Chiral Discrimination And Assay Of Drug Stereoisomers By Metal Complexes-mass Spectrometry

Recent years,the pharmaceutical industry has a great interest in development of single enantiomeric drugs because individual enantiomers differ in their biological activity,mechanism and toxicity,thus enantiomerscan provide superior therapy by reducing the doses,increasing the potency and improving the safety profile.In the research progress of chiral drugs,enantiomeric impurity analysis is very important for the drug safety.Bucause the properties on chemical and physical is basically the same,chiral analysis of enantiomers is one of hot topics and difficult in the analytical chemistry.Mass spectrometry is a powerful analytical technique due to its remarkable features like sensitivity,speed,molecular specificity.Electrospray ionization ion trap multistage mass spectrometry provides abundant structural information for compound identification and also useful stereochemical information derived from sterically controlled fragmentations.Thus,the relative intensities of some characteristic fragment ion peaks in the mass spectra facilitate differentiation between stereoisomers,but it is still difficult in chiral drugs analysis by mass spectrometry,especially the chiral drugs which have multiple chiral centers.We successfully applied the MS method to fastly analyze tadalafil which has two chiral centers through CID(Collision Induced Dissociation)of metal bound diastereoisomeric clusters by using different chiral references.Based on the technology of a series of chiral drugs isomer impurity detection is studied,the study results are summrized as the followings:1.Chiral analysis of tadalafil enantiomers by CID of dimeric cluster ions composed of metal ions,L-Trp and tadalafil.Nickel-tadalafil complexes,[NiⅡ(Tadalafil)(L-Trp)-H]+,produced a characteristic fragment ion via collision-induced dissociation(CID).The relative abundance of this fragment ion contributed to differentiate tadalafil enantiomers,and to determine molar composition of tadalafil in the enantiomeric mixture as well.The method was validated in different commercial mass spectrometers(AB Q-TOF and Bruker ion-trap),and also verified by a chiral HPLC/Q-TOF.Comparing with chiral HPLC-MS method,this method provides a rapid,accurate and stable quantative result.2.One stone,two birds method.Discrimination and quantification of two type of chiral drugs by using each other as reference in mass spectrometry:(1)Chiral durgs tadalafil and three PPIs used as reference for differentiating each other.Differentiation of enantiomeric PPIs(pantoprazole,lansoprazole and omeprazole)was achieved by using RR-tadalafil as reference;esomeprazole was chosen to be optimized reference to differentiation all four tadalafil isomers.(2)Chiral durgs ezetimibe(EZM)and ambrisentan(AMB)were used as reference for differentiating each other.Differentiation of enantiomeric AMB were achieved by using SRS-EZM as reference;S-AMB was used as reference to differentiation all four isomers of SRS-EZM(RSR,RRS and SSR).(3)S-AMBwas used as reference for the chiral differentiation of atorvastatin(ATO)enantiomer,which was combined with ezetimibe as co-drug.Experimental results showed that the binary mixture of EZM and ATO enantiomers can be determined simultaneously without prior separation.This is very helpful for recognizing chiral impurity of a series of statins analogs by MS.Theone stone,two birds mehtod was firstly introduced here by using a same metal bound clusters to different two kinds of chiral drugs.Both KM and CR method were used to construction of a calibration curve for chiral quantitation.This method is rapid,accurate,sensitive and high selectivityfor analysis of these chiral drug impurities.3.Angiotensin Converting Enzyme Inhibitors(ACEIs)drugs were used as references for the recognition and quantitation of tadalafil and its two intermediates enantiomers.Both tadalafil and its two intermdeiates have the same chiral centers,so each of them has four isomers.Find a reference that could differentiate both of tadalafil and its two intermediates is difficult.To achieve this purpose,seven ACEIs drugs were selected as chiral references.Enantiomeric and diastereoisomeric discrimination is achieved by investigating the CIDspectra of the doubly-charged trimeric metal complexes,the results showed the optimal referenceis ramipril.Monitoring chiral impurities of both chiral intermediates and products by a single reference provide a high selectivity method.