Herbicidin

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]. 

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. 

Yoshikawa, H, Takiguchi, Y, Terao, M, Terminal steps in the biosynthesis of herbicidins, nucleoside antibiotics, J. Antibiot., 36, 30-35, 1983. 

To illustrate the possible use of sugar-derived vinylic anions, we will focus on the synthesis of herbicidin, a complex nucleoside isolated from strains of Streptomyces showing interesting herbicidal properties (see Scheme 11.74). The most challenging part of the synthesis is obviously the construction of a carbon-carbon bond between two sugar units. 

Fairbanks, A J, Perrin, E, Sinay, P, Synthesis of the carbon skeleton of the herbicidins via a temporary silaketal tether, Synlett, 679-681, 1996. 

Bearder, J R, Dewis, M L, Whiting, D A, Methods for the formation of the Cl (hexose)-C5 (pentose) bond an approach to the synthesis of undecoses related to herbicidin, Synlett, 805-806, 1993. 

Binch, H M, Gallagher, T, Studies directed towards the synthesis of herbicidins. Model study based on late stage A-glycosylation, J. Chem. Soc., Perkin. Trans. 1, 401-402, 1996. 

Ichikawa, S, Shuto, S, Matsuda, A, The first synthesis of herbicidin B. Stereoselective construction of the tricyclic undecose moiety by a conformational restriction strategy using steric repulsion between adjacent bulky silyl protecting groups on a pyranose ring, J. Am. Chem. Soc., 121, 10270-10280, 1999. 

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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