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A variety of new symmetrical and unsymmetrical diketopiperazines have been prepared from free amino acids by using a previously developed microwave-assisted protocol. This included the successful incorporation of L-pyroglutamic acid as an unusual building block. The diketopiperazines were then thiolated electrophilically to the corresponding bis(methylthio)- and epidithiodiketopiperazines. Initial experiments showed a promising activity towards the generation of reactive oxygen species in HeLa cells.

We report a metal-free radical perfluoroalkylation method which uses inexpensive and commercially available perfluorocarboxylic anhydrides as an easy to use source of perfluoroalkyl radicals. This approach allows the perfluoroalkylation of different arenes, such as benzene derivatives, furans, thiophenes, and pyrroles, including highly functionalized compounds.

The introduction of sulfur units into a variety of symmetrical and unsymmetrical diketopiperazines (DKPs) is described. We investigated different thiolation methods utilizing several bases and electrophilic sulfur reagents, leading to monomethylthio-, bis(methylthio)-, and epithio-DKPs. Their formation proceeded diastereoselectively, facilitating the application in total syntheses of many thiodiketopiperazine (TDKP) natural products. Furthermore, possible side reactions as well as mechanistic studies and stereochemical structural assignments of the obtained products are given.

A versatile strategy for the formation of hydroindole derivatives is reported. The molecules synthesized are highly functionalized and bear up to six stereogenic centers. We were able to develop a stereoselective route starting from nonchiral commercially available materials. Key steps in the formation of the bicyclic products are an organocatalytic vinylogous Mukaiyama–Mannich and a Diels–Alder reaction. The former uses a 1,1′-bi-2-napthol (BINOL)-based chiral Bronsted acid catalyst to build the first stereogenic center. The [4+2] cycloaddition proceeds highly diastereoselectively and furnishes one main stereoisomer, which represents the scaffold of the mycotoxins Rostratin B–D. Other transformations include iodolactonization, a Curtius rearrangement, additions, oxidations, and reductions.

A diverse set of highly substituted 4-aminoquinolines was synthesized from ynamides, triflic anhydride, 2-chloropyridine, and readily accessible amides in a mild one-step procedure.

Inexpensive and commercially available perfluorocarboxylic anhydrides are used as source of perfluoroalkyl radicals for the perfluoroalkylation of various arenes, such as benzene derivatives, furans, thiophenes, and pyrroles.

The stereoselective synthesis of a variety of functionalized hydroindoles suitable as building blocks for thiodiketopiperazine natural products such as rostratins B-D is reported. The key precursor for all transformations is a previously reported hexahydroindole compound. All functional groups were installed with the desired stereochemistry and the feasibility of the synthetic strategy was exemplified by dimerization of two hydroindole units to form the pentacyclic C2 -symmetric scaffold of rostratin C.

Additional file 1. NMR-spectra of pNO2PheDU (4a) and NCarbpNO2 βPhe (5a).

Only 3-vinylindoles afford the products (III) and (V), whereas the reaction of 2-vinylindole gives the amino acid derivative (VII).

We developed an asymmetric organocatalytic synthesis of 4{,}6-bis(1H-indole-3-yl)-piperidine-2-carboxylates using 10 mol% of a chiral phosphoric acid. The products{,} which are novel bisindole-piperidine-amino acid hybrids{,} can be obtained in one step from 3-vinyl indoles with imino esters in dichloromethane at room temperature after 1 h of reaction time. A variety of these compounds could be synthesized in up to 70% yield and 99% ee{,} and they were experimentally and computationally analyzed regarding their relative and absolute stereochemistry.

The resorcylic acid lactones (RALs) are a family of benzannulated macrolides, which are produced by a variety of fungi and show versatile biological activities (6). According to their name, they consist structurally of a partially substituted β-resorcylic acid scaffold, which is linked to a 12- or 14-membered macrolactone moiety. Selected members of this group are shown in Fig. 9.1.

A novel substrate, 6-(4-nitrophenyl)dihydropyrimidine-2,4(1H,3H)-dione (pNO2PheDU), was chemically synthesized and analytically verified for the potential biocatalytic synthesis of enantiopure β-amino acids. The hydantoinase (EC 3.5.2.2) from Arthrobacter crystallopoietes DSM20117 was chosen to prove the enzymatic hydrolysis of this substrate, since previous investigations showed activities of this enzyme toward 6-monosubstituted dihydrouracils. Whole cell biotransformations with recombinant Escherichia coli expressing the hydantoinase showed degradation of pNO2PheDU. Additionally, the corresponding N-carbamoyl-β-amino acid (NCarbpNO2βPhe) was chemically synthesized, an HPLC-method with chiral stationary phases for detection of this product was established and thus (S)-enantioselectivity toward pNO2PheDU has been shown. Consequently this novel substrate is a potential precursor for the enantiopure β-amino acid para-nitro-β-phenylalanine (pNO2βPhe). Electronic supplementary material The online version of this article (doi:10.1186/s13568-015-0174-8) contains supplementary material, which is available to authorized users.