Cardioselective antiischemic ATP-sensitive potassium channel (KATP) openers. 5. Identification of 4-(N-aryl)-substituted benzopyran derivatives with high selectivity.

This paper describes our studies aimed at the discovery of structurally distinct analogs of the cardioprotective KATP opener BMS-180448 (2) with improved selectivity for the ischemic myocardium. The starting compound 6, derived from the indole analog 4. showed good cardioprotective potency and excellent selectivity compared to 2 and the first-generation KATP opener cromakalim (1). The structure-activity studies indicate that increasing the size of the alkyl ester leads to diminished potency as does its replacement with a variety of other groups (nitrile, methyl sulfone). Replacement of the ethyl ester of 6 with an imidazole gave the best compound 3 (BMS-191095) of this series which maintains the potency and selectivity of its predecessor 6. The results described in this publication further support that there is no correlation between vasorelaxant and cardioprotective potencies of KATP openers. Compound 3 is over 20- and 4000-fold more selective for the ischemic myocardium than 2 and cromakalim (1), respectively. The selectivity for the ischemic myocardium is achieved by reduction of vasorelaxant potency rather than enhancement in antiischemic potency. As for cromakalim (1) and 2, the cardioprotective effects of compound 3 are inhibited by cotreatment with the KATP blocker glyburide, indicating that the KATP opening is involved in its mechanism of cardioprotection. With its good oral bioavailability (47%) and plasma elimination half-life (3 h) in rats, compound 3 offers an excellent candidate to investigate the role of residual vasorelaxant potency of 2 toward its cardioprotective activity in vivo.

Pharmacokinetics and oral bioavailability of exogenous melatonin in preclinical animal models and clinical implications.

A review of the literature indicates that the absolute oral bioavailability of exogenous melatonin in humans or in preclinical animal models has not been adequately characterized; hence, this study was undertaken. Pharmacokinetics of melatonin was studied in rats, dogs, and monkeys following intravenous and oral administrations, and the absolute oral bioavailability of melatonin was calculated from the area under the plasma concentration-time curve. The apparent elimination half-life of melatonin following an intravenous dose of 3 mg/kg (5 mg/kg in rats) was 19.8, 18.6, and 34.2 minutes, respectively, in rats, dogs, and monkeys. The dose normalized oral bioavailability of melatonin following a 10 mg/kg oral dose was 53.5% in rats, while it was in excess of 100% in dogs and monkeys. Further, bioavailability of melatonin following a 10 mg/kg intraperitoneal administration in rats was 74.0%, suggesting the lack of substantial first-pass hepatic extraction of melatonin in rats. However, the oral bioavailability of melatonin in dogs decreased to 16.9% following a 1 mg/kg oral dose, indicating dose-dependent bioavailability in dogs. In vitro permeability studies with CACO-2 cells suggest that melatonin is likely to be well absorbed in humans. In vitro metabolism studies with fresh liver slices from rats as well as human donors were conducted to compare the initial rates of metabolism of melatonin between the two species and the results suggest that the intrinsic clearance of melatonin in humans may be lower than that in rats.

Multi-residue confirmation of aminoglycoside antibiotics and bovine kidney by ion spray high-performance liquid chromatography/tandem mass spectrometry.

An ion spray high-performance liquid chromatographic/tandem mass spectrometric (HPLC/MS/MS) method capable of determining the following six aminoglycosides in bovine kidney is presented: spectinomycin, hygromycin B, streptomycin, dihydrostreptomycin, gentamicin C complex and neomycin B. Tobramycin was used as an internal standard. This method uses an improved matrix solid-phase dispersion (MSPD) method for tissue extraction. A gradient HPLC separation was developed with mobile phases consisting of aqueous 20 mM pentafluoropropionic acid and acetonitrile. Protonated molecules served as precursor ions for collision-induced dissociation (CID) and three product ions were chosen for each analyte for selected reaction monitoring (SRM) where possible. A validation study was conducted for the confirmation of dihydrostreptomycin, neomycin B and four major components of the gentamicin C complex through SRM HPLC/MS/MS analysis of negative control, fortified and incurred bovine kidney samples. All of the samples analyzed could be confirmed with ion ratios within 15% of the daily mean of fortified standards and 90% of the samples had ion ratios within 10%. All compounds except spectinomycin could be detected (while monitoring three ions by SRM) in bovine kidney tissue at or below the regulatory level of concern. MSPD recoveries were acceptable with the exception of the 27% value observed for spectinomycin.

