Tandem mass spectra of transition‐metal ion adducts of glycosyl dithioacetals; distinction among stereoisomers

Abstract Electrospray ionization mass spectra of some glycosyl dithioacetals recorded in the presence of transition‐metal chlorides, XCl 2 (where X = Co, Mn and Zn), give abundant adduct ions such as [M+XCl] + and [2MH+X] + and minor ions such as [MH+X] + and [2M+XCl] + . The tandem mass spectra of these adducts show characteristic elimination of neutral molecules such as H 2 O, HCl, EtSH, CH 2 O, C 2 H 4 O 2 /C 2 H 4 O. [M+XCl] + ions fragment readily and the fragmentation appears to be stereochemically controlled as the relative abundances of the fragments are different for three stereoisomers. The added metal is lost as neutral molecules in the form of XCl(OH) and XCl(SEt). This is a predominant pathway in the ZnCl + adducts. [2M+XCl] + ions fragment preferentially by elimination of HCl, indicating strong metal interactions in the resulting dimeric [2MH+X] + ion. As there are several electron‐rich centers in the molecule, the dimeric complex [2MH+X] + can have several structures and the observed fragmentations may reflect the sum of those of all these structures. The dimeric complexes fragment by elimination of neutral molecules leaving the dimeric interactions intact. The extent of fragmentation varies for the stereoisomers, leading to stereochemical differentiation. Copyright © 2005 John Wiley & Sons, Ltd.