Retention behaviour of analytes in reversed-phase high-performance liquid chromatography-A review.

The understanding of principles that drive the separation in reversed-phase chromatography plays an important role in the prediction of the elution of solutes in RP-HPLC. The separation in RP-HPLC is based on the principle of adsorption and partition. In addition, the logP value, the pKa value of the drug and chromatographic parameters like mobile phase pH, buffer concentration, organic modifier and mobile phase additives also influence the retention and selectivity of the analyte. It was found that hydrophobic, electrostatic, hydrogen bonding and other specific interactions between the stationary phase and the solutes, along with the hydrophobicity of an analyte molecule (logP), modify the retention behaviour of the analytes. This article gives special attention to the influence of ionization and ion interaction on the separation of analytes. The drug molecules with different logP values containing protonated and deprotonated acids, bases and zwitterions are selected as examples and this article addresses various issues related to the method development, relationships between analyte retention and mobile phase pH and the pKa value of the analyte. The advances in this regard, with highlights on topics such as mechanisms of retention and various factors that influence the retention behaviour of analytes, are also updated with suitable examples.

Design, Synthesis, and Pharmacological Evaluation of Novel Tacrine Derivatives as Multi-target ANTI-Alzheimer's Agents In Rat Models.

BACKGROUND: Alzheimer's disease is a progressive neurodegenerative disorder for which no curative drugs are available and treatment available is just palliative. OBJECTIVES: Current research focused on design of Tacrine-Flavone hybrids as multitargeted cholinesterase and monoamine oxidase B inhibitors. METHODS: A total of 10 Tacrine- Flavone hybrids were designed, synthesized and characterized. The in vitro neurotoxicity and hepatotoxicity of the synthesized compounds determined using SHSY5Y cell line and HEPG2 cell line. One most active compound (AF1) with least toxicity in in vitro studies was chosen for in vivo studies. Acute and subacute toxicity of the novel compound AF1 conducted on Wistar rats according to OECD guideline 423 and 407. The LD50 value of the novel compound calculated according to Finney's method using Probit analysis. Anti-Alzheimer's activity studies conducted on male Wistar rats. Behavioral studies conducted and AChE and MAO-B activity determined in rat brain. RESULTS AND DISCUSSION: All the compounds exhibited good inhibitory effect on MAO B and AChE. The neurotoxicity studies of the active compound AF1 did not show toxicity up to 100µg. The hepatotoxicity study of the most active compound AF1, showed the compound to be safe up to 200µg. The LD 50 value of the novel compound after a single oral administration was found to be 64 mg/kg bodyweight in rats. Subacute toxicity studies did not show any remarkable toxicity in the vital organs up to 40 mg/kg. Activity studies showed comparable results with standard at 20 mg/kg. CONCLUSION: The results showed that the novel Tacrine-Flavone hybrids are multitarget-directed ligands, which are safe and active compared to tacrine and can be a promising lead molecule for further study.

Estimation of minoxidil in human plasma using UHPLC-MS/MS and its application in pharmacokinetic study.

Measurement of drug concentration in biological matrices (such as serum, plasma, blood, urine, and saliva) is important to determine Bioavailability (BA) and/or Bioequivalence (BE) of a drug product which are required during the drug product development and approval process to support applications for new active substances (INDs, NDAs) and generic (ANDAs) drug products to make critical decisions on safety and efficacy. Because of their vital role, bioanalytical methods should be well-characterized, fully validated and documented to yield reliable results. In present work, a simple, specific, high throughput, accurate and sensitive UHPLC-MS/MS method has been developed and validated for quantification of Minoxidil in human plasma. The analyte and the internal standard were extracted from plasma by Liquid-Liquid Extraction using ethyl acetate. The chromatographic separation was achieved on Thermo Hypersil Gold column (4.6x50mm, 5µm) using acetonitrile-0.1% formic acid in water (60:40, v/v) at a flow rate of 0.400 ml/min. Detection by turbospray positive ionization mass spectrometry in the multiple reaction monitoring mode with a mass transition ion-pair of m/z 210.152 → 163.965 (Minoxidil) and m/z 220.267 → 169.089 (Internal Standard-Minoxidil D10) was found to be linear over the concentration range of 1.280 to 151.075 ng/ml. The method was fully validated as per USFDA guidelines and the results were within regulatory limits. The inter and intra-day precision ranged from 5.42 to 9.27% and 2.55-9.42% respectively. The inter and intra-day accuracy ranged from 89.2 to 98.9% and 102-105% respectively. The method was successfully applied to a BE study involving human volunteers.

