Glycosyl Bunte Salts: A Class of Intermediates for Sugar Chemistry.
S-Glycosyl thiosulfates have been discovered as a new class of synthetic intermediates in sugar chemistry, named "glycosyl Bunte salts" after 19th-century German chemist, Hans Bunte. The synthesis was achieved by direct condensation of unprotected sugars and sodium thiosulfate using a formamidine-type dehydrating agent in water-acetonitrile mixed solvent. The application of glycosyl Bunte salts is demonstrated with transformation reactions into other glycosyl compounds such as a 1-thio sugar, a glycosyl disulfide, a 1,6-anhydro sugar, and an O-glycoside.
Glycosyl Halides in Oligosaccharide Synthesis
Glycosyl halides are versatile easily prepared intermediates which for the last century have provided the basis for major advances in glycoside synthesis. Although the emphasis has shifted away from these traditional synthons in the last two decades, glycosyl halides continue to play a central role in flexible strategies for the assembly of complex oligosaccharides. As the diverse biological functions of glycolipids and glycoproteins are revealed, these glycoconjugates continue to challenge chemists with biologically relevant targets that often draw upon the full range of advances in methodology.
Neue reaktive Bromierungsagentinen
Die Bromierung von Nitrobenzol mit elementarem Brom und Friedel-Crafts-Katalysatoren erfordert mehrstundiges Erhitzen auf ~ 150°, um gute Ausbeuten an m-Bromonitrobenzol zu erzielen. In Gegenwart von Silbersulfat in Schwefelsaure gelingt dagegen die Bromierung in vergleichbaren Ausbeuten schon bei Raumtemperatur. Als angreifendes Agens wird dabei das Brom-Kation angenommen. Hinweise auf die Moglichkeit eines Anionen-Einflusses werden nicht gemacht. Wir haben nun gefunden, das mit einem Gemisch von Kaliumperoxodisulfat und Brom (Molverhaltnis 1:1,2) in Schwefelsaure mit 5% SO3-Gehalt, Nitrobenzol bei Raumtemperatur mit 30% Ausbeute bromiert werden kann.