Several Applications Of Chiral Spectroscopy

1.Molecular interactions of sodium houttuyfonate with two kinds of serum albumin:multiple spectroscopic and molecular docking investigationSodium houttuyfonate(SH)is the sodium bisulfite adduct of the natural product houttuynin,and is widely used as an antimicrobial agent in China.In order to deeply understand the molecular basis of its pharmacokinetic behavior,we utilized a range of spectroscopy and calculations to investigate the interactions between SH and two carrier proteins,BSA and HSA under typical physiological conditions.With the addition of SH to the BSA and HSA solution,the UV absorption intensity of BSA and HSA at 280 nm decreased and produced a new absorption band at 310 nm,which demonstrates that it is indeed a static quenching process occurring in two systems.The association constants,binding site numbers and corresponding thermodynamic parameters were used to investigate the nature of the quenching mechanism involved.It was showed that the binding constant between SH and two kinds of serum albumin were both in the order of 106M-1.Stern-Volmer quenching constants gradually decreased with the increase in temperature,getting the same conclusion as UV spectrum that the quenching mode was static.Moreover,the apparent distance of 2.83 nm between SH and Trp-212 of BSA and 3.06nm between SH and Trp-214 of HSA,were observed through the use of fluorescence resonance energy transfer techniques.The alterations of BSA and HSA secondary structure in the presence of SH were demonstrated with circular dichroism spectroscopy.Displacement experiments showed that SH could decrease complexation of BSA with drugs known to bind to drug site,while decrease complexation of HSA with drugs known to bind to drug site I,which are consistent with the molecular modeling results demonstrating that SH can indeed bind within the hydrophobic pocket of BSA via hydrophobic contacts near domain II of BSA and I of HSA.This study provides useful information about the pharmacokinetic characteristics of SH and will be valuable for the development of novel SH-derived drugs.2.Establishment and application of detection method of 2-amino-l-butanol absolute optical purity based on chiroptical spectroscopy2-amino-1-butanol is the key intermediate to synthesize ethambutol(EMB),one of the front-line drugs against tuberculosis.(S,S)-EMB is the most effective agent against almost all the strains of Mycobacterium sps.,causing an up to 200-fold activity enhancement than(R,R)-enantiomer and meso-isomer.Moreover,it is reported that optical impurity(R,R)-EMB could lead to serious visual impairment,which is the main side-effect in the clinic application of EMB.The classical and widespread methods to synthesize EMB mainly involved reacting 1,2-dihaloethane with(S)-1.Accordingly,it is apparent that the enantiopurity of 1 predominantly dominates the optical purity of EMB.Using NMR and ORD to determine 2-amino-1-butanol enantiomeric excesses(ee's)showed up inevitable flaw in its accuracy and sensitivity.A concise and efficient reverse-phase high-performance liquid chromatography(RPLC)method has been established for absolute optical purity assay of 2-amino-1-butanol.These enantiomers were derivatized with methyl(5-fluoro-2,4-dinitro-phenyl)-(S)-prolinate,which can be regarded as a structural variant of Marfey's reagent.The resultant diastereomers were further cyclized by using bis(trichlormethyl)carbonate to form oxazolidin-2-one ring,leading to distinct difference in their electronic circular dichroism(ECD)spectra.Time-dependent density functional theory(TDDFT)was then applied to simulate theoretical ECD spectra for unambiguous absolute configuration assignment of cyclized products without putative samples.Both pairs of diastereomers could be separated on a reverse-phase C18 column using a mobile phase of methanol or acetonitrile and water with UV detection at 336 nm.The tandem reactions could be integrated into one-pot synthesis with high yield.Thus,exact absolute optical purity of 2-amino-1-butanol could be directly determined by monitoring the peak ratios of these epimers.This method was then applied to the absolute optical purity assessment of four commercially available samples.They were assessed for their enantiomeric excess using both external standard method and peak area normalization method.Therefore,in a typical routine determination without requirement of system suitability evaluation,peak area normalization method with correction factor is sufficient to give reliable results without preparing standard curves.Furthermore,it consequently affords a promising prospect for analysis of other chiral amino alcohols as well.3.Systematic investigation of electronic circular spectra of matrine-type alkaloidsthrough time-dependent density-functional theory calculationsMatrine-type alkaloids are available from the dry roots of Sophora flavescens with potentially pharmacological effects such as anti-inflammatory,anti-tumor,and for the treatment of Alzheimer' s disease.It is paramount to investagate the stereochemical characterizations of matrine-type alkaloids which is essential to establish reliable structure-activity relationships.Electronic circular dichroism(ECD)spectra of three matrine-type alkaloids matrine,sophoridine and oxymatrine were measured down to 170 nm in aqueous solution using vacuum-ultraviolet(VUV)synchrotron radiation.Their ECD spectra showed a positive CE Effect(CE)near 220 nm,but varied greatly in the region of 170-210 nm.To interpret the difference of their ECD spectra,time-dependent density functional theory(TDDFT)and continuum solvation model were employed to simulate their theoretical ECD spectra.To select suitable calculation parameters to achieve the optimal match of theoretical and experimental data,various functional and basis set combinations with PCM solvation model for water were tried to calculate the VUV-ECD spectra of these compounds.Through similarity analysis,the optimal calculated VUV-ECD spectra of matrine-type compounds in water were obtained.The most suitable combinations to calculate ECD spectra of matrine and sophoridine are B3LYP/cc-pvdz and Cam-B3LYP/aug-cc-pvdz,respectively.The corresponding degrees of fitting are 0.9980 and 0.9887.Cam-B3LYP/cc-pvdz is the most suitable to calculate the ECD spectrum of oxymatrine with the degree of fitting being 0.9887.Analysis molecular orbitals of the representative conformers for matrine,oxymatrine and sophoridine have provided an understanding of the experimentally observed ECD spectra at the molecular level.The positive CEs at around 220 nm were attributed to the n??*transition of the amide group,and the CEs near 190 nm were originated from the ???*transition of amide group.There are different ECD signal results from the electron of N1 participation transition between matrine and sophoridine.ECD spectra were also obtained in organic solvents with different dielectric constants and hydrogen-bonding characteristics.It was demonstrated that the greater the polarity of solvent,the absorption maximum in the n??*region(experimentally at 220 nm)would shift to the shorter wavelength.