Exclusive regio-and stereoselectivity with exo-galactal. Exclusive regio-and very high stereoselectivity with exo-xylal. Disaccharide mimicks of Gly-CH 2 -S-Gly scaffolds. Contents lists available at ScienceDirectCarbohydrate Research j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m/ l o c a t e / c a r r e s a b s t r a c tRadical-mediated addition reactions of thiols to O-peracetylated exo-galactal and exo-xylal with 2,2-dimethoxy-2-phenylacetophenone as the photoinitiator resulted in high yielding formation of the corresponding b-D-glycopyranosylmethyl-sulfide derivatives (2,6-anhydro-1-deoxy-1-S-substituted-1-thioalditols) with exclusive regio-and very high stereoselectivity, including disaccharide mimicks with Gly-CH 2 -S-Gly scaffolds. © 2015 Published by Elsevier Ltd.Glycomimetic compounds are widely used for deciphering the biological roles of carbohydrate derivatives.1 Glycomimetics resemble natural carbohydrates in their structure and/or biological function and often serve as lead compounds for drug design. 2 One of the most important features of such compounds is the hydrolytic stability of the bond(s), which replace the natural O-glycosidic linkage(s). A wide range of such replacements were suggested, among others S-glycosides and C-glycosyl derivatives with a sulfur atom or a methylene group, respectively, in the position of the glycosidic oxygen. 1 In addition, in a number of examples two (or even more) atoms are inserted between the glycon and aglycon 3 in the form of e.g., SeS, 4e8 SeSe, 8e10 SO 2 eN, 11e13 NeC(¼O)eN linking moieties. 14e17Carbohydrate derivatives displaying Gly-CH 2 -S-R scaffolds are much less represented among glycomimetics although some synthetic methods, mostly limited to the application of O-perbenzylated exo-glycals, can be found in the literature. Thus, exo-glucal was transformed in several steps into a Glc-CH 2 -I derivative, 18e20 which was reacted under basic conditions with aliphatic and aromatic thiols including sugar derivatives to give the above structures. Ring openings by nucleophiles of an exo-glucal-derived spiro-epoxide 21 as well as a spiro-episulfonium ion 22 resulted in ulose derivatives featuring the above structure. Radical-mediated addition of AcSH to exo-glycals furnished S-(b-D-glycosylmethyl) thioacetates. 23The thiol-ene addition chemistry, 24,25 either in ionic or radicalmediated versions, has found several applications in carbohydrate chemistry for S-glycoconjugation, wherein the sugar derivative generally plays the role of the thiol or is functionalized by O-or Cappended unsaturated moieties. 26 Much less work has been devoted to additions of thiols to sugar 'ene'-s in which the double bond is part of or directly attached to the sugar ring: thus, additions to sugar derived enones 27 and some reactions of endo28e30 and recently also exo-glycals 30e33 as well as derivatives with an exomethylene group in the 4-and a 5-position of a furanoside and a pyranoside, 34 respectively, and a 3-exomethylene-glucofuranose 31,32 have been report...

Photoinitiated addition of thiols to 2-deoxy-exo-glycals obtained from endo-glycals of d-arabino, d-lyxo, d-erythro and d-threo configurations resulted in highly regio- and stereoselective formation of glycosylmethyl sulfide type glycomimetics.

A synthetic procedure was elaborated for O-peracylated exo-mannals. Thiol-ene additions to pyranoid and furanoid exo-mannals gave mannosylmethyl sulfide type adducts with exclusive regio- and β(d)-stereoselectivities including disaccharide mimetics.

[2+2] Cycloadditions of methylene exo‐glycal derivatives with chlorosulfonyl isocyanate and dichloroketene were studied in detail, investigating the effect of the carbohydrate moiety, protecting groups as well as reaction temperature on the yields of the transformations. These reactions gave new anomeric spiro‐β‐lactam and spiro‐cyclobutanone derivatives, whose structure was established by 1D and 2D NMR and MS experiments. The transformation of spiro‐cyclobutanone into spiro‐γ‐lactone was also demonstrated.