Target preparation linear synthesis

Anti-tumor compound (205)-irinotecan (1) was prepared in 13 steps with an overall yield of 1.15 % for the longest linear synthesis. The short and selective preparation of aryl iodide 11 features two key steps - ortho metalation and Sharpless asymmetric dihydroxylation. In only one step 11 is transformed into the target molecule 1 by application of a radical domino annulation with isonitrile 15. This method gives access to the broad family of campthotecin derivatives because of the quite impressive generality of the substrates that can be employed. 

The computation time for the 3-D reconstruction depends mainly on the normal matrix preparation step and the Fourier-Bessel synthesis step. The time for the normal matrix calculation increases roughly linearly with the particle numbers and the targeted resolution. The Fourier-Bessel... 

Nowadays, many elegant syntheses of steroids, alkaloids and affiliated products are prepared from several five- or six-membered rings. Usually, the preferred steps of such syntheses correspond to the polycyclizations of educts, that contain many multiple bonds, and one or two other functional groups of further educts can often also participate [17]. However, in recent years a new type of the radical chemistry of the isocyanides has been introduced [47].This is illustrated by the one-pot synthesis of (20S)-camptothecin 25 from phenyl isocyanide 13a and 24. Such preparations of cyclopenta-fused quinolines are seldom found in tandem-domino chemistry [16], and this procedure is also closely related to the MCRs of the isocyanides. The previous multistep synthesis of 25 was accomplished by Danishefsky and Volkmann [47b], and uses a large number of linear synthetic steps with only small overall transformations towards the target. 

Similar in approach to linear methods discussed previously, the cyclodehydration of a-amido ketones is an alternative strategy for preparation of the oxazole nucleus. Treatment of the ketone with PPhs and I2 results in cyclization to provide the fully substituted oxazole nucleus in excellent yield. This strategy was recently used in the synthesis of oxazole-modified glycopeptides, designed to target two classes of arthritis-associated proteins. The oxazole was probed as a conformationally locked dipeptide mimic. 

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