Xylose diethyl dithioacetal, preparation

Enzymic syntheses are considered next. Xylitol is a substrate for sheep-liver L-iditol dehydrogenase, a NAD-linked enzyme. 1-Deoxy-D-xylitol, prepared by Raney nickel reduction of D-xylose diethyl dithioacetal in a 27% overall yield from D-xylose, was also reported31 to be a substrate, although with a higher Km and lower Vmax. The product was assumed to be l-deoxy-D-f/ireo-pentulose because of the appearance of a yellowish fluorescent spot when a chromatogram was sprayed with acidic 3,5-aminobenzoic acid, resembling that formed from 1 -deoxyfructose. There was no more-rigorous characterization. 

The same diamino sugar was also prepared through treatment of 5-azido-5-deoxy-2,3-0-isopropylidene-4-0-(mediylsulfonyl)-D-arabi-nose diethyl dithioacetal with sodium azide. Besides the normal reaction product of Sjv2 substitution, namely 4,5-diazido-4,5-dideoxy-2,3-0-isopropylidene-L-xylose diethyl dithioacetal, there was obtained a small proportion of 4,5-diazido-4,5-dideoxy-2,3-0-isopropyli-... 

Deoxy-5-seleno-D-arabino-, D-ribo- and D-xylo-selenoformates 8, 9 and 10 have been prepared from D-arabinose and known 2,3,4-tri-O-benzyl-D-ribose and -D-xylose diethyl dithioacetals, respectively/ The thermolysis of these compounds to afford l,5-anhydro-5-deoxy-5-seleno-D-pentitols is covered in Chapter 11. 

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