S- and Se-Glycosides

The use of sulfoxides as leaving groups in glycoside synthesis is less common, but compound 92 has been employed to couple with a secondary alcohol in the synthesis of hikizimycin (See Chapter 20). 

In the field of reactions of thioglycosides the photobromination of phenylthio compounds has been covered in a review. As has been noted before, and has been used usefully in synthesis of 2-deoxy compounds, the alkylthio group of thioglycosides may migrate to C-2 under certain conditions. Thus, as well as compound 93 giving the expected 2,3-orthoester on treatment with alkyl orthoesters in acid conditions, it gave compound 94 

Many examples, as usual, of the use of thioglycosides in 0-glycoside synthesis 

Chemoenzymic methods have been used to make polyoxyalkyl dendimers carrying six copies of p-5-linked p-o-Lac and -P-d-G1cNAc which were used as precursors for the synthesis of lactose 3 -sulfate (chemical methods) and LacNAc (enzymic methods), respectively.  

iV-Dialkyl-S-glycosylsulfenamides e.g. 121 were made from the corresponding glycosyl 5-acetate by treatment with secondary amines in the presence of NBS.2  

Compounds such as the seleno-linked 122 with the a-manno- or a- or fi-gluco-configurations, together with carboxylic acids and in the presence of silver salts, give the glycosyl carboxylates in quantitative yield.  

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The important feature of the Lewis acid-catalyzed rearrangement is that these reactions are applicable to C-glycosides tScheme 12.10. 30 31) when the substrates possess electron-donating aglycons. S- and Se-Glycosides also afforded the corresponding carbocycles (32 33)P... 

Carbocycles are formed on subjecting unsaturated S-, Se-, and C-glycosides to i-BuiAl. Claisen rearrangement followed by reduction of the resulting ketones is accomplished in one step. ... 

During the last three decades, electrochemical glycosylation performed by anodic oxidation of 0-, S-, Se-, and 7e-glycosides or by cathodic reduction of glycosyl halides has allowed the synthesis of a large number of complex 0-, N-. and C-glycosyl derivatives. 

Stevia Stevia rebaudiana) Uses Natural sweetener, hypoglycemic and hypotensive properties Actions Multiple chemical components sweetness d/t glycoside, stevioside hypotensive effect may be d/t diuretic action or vasodilation action Available forms Liq extract, powder, caps Notes/SE HA, dizziness, bloating Interactions T Hypotensive effects W/ antihypertensives esp CCB, diuretics EMS Monitor BP does not encourage dental caries may -1-glucose St. John s Wort (Hypericum perforatum) Uses Mild-mod depression, anxiety, anti-inflammatory, immune stimulant/anti-HIV/antiviral, gastritis, insomnia, vitiligo Action MAOI in vitro, not in vivo bacteriostatic bactericidal, T capillary blood flow, uterotonic activity in animals Efficacy Variable benefit w/ mild-mod depression in several trials, but not always seen in clinical practice Available forms Teas, tabs, caps, tine, oil ext for topical use Dose 2-4 g of herb or 0.2-1 mg of total hypericin (standardized extract) daily Notes/SE Photosensitivity (use sunscreen) rash, dizziness, dry mouth, GI distress Interactions Enhance MAOI activity, EtOH, narcotics, sympathomimetics EMS T Risk of photosensitivity Rxns t effects of opioids and sympathomimetics... 

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