Stereospecific Syntheses from Carbohydrates

Hanessian has provided a useful review of this rapidly developing subject covering examples in which carbohydrate rings are retained in tetrahydrofuran and tetra-hydropyran moieties of the products, and some in which sugars are used to provide the bases of acyclic synthons.  

Three publications from Bernet and Vasella have made an important contribution to the topic of synthesis of functionalized cyclopentanes from carbohydrate compounds (see Chapter 17). 

Reagents i, HC(OMe)jNMej ii, ACjO iii, MeO iv, ClCO Me-Py v, CuS04-H20-Me0H  

MeCH(OBut)CH(NHCbz)COjH-DCC vi, HOAc vii, CrOj-, viii, CFjCOjH ix, (2-py-S)j-Ph3P x, AgClO xi, H -Pd 

Reagents i, PhjP CHCO Et ii, MeJC(OMe)J-H iii, LiCu[CH2C(Me) = CHjj iv, BH3  

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The most well known and most widely used compounds mentioned in the chapter are the doubly protected monosaccharide derivatives (cf. Schemes 16-18 and 27-29), which serve as building blocks for the regio- and stereospecific synthesis of a host of more complex carbohydrates. A number of newly discovered alkaloids contain fused 5 6 6-triheterocyclic systems these compounds may come from not only traditional (plant) sources, for example, compounds 96, 292-294, 446, and 447, but also insects (compounds 531-533), marine animals of various kinds, for example, sponges (compounds 58 R = H or OH) and ascidians (compound 289), and amphibians (compound 535). Although the majority of these alkaloids are known to be toxic in sufficient quantity, any possible therapeutic applications have apparently not yet been disclosed. 

A [2,3]- Wittig rearrangement carried out on a carbohydrate template has been used in a route to 3-alkyl malic acids, as indicated in Scheme 24. The product of opposite chirality at C-3 could be obtained from the cis-alkene, and transition-state models were proposed to rationalize the results.93 Somewhat similar intermediates were used in a synthesis of the stereospecifically-deuteriated ester (llO), required as a standard in a study of enzyme stereospeciflcity in this case C-3 of D-glucose became C-1 of the carbojqrlic acid by oxidative cleavage.94... 

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