Simple Synthesis of 1,2-Dideoxy-2-Vinyl Carbohydrates by Tin-Free Radical Reactions of Xanthates.

Vinyl-substituted carbohydrates have been synthesized from glycals derived from hexoses and pentoses. Key step is the radical reaction of xanthates in the presence of triethylborane, a non-toxic reagent. The mechanism has been investigated by isolation of various side products, which speak for a reversibility of the cyclopropylmethyl radical ring-opening.

2D-IR spectroscopy of carbohydrates: Characterization of thiocyanate-labeled β-glucose in CHCl and HO.

Carbohydrates constitute one of the four key classes of biomacromolecules but have not been studied by 2D-IR spectroscopy so far. Similarly as for proteins, a lack of native vibrational reporter groups, combined with their huge structural diversity, leads to spectrally congested infrared spectra already for single carbohydrates. Biophysical studies are further impeded by the strong overlap between water modes and carbohydrate modes.

Influence of Functional Groups on the Ene Reaction of Singlet Oxygen with 1,4-Cyclohexadienes.

The photooxygenation of 1,4-cyclohexadienes has been studied with a special focus on regio- and stereoselectivities. In all examples, only the methyl-substituted double bond undergoes an ene reaction with singlet oxygen, to afford hydroperoxides in moderate to good yields. We explain the high regioselectivities by a "large-group effect" of the adjacent quaternary stereocenter.

Radical Clock Probes to Determine Carbohydrate Radical Stabilities.

Carbohydrate radical stabilities in the 1- and 2-position have been determined by a radical clock approach, starting from cyclopropanated sugars with xanthates as precursors. Various hexoses and pentoses afforded 1-deoxy sugars as main products, indicating that anomeric radicals are more stable than radicals in the 2-position. An additional influence of the configurations on radical stabilities has been observed.