Glycoside Structure

The interaction between Drosophila, yeasts and columnar cacti of the Sonoran Desert has been the subject of much recent interest (37) As a coevolved system, perhaps more is known about this interaction than any other. The chemistry of the cacti (70 spp.) has been postulated to play a significant role in the establishment of this system (38 ), but this was based upon reports of a relatively small number of relatively simple alkaloids, and a small number of terpenoid compounds. Only recently, the diversification of plant compounds has been discovered to be much greater (5). In their section on alkaloids in the above work, BajaJ and McLaughlin report the presence of some thirty-five structures. In addition, I have been able to isolate some sixty triterpenoid glycosides (structures were not determined) and more were detected but not Isolated. 

Previously (3 ), some sixteen distinct triterpene skeletons in two classes were isolated and reported from this group of cacti. Standard isolation procedure for these compounds requires hydrolysis of sugars, so the glycosidic structures have not been described. As the data presented previously imply, individual glycosides are the compounds of ecological interest. 

Fig. 17 Typical glycosidic structures in the aroma precursor glycosides...

K. Repke (1985). New developments in cardiac glycoside structure-activity relationships. Trends Pharmacol. Sci. 6 275-278. 

In contrast to enzyme activities, the definition of the proteo-hormone measurands as well as of many tumor markers and cardiac markers is very critical and several aspects have to be regarded as it concerns the epitope to be detected, the sub-unit to be measured (/3-chain or complete molecule) and finally the glycosidic structure of the molecule. 

Applications of the same enolate alkylation procedure to furnish gem-dialkylated compounds have been used in the synthesis of onnamide A [118]. This type of gem-2-C-dimethyl group is also found in pederin and mycalamides A and B. As shown from the retrosynthetic analysis of some members of this class of compounds (Scheme 11.38), C-glycosidic structure 158 could be obtained from the a-glycoside 159. The latter could be prepared from the ketone 160 via gem-dialkylation of the corresponding enolate, as described for the synthesis of 8. 

Since most flavonoids are isolated in small amounts, their structure are primarily determined by spectral methods, expecially UV, iH and NMR and MS [183]. The more recent approach to glycoside structural elucidation is a combination of the modeme ID and 2D NMR techniques, which are very sensitive and non-destructive. In fact, the non-invasive nature of NMR methods allows easy recovery of the intact material by simple removal of solvent for successive biological evaluations [79,113-115,117,118]. 

Natural products Glycosides Structure-activity relations Glycorandomization Ravonoid glycosides Vitamin glycosides Antibiotics Alkaloid glycosides Steroid glycosides DNA interactions... 

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