N-ヒドロキシメチルピロリドンカルボン酸の結晶構造解析 L-ピログルタミン酸とホルマリンとの反応生成物の構造決定

抄録

Structure of the reaction product of DL-pyroglutamic acid (pyrrolidonecarboxylic acid) with formaldehyde was determined by the X-ray diffraction method. An attempt was first made to determine the structure by a direct method using the crystal of the free acid, but did not succeed. Finally the structure was solved by the heavy atom method using a crystal of barium salt, (C₆H₈NO₄)₂·Ba·H₂O. The barium salt crystallized in the orthorhombic space group Pbcn with a=12.73, b=14.20, c=8.935 Å, Z=8. Three dimensional X-ray diffraction data were collected by an automatic diffractometer. The atomic parameters were refined by the block-diagonal least-squares method leading to a final R-value of 7% for 658 observed reflections. This reaction product was found to be N-hydroxymethylpyrrolidonecarboxylic acid. The pyrrolidone ring is almost planar, and carbon atom of the hydroxymethyl group and oxygen atom of the carbonyl group are also approximately in this plane. The hydroxyl group and the carboxyl group are stretched to the opposite side of the ring plane. There are 8 molecules in the unit cell, and the barium atom and the oxygen atom of the water of crystallization occupy special positions on the two-fold axis.