海藻MGMG型甘油糖脂的研究

目的鉴定中药海藻(羊栖菜Sargassum fusiforme)中的单半乳糖基单酰基甘油酯(monogalactosylmonoacylglycerol,MGMG),分析sn-1型和sn-2型位置异构体的化学特征。方法利用多种色谱手段分离得到MGMG,采用NMR、HR-ESI-MS等谱学方法鉴定结构,采用HPLC、HPLC-ESI-MS/MS分析位置异构体的互变及其色谱-质谱特征。结果分离到并鉴定5个MGMG,酰基分别为十八碳四烯酰基、十八碳三烯酰基、二十碳四烯酰基、十八碳二烯酰基和十八碳单烯酰基;sn-1型和sn-2型MGMG单体均不稳定,会相互迅速转变直至sn-1型为主(相对峰面积85∶15)的平衡状态。sn-2型在反相色谱柱上的保留时间较sn-1型小,先被洗脱;两者二级质谱碎片离子丰度有较大差异,以[M+Na-Gal]~+为基峰(100%),sn-2型的[M+Na-RCOOH]~+丰度50%,sn-1型的[M+Na-RCOOH]~+丰度20%。结论首次从褐藻门中分离鉴定上述5个MGMG,阐明了sn-1型和sn-2型MGMG之间的互变过程,首次报道这2种位置异构体的色谱-质谱特征,可用于MGMG类化合物酰基取代位置的鉴定。

Study on monogalactosylmonoacylglycerol in marine algae (Sargassum fusiforme)

Objective To indentify monogalactosylmonoacylglycerol (MGMG) and analyze the chemical characteristics of sn-1 and sn-2 type isomers in Marine TCM Sargassum fusiforme. Methods The MGMG compounds were isolated by multiple chromatography methods and their structures were determined by spectroscopic methods such as NMR and HRESI-MS. The interconversion and chromatography-mass spectrometry feature of MGMG positional isomers were analyzed through HPLC and HPLC-ESI-MS/MS. Results Five MGMGs were isolated from Sargassum fusiforme, and the fatty acyl compositions were stearidonoyl, linolenoyl, arachidoyl, linoleyl, and oleyl. The sn-1 and sn-2 type of MGMG were unstable. The interconversion tended to be sn-1 type rapidly, and kept balanced content at 85:15. The relative retention time of sn-2 type was less than sn-1 type on C₁₈ reverse phase chromatography. The abundant fragment ions of MS/MS were significantly differences. The base peak was[M+Na-Gal]⁺ (100%), and the peak intensity of[M+Na-RCOOH]⁺ was always more than 50% from sn-2 type while less than 20% from sn-1 type. Conclusion Five MGMGs were isolated from brown algae for the first time. This was the first report about the interconversion and chromatography-mass spectrometry feature of sn-1 and sn-2 type. It can use to determine the fatty acyl attachment in each MGMG.