporating different lipids at different concentrations of various surfactants was investigated. The VIN SLNs were characterized by entrapment efficiency percent (EE%), particle size distribution, zeta-potential, and cumulative released percent after 96 h. The EE% ranged between 83.34% ± 0.95-94.56% ± 0.11 due to the lipophilic character of VIN. The mean particle size measured ranged from 123 nm-464 nm. The cumulative released percent after 96 h ranged from 23.55% to 75.67% showing a controlled release profile. Formula (F32) composed of 5% glyceryl monostearate (GMS) and stabilized by 2% surfactant mixture [Tween 80, Pluronic F 68 (1:1)] was the most appropriate formula for brain delivery having EE% of 89.09% ± 1.49, zero-order release kinetics with cumulative released percent of 72.12% after 96 h, zeta-potential of -11.3 ± 0.97 mV. It showed a unimodal size distribution with particle size ≈ 90 nm and polydispersity index of 0.121. The formula of choice in this study exhibited a zero-order sustained release profile and met the requirement for a brain targeted SLN so it could be a promising formula to deliver VIN to the brain.

The Determination of Partition Coefficient of 6-Mercaptopurine Derivatives by Thin Layer Chromatography

Mercaptopurine and its derivatives are used in the treatment of leukemia. To estimate their lipophilicity, a simple and novel thin layer chromatography method was developed. The mobile phase was the mixture of acetonitrile and water. The acetonitrile content varied by 5% from 50% to 80%. The linear relationship between and for substances with known lipophilicity was found. The lipophilicity of purine derivatives was worked out from the calibration curve. The most lipohilic compound was methylazathioprine (0.64).

Species-specific lipophilicity of thyroid hormones and their precursors in view of their membrane transport properties

A total of 30 species-specific partition coefficients of three thyroid hormones (thyroxine, liothyronine, reverse liothyronine) and their two biological precursors (monoiodotyrosine, diiodotyrosine) are presented. The molecules were studied using combined methods of microspeciation and lipophilicity. Microspeciation was carried out by (1)H NMR-pH and UV-pH titration techniques on the title compounds and their auxiliary derivatives of reduced complexity. Partition of some of the individual microspecies was mimicked by model compounds of the closest possible similarity, then correction factors were determined and introduced. Our data show that the iodinated aromatic ring system is the definitive structural element that fundamentally determines the lipophilicity of thyroid hormones, whereas the protonation state of the aliphatic part plays a role of secondary importance. On the other hand, the lipophilicity of the precursors is highly influenced by the protonation state due to the relative lack of overwhelmingly lipophilic moieties. The different logp values of the positional isomers liothyronine and reverse liothyronine represent the importance of steric and electronic factors in lipophilicity. Our investigations provided clear indication that overall partition, the best membrane transport - predicting physico-chemical parameter depends collectively on the site-specific basicity and species-specific partition coefficient. At physiological pH these biomolecules are strongly amphipathic due to the lipophilic aromatic rings and hydrophilic amino acid side chains which can well be the reason why thyroid hormones cannot cross membranes by passive diffusion and they are constituents of biological membranes. The lipophilicity profile of thyroid hormones and their precursors are calculated and depicted in terms of species-specific lipophilicities over the entire pH range.

Engineering and validation of a novel lipid thin film for biomembrane modeling in lipophilicity determination of drugs and xenobiotics

Background

Determination of lipophilicity as a tool for predicting pharmacokinetic molecular behavior is limited by the predictive power of available experimental models of the biomembrane. There is current interest, therefore, in models that accurately simulate the biomembrane structure and function. A novel bio-device; a lipid thin film, was engineered as an alternative approach to the previous use of hydrocarbon thin films in biomembrane modeling.

Results

Retention behavior of four structurally diverse model compounds; 4-amino-3,5-dinitrobenzoic acid (ADBA), naproxen (NPX), nabumetone (NBT) and halofantrine (HF), representing 4 broad classes of varying molecular polarities and aqueous solubility behavior, was investigated on the lipid film, liquid paraffin, and octadecylsilane layers. Computational, thermodynamic and image analysis confirms the peculiar amphiphilic configuration of the lipid film. Effect of solute-type, layer-type and variables interactions on retention behavior was delineated by 2-way analysis of variance (ANOVA) and quantitative structure property relationships (QSPR). Validation of the lipid film was implemented by statistical correlation of a unique chromatographic metric with Log P (octanol/water) and several calculated molecular descriptors of bulk and solubility properties.

Conclusion

The lipid film signifies a biomimetic artificial biological interface capable of both hydrophobic and specific electrostatic interactions. It captures the hydrophilic-lipophilic balance (HLB) in the determination of lipophilicity of molecules unlike the pure hydrocarbon film of the prior art. The potentials and performance of the bio-device gives the promise of its utility as a predictive analytic tool for early-stage drug discovery science.