Electrochemical Characterization of 6-Iodomaltose, 6'-Iodomaltose and 6-Iodomaltotriose on a Silver Cathode and Their One-Pot Electrochemical Dimerization to New Mixed O/C Maltotetraose and Maltohexaose Mimics.

The electrochem. redn. on silver of peracetylated 6-iodo-6-deoxy--maltose (I), 6-iodo-6-deoxy--maltotriose (II) and 6'-iodo-6'-deoxy--maltose (III) has been investigated by cyclic voltammetry and performed on a preparative scale, according to the stoichiometry, -CH2I + e-  CH2 + I-. In agreement with the preparative electrolysis results, cyclic voltammetry showed different profiles for the reducing terminal-iodinated I and II and for the non-reducing terminal-iodinated III. Compds. I and II partly dimerized to maltotetraoses mimics (6,6-dimer) and (5',5'-dimer) in 38% overall yield and to maltohexaose mimics (6,6-dimer) and (5',5'-dimer) in 30% overall yield, resp. In turn, III afforded only the 6',6'-dimer maltotetraose mimic in 60% yield, accompanied by the reduced maltose in 20% yield, in which the starting CH2I became CH3. Final compds. belong to a class of mixed O/C malto-mimic oligosaccharides wherein an unnatural C-C bond between two saccharide units increases metabolic stability compared to their O-analogs and modulates the sugar chain conformational flexibility, a fundamental parameter in detg. protein-carbohydrate binding. Direct and spin-trapping EPR studies substantiated the radical-based nature of the dimerization processes and allowed the identification of some of the paramagnetic species involved.