草酸龙脑酯手性异构体的合成及谱学性质对比研究

分别以左旋龙脑(艾片)、右旋龙脑(冰片)、艾片及冰片组成的外消旋龙脑为原料,与草酰氯发生间接酯化反应合成了3种光学活性的草酸龙脑酯,经乙醇重结晶后GC纯度99.9%,通过手性液相色谱分析证明合成的消旋龙脑酯中同时含有左旋体、内消旋体和右旋体,其质量比近似为1∶2∶1。利用二维核磁共振技术~1H-~1H COSY、HSQC及HMBC等手段对左旋的草酸龙脑酯的碳原子及氢原子进行归属,并采用GC-MS、FT-IR、~1H NMR、~(13)C NMR等对比研究了所合成的左旋、右旋及消旋的草酸龙脑酯的谱学性质,还进一步对比了合成的消旋龙脑酯与人工混合而成的外消旋体的谱学特征。结果表明:左旋、右旋及人工混合的外消旋的草酸龙脑酯虽然旋光性不同,但其谱学性质没有明显的差别,而由外消旋龙脑与草酰氯合成得到的消旋产物中所含的内消旋体,其分子两侧的碳氢原子却表现出比较明显的核磁化学环境及谱学性质差异,主要体现在8-与8'-、3-与3'-位上的氢及1-与1'-、3-与3'-、11-与11'-位上的碳的化学位移值不相等。

Synthesis and Spectral Properties of Chiral Isomers of Dibornyl Oxalate

Dibornyl oxalates with different optical activity were synthesized by indirect esterification method from different chiral borneol with oxalyl chloride, and the target products could be easily purified to 99.9% (GC) through recrystallization with alcohol.The composition of the synthesized dibornyl oxalates were analyzed by chiral high-performance liquid chromatography (HPLC), and it was proved that there were (-)-dibornyl oxalate, mesomer and (+)-dibornyl oxalate in the synthesized racemic dibornyl oxalate, and the mass ratio was nearly 1∶2∶1.The location of hydrogen and carbon atoms in (-)-dibornyl oxalate was determined by means of 1H-1H COSY, HSQC and HMBC, and the spectra of different chiral dibornyl oxalate were contrasted including GC-MS, IR, 1H NMR and 13C NMR.Furthermore, the synthetic racemic dibornyl oxalate was compared with the mixture of equal (+) and (-) dibornyl oxalates.The results showed that the spectral properties of (+), (-) and racemic dibornyl oxalate were similar, however these oxalates could be distinguished via optical activity.The mesomer, which contained in the synthesized racemic dibornyl oxalate from the reaction of racemic borneol and oxalyl chloride, owned different nuclear magnetic chemical environment and spectral properties of the carbon and hydrogen atoms on both sides.This reflected in the different chemical shifts of the hydrogen atoms on 8-and 8′-, 3-and 3′-, and the carbon atoms on 1-and 1′-, 3-and 3′-as well as 11-and 11′-positions.