The stntctlo'e, properties, distribution in nature, and biological activity of sterol glycosides and acylglycosides are reviewed.Sterols are one of the most widely distributed natural substances [1][2][3]. They exist in animals and plants in the free state and as derivatives. Glycoside and acylglycoside derivatives of sterols have been known for a long time. In the plant world, these compounds are found in higher plants [2,[4][5][6], algae [7], fungi [8][9][10], and bacteria [11][12][13][14][15][16]. In the animal kingdom, these substances have been identified in soft coral [17], holothuriae [18-20[, amphibians [211, snakes [21, 22], and birds [21,23]: Such a wide distribution in nature suggests that sterol glycosides and acylglycosides possess important physiological functions. Therefore, these compounds are constantly under intense scientific scrutiny. Sterol glycosides and acylglycosides are usually isolated from natural sources as very complicated mixtures that cannot always be separated into, the pure components. However, several physicochemical methods have recently been proposed for separating, analyzing, and identifying them [23][24][25][26][27][28][29][30][31][32][33][34]. Use of these methods greatly facilitates the investigation of glycosides and acylglycosides.Owing to the wide distribution in nature and the variety of physiological functions for glycosides and acylglycosides, research articles about them are published in a wide range of scientific literature. However, this subject has not yet been reviewed. The present work is intended to fill that gap. It should be noted that we pay the most attention to discreet natural compounds that can be isolated pure and for which the structures are reliably proved since this is where our interest lies. Substances that have been isolated as mixtures and are insufficiently characterized are examined in less detail.Some of the most widely distributed sterol glycosides are ~sitosterol 3-O-~D-glucopyranoside (1). This compound was isolated from higher plants early in the 20th century under various names: ipuranol, citrullol, trifolianol, etc. [35,36]. Later glycoside 1 was prepared by chemical synthesis via glycosylation of I~-sitosterol [37]. Direct comparision with this synthesized compound provided final structural proof tbr various natural samples of I [36]. Glycoside 1 is the most typical sterol glycoside of higher plants and is usually observed in preliminary phytochemical analysis of them. Hydrolysis of glycoside 1 by sulfuric acid in ethanol with boiling lbr 22 h yields [~-sitosterol and D-glucose [41]. The same result is obtained by hydrolysis in 6% HCI with heating lbr 50 min [46]. Hydrolysis of compound 1 to give ~sitosterol

Although the involvement of 3-oxo-delta 4 compounds as intermediates in arthropod ecdysteroid biosynthesis has been postulated for a long time, it has not yet been directly demonstrated. In the present study, 3-oxo-delta 4-steroids have been synthesized and incubated in vitro with dissociated moulting gland cells from the crab Carcinus maenas. The tritiated compounds were converted into 3-dehydroecdysone, ecdysone and/or 25-deoxyecdysone, i.e. final ecdysteroids. This means that the 3-oxo-delta 4 compounds had undergone a 5 beta-reduction, to give the 5 beta-conformation of ecdysteroids. Our results suggest that the 3-oxo-delta 4-steroid 4,7-cholestadien-14 alpha-ol-3,6-dione may be an intermediate in the biosynthetic pathway. The 5 beta-reduction reaction involves a cytosolic enzyme which requires NADPH as electron donor and seems specific for 3-oxo-delta 4 substrates. This reaction was the most active in crab Y-organs, as compared with other tissues. The characteristics of the 5 beta-reductase (subcellular localization, substrate and cofactor requirements) appear similar to those of the vertebrate 3-oxo-delta 4-steroid 5 beta-reductase involved in steroid hormone catabolism and bile acid biosynthesis.

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