Hydrotalcite-supported Pt nanoparticles catalyze the direct transformation of furfural to 1,2-pentanediol in a high yield of 73% under additive-free conditions. The Pt nanoparticle catalyst is easily recoverable and reusable while maintaining high activity and selectivity.

Tungsten oxide-supported platinum nanoparticles containing aluminum oxide species (Pt–AlOx/WO3) act as a highly efficient heterogeneous catalyst for the hydrogenolysis of glycerol to 1,3-propanediol without any additives. High 1,3-propanediol selectivity was observed due to the concerted effect of the Pt nanoparticles, aluminum oxide, and tungsten oxide support. The Pt–AlOx/WO3 catalyst is reusable with maintaining its high catalytic performance.

Multiple-drug resistance toward cell-cycle inhibitors frequently becomes an obstacle in cancer chemotherapy. One strategy for circumventing this problem is to develop antimitotic agents that operate by a new mode of action. Two such compounds, tryprostatins A and B, were isolated in 1995 from the fermentation broth of Aspergillus fumigatus BM939 by Osada and co-workers.[1] Tryprostatin A holds great promise, because it selectively arrests the cell cycle at the mitotic phase in tsFT210 cells.[2] Interesting biological activity combined with an apparently simple structure has stimulated the synthetic community, and several total syntheses have already been reported. [3,4] Our research group has long been involved with the radical-mediated construction of a variety of indole cores and the application of these methods to natural product synthesis. [5,6] We envisioned that our method could also be applied to the synthesis of the 2,3-disubstituted indole moiety of the tryprostatins. The interesting structural features as well as the therapeutic potential of tryprostatin A analogues indicated in a recent structure-activity-relationship study [4e] prompted us to launch a program toward the synthesis of tryprostatins.We reasoned that radical-mediated cyclization and subsequent palladium-mediated coupling with a prenyl-group donor would enable facile construction of the 2,3-disubstituted indole core structure 3 (Scheme 1). The requisite orthoalkenyl isocyanide 4 would be prepared from the alkyne 5, which in turn could be accessed by Sonogashira coupling of the aromatic iodide 6 with the terminal alkyne 7. To enable synthesis of the target compounds with high enantiomeric purity, the alkyne 7 derived from the Garner aldehyde (8) [7] was employed as a latent amino acid unit to be incorporated into the diketopiperazine.Initially, we focused our efforts on the synthesis of the isocyanide 12 as a radical-cyclization precursor (Scheme 2). The alkyne 7 was prepared from 8 according to the known protocol [8] with a slight modification. After the Sonogashira coupling between 7 and 2-iodoformanilide (9), partial reduction of the triple bond was examined. Whereas the use of the Lindlar catalyst, Pd/C, nickel boride, [9] or diimide [10] resulted in no reaction or overreduction, treatment with Zn/LiCuBr 2 in ethanol [11] gave the desired product 11 along with the corresponding amine. The use of 2,2,2-trifluoroethanol [12] as the solvent suppressed the undesired solvolysis and improved the yield of 11 to 99 %. Subsequent dehydration with bis(trichloromethyl) carbonate (triphosgene) gave the ortho-alkenyl isocyanide 12 and thus set the stage for a radical-mediated cyclization.When isocyanide 12 thus obtained was subjected to our previously established radical-cyclization conditions,[5a] the desired 5-exo adduct 13 was obtained in moderate yield after acidic treatment with silica gel along with a considerable amount of products 14 and 15 of a 6-endo cyclizationcleavage process (Scheme 3). We were aware of the tendency of this imidoy...

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Gezähmte Radikale: Die Entwicklung verlässlicher Bedingungen für die radikalvermittelte Bildung von Indolen führte zur effizienten Synthese der Tryprostatine A und B. Mit dem Radikalstarter 2,2′‐Azobis(4‐methoxy‐2,4‐dimethylvaleronitril) gelang die radikalische Cyclisierung schon bei 30 °C, sodass die Bildung von Nebenprodukten unterdrückt war.