Chromatographic separation of piracetam and its metabolite in a mixture of microsomal preparations, followed by an MS/MS analysis

Application of carbamyl in structural optimization

Carbamyl is considered a privileged structure in medicinal chemistry. It has a wide range of biological activities such as antimicrobial, anticancer, anti-epilepsy, for which the best evidence is a number of marketed carbamyl-containing drugs. Carbamyl is formed of primary amine and carbonyl moieties that act as hydrogen bond donors and hydrogen acceptors with residues of targets respectively, which are benefit for improving pharmacological activities. In other cases, the introduced carbamyl improves drug-like properties including oral bioavailability. In this review, we introduce the carbamyl-containing drugs and the application of carbamyl in structural optimization as a result of enhancing activities or/and drug-like properties.

Assessment of pharmacokinetic interaction between piracetam and l-carnitine in healthy subjects

A rapid, sensitive and specific method for quantifying piracetam in human plasma using Piracetam d-8 as the internal standard (IS) is described. The analyte and the IS were extracted from plasma by one-step precipitation of protein using an acetonitrile (100%). The extracts were analyzed by high-performance liquid chromatography coupled with electrospray tandem mass spectrometry (HPLC-MS/MS). The method had a chromatographic run time of 3.8 min and a linear calibration curve over the range 0.5-50 µg/mL (r > 0.99). This LC-MS-MS procedure was used to assess the bioavailability of two piracetam formulations: piracetam + l-carnitine (Piracar®; 270/330 mg tablet) and piracetam (Nootropil®; 800 mg tablet) in healthy volunteers of both sexes. The geometric means with corresponding 90% confidence interval (CI) for test/reference percentage ratios were 88.49% (90% CI = 81.19 - 96.46) for peak concentration/dose and 102.55% (90% CI = 100.62 - 104.51) for AUCinf /dose. The limit of quantitation of 0.5 µg/mL is well suited for pharmacokinetic studies in healthy volunteers. It was concluded that piracetam (Piracar®; 270/330 mg tablet) has a bioavailability equivalent to the piracetam (Nootropil®; 800 mg tablet) formulation with regard to both the rate and the extent of absorption.

Metabolism-directed structure optimization of benzimidazole-based Francisella tularensis enoyl-reductase (FabI) inhibitors

1. FabI is a potential antibiotic target against Francisella tularensis, which has been classified as a Category A biowarfare agent of high risk to public health. Our previous work demonstrated that N-benzyl benzimidazole compounds possess promising FabI inhibitory activity, but their druggability properties, including metabolic stability, are unknown. 2. The objective of this study was to characterize structure-metabolism relationships of a series of N-benzyl benzimidazole compounds to guide chemical optimization for better metabolic stability. To this end, metabolic stability data were obtained for 22 initial lead compounds using mouse hepatic microsomes. 3. Metabolic hotspots on the benzimidazole core structure as well as the benzyl ring were identified and verified by metabolite identification studies of four model compounds. Interestingly, the proposed structure-metabolism relationships did not apply to nine newly synthesized cyclopentane or oxacyclopentane derivatives of N-benzyl benzimidazole. 4. Subsequently, in silico quantitative structure-property relationship models were developed. Four molecular descriptors representing molecular polarity/polarisability, symmetry and size were identified to best explain variability in metabolic stability of different compounds. Multi-linear and non-linear regression models based on the selected molecular descriptors were developed and validated. 5. The structure-metabolism relationships for N-benzyl benzimidazole compounds should help optimization of N-benzyl benzimidazole compounds for better pharmacokinetic behavior.