Study Of Synthesis Of Antihypertensive Drugs And Preparation Of Drug-loaded Nanofibre Membranes Via Electrospinning

Hypertension is a very common and serious condition that can lead to many health problems. It is also an important worldwide public-health challenge because of its high frequency and concomitant risks of cardiovascular and kidney disease. It has been identified as the leading risk factor for mortality, and is ranked third as a cause of disability-adjusted life-years. Therefore cost effective approaches to optimally control blood pressure are very much needed. Pulmonary arterial hypertension (PAH) is perhaps one of the most severe and disabling type of hypertension. PAH disease progression leads to right heart failure and death. Treatment options for PAH include various standard cardiovascular drugs, such as anticoagulants, diuretics and so on. A number of agents specifically approved for PAH have also been available for several years. The oral endothelin-receptor antagonist bosentan is one of these. As two other endothelin-receptor antagonists, ambrisentan and darusentan have been assessed in clinical trials for PAH, and ambrisentan has been FDA-approved for this indication in 2007. In recent years, much research work has been done in preparation of ambrisentan and darusentan, but most reports focus on the synthesis of the targeted molecule. The intermediates in the process of preparation and the new dosage forms about these drugs have not been discussed.Base on the fruit of those works, the processing, the affecting factors and announcements in the process of preparation for ambrisentan and darusentan are primarily discussed in this paper. The two intermediates,4,6-Dimethyl-2-(methylsulfonyl)pyrimidine and 4,6-Dimethoxy-2-(methylsulfonyl)pyrimidine were synthesized. The possible mechanism of S-methylated and the effect of by product formation were discussed. And then ambrisentan and darusentan were prepared. As the new dosage forms, drug-loaded nanofibres have been successfully prepared by an electrospinning technique, using ambrisentan or captopril as model drug. The structures of the electrospun drug-loaded nanofibers were characterized. And the in vitro dissolution tests were also systematically examined. The main research can be summarized as following:(1) 2-(Methylthio)benzothiazole was synthesized from 2-mercaptobenzothiazole(MBT) and dimethyl carbonate(DMC) in the presence Phase-transfer catalyst(PTC) and K2CO3. The processing, the affecting factors and announcements in the process of preparation for 2-(Methylthio)benzothiazole were discussed. Tetrabutylammonium bromide(Bu4NBr) was the best PTC. The optimum reaction conditions were n(MBT):n(DMC):n(K2CO3): n(Bu4NBr)=1:18:1.5:0.2, reaction temperature 90℃under atmospheric pressure, and reaction time 3h. The yield of 2-(Methylthio)benzothiazole was 76.4% while the conversion of MBT was 100% under these conditions. Meanwhile, the results of GC-MS showed that the byproducts were N-methylated derivative. The possible formation mechanism of N-methylated derivative and the effect of by product formation on the yield of 2-(Methylthio)benzothiazole were discussed. The S-methylated of some kinds of SH-containing heterocycles with DMC was studied in the presence of K2CO3 and Bu4NBr under the same conditions. Methylation with DMC has been found to be a convenient method to prepare heteroaryl methyl thioethers. K2CO3-Bu4NBr showed a high catalytic activity for SH-methylating types of mercapto group on heterocyclic rings. SH-containing heterocycles can be converted into their corresponding thioethers in high selectivity and yields. Therefore, it provides an alternative clean and easy route to S-methylated of SH-containing heterocycles and is help to synthesize 4,6-Dimethyl-2-(methylsulfonyl) pyrimidine. The structures of products were determined by 1HNMR,13CNMR and MS.(2) In order to investigate the catalytic activity of room temperature ionic liquids(RTILs) and the effect of other conditions, the reaction of MBT with DMC was selected as a model reaction. [Bmim]Cl was the best catalyst. The optimum reaction conditions were n(MBT): n(DMC):n([Bmim]Cl)=1:2:2, reaction temperature 110℃under atmospheric pressure, and reaction time 3h. The yield of 2-(Methylthio)benzothiazole was 82.0% while the conversion of MBT was 100% under these conditions. The byproducts were N-methylated derivative. The S-methylated of some kinds of SH-containing thiols with DMC was studied in the presence of [Bmim]Cl under the same conditions. Results indicated that the alkyl thiols were found to lower the reactivity. Higher yields of aryl methyl thioethers were obtained compared to alkyl methyl thioethers. Heterocyclic thiols were converted into the corresponding heteroaryl methyl thioethers giving high yields and good regioselectivity. Clearly temperature is an influencing factor on the yields and reaction time. We further investigated the recyclability of ionic liquid. [Bmim]Cl was further recycled in four subsequent runs with little decrease in activity. The yield of 4,6-dimethyl-2-(methylthio) pyrimidine was 92.3%. And this research lays a foundation for the preparation of 4,6-Dimethyl-2-(methylsulfonyl)pyrimidine. The structures of products were determined by 1H NMR,13C NMR and MS. To study the possible mechanism relating to the S-methylated using DMC in [Bmim]Cl, the change of proton chemical shift of mercapto group of the pyrimidine was investigated using 1H NMR. Results indicated that the possible mechanism relating to the S-methylated is BAl2 mechanism.