Novel Isoindolinone-Based Analogs of the Natural Cyclic Peptide Fenestin A: Synthesis and Antitumor Activity

Small- and medium-sized cyclopeptides have been found to have extensive bioactivities and have drawn much attention from medicinal chemists. In the work described in this paper, various cyclic peptide analogs of Fenestin A were synthesized by intramolecular photoinduced electron-transfer cyclization reactions to study the influence of slight structural changes on the bioactivity of small cyclopeptides. The incorporation of thiazole and rigid isoindolinone fragments was found to improve the bioactivity of the cyclopeptide. Detailed in vitro studies of the apoptosis mechanism, mitochondrial membrane potential, cell cycle, intracellular Ca²⁺ concentration, and lactate dehydrogenase activity following treatment with a cyclopeptide showed that the cyclopeptide could induce apoptosis of tumor cells and lead to cycle arrest in the G2/M phase. The research also suggested that the photoinduced reaction could be applied to construct cyclic peptides stereoselectively, and the introduction of rigid fragments could enhance the biological activity of cyclopeptide drugs.

Photo-induced synthesis, structure and in vitro bioactivity of a natural cyclic peptide Yunnanin A analog

A cyclic analog of natural peptide Yunnanin A was synthesized via photoinduced single electron transfer reaction (SET) in the paper. The resulting compound exhibited potent bioactivity (with IC₅₀ values 29.25 μg mL⁻¹ against HepG-2 cell lines and 65.01 μg mL⁻¹ against HeLa cell lines), but almost have no toxicity to normal cells (with IC₅₀ values 203.25 μg mL⁻¹ against L929 cell lines), which may be served as a potential antitumor drug for medical treatment. The spatial structure was examined by experimental electronic circular dichroism (ECD) and quantum chemistry calculations. Moreover, the theoretical study suggested that special intramolecular hydrogen bonds and γ, β-turn secondary structures may be possible sources affecting cyclic peptide's bioactivity.

The photo-induced synthesis, structure and in vitro bioactivity study of a Yunnanin A cyclopeptide analog was presented.

Photo-induced synthesis of Axinastatin 3 analogs, the secondary structures and their in vitro antitumor activities

Cyclic peptides combine several favorable properties such as good binding affinity, target selectivity and low toxicity that make them an attractive modality for drug development. In an effort to identify what conformation could be accounting for the bioactive disparity of natural and synthetic cyclic peptides, some structurally-constrained analogs of cyclopeptide Axinastatin 3 were prepared by photo-induced single electron transfer (SET) reaction. Detailed stereochemistry study was performed by experimental electronic circular dichroism combined with theoretical calculations. Our study suggested that the cyclopeptide 1 with βI-turn presented stronger antitumor activity comparing with those without such secondary structures. Moreover, a rare 'π helix unit' (compound 3) was realized because of the constrained cyclic structure, which could be considered an important research object for future study of unique helix secondary structures.

Photo-induced synthesis of chiral galaxamide analogs and the biological activities against human tumor cells

Two chiral analogs of galaxamide were synthesized by a photoinduced cyclization reaction.