Structural scaffold of 18-crown-6 tetracarboxylic Acid for optical resolution of chiral amino acid: x-ray crystal analyses of complexes of D- and L-isomers of serine and glutamic acid.
(+)-18-crown-6 tetracarboxylic acid (18C6H4) has been used as a chiral selector for D/L-amino acids in HPLC, where L-isomer is usually eluted prior to D-isomer, except for the case of serine. To clarify why serine exhibits the reverse order for the elusion, the chiral interactions of D- and L-serines with (+)-18C6H4 were investigated by the X-ray single crystal analyses, together with the case of D- and L-glutamic acids, which exhibit the usual elution order in HPLC. The backbone structures (amino, Calpha-H and carboxyl groups) of these four amino acids showed the nearly same interaction with (+)-18C6H4 despite their different chirality. In contrast, the hydroxyl group of L-serine side chain formed a hydrogen bond with the carboxyl group of (+)-18C6H4, whereas such a interaction was not formed for the side chain of D-serine and D- and L-glutamic acids. Thus, it was shown that the exception of D/L-serine from the first elution rule of L-isomer in HPLC is due to the presence and absence of a hydrogen bond formation of its side chain OH group.
Nagata
Hiroomi
H
Tanabe Seiyaku Co., Ltd., Osaka, Japan. nagata@tanabe.co.jp
Nishi
Hiroyuki
H
Kamigauchi
Miyoko
M
Ishida
Toshimasa
T
D000596:Amino Acids / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D043844:Crown Ethers / Q000737:chemistry*; D018360:Crystallography, X-Ray; D018698:Glutamic Acid / Q000737:chemistry*; D007536:Isomerism; D015394:Molecular Structure; D012694:Serine / Q000737:chemistry*
D000596:Amino Acids; D043844:Crown Ethers; C090732:18-crown-6 2,3,11,12-tetracarboxylic acid; D018698:Glutamic Acid; D012694:Serine