A quest for oleandrin in decayed human tissue.

This forensic case taught us several lessons. First, there is a need for improved sample cleanup and treatment of severely decayed tissue samples when trace determinations of target analytes are needed. With the exception of a few reports the literature is lacking in information with regard to the most modern sample preparation techniques. Second, the coupling of LC/LC with tandem MS provides an effective means of "on-line" samples cleanup for complex sample matrices. The improvements in selectivity shown in Figure 3 reveal the analytical power available when these techniques are combined. Third, once we decided to use LC/LC/MS/MS, we were able to analyze more than 50 samples in a semi-automated fashion over approximately three days. The reliability and ruggedness of the combined techniques and equipment suggest this approach may have merit for common applications in which large numbers of biological samples (e.g., plasma and urine) must be analyzed. As a postscript, when this project was completed we proposed that the use of antibodies for isolating oleandrin and its relatives might be a more selective means for trace enrichment of the target analytes. For example, a high-pressure immunoaffinity column could have been coupled on line as column 1 in Figure 4. After pumping a relatively high volume of aqueous tissue extract through an immunoaffinity column during trapping and trace enrichment conditions, the column could be rinsed with phosphate-buffered saline. Then the pH could be lowered to unfold the antibody protein and allow release of the trapped analyte from this column with subsequent trapping on column 2 in Figure 4.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of aminoglycoside antibiotics by reversed-phase ion-pair high-performance liquid chromatography coupled with pulsed amperometry and ion spray mass spectrometry.

This work constitutes a preliminary investigation of a high-performance liquid chromatographic (HPLC)-mass spectrometric (MS) method for confirming aminoglycoside residues in bovine tissues. A reversed-phase ion-pair HPLC method for the separation of four aminoglycosides was developed using volatile ion-pairing agents and optimized for detection with an ion spray HPLC-MS interface. The method is also compatible with a commercial pulsed amperometric detector that was used for HPLC method development and that may be useful for the screening and quantification phases of a regulatory method. Several column phases, eluent compositions, and pairing ions were evaluated for optimum HPLC-MS sensitivity. Detection limits are in the low nanogram range with the pulsed amperometric detector and with HPLC-MS in the selected ion monitoring mode. Results with bovine kidney, fortified to 20 ppm and extracted by matrix solid-phase dispersion, obtained using both detectors are presented.

Determination of dexamethasone in bovine tissues by coupled-column normal-phase high-performance liquid chromatography and capillary gas chromatography-mass spectrometry.

A new method for the determination of dexamethasone in bovine liver and muscle tissues has been developed. Crude tissue extracts were obtained by means of a three-phase liquid-liquid extraction scheme. The resulting residue was subjected to coupled-column normal-phase high-performance liquid chromatography which served to isolate the drug for the purpose of screening and quantification. Sample was injected onto the first column of the system, a phenyl column, from which a heart-cut was diverted to a short silica column which retained dexamethasone. The contents of this column were backflushed onto a cyanopropyl column which isolated dexamethasone. Mobile phases consisted of hexane modified with 2-propanol, acetic acid, and water. Analysis of each sample was completed in 15 min. Quantitation was performed by external standard calibration of ultraviolet response at 239 nm. Limits of detection were estimated to be 4 and 6 ppb in muscle and liver, respectively. In addition to screening and quantitation, the coupled-column system purified tissue extracts for gas chromatographic-mass spectrometric analysis which, in the selected-ion monitoring mode, confirmed the identity of the trimethylsilyl-enol-trimethylsilyl derivative of dexamethasone.