Synthesis of Tumor-Associated Le^aLe^x Hexasaccharides: Instability of a Thiol-Containing Oligosaccharide in Mass Spectrometry and Hypermetalation Detected by ESI FAIMS

Abstract

We report the efficient synthesis of three analogues of the tumor associated carbohydrate antigen Le a Le x . This hexasaccharide was prepared as a soluble inhibitor hexyl glycoside, a 6-aminohexyl glycoside for conjugation to proteins, and as 6-thiohexyl glycoside for immobilization to a gold surface. These three analogues were obtained from a common hexasaccharide intermediate and isolated pure following efficient deprotection reactions that involved metal dissolving conditions. While all other intermediates and analogues gave the expected molecular ions in ESI HRMS, the 6-thiohexyl glycoside final compound gave a complex spectrum in which no signal matched the molecular ion. Using ESI FAIMS HRMS, we were able to prevent ion dissociation reactions and obtained high quality spectral data. The ions 2 detected could be characterized unambiguously from their accurate masses and gave insight into the behavior of the thiohexyl analogue in the gas phase. These results indicate that the 6-thiohexyl glycoside lost water and led to the formation of "hyper-metalated" species which we propose are cyclic.