Herbicidine glycoside

Newcombe, N J, Mahon, M F, Molloy, K C, Alker, D, Gallagher, T, Carbohydrate-based enolates as heterocyclic building blocks. Synthesis of the herbicidin glycoside, J. Am. Chem. Soc., 115, 6430-6431, 1993. 

Perrier [102] showed that 1,6-anhydropyranoses may undergo regioselective photobromination at C-6. This observation was exploited by Gallagher [103] during the synthesis of herbicidin glycoside 160 and by Fraser-Reid [104] during the preparation of a precursor 161 to the carbocyclic core of tetrodotoxin (Scheme 26). 

Although the previous reaction involved the use of an unactivated olefin, this was apparently not the source of the lack of stereochemical induction. This is illustrated by work reported by Herscovici et al. [70,71], shown in Scheme 7.13, where several unactivated olefins were successfully used to produce a-C-glycosides in good to excellent yields. Additional work in this area resulted in a facile route to fused-ring C-glycosides [72] similar to the core structures of natural products including the halichrondrins [73], the herbicidins [74-76], and octosyl acid [77]. 

The first total synthesis of the nucleoside antibiotic herbicidin B was accomplished in the laboratory of A. Matsuda. The key step was a novel aldol-type C-glycosidation reaction promoted by Sml2 between a 1-phenylthio-2-ulose derivative and a 1- 3-D-xylosyladenine-5 -aldehyde derivative. During the preparation of the phenylthio sugar subunit, the Moffatt oxidation was applied to convert the primary alcohol to the corresponding aldehyde, which was immediately oxidized with PDC in DMF/MeOH to the methyl ester. The reaction conditions were completely compatible with the silyl protecting group as well as the thioacetal functionality. 

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