(3) 4,6-Dimethyl-2-(methylsulfonyl)pyrimidine was synthesized from 4,6-dimethyl-2-mercaptopyrimidine(DLMP) by the methylation and oxidation via environment-friendly processes. The optimum reaction conditions in the methylation were n(DLMP):n(DMC):n([Bmim]Cl)=1:1.5:2, reaction temperature 110℃under atmospheric pressure, and reaction time 3h. The yield of 4,6-dimethyl-2-(methylthio)pyrimidine was 93.5%. [Bmim]Cl can be recycled in four subsequent runs with only a gradual decrease in activity. The yield of the oxidation was 92.7%. And the total yield of 4,6-Dimethyl-2-(methylsulfonyl) pyrimidine was 86.7%.4,6-Dimethoxy-2-(methylsulfonyl) pyrimidine was synthesized from 2-thlobarblturic acid(TBA) by the methylation and oxidation via environment-friendly processes. The yield of 4,6-Dimethoxy-2-(methylthio)pyrimidine was 66.7%. The yield of the oxidation was 91.2%. And the total yield of 4,6-Dimethoxy-2-(methylsulfonyl)pyrimidine was 60.8%. The structures of products were determined by FTIR,1H NMR,13C NMR and MS.Ambrisentan and darusentan, two ETA selective endothelin receptor antagonists, were synthesized using diphenyl ketone as a starting material. The target compound was synthesized via several steps, involving in Darzens condensation with ethyl chloroacetate, methanolysis catalyzed by p-toluene sulfonic acid, alkaline hydrolysis, and salt-formation. The total yield of (S)-p-Chlorophenylethylammonium-(S)-2-hydroxy-3-methoxy-3, 3-diphenylprop-ionate(9) was 20.5%. Darusentan was obtained via two steps, involving in a nucleophilic substitution by treating (9) with 4,6-Dimethoxy-2-(methylsulfonyl)pyrimidine in the presence of LiNH2 and acidizing with dilute sulfuric acid. The process for the synthesis of darusentan achieved a total yield of 16.8%. Ambrisentan was obtained via two steps, involving in a nucleophilic substitution by treating (9) with 4,6-Dimethyl-2-(methylsulfonyl)pyrimidine in the presence of LiNH2 and acidizing with dilute sulfuric acid. The process for the synthesis of ambrisentan achieved a total yield of 16.2%. The HPLC methods were established for the enantiomeric separation and determination of intermediate, darusentan and ambrisentan. The chemical structures of the target compounds were verified using FTIR,1H NMR,13C NMR and MS.(4) Drug-loaded nanofibre membranes have been successfully prepared by an electrospinning technique, using ambrisentan, polyvinylpyrrolidone K60 (PVP K60) and dimethylacetamide (DMAC) as the starting materials. The effect of fabrication parameters was determined. The structures of the electrospun drug-loaded nanofibers were characterized by SEM, DSC and XRD et al. The results indicated that the products were the three-dimensional continuous web structure nanofibres with 300-600 nm in average outer-diameter. The state of ambrisentan in the nanofibres was also discussed. Results from SEM, DSC and XRD showed that the drug was distributed evenly in nanofibers. FTIR results demonstrated that the main interactions between PVP and ambrisentan were hydrogen bonding. In vitro wetting and dissolution tests showed that the drug-loaded nanofiber membranes were able to absorb water and dissolve on the water surface in 60s through the polymer-controlled mechanism. The drug-loaded nanofibers obviously improved ambrisentan's solubility. The Drug-loaded PVP nanofiber was useful for the possible applications as new dosage forms of antihypertensive drugs.(5) Ultrafine captopril(Cpl)-loaded polyacrylonitrile(PAN) fibers were successfully prepared by electrospinning method from co-dissolving solutions of PAN and captopril in dimethylacetamide (DMAC) as the spinning solutions. The effect of fabrication parameters was determined. The samples thereby obtained were characterized by SEM, DSC, XRD and FTIR measurements. SEM was carried out to observe the morphology of the nanofibers. DSC and XRD were conducted to clarify the states of the drug. FTIR was conducted to clarify the interactions between the drug and the polymer. Drug release profiles were investigated using in vitro dissolution tests. Results from SEM, DSC and XRD showed that the drug was distributed evenly in PAN nanofibers. FTIR results demonstrated that the main interactions between PAN and Cpl were hydrogen bonding. In vitro release study showed that after a burst release at the early stage, a sustained release was achieved and 79.7% of Cpl was released from the sample in 48h. It was shown that the drugs were capsulated inside of the fibers and the drug release in the presence of Cpl followed nearly Ritger-Peppas model. All the results demonstrated that the Drug-loaded PAN nanofiber was useful for the possible applications as transdermal drug delivery systems.