Royal Botanic Gardens, Kew, Richmond TW9 3AB, UK.
Rapid Commun Mass Spectrom. 2011 Sep 30;25(18):2579-90. doi: 10.1002/rcm.5154.
Flavonoid O-glycosides are a ubiquitous and important group of plant natural products in which a wide variety of sugars are O-linked to an aglycone. Determining the identity of the sugars, and the manner in which they are linked, by mass spectrometry alone is challenging. To improve the identification of common O-linked di- and trisaccharides when analysing mixtures of flavonoid O-glycosides by liquid chromatography/mass spectrometry (LC/MS), the fragmentation of electrosprayed sodium adducts in an ion trap mass spectrometer was investigated. The sodium adducts M + Na of kaempferol 3-O-glycosides generated sodiated glycosyl groups by the neutral loss of kaempferol. The product ion spectra of these sodiated glycosyl groups differed between four isomeric kaempferol 3-O-rhamnosylhexosides and four isomeric kaempferol 3-O-glucosylhexosides in which the primary hexose was either glucose or galactose and bore the terminal glucose or rhamnose at either C-2 or C-6. Fragmentation of sodiated glycosyl groups from linear O-triglucosides and branched O-glucosyl-(1 → 2)-[rhamnosyl-(1 → 6)]-hexosides produced sodiated disaccharide residues, and the product ion spectra of these ions assisted the identification of the complete sugar. The product ion spectra of the sodiated glycosyl groups were consistent among flavonoid O-glycosides differing in the position at which the sugar was O-linked to the aglycone, and the nature of the aglycone. The abundance of sodiated species was enhanced by application of a pre-trap collision voltage, without the need to dope with salt, allowing automated LC/MS methods to be used to identify the glycosyl groups of common flavonoid O-glycosides, such as rutinosides, robinobiosides, neohesperidosides, gentiobiosides and sophorosides.
类黄酮 O-糖苷是植物天然产物中普遍存在且重要的一类，其中各种糖通过 O-键连接到糖苷配基上。仅通过质谱法确定糖的身份及其连接方式具有挑战性。为了提高通过液相色谱/质谱（LC/MS）分析类黄酮 O-糖苷混合物时常见的 O-连接二糖和三糖的鉴定能力，研究了在离子阱质谱仪中电喷雾钠离子加合物的碎裂。通过槲皮素中性丢失，生成带钠离子的糖苷配基，使 kaempferol 3-O-糖苷的钠离子加合物 M + Na 。这些带钠离子的糖苷配基的产物离子谱在 4 种异槲皮素 3-O-鼠李糖基己糖苷和 4 种异槲皮素 3-O-葡萄糖基己糖苷之间有所不同，其中的初级己糖为葡萄糖或半乳糖，并且末端葡萄糖或鼠李糖位于 C-2 或 C-6 位。线性 O-三葡萄糖苷和支链 O-葡萄糖基-(1 → 2)-[鼠李糖-(1 → 6)]-己糖苷的带钠离子的糖苷配基的碎裂产生带钠离子的二糖残基，这些离子的产物离子谱有助于鉴定完整的糖。糖与糖苷配基的 O-键连接位置以及糖苷配基的性质不同，类黄酮 O-糖苷的带钠离子的糖苷配基的产物离子谱是一致的。通过施加预阱碰撞电压增强了带钠离子的物种的丰度，而无需加盐掺杂，从而允许使用自动化 LC/MS 方法来鉴定常见的类黄酮 O-糖苷，如芦丁苷、罗宾糖苷、新橙皮苷、槐糖苷和槐糖苷的糖苷基团。
