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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We have used fluorescence spectroscopy methods to show that imidacloprid and its structural analogs form complexes with human serum albumin (HSA). The nature of the spectral changes in the ligand×protein systems and the calculated complexation parameters suggest that these low molecular weight compounds mainly bind to a specific section of the protein molecule, near the tryptophan residue in the 214 position of the polypeptide chain. We have found that the association constants are on the order of 10 4 M -1 , and the affinity of the ligands for HSA varies in the series 6-chloronicotinic acid > 6-methoxynicotinic acid = imidacloprid > the keto analog of imidacloprid. The major contribution to the complexation energy probably comes from hydrophobic interaction forces with participation of the aromatic pyridine ring of the ligands, while additional enhancement of ligand-protein affinity can be provided by the nitroimine group of imidacloprid.Key words: human serum albumin, neonicotinoid, imidacloprid, quenching of fluorescence, ligand-protein binding.Introduction. Neonicotinoids are a new and very important class of insecticides with selective action which are increasingly aggressively displacing pyrethroids, organophosphorus compounds, and methylcarbamates from the area of application for protection of plants from insect pests. The selectivity of action of neonicotinoids is determined by the properties of their molecular target: the nicotinic acetylcholine receptor. These pesticides have high affinity for the insect receptor and bind weakly to other types of receptors, in particular exhibiting low toxicity for mammals [1,2]. The molecular aspects of high affinity and selectivity for binding of neonicotinoids and their analogs by receptor proteins and the physicochemical nature of the interactions in the complexes formed have been studied in many papers. As a result, some structural elements and also chemical groups have been identified in the insecticides and the receptor that are involved in complexation, and computer models of the ligand×protein interaction have been proposed based on a quantum chemical method [1,[3][4][5][6].Another important direction in studies of the biological properties of pesticides is directly related to protection of the health of humans and agricultural animals, and includes study of the interactions between these xenobiotics and proteins, enzymes, and receptors in blood plasma and tissues. The chemical structure of many pesticides, including insecticides in the neonicotinoid class, contains sections and groups capable of forming electrostatic, hydrophobic, and hydrogen bonds as well as other types of bonds typical of endogenous ligands in their complexes with proteins. Therefore many pesticides can play the role of exogenous ligands and alter their own properties within the composition of protein complexes, as is true for natural bioregulators such as hormones. These changes can involve metabolic parameters and biological effects of the pesticides in the human body and in the bodies of...

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