A New Benzotriazole-Mediated Stereoflexible Gateway to Hetero-2,5-diketopiperazines

On Demand Flow Platform for the Generation of Anhydrous Dinitrogen Trioxide and Its Further Use in N-Nitrosative Reactions

Dinitrogen trioxide (N2 O3 ) is a powerful and efficient nitrosating agent that comes with an unprecedented atom economy. However, the synthetic application of N2 O3 is still underdeveloped mostly due to its inherent instability and the lack of reliable protocols for its preparation. This paper presents an open-source setup and procedure for the on-demand generation of anhydrous N2 O3 solution (up to 1 M), which can be further used for reactions under batch and flow conditions. The accuracy and stability of N2 O3 concentration are guaranteed with the absence of head-space in the setup and with the synchronization of the gas flows. The reliability of this protocol is demonstrated by >30 worked examples in the nitrosative synthesis of heterocycles-a library of structurally diverse benzotriazoles and sydnones. Kinetic and mechanistic aspects of the N-nitrosative steps are also explored.

An economical approach for peptide synthesis via regioselective C-N bond cleavage of lactams

An economical, solvent-free, and metal-free method for peptide synthesis via C-N bond cleavage using lactams has been developed. The method not only eliminates the need for condensation agents and their auxiliaries, which are essential for conventional peptide synthesis, but also exhibits high atom economy. The reaction is versatile because it can tolerate side chains bearing a range of functional groups, affording up to >99% yields of the corresponding peptides without racemisation or polymerisation. Moreover, the developed strategy enables peptide segment coupling, providing access to a hexapeptide that occurs as a repeat sequence in spider silk proteins.

New Chlorinated 2,5-Diketopiperazines from Marine-Derived Bacteria Isolated from Sediments of the Eastern Mediterranean Sea

From the organic extracts of five bacterial strains isolated from marine sediments collected in the East Mediterranean Sea, three new (15, 16, 31) and twenty-nine previously reported (1–14, 17–30, 32) metabolites bearing the 2,5-diketopiperazine skeleton were isolated. The structures of the chlorinated compounds 15, 16, and 31 were elucidated by extensive analysis of their spectroscopic data (NMR, MS, UV, IR). Compounds 15 and 16 were evaluated for their antifungal activity against Candida albicans and Aspergillus niger but were proven inactive. The relevant literature is supplemented with complete NMR assignments and revisions for the 29 previously reported compounds.

Beyond the Diketopiperazine Family with Alternatively Bridged Brevianamide F Analogues

A method for the preparation of 3,5-bridged piperazin-2-ones from a tryptophan-proline-based diketopiperazine is described using diphosgene to induce the ring closure. Density functional theory calculations were conducted to study the mechanism of this C-C bond formation. Several derivatives of the thus obtained α-chloroamine were synthesized by substitution of the chlorine atom using a range of O-, N-, S-, and C-nucleophiles. This novel class of brevianamide F analogues possess interesting breast cancer resistance protein inhibitory activity.

A benzotriazole-mediated route to protected marine-derived hetero-2,5-diketopiperazines containing proline

A procedure for the cyclization of dipeptidoyl benzotriazolides containing proline derivatives promoted by triethylamine under MW activation is introduced. The reaction is general for a variety of dipeptidoyl benzotriazolides and represents a very practical and convenient method for the preparation of Pro- or Hyp-derived 2,5-diketopiperazines (2,5-DKPs) and bis-DKPs with a disulfide linker. This method can be used for the construction of 2,5-DKP compound libraries and for the synthesis of natural products with diketopiperazine cores.