Quantitative Structure-Activity Relationship Studies On Coumarin Prodrug Release And Properties Of Hydantoin Analogs In Chiral Stationary Phases

In recent two decades,the studies of quantitative structure-activity relationship(QSAR)have been widely used in the field of drug discovery,pesticide discovery and environmental evaluation,which include prediction of physical and chemical properties,released kinetic of the drug,and chromatographic retention.Especially in recent years,quantum chemical calculations(such as DFT,Hartree-Fock and so on)have been used in QSAR studies and significantly increased the accuracy of QSAR.On the other hand,better statistical analysis methodology could help the scientist to analyze the important and complicated issues in QSAR,such as the relationships associated with compound structure and its pharmacokinetics,or the compound structure and the chromatographic separation parameter(retention,elution sequence,and so on).In the first part of our studies,density functional theory(DFT)was applied in the quantitative structure-property relationship studies on coumarin-based prodrugs.This prodrug system was developed by our group and could be used to release amino acid or peptide in vivo.The mechanism of coumarin-based prodrug firstly related with the hydrolyzed prodrug by the esterase,which trigger the spontaneous lactonization and generate non-toxic coumarin and the amines acid(or peptides).The preliminary studies in our lab suggest that structural changes could affect the rate of drug release in coumarin-based prodrug.To further illustrate the relationships between structural and rate of drug release,the structures of 27 coumarin-based prodrugs prepared in our lab were modeled and calculated at a B3LYP/6-31+G(d,p)level using Gaussian 03 program.The calculated structural parameters were used as descriptors to establish five novel QSPR models.The SMLR linear model(q2=0.427,r2=0.516)and the PLS linear model(q2=0.584,r2=0.663)were developed with descriptors selected by an Unsupervised Forward Selection method.Another three nonlinear QSPR models were established using a Polynomial Neural Network(PNN)Simulation method(q2=0.692,0.675,0.663;r2=0.700,0.688,0.672).We suggest that the QSPR models derived here,especially the PNN models,can be used to predict the release kinetics of coumarin-based prodrugs as well as design new derivatives of coumarin-based prodrug candidates.The second part mainly discuss the synthesis and the quantitative structure-retention relationship of 3,5-disubstituted chiral hydantoin analogs.Hydantoin is an important heterocyclic which existed in some drugs or active natural products.In recent years,3,5-disubstituted hydantoin chiral compounds could be used as chiral ligands to catalyze asymmetric Aldol reactions or Mannich reactions.We developed a new methodology to prepare chiral 3,5-disubstituted hydantoin derivatives.In this method,methyl ester of L-leucine ureido derivative were synthesize and then were convert to chiral hydantoins through cyclization under basic conditions.This reaction was optimized by changing the different bases,solvents,the reaction time and temperature.The results showed that conversion of the a-amino acid ureido to the corresponding 3,5-disubstituted hydantoins could be performed in the mixture of NaH and anhydrous THF at low temperature(-20?)This method could prepare configuration keeping hydantoins with the advantage of simple procedure,short reaction time,high isolated yields,and good enatiomeric purity.In addition,this method affords a new way not only to introduce aliphatic side chain,but also the aryl group in the substitution of N3 position for 3,5-disubstituted hydantoin derivatives.Totally,eleven racemic and(S)-3,5-disubstituted hydantoin were synthesized and studied their chiral resolution on Chiralpak IA or Chiralpak IC.The results suggested that structural variations could significantly affect the retention factors.And also the different polysaccharide chiral stationary phases(CSP)also give different chiral separation result.In general,Chiralpak IA exhibit better chiral separation than Chiralpak IC.For example,all the compounds obtained baseline resolution in n-hexane/EtOH(80/20,v/v).However,nearly half of eleven hydantoin compounds could not obtain the baseline separation in 20%EtOH or 20%isopropanol when using Chiralpak IC column.We also found that the resolutions for these eleven hydatoins also were related with polar alcoholic modifier and column temperature.For example,different polar modifier,such as ethanol,propanol,isopropanol and butanol,showed various retention factors in Chiralpak IA column.Usually,S-enantiomer elutes first when using Chiralpak IA column.On the other hand,R-enantiomer elutes first when using Chiralpak IC column with 20%EtOH,and S-enantiomer became the first eluting enantiomer using Chiralpak IC column with 20%isopropanol.Poor chiral separation could be improved by decreasing the content of polar modifier for some hydatoin compounds(4 and 9)in Chrialpak IA column.But some compounds(compound 7 and 11)can not achieved baseline separation after lower concentration of polar modifier when using Chrialpak IC column.According to the van't Hoff equation,we proposed that column temperature of the compound 7 and 11 may be close to Tiso,which lead to the separation locates in the blind zone induced by temperature.Therefore,the effect of column temperature influencing enantioseperation and retention were studied with different CSP and concentration of polar modifier.The result showed that the Tiso of compounds 6 and 9 were more close to room temperature(20.6? and 30.8? respectively)with 20%IPA and Chrialpak IA column,which illustrated the reason why it is difficult to achieve baseline separations at room temperature.The similar phenomena were also observed in compound 7 and 9 with Chrialpak IC column using 20%EtOH and 20%IPA(20.3? and 11.8? respectively).Based on the thermodynamic theory,baseline separation could be obtained by changing the temperature and lowering the concentration of polar modifier when the compounds existed in the blind zone induced by temperature.The enantiomer elution order reversal could occur at this time.In our studies,poor enantioseparation of some 3,5-disubstituted hydatoins(compounds 6 and 9 in Chrialpak IA column,compounds 7 and 11 in Chrialpak IC column)could be solved when changing the temperature and lowering the concentration of polar modifier.At the same time,temperature-induced enantiomer elution order reversal were firstly found in hydatoin chiral compounds using CSP,which is helpful to study the interaction with the hydatoin compounds and polysaccharide CSP.On the other hand,chiral hydantoins with different substitution were found showing obvious difference on retention.To elucidate the chiral separation mechanism of these hydantoins,CoMFA was used to study the three-dimensional structure of the compounds and the association with retention factor.Based on the optimal parameters,the CoMFA models were successfully constructed with cross-validation q2>0.528,and noncross-validation rz>0.926.These CoMFA models with high predictive abilities could be helpful in further studies to detect the chromatographic retention behavior of 3,5-disubstituted hydantoins.