Characterization of tms derivatives of glycosyl-inositols by GC-MS

Abstract

Glycosyl-inositols are constituted by one or several (up to four) galactosyl residues and an inositol or a methyl-inositol. These compounds are especially abundant in legumes but they can be found in seeds of other plants such as buckwheat or pine nuts. Several bioactive properties, mainly associated with insulin resistance, have been attributed to them. Up to now, HPLC and GC [1,2] have been used for glycosyl-inositol analysis, but no comprehensive method is available for the characterization of these compounds, probably due to the lack of enough adequate standards. GC-MS can provide valuable qualitative and quantitative information for the characterization of these compounds along with other soluble carbohydrates, after derivatisation and avoiding tedious fractionation processes. Linear retention indices (IT) are only available for a very few glycosyl-inositols and a systematic study of their mass spectra (MS) is also lacking. Therefore, the aim of this work was to correlate the chemical structure of different glycosyl-inositols with their IT values and MS data in an attempt to help in further identification of unknown compounds. Several glycosyl-inositols with different structures (derived from chiro-, myo-, and methyl-inositols, and also mono-, di- and triglycosyl- compounds) from plant extracts (buckwheat, chickpea and grasspea) were considered as standards. Different saccharides were used for comparative purposes. These compounds, previously derivatised, were analysed by GC-MS using a methylsilicone capillary column. Regarding GC retention, galactosyl-cyclitols derived from chiro-inositol eluted before those derived from myo-inositol. Moreover, galactosyl-cyclitols (degree of polymerization (DP2) eluted within sucrose and raffinose, digalactosyl-cyclitols (DP3) within raffinose and stachyose and trigalactosyl-cyclitols (DP4) were eluted within stachyose and verbascose. MS data revealed a lower abundance of ion at m/z 361 for glycosyl-cyclitols compared to saccharides. Ratios of m/z ions 133/129, 260/265 and 375/361 were proposed for the first time in this work to distinguish glycosyl-inositols from glycosyl-methyl-inositols, as they allowed the unequivocal characterization of them. Results have afforded the characterization of different non-previously identified glycosyl-cyclitols appearing in chickpeas, adzuki beans and leaves of Coriaria myrifolia and Coriaria ruscifolia.