Ding Y. Liu

Synthesis of 2-amido-3-hydroxypyridin-4(1H)-ones: novel iron chelators with enhanced pFe3+ values.

The synthesis of a range of 2-amido-3-hydroxypyridin-4-ones as bidentate iron(III) chelators with potential for oral administration is described. The pKa values of the ligands together with the stability constants of their iron(III) complexes have been determined. Results indicate that the introduction of an amido substituent at the 2-position leads to an appreciable enhancement of the pFe3+ values. The ability of these novel 3-hydroxypyridin-4-ones to facilitate the iron excretion in bile was investigated using a 59Fe-ferritin loaded rat model. The optimal effect was observed with the N-methyl amido derivative 15b, which has an associated pFe3+ value of 21.7, more than two orders of magnitude higher than that of deferiprone (1,2-dimethyl-3-hydroxypyridin-4-one) 1a (pFe3+ = 19.4). Dose response studies suggest that chelators with high pFe3+ values scavenge iron more effectively at lower doses when compared with simple dialkyl substituted hydroxypyridinones.

Iron Chelator Chemistry

Iron overload is a serious clinical condition which can be largely prevented by the use of iron-specific chelating agents. Desferrioxamine-B(1)the most widely used iron chelator in haematology over the past thirty years, has a major disadvantage of being orally inactive’. Consequently, the successful design of an orally active, non-toxic, selective iron chelator has become a much sought after goal.

Gradient ion-pair high-performance liquid chromatographic method for analysis of 3-hydroxypyridin-4-one iron chelators

A gradient ion-pair HPLC separation of highly hydrophilic 3-hydroxypyridin-4-one (HPO) iron chelators is described. The separation of HPOs was performed using a reversed-phase polymer HPLC column (PLRP-S 100 A, 15x0.46 cm ID, 5 microm). The ion-pair buffer contained 1-heptanesulfonic acid (sodium salt) (5 mM) and the pH was adjusted to 2.0 using HCl. The gradient was 2%-35% CH3CN in 20 min and post-run was followed for 5 min using 2% CH3CN and 98% buffer. The flow-rate was 1 ml/min and the analytes were monitored at 280 nm. The retention times of 30 hydrophilic HPOs fell in the range of 10-18 min with sharp peak shapes, although these iron chelators possess various functional groups and distribution coefficients. The application of this HPLC method in the analysis of HPO chelators and their metabolites in rat bile and urine is described.

Solid phase extraction and HPLC determination of 9-benzyladenine and isomeric 9-(nitrobenzyl)adenines and their metabolic N1-oxides present in microsomal incubates

9-Benzyladenine, 9-(2-nitrobenzyl)adenine, 9-(3-nitrobenzyl)adenine and 9-(4-nitrobenzyl)adenine were metabolized to 9-benzyladenine-N1-oxide, 9-(2-nitrobenzyl)adenine-n1-oxide, 9-(3-nitrobenzyl)adenine-N1-oxide and 9-(4-nitrobenzyl)adenine-N1-oxide, respectively, by animal hepatic microsomes. For the quantitative determination of the substrates and metabolites present in microsomal incubates, an off-line solid phase extraction procedure, using columns paced with C18 silica bonded phase, was developed. The extraction recovery for these 9-alkyladenines and their N1-oxides was in the range of 92-101%. A reversed-phase HPLC method was established with an ODS column at a column temperature of 50 degrees C. The mobile phase consisted of H20-MeOH-diethylamine (65:35:0.5, v/v/v). pH 6.8. The above analytes were monitored at 233 nm and retention times of all analytes were within 6-14 min. The within-day coefficients of variation (CV) for the determinations were in an acceptable range. The biotransformation of BA and NBAs to N1-oxides by hamster microsomes was determined under the experimental conditions employed.

Metabolism of 9-(2-chlorobenzyl)-, 9-(2-methylbenzyl)-and 9-(2-methoxybenzyl)-adenines by hamster hepatic microsomes

SummaryIt was previously found that 9-benzyladenine (BA) was extensively N1-oxidised by animal hepatic microsomes; further, mononitrosubstitution in the phenyl moiety of BA significantly modified the N1-oxidation rates of the corresponding substrates. In order to establish whether the electronic nature or a steric effect of the substituents in the phenyl moiety is the reason for the modification of N1-oxidation rate, the metabolism of some 2′-substituted 9-benzyladenines, i.e. 9-(2-chlorobenzyl)adenine (2CBA), 9-(2-methylbenzyl)adenine (2MBA) and 9-(2-methoxybenzyl)adenine (2MOBA), by hamster hepatic microsomes was studied. It was found that the N1-oxide was still the major metabolite for 2CBA. However, only minor amounts of N1-oxides were formed during microsomal incubation with 2MBA and 2MOBA. On the other hand, in spite of the higher N1-oxidation rate of 2CBA, its total biotransformation rate was slightly lower than the other two substrates. Like other 9-aralkyladenines previously studied, dealkylation occurred for all three substrates. It was also found that another two metabolites formed in significant amounts in the incubates from both 2MBA and 2MOBA. These metabolites were not fully characterised and their structures remain unknown.