Strategies for the Solid-Phase Diversification of Poly-l-proline-Type II Peptide Mimic Scaffolds and Peptide Scaffolds Through Guanidinylation

Amino acids/peptides conjugated heterocycles: A tool for the recent development of novel therapeutic agents

Amino acids/peptide conjugated heterocycles represent an important class of therapeutical agents. Biologically active heterocycles are conjugated with amino acids or peptides to increase the drug resistance. Furthermore, the amino acid/peptide based drugs have low toxicity, ample bioavailability and permeability, modest potency and good metabolic and pharmacokinetic properties. Synthetic amino acid/peptides based heterocyclic conjugates constitute a promising choice for the development of new, less toxic and safer conventional pharmaceutical drugs in the near future. In this review, we discuss and highlight the recent findings of the structural features that encourage biological applications of amino acid/peptides based conjugates.

Synthesis and conformational analysis of peptides embodying 2,3-methanopipecolic acids

When 2,3-methanopipecolic acids replace a proline in peptides, a marked preference (42–92%) for thecisgeometry around the pipecolic amide bond is observed in both water and organic solvents.

Uncatalysed diaryldiazo cyclopropanations on bicyclic lactams: access to annulated prolines

The uncatalysed cycloaddition of substituted diaryldiazo compounds onto bicyclic unsaturated lactams derived from pyroglutamic acid efficiently leads to highly functionalised azatricyclononanes.

Synthesis and evaluation of a (3R,6S,9S)-2-oxo-1-azabicyclo[4.3.0]nonane scaffold as a mimic of Xaa-trans-Pro in poly-l-proline type II helix conformation

Stereoselective synthesis of a (3R,6S,9S)-2-oxo-1-azabicyclo[4.3.0]nonane mimic of Xaa-trans-Pro in poly-l-proline type II helix conformation is reported.

A convenient solid-phase strategy for the synthesis of antimicrobial cyclic lipopeptides

A concise solid-phase synthesis of cyclic lipopeptides derived from the antimicrobial peptide c(Lys-Lys-Leu-Lys-Lys-Phe-Lys-Lys-Leu-Gln) (BPC194) was accomplished. Three different synthetic routes were explored. Best results were obtained using a protocol that includes as key steps: (i) synthesis of the cyclic peptidyl resin incorporating the Lys residue to be acylated protected at the N(ε)-amino group with an ivDde group, (ii) selective removal of the ivDde group, and (iii) acylation. These compounds were screened for their in vitro growth inhibition of bacterial and fungal phytopathogens and for their cytotoxic effects on eukaryotic cells. A sequence with high antimicrobial activity and low hemolysis was identified, constituting a good candidate for the design of new antimicrobial agents.

Synthesis and antibacterial evaluation of amino acid-antibiotic conjugates

Amino acid conjugates of quinolone, metronidazole and sulfadiazine antibiotics were synthesized in good yields using benzotriazole methodology. All the conjugates were screened for their antibacterial activity using methods adapted from the Clinical and Laboratory Standards Institute. Antibiotic conjugates were tested for activity in four medically relevant organisms; Staphylococcus aureus (RN4220), Escherichia coli (DH5α), Pseudomonas aeruginosa (PAO1), and Bacillus subtilis (168). Several antibiotic conjugates show promising results against several of the strains screened.

Synthesis of uriedo and thiouriedo derivatives of peptide conjugated heterocycles - A new class of promising antimicrobials

Forty five new derivatives of ureas and thioureas were synthesized by the reaction of peptide conjugated heterocycles with isocyanates and isothiocyanates respectively. All the compounds have been characterized by IR, (1)H NMR, mass and elemental analysis. The compounds were evaluated for their ability to inhibit the growth of a panel of microorganisms and all the synthesized compounds displayed an excellent antimicrobial activity. From structure-activity relationship studies, it was apparent that thioureas infact is slightly more active than ureas. Also, substituents on the phenyl ring of the title compounds play a key role in the activity. Further, compound 40 is nearly twenty times more potent than the standard used. These results present a platform for the further studies in this line.

On-resin synthesis of novel arginine-isostere peptides bearing substituted amidine headgroups

A methodology is presented for the facile synthesis of Arg-containing peptides modified at the guanidine headgroup as substituted amidine cores. This process allows for the iterative construction of these Arg isosteres while the peptide is being built out on the solid support, providing a high potential for diversity in substitution pattern in the resulting peptide. A series of N-Pmc-substituted thioamides were condensed with deprotected δ-N Orn-bearing peptides while attached to the solid support using Mukaiyama's reagent as coupling reagent, yielding isosteric Arg-containing analogs. Peptides were cleaved using trimethylsilyl trifluoromethanesulfonate/TFA and analyzed in their crude form in order to illustrate the amenability of this process toward production of peptide isolates in high crude purity. Arg-containing peptides having a single Arg isostere were utilized to show the general utility of this approach as well as a multiple-Arg-containing construct, illustrating the amenability of this method toward stepwise construction of differently substituted amidine headgroups within the same peptide.

Application of ring-closing metathesis to Grb2 SH3 domain-binding peptides

Molecular processes depending on protein–protein interactions can use consensus recognition sequences that possess defined secondary structures. Left-handed polyproline II (PPII) helices are a class of secondary structure commonly involved with cellular signal transduction. However, unlike -helices, for which a substantial body of work exists regarding applications of ring-closing metathesis (RCM), there are few reports on the stabilization of PPII helices by RCM methodologies. The current study examined the effects of RCM macrocyclization on left-handed PPII helices involved with the SH3 domain-mediated binding of Sos1–Grb2. Starting with the Sos1-derived peptide “Ac-V1-P2-P3-P4-V5-P6-P7-R8-R9-R10-amide,” RCM macrocyclizations were conducted using alkenyl chains of varying lengths originating from the pyrrolidine rings of the Pro4 and Pro7 residues. The resulting macrocyclic peptides showed increased helicity as indicated by circular dichroism and enhanced abilities to block Grb2–Sos1 interactions in cell lysate pull-down assays. The synthetic approach may be useful in RCM macrocyclizations, where maintenance of proline integrity at both ring junctures is desired.