高效液相色谱法考察银杏内酯B与其衍生物的变化规律

通过半制备色谱柱从银杏内酯B(GB)中分离出一种衍生物。高效液相色谱结果显示:该衍生物色谱峰的保留时间是GB的3.0倍左右;紫外光谱结果显示:该衍生物的最大紫外吸收波长为212.1 nm,最大吸光值为2.29×104,大约是GB的最大吸光值的100倍,说明是π→π*电子跃迁的结果,表明其分子结构中存在共轭双键;高效液相色谱-质谱分析结果显示:该衍生物在正离子模式下产生的分子离子峰为m/z 429.1(M+Na)+,负离子模式下产生的分子离子峰为m/z 405.2(M-H)-,与GB的分子离子峰质荷比相差18,且与GB具有相似的解离模式。GB对热稳定,而该衍生物对热相对不稳定。pH对两者的关系影响不大,当pH值逐渐增高时,衍生物的开环速度比GB快。溶剂和温度的综合作用对衍生物的稳定性影响更加显著,GB在聚乙二醇溶液中分别于50 ℃下保存15 h和120 ℃下保存4 h后其中的衍生物峰全部消失；将该溶液于120 ℃下保存4 h后分析，除有主峰GB外,在保留时间为1.2～3.0 min范围还伴随有小峰出现,这说明衍生物处于高能态,GB相对较为稳定,两者共存,且相互转化；在特定条件下衍生物能全部转化为GB。

Investigation on the convertion between ginkgolide B and its derivative

A derivative decomposed from ginkgolide B (GB) was isolated by semi-preparative chromatography. The results of the high performance liquid chromatography (HPLC) showed that the retention time of the derivative was approximately three times of that of GB with ultraviolet detection (UV), and the derivative can not exist independently without the presence of GB. The UV spectrum showed that the lamdamax of the derivative was 212.1 nm and the epsilonmax was 2.29 x 10(4), which were approximately 100 times higher than those of GB. This means a new conjugation bond has been formed and that means that the conjugation bond's pii-pi* electron jump occured in the derivative. Liquid chromatography-mass spectrometry showed the molecular ion peaks of the derivative in the positive mode and negative mode were m/z 429.1 (M + Na)+ and m/z 405.2 (M-H)-, respectively. The relative molecular mass of the derivative is 406.2. The derivative showed the same mode of fragment ion as GB in the mass spectrum, which might be due to the loss of a H2O from GB. Thermal stability of GB was greater than that of the derivative. They were both easily to be dissolved in dilute alkali. When the pH gradually increases, the ring-opening speed of the derivative is higher than that of GB. The derivative was obviously affected by solvent and higher temperatures. When GB was dissolved in PEG, the peak of the derivative disappeared at 50 degrees C for 15 h or at 120 degrees C for 4 h. Besides the main peak of GB, there appeared a small peak with a retention time of 1.2-3.0 min after heating 4 h at 120 degrees C. The result showed that the derivative was in a high energy state, and GB had a better stabilization. They coexisted and converted to each other. Under some specific conditions, the derivative could all convert to GB.