Reversible isomerization of rapamycin demonstrated by liquid chromatography

Development of a validated high-throughput LC-ESI-MS method for determination of sirolimus on dried blood spots

A high-throughput liquid chromatography-electrospray ionization mass spectrometric (LC-ESI-MS) method for screening of sirolimus on dried blood spots (DBS) was developed and validated. It involves solvent extraction of a punch of DBS followed by reversed-phase LC on a relatively new monolithic column consisting of a silica rod with bimodal pore structure and detection by ESI-MS. The run time was less than 3 min with a very low backpressure at a flow rate of 0.5 mL/min. The method can analyze more than 100 samples in an 8 h working day, including sample preparation. The assay was linear from 1 to 100 ng/mL. The mean recovery was 92.42%. The mean inter-day and intra-day precisions were 1.23 and 1.41%, respectively. The developed method is simple, rapid and useful for clinical applications.

Evaluation of rapamycin chemical stability in volatile-organic solvents by HPLC

Rapamycin or sirolimus is a carboxylic lactone-lactam macrolide with a potent immunosuppressive activity. It can be successfully used to impregnate stents inserted in coronary arteries during surgical applications, preventing fatal infection and rejection adverse effect. The chemical stability of rapamycin in several organic-volatile solvents (acetone, chloroform, dichloromethane, hexane, ethyl alcohol, ethyl acetate, methyl alcohol, pentane and tetrahydrofurane) was established by HPLC-DAD-MS in reverse phase analysis. Results permitted to exclude rapamycin chemical degradation and to reveal a typical chemical isomerization, favoured in accordance to the solvent used. Two typical peaks appear, denominated beta and gamma, the time retention of which are, respectively, 11.3 and 15.0 min. Thanks to data recovered by NMR, spectrophotometric UV and mass analyses, it was possible to establish that both peaks correspond to two different isomeric forms of rapamycin. In addition, it was possible to establish that the relative percentage peak area varies according to the solvent and to the experimental time. The two isomeric forms are in equilibrium and each solvent concurs to differently displace this equilibrium versus one form rather than another, according to their both polarity index and aproticity.

HPLC Profile of Captopril Disulfide That Undergoes Reversible cis-trans Conversion among Three Isomers

Peculiarly shaped chromatograms of some compounds that consist of two reversible isomers have been reported. Those of a compound that consists of three reversible isomers are described here. Because disulfide of captopril has two cis-trans convertible bonds, it exists in three forms of cis-cis, cis-trans and trans-trans isomers. The disulfide has produced various HPLC-UV profiles under various conditions, such as three split peaks, three peaks with bridging plateaus and one broad peak. The effect of the column temperature and the eluent flow rate on the profile was investigated and explained by interconversion among three isomers. A profile analysis could provide some kinetic constants of this reaction.

Simultaneous on-line extraction and analysis of sirolimus (rapamycin) and ciclosporin in blood by liquid chromatography-electrospray mass spectrometry

We developed a sensitive and specific semi-automated liquid chromatography-electrospray mass spectrometric (HPLC-ESI-MS) assay for the simultaneous quantification of sirolimus and ciclosporin in blood. Following a simple protein precipitation step, the supernatants were injected into the HPLC system and extracted on-line. After column switching, the analytes were backflushed from the extraction column onto the analytical narrow-bore column and eluted into the ESI-MS system. The assay was linear from 0.4 to 100 microg/l sirolimus and from 2 to 1500 microg/l ciclosporin. The mean recoveries of sirolimus and ciclosporin were 98 and 96%, respectively. The mean interday precision/accuracy was 8.6%/-4.8% for sirolimus and 9.3%/-2.9% for ciclosporin.

Lipophilic benzamide and anilide derivatives as high-performance liquid chromatography internal standards: application to sirolimus (rapamycin) determination

Finding a suitable internal standard in reversed-phase high-performance liquid chromatography is often difficult. A general approach for selecting and synthesizing the proper internal standard is presented and applied to a validated method for quantitation of sirolimus in several biological matrices. A series of fifteen N-alkylbenzamides, N-alkyltoluamides and N-alkanoylanilines with a log P range of 3.51 to 6.68 were synthesized as internal standards; N-undecyl-o-toluamide was evaluated most extensively. Sirolimus quantitation involves a simple sample clean-up procedure followed by isocratic chromatography on a heated C18 analytical column with an 70% methanol-water mobile phase and ultraviolet detection at 278 nm. This method was linear from 2.5 to 200 ng with a limit of quantitation of 2.5 ng using a 1-ml blood sample. Sirolimus recovery was above 72.1%. The intra-day and inter-day coefficients of variation were less than 11.7%. Several drugs and sirolimus metabolites do not interfere with the analysis. This method was used to measure sirolimus in blood from rats, rabbits and humans.