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441.
442.
Acetalation of 1,6-anhydro-1(6)-thio-D-glucitol (1a) with acetone, formaldehyde, or benzaldehyde afforded 2,3:4,5-diacetals (2a, 2b, and 2c) whose structure, after desulfurization, was proved by mass spectrometry. Upon partial hydrolysis of 2a, one of the isopropylidene groups was split off, and the other migrated to O-3,O-4 to give 4b. In 4b, in the stable conformation, OH-2 occupies an equatorial position, whereas OH-5 is axially oriented. Accordingly, OH-2 reacts faster than OH-5 on methylation of 4b, giving 4e. Hydrolysis of the isopropylidene group of the 2,5-di-O-methyl derivative 4d and subsequent mesylation afforded the corresponding 3,4-di-O-mesyl compound 1c, which showed significant ulcerostatic activity. 相似文献
443.
Effect of fluoride (10 and 50 mM) on the activities of sucrose metabolizing enzymes, alkaline inorganic pyrophosphatase, and
transaminases in relation to the accumulation of free sugars, starch, and soluble protein was studied in detached ears of
wheat cultured in a liquid medium. Culturing for 5 d in the presence of fluoride reduced the amount of grain starch whereas
contents of total free sugars, particularly sucrose, and soluble protein increased. Fluoride inhibited the activities of soluble
acid and neutral invertases, as well as sucrose synthase acting in the cleavage direction. Uptake of uniformly labelled 14C-sucrose or fructose was also drastically reduced by fluoride. Glutamate-oxaloacetate transaminase (GOT) and glutamate-pyruvate
transaminase (GPT) activities also increased with fluoride addition in correspondence with an increase in soluble protein.
Apparently, the wheat grain responds to fluoride-mediated disruption of carbon metabolism by a compensatory effect on nitrogen
metabolism.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献