As early as 1550 B.C., Egyptians realized the benefits of garlic as a remedy for a variety of diseases. Many epidemiological studies support the protective role of garlic and related allium foods against the development of certain human cancers. Natural garlic and garlic cultivated with selenium fertilization have been shown in laboratory animals to have protective roles in cancer prevention. Certain organoselenium compounds and their sulfur analogs have been identified in plants. Organoselenium compounds synthesized in our laboratory were compared with their sulfur analogs for chemopreventive efficacy. Diallyl selenide was at least 300-fold more effective than diallyl sulfide in protecting against 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary adenocarcinomas in rats. In addition, benzyl selenocyanate inhibited the development of DMBA-induced mammary adenocarcinomas and azoxymethane-induced colon cancer in rats and benzo[a]pyrene-induced forestomach tumors in mice. The sulfur analog, benzyl thiocyanate, had no effect under the same experimental conditions. Furthermore, we showed that 1,4-phenylenebis(methylene)selenocyanate, but not its sulfur analog, significantly inhibited DMBA-DNA adduct formation and suppressed DMBA-induced mammary carcinogenesis. Collectively, these results indicate that structurally distinctive organoselenium compounds are superior to their corresponding sulfur analogs in cancer chemoprevention. Additionally, synthetic aromatic selenocyanates are more effective cancer chemopreventive agents than the naturally occurring selenoamino acids. Because plants are capable of utilizing selenium in a manner similar to that in sulfur assimilation pathways, future studies should aim at determining whether, under appropriate conditions, these potent cancer chemopreventive synthetic selenium compounds can be synthesized by garlic and related allium foods.

Cancer Chemoprevention by Garlic and Garlic-Containing Sulfur and Selenium Compounds

Compounds in garlic work synergistically to produce various effects, but, because of garlic’s chemical complexity, processing methods yield preparations with differing efficacy and safety. Although thiosulfinates such as allicin have been long misunderstood to be active compounds due to their characteristic odor, it is not necessary for garlic preparations to contain such odorous compounds to be effective, and they decompose and disappear during any processing. Garlic exhibits hypolipidemic, antiplatelet, and procirculatory effects. It prevents cold and flu symptoms through immune enhancement and demonstrates anticancer and chemopreventive activities. In addition, aged garlic extract possesses hepatoprotective, neuroprotective, antioxidative activities, whereas other preparations may stimulate oxidation. Additional effects may be caused by S-allylcysteine, S-allyl mercaptocysteine), saponins, N-fructosyl arginine, and other substances formed during a long-term extraction process. Although not all of active ingredients of garlic are known, and allicin-like transient components are not directly active, ample research suggests that an allicinfree garlic preparation that is standardized with a bioavailable component such as S-allylcysteine, is active and various effects of garlic may be attributed to it. Furthermore, various chemical constituents in garlic products, including nonsulfur compounds such as saponins, may contribute to the essential biological activities of garlic. Further studies are needed to confirm their bioavailability and associated activities. J. Nutr. 136: 716S–725S, 2006.

Significance of Garlic and Its Constituents in Cancer and Cardiovascular Disease

Synthesis and Characterization of Allylic and Propargylic Selenols

Organic diselenides and ditellurides represent very important classes of compounds, which find valuable applications in organochalcogen chemistry and in organic synthesis. The review describes the main efficient and reliable approaches to organic diselenides and ditellurides and their principal chemical reactions. Examples of syntheses of tri- and polyselenides and -tellurides have been presented. Typical reactions of organic diselenides and ditellurides with nucleophiles, electrophiles, radicals, carbenes and compounds containing the element-element bond have been discussed in the review. Regio- and stereoselective reactions of organic diselenides and ditellurides with unsaturated compounds provide various chalcogenyl and bis(chalcogenyl) derivatives, which are often used in further transformations including stereoselective synthesis of functionalized alkenes. Along with valuable chemical reactions, organic diselenides and ditellurides act as precursors of both nucleophilic and electrophilic selenium and tellurium species, which participate in various useful transformations. The remarkable property of reacting with high regio- and stereoselectivity finds widespread application of selenium and tellurium species in organic synthesis. Besides valuable synthetic applications, organic diselenides and ditellurides exhibit various biological activities including glutathione peroxidase-like action. Aspects of biological activity of these compounds as well as a comparison of selenol–diselenide and thiol–disulfide reversible exchange reactions have been discussed in the review.


Keywords:

diselenides;
ditellurides;
triselenides;
tritellurides;
polyselenides;
polytellurides;
selenium;
tellurium

Organic Diselenides, Ditellurides, Polyselenides and Polytellurides. Synthesis and Reactions

Regioselective reactions of sulfur, selenium and tellurium chlorides with allyl trimethyl silane

Synthesis of diallyl selenide

(1991). SYNTHESIS OF DIALLYL SELENIDE. Organic Preparations and Procedures International: Vol. 23, No. 2, pp. 207-208.

V. A. Potapov

Papers

Synthesis of diallyl selenide

Synthesis of Diallyl Selenide.