Aizawa Sen-Ichi, Okano Masaru, Kidani Takahiro
Graduate School of Science and Engineering, University of Toyama, Toyama, Japan.
Chirality. 2017 Jun;29(6):273-281. doi: 10.1002/chir.22681. Epub 2017 Apr 12.
Enantiomeric H and C NMR signal separation behaviors of various α-amino acids and DL-tartarate were investigated by using the samarium(III) and neodymium(III) complexes with (S,S)-ethylenediamine-N,N'-disuccinate as chiral shift reagents. A relatively smaller concentration ratio of the lanthanide(III) complex to substrates was suitable for the neodymium(III) complex compared with the samarium(III) one, striking a balance between relatively greater signal separation and broadening. To clarify the difference in the signal separation behavior, the chemical shifts of β-protons for fully bound D- and L-alanine (δ (D) and δ (L)) and their adduct formation constants (Ks) were obtained for both metal complexes. Preference for D-alanine was similarly observed for both complexes, while it was revealed that the difference between the δ (D) and δ (L) values is the significant factor to determine the enantiomeric signal separation. The neodymium(III) and samarium(III) complexes can be used complementarily for higher and smaller concentration ranges of substrates, respectively, because the neodymium(III) complex gives the larger difference between the δ (D) and δ (L) values with greater signal broadening compared to the samarium(III) complex.
以钐（III）和钕（III）与（S，S）-乙二胺-N，N'-二琥珀酸形成的配合物作为手性位移试剂，研究了各种α-氨基酸和DL-酒石酸盐的对映体氢和碳核磁共振信号分离行为。与钐（III）配合物相比，钕（III）配合物与底物的浓度比相对较小更合适，在相对较大的信号分离和展宽之间取得平衡。为了阐明信号分离行为的差异，获得了两种金属配合物中完全结合的D-和L-丙氨酸β-质子的化学位移（δ（D）和δ（L））及其加合物形成常数（Ks）。两种配合物都类似地观察到对D-丙氨酸的偏好，同时发现δ（D）和δ（L）值之间的差异是决定对映体信号分离的重要因素。钕（III）配合物和钐（III）配合物可分别用于底物浓度较高和较低的范围，起到互补作用，因为与钐（III）配合物相比，钕（III）配合物在δ（D）和δ（L）值之间给出的差异更大，信号展宽也更大。
