B

reaction conditions in solution Product spent _

reagent filtration in solution (insoluble)

Fig. 2.7. The principle of polymer-supported reagents.

product in solution in solution (insoluble)

Fig. 2.7. The principle of polymer-supported reagents.

Fig. 2.8. The total synthesis of (G)-oxomaritidine and (G)-epimaritidine.

chemistry (Fig. 2.8). The versatility of this approach has been proved by Ley et al. in the total synthesis of two natural products, (G)-oxomaritidine and (+)-epimaritidine.

Another possibility to deal with the problem of excess reagents in solution-phase combinatorial chemistry is the use of fluorous tagging and extraction with fluorinated solvents (Fig. 2.9). Substrate A is attached to a moiety which is polyfluo-rinated. Because of the fluorous tag the product of the reaction is exclusively soluble in the fluorous solvents. After reaction with excess quantities of reagent B an extraction with a polyfluorinated solvent is performed. Reagent B is more solu-

transformation with transformation with

Fig. 2.9. Fluorous tagging - a powerful tool for solution-phase chemistry.

ble in the organic phase and can be separated from the product. Finally the fluo-rous tag is cleaved off, removed by another extraction and the pure product can be isolated.

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