Polyhydroxylated glycosides

When there are more than two hydroxyl groups on the same molecule, the tin atom may span several different pain of oxygen atoms. Apparently, for either kinetic or thermodynamic reasons, one is preferred. This is clear in competitive experiments [8], For instance, refluxing an equimolecular mixture of glycosides 4, 6, and BujSnO appears to give overwhelmingly the stannylene of 4, for subsequent benzoylation gave the benzoate 5 in 98% yield. Finally, there is evidence that, at least in some cases, a minor imperceptible stannylene in a polyhydroxylated molecule is in rapid equilibrium with die major one. 

Vazquez, M. J., Quinoa, E., Riguera, R., San-Martin, A., and Darias, J., Antarctic marine metabolites new polyhydroxylated steroidal glycosides from the starfish Odontaster validus, Liebigs Ann. Chem., 1257, 1993. 

Glycosidase-inhibiting alkaloids from plants are classified into five structural classes polyhydroxylated pyrrolidines, piperidines, indolizidines, pyrrolizidines, and nortropanes. Furthermore, they also occur as the glycosides. This review describes recent studies on isolation, characterization, glycosidase inhibitory activity, and therapeutic application of the sugar-mimicking alkaloids from plants. 

Carbohydrates have long been a source of scientific interest because of their abundance in nature, and to the synthetic challenges posed by their polyhydroxylated structures. However, the commercial use of carbohydrates has been significantly limited by the hydrolytic lability of the glycosidic bond. With the advent of C-glycosides, this limitation promises to be overcome, thus paving the way for a new generation of carbohydrate-based products. 

In addition to Asteroidea and Holothuroidea, the phylum Echinodermata (Greek echinos, spiny derma, skin) comprises the classes Ophiuroidea (brittle stars), Crinoidea (sea lilies and feather stars) and Echinoidea (sea urchins). There is no report of occurrence of steroid or triterpenoid glycosides in sea lilies, feather stars or sea urchins. Brittle stars contain sulfated polyhydroxylated steroids [10-12] and only two sulfated steroidal monoglycosides have been isolated from the brittle star Ophioderma longicaudum [13]. 

More than one hundred polyhydroxylated steroidal glycosides have been characterized but only few reports on their biological activity have been published. Recently, several examples of new bioactive mono- and diglycosides of polyhydroxysteroids as well as biological studies on known compounds have been reported. 

The starfish Certonardoa semiregularis has shown to be a rich source of bioactive sterols and glycosides of polyhydroxylated steroids. Purification of the brine shrimp active fraction of the methanolic extract of C. semiregularis led to the isolation of nine new sulfated polyhydroxylated steroidal diglycosides [41],... 

Much work has been done in the last thirty years on the isolation and structural characterization of saponins and polyhydroxylated steroid glycosides from starfishes and sea cucumbers. The wide spectrum of biological activities these compounds show must be related to their role in the organisms that produce them and this task must be addressed in future investigations. 

Changes in monoterpene composition with grape development. Several studies have been conducted in which changes were recorded in the concentration of free monoterpenes in ripening grapes (11,38,64-66) However, most of these works were carried out before the presence of glycosidically bound or polyhydroxylated forms of monoterpenes in fruit were recognized. 

Nishida, F., Mori, Y, Rokkaku, N., Isobe, S., Furuse, T., Suzuki, M., Meevootisom, V., Flegel, T.W., Thebtaranonth, Y, and Intararuangsom, S., Structure elucidation of glycosidic antibiotics, glykenins, from Basidiomycetes sp. Part 2. Absolute structures of unusual polyhydroxylated C26-fatty acids, aglycones of glykenins, Chem. Pharm. Bull., 38, 2381, 1990. 

Another class of compound that can be difficult to purify is the saponins found in Echinoderms. Almost all echinoderms examined to date contain either polyhydroxylated sterols or terpene glycosides, many of which contain sulfate ester functionality. The purification of compounds (Schemes 6-9) (40) from the starfish Nardoa tuberculata exemplifies the procedure most often used to purify these metabolites (Fig. 2). 

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