Ketals of sugars

Peaks at m/e 113 and 85 have been found in the mass spectra (12) of other O-isopropylidene ketals of sugars, as well as in Figure 7. Since these shift to m/e 119 and to m/e 88 and 91 in the mass spectrum of 10a as they did for the d6-analogs in Reference 12, the structures, 17, 18, and 19 from Reference 12 are shown as possible explanations. The peak at m/e 85 (91) could alternatively be from m/e 113 (119) by loss of carbon monoxide (28 mass units) from the six-membered-ring of structure 17b. 

The structures of the brightly colored (red-violet and yellow) alkaloids found in the order Centrospermae (cacti, red beet, etc) remained unknown until the 1960s. In part this was doubtlessly due to the fact that these pigments, called betacyanins or betaxanthins, are relatively unstable and they are water soluble zwitterions. Invariably, in these plants they are found as acetals or ketals of sugars and one of two aglycone fragments called betanidine (96,... 

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