title: Precise Determination of Enantiomeric Excess by a Sensitivity Enhanced Two-Dimensional Band-Selective Pure-Shift NMR.
abstract: Unambiguous identification and precise quantification of enantiomers in chiral mixtures is crucial for enantiomer specific synthesis as well as chemical analysis. The task is often challenging for mixtures with high enantiomeric excess and for complex molecules with strong (1)H-(1)H scalar (J) coupling network. The recent advancements in (1)H-(1)H decoupling strategies to suppress the J-interactions offered new possibilities for NMR based unambiguous discrimination and quantification enantiomers. Herein, we discuss a high resolution two-dimensional pure-shift zCOSY NMR method with homonuclear band-selective decoupling in both the F1 and F2 dimensions (F1F2-HOBS-zCOSY). This advanced method shows a sharp improvement in resolution over the other COSY methods and also eliminates the problems associated with the overlapping decoupling sidebands. The efficacy of this method has been exploited for precise quantification of enantiomeric excess (ee) ratio (R/S) up to 99:1 in the presence of very low concentrations of chiral lanthanide shift reagents (CLSR) or chiral solvating agents (CSA). The F1F2-HOBS-zCOSY is simple and can be easily implemented on any modern NMR spectrometers, as a routine analytical tool.
authors.affiliation: Centre for NMR and Structural Chemistry, CSIR-Indian Institute of Chemical Technology, Uppal Road, Tarnaka, Hyderabad-500 007, Telangana, India.
authors.forename: Kavitha
authors.initials: K
authors.lastname: Rachineni
authors.affiliation: Centre for NMR and Structural Chemistry, CSIR-Indian Institute of Chemical Technology, Uppal Road, Tarnaka, Hyderabad-500 007, Telangana, India.
authors.forename: Veera Mohana Rao
authors.initials: VM
authors.lastname: Kakita
authors.affiliation: Centre for NMR and Structural Chemistry, CSIR-Indian Institute of Chemical Technology, Uppal Road, Tarnaka, Hyderabad-500 007, Telangana, India.
authors.forename: Satyanarayana
authors.initials: S
authors.lastname: Dayaka
authors.affiliation: Centre for NMR and Structural Chemistry, CSIR-Indian Institute of Chemical Technology, Uppal Road, Tarnaka, Hyderabad-500 007, Telangana, India.
authors.forename: Sahithya Phani Babu
authors.initials: SP
authors.lastname: Vemulapalli
authors.affiliation: Centre for NMR and Structural Chemistry, CSIR-Indian Institute of Chemical Technology, Uppal Road, Tarnaka, Hyderabad-500 007, Telangana, India.
authors.forename: Jagadeesh
authors.initials: J
authors.lastname: Bharatam
mesh_terms: D001596:Benzylamines / Q000032:analysis* / Q000737:chemistry; D007189:Indans / Q000032:analysis* / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008610:Menthol / Q000032:analysis*; D015394:Molecular Structure; D012015:Reference Standards; D013237:Stereoisomerism
chemical_list: D001596:Benzylamines; D007189:Indans; D008610:Menthol; C016992:1-aminoindan