Synthesis of indoles and tryptophan derivatives via photoinduced nitrene C–H insertion

Functionalized indoles and tryptophans can be obtained from stannylated alkenes and o-iodoanilines via Stille coupling.

Total syntheses and biological evaluation of miuraenamides

The miuraenamides, relatively simple representatives of a class of cyclodepsipeptides with high antitumor activity, can be easily and flexibly obtained by the concept of peptide modification. A reaction sequence consisting of an aldol reaction, oxidation, and methylation of the glycine subunit of the cyclodepsipeptides allows the incorporation of the unusual α,β-unsaturated dehydroamino acid in one of the last steps of the synthesis.

[(p-Cymene)RuCl2 ]2 : an efficient catalyst for highly regioselective allylic alkylations of chelated amino acid ester enolates

Chelated amino acid ester enolates are excellent nucleophiles for ruthenium-catalyzed allylic alkylations. Although [Cp*Ru(MeCN)3 ]PF6 was found to be the most reactive catalyst investigated, with the resulting allyl complexes reacting at temperatures as low as -78 °C, unfortunately the process took place with only moderate regio- and diastereoselectivity. In contrast, [(p-cymene)RuCl2 ]2 allowed allylations to be performed with a high degree of regioretention. Secondary allyl carboxylates with a terminal double bond were found to be the most reactive substrates, giving rise to the branched amino acids with perfect regioretention and chirality transfer. In this case, no isomerization of the Ru-allyl complex formed in situ was observed, in contrast to the analogues palladium complexes. This isomerization-free protocol can also be used for the synthesis of (Z)-configured γ,δ-unsaturated amino acid derivatives, starting from (Z)-allylic substrates. Here, the more reactive phosphates were found to be superior to the carboxylates, providing the required amino acids in almost quantitative yield with perfect regio- and stereoretention. Therefore, the Ru-catalyzed allylation reactions are well positioned to overcome the drawbacks of Pd-catalyzed processes.

Highly stereoselective modifications of peptides via Pd-catalyzed allylic alkylation of internal peptide amide enolates

Pd-catalyzed allylations are excellent tools for stereoselective peptide modifications, showing several advantages compared to normal alkylations. Reactions of internal peptide amide enolates with Pd-allyl complexes proceed not only with high yields of up to 86%, they show also high regio- and diastereoselectivities (88-99%), giving rise to the trans-configured products. Therefore, this protocol is a powerful synthetic tool for the synthesis of natural product and drug molecules.

Diastereotopos-differentiating allylic alkylation as a key step in the synthesis of gamma-glutamyl boletine

A straightforward approach towards gamma-glutamyl boletine is described, based on a diastereotopos-differentiating allylic alkylation of chelated amino acid ester enolates. Independent of the configuration of the leaving group in the allylic substrate, the allylation product is obtained as a single stereoisomer. Its configuration is solely controlled by the stereogenic center adjacent to the pi-allyl complex formed.