Design Synthesis and in vitro Evaluation of Tacrine-flavone Hybrids as Multifunctional Cholinesterase Inhibitors for Alzheimer's Disease.

BACKGROUND: Alzheimer's disease (AD) is a multifactorial neurodegenerative disorder. The multifactorial etiology of AD has led to the design of multitarget directed ligands (MTDL) for AD. Tacrine an acetylcholinesterase (AChE) inhibitor was the first FDA approved drug for AD but is discontinued due to hepatotoxicity. OBJECTIVE: Present research focused on incorporating a flavone to the tacrine nucleus to enhance the anti-Alzheimer's property of the tacrine with the synergistic effect of flavone which is a very good antioxidant. It is expected that the antioxidant property and hepatoprotective nature of flavones will reduce the hepatotoxic side effect of tacrine. METHODS: We designed and synthesized ten flavone substituted tacrine derivatives and evaluated for in vitro AChE and BuChE inhibitoy activity by modified Ellman's method using eeAChE and eqBuChE. In vitro antioxidant activity was studied by DPPH radical scavenging assay. Molecular modeling studies were conducted in Schrodinger and AutoDock Vina with TcAChE(PDB ID:1H23),hAChE(PDB ID:4EY7) and hBuChE(PDB ID:4TPK). RESULTS: All the compounds exhibited potent inhibitory effect on AChE and BuChE with IC50 values in µM concentration. The compounds exhibited very good antioxidant activity in DPPH radical scavenging assay. Among the compounds the compound AF1 showed highest activity with IC50 value of 0.93 µM for AChE and 1.48 µM for BuChE and also showed significant antioxidant activity (2.6 nM). A correlation graph was plotted for IC 50 values vs Dock score and the results are promising with r2 values of 0.62 and 0.73 for AChE and BuChE inhibition respectively which proved the reliability of docking approaches. CONCLUSION: The results highlighted the multifunctional nature of the novel Tacrine-Flavone hybrids and they may be promising MTDL for AD.

A Review of Different Analytical Techniques for Fexofenadine Hydrochloride and Montelukast Sodium in Different Matrices.

Fexofenadine hydrochloride is an antihistamine agent used for the treatment of allergic disorders like rhinitis. It is a second generation antihistamine. Montelukast sodium is an anti-asthmatic agent and leukotriene receptor antagonist used in the treatment of respiratory disorders. This article exemplifies the reported analytical methods like electrometric methods, ultraviolet spectroscopy, mass spectroscopy, thin layer chromatography, high performance liquid chromatography, high performance thin layer chromatography and tandem spectroscopy for determination of fexofenadine HCl and montelukast sodium in dosage form and in biological matrices. This review covers almost all the analytical methods for fexofenadine hydrochloride and montelukast sodium form 1968-2018 years. Complete analytical validation parameters reported are discussed in this review for both analytes. Among various analytical methods, HPLC and UV-visible spectrophotometry were found to be the most extensively used methods by the researchers.

An Investigation on Enhancement of Solubility of 5 Fluorouracil by Applying Complexation Technique- Characterization, Dissolution and Molecular-Modeling Studies.

The drug 5 fluorouracil is sparingly soluble in water. The aqueous solubility and dissolution rate of 5-fluorouracil can be increased by inclusion complexation with β-cyclodextrin. Molecular-modeling studies support the formation of stable molecular inclusion complexation of 5-fluorouracil with β-cyclodextrin monomer (1:1). Complexes were prepared by physical mixture, kneading, co evaporation and freeze drying methods. Two ratios 1:1 and 1:2 were formulated. These eight complexes were subjected to Phase-solubility study, molecular modeling and dissolution study. The complexes formed were confirmed by DSC studies. Phase solubility profile indicated that the solubility of 5-fluorouracil increased in the presence of β-cyclodextrin monomer. Results obtained by different characterization techniques clearly indicate that the freeze-drying method leads to formation of solid state complexes between 5-fluorouracil and β-cyclodextrin. The complexation of 5-fluorouracil with β- cyclodextrin lends an ample credence for better therapeutic efficacy.