Synthesis of 3-hexuloses from 1,2:5,6-di-O-isopropylidenehexitols.

A simple, but low-yielding method for the synthesis of 3-hexuloses has been elaborated. Oxidation of 1,2:5,6-di-O-isopropylidenehexitols with bromine in the presence of barium carbonate, followed by mild-acid hydrolysis of the oxidation products gave the free hexuloses. Oxidation occurred at only one of the carbon atoms bearing free hydroxyl groups. From the D-mannitol derivative, D-arabino-3-hexulose was obtained via the di-O-isopropylidene derivative, whereas the D-glucitol derivative gave a mixture of the 1,2:5,6-di-O-isoprpylidene derivatives of L-xylo- and D-ribo-3-hexulose, separable by column chromatography. Mild-acid hydrolysis of the oxidation products afforded the free hexuloses.

Carbohydrate content and glycosidase activities following cold hardening in two grass species.

The freezing resistance of the grass species Phleum pratense L. (timothy) and Phalaris arundinaces L. increases significantly after cold hardening. The content and composition of soluble carbohydrates were determined in the plants after short day treatment, cold hardening and dehardening. The amounts of mono-, di- and trisaccharides were reduced during the short day treatment, increased during cold hardening and decreased again during dehardening. The total amounts of soluble carbohydrates (mono-, di-, tri- and polysaccharides) were the same in hardened and dehardened plants, indicating that during hardening soluble polysaccharides (fructose polymers, fructans) were converted to mono- and oligosaccharides. Sucrose increased most after hardening conditions and, in P. arundinacea, a significant increase in 1-F-fructosylsucrose (isokestose) was also observed. Invertase (ß-fructofuranosidase. EC 3.2.1.26) activity increased following cold hardening and decreased following dehardening, while the α-galactosidase (EC 3.2.1.22) activity seemed to increase after dehardening. The glycosidases are probably involved in the mobilisation of polysaccharides during cold hardening.