Synthesis of Alkyne-Bridged Cyclic Tripeptides toward Constrained Mimics of Vancomycin

Vancomycin mimicry: towards new supramolecular antibiotics

Vancomycin is the best-known of the glycopeptide group antibiotics (GPAs), a family of agents which operate by binding the C-terminal deptide D-Ala-D-Ala. This anionic epitope is an interesting target because it plays a central role in bacterial cell wall synthesis, and is not readily modified by evolution. Accordingly, vancomycin has been in use for >60 years but has only provoked limited resistance. Agents which mimic vancomycin but are easier to synthesise and modify could serve as valuable weapons against pathogenic bacteria, broadening the scope of the GPAs and addressing the resistance that does exist. This article gives an overview of vancomycin's structure and action, surveys past work on vancomycin mimicry, and makes the case for renewed effort in the future.

Peptide macrocyclization by transition metal catalysis

Peptide macrocyclization has traditionally relied on lactam, lactone and disulfide bond-forming reactions that aim at introducing conformational constraints into small peptide sequences. With the advent of ruthenium-catalyzed ring-closing metathesis and copper-catalyzed alkyne-azide cycloaddition, peptide chemists embraced transition metal catalysis as a powerful macrocyclization tool with relevant applications in chemical biological and peptide drug discovery. This article provides a comprehensive overview of the reactivity and methodological diversification of metal-catalyzed peptide macrocyclization as a special class of late-stage peptide derivatization method. We report the evolution from classic palladium-catalyzed cross-coupling approaches to more modern oxidative versions based on C-H activation, heteroatom alkylation/arylation and annulation processes, in which aspects such as chemoselectivity and diversity generation at the ring-closing moiety became dominant over the last years. The transit from early cycloadditions and alkyne couplings as ring-closing steps to very recent 3d metal-catalyzed macrocyclization methods is highlighted. Similarly, the new trends in decarboxylative radical macrocyclizations and the interplay between photoredox and transition metal catalysis are included. This review charts future perspectives in the field hoping to encourage further progress and applications, while bringing attention to the countless possibilities available by diversifying not only the metal, but also the reactivity modes and tactics to bring peptide functional groups together and produce structurally diverse macrocycles.

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.

Synthesis of bisarylethyne–peptide conjugates

Convenient preparation of bisarylethyne–peptide conjugates, and a mild procedure for the H- or D-reduction of the bisarylethyne triple bond.

Design and synthesis of anti-cancer cyclopeptides containing triazole skeleton

We describe the design and synthesis of some hypothetical heptapeptides specifically to overcome the neoplastic activity of ras oncogene and their anti-cancer activities were studied. To improve the anti-cancer activity of the synthesized peptides, their structure modifications were done based on a sequential Ugi/Huisgen 1,3-Dipolar cyclization reaction. The cyclopeptides which contained triazole skeleton showed significant anti-cancer activity against cancer cells with mutated ras oncogene such as A549, PC3 and C26 cells. This study clearly shows the importance of triazole skeleton in biological activity of the peptides. It might be possible to overcome the difficulties involved in making complex peptides by employing this elegant chemistry.

Cu(I)- and Ru(II)-mediated "click" cyclization of tripeptides toward vancomycin-inspired mimics

Structural mimics comprising 1,4- and 1,5-disubstituted triazole-containing cyclic tripeptides with excellent resemblance toward the DE-ring of vancomycin are conveniently accessible using Cu(I)- or Ru(II)-assisted "click" cyclization.

Sequence-Dependent Binding of Dipeptides by an Artificial Receptor in Water

An artificial dipeptide receptor (1) was designed and observed to bind the deprotonated dipeptide Ac-D-Ala-D-Ala-OH in buffered water with K = 33,100 M(-1), whereas other dipeptides such as Ac-Gly-Gly-OH or Ac-D-Val-D-Val-OH were bound less efficiently, by factors of more than 10 (K < 3000 M(-1)). The efficient binding and the pronounced sequence selectivity are the result of a combination of strong electrostatic contacts and size-discriminating hydrophobic interactions. To provide such a combination, a guanidiniocarbonylpyrrole cation was attached to a novel cyclotribenzylene-substituted alanine derivative 5, to provide a hydrophobic bowl-shaped cavity just large enough to bind a methyl group but not any larger alkyl chains, thus causing the receptor to prefer alanine to valine. We describe the synthesis of 1 and the evaluation of its complexation properties in UV and fluorescence titration studies.