Elevated levels of activated protein kinase B (PKB/Akt) have been detected in many types of cancer. Substrate-based peptide inhibitors have the advantage of selectivity due to their extensive interactions with the kinase-specific substrate binding site but often lack necessary pharmacological properties. Chemical modifications of potent peptide inhibitors, such as cyclization, may overcome these drawbacks while maintaining potency. We present an extensive structure-activity relationship (SAR) study of a potent peptide-based PKB/Akt inhibitor. Two backbone cyclic (BC) peptide libraries with varying modes of cyclization, bridge chemistry, and ring size were synthesized and evaluated for in vitro PKB/Akt inhibition. Backbone-to-backbone urea BC peptides were more potent than N-terminus-to-backbone amide BC peptides. Several analogues were up to 10-fold more active than the parent linear peptide. Some activity trends could be rationalized using computational surface mapping of the PKB/Akt kinase catalytic domain. The novel molecules have enhanced pharmacological properties which make them promising lead candidates.

 

Restricting linear peptides to their bioactive conformation is an attractive way of improving their stability and activity. We used a cyclic peptide library with conformational diversity for selecting an active and stable peptide that mimics the structure and activity of the HIV-1 integrase (IN) binding loop from its cellular cofactor LEDGF/p75 (residues 361-370). All peptides in the library had the same primary sequence, and differed only in their conformation. Library screening revealed that the ring size and linker structure had a huge effect on the conformation, binding and activity of the peptides. One of the cyclic peptides, c(MZ 4-1), was a potent and stable inhibitor of IN activity in vitro and in cells even after 8 days. The NMR structure of c(MZ 4-1) showed that it obtains a bioactive conformation that is similar to the parent site in LEDGF/p75. (C) 2010 Elsevier Ltd. All rights reserved.

Cyclization of bioactive peptides, utilizing functional groups serving as natural pharmacophors, is often accompanied with loss of activity. The backbone cyclization approach was developed to overcome this limitation and enhance pharmacological properties. Backbone cyclic peptides are prepared by the incorporation of special building units, capable of forming amide, disulfide and coordinative bonds. Urea bridge is often used for the preparation of cyclic peptides by connecting two amine functionalized side chains. Here we present urea backbone cyclization as an additional method for the preparation of backbone cyclic peptide libraries. A straightforward method for the synthesis of crystalline Fmoc-N-alpha [omega-amino(Alloc)-alkyl] glycine building units is presented. A set of urea backbone cyclic Glycogen Synthase Kinase 3 analogs was prepared and assessed for protein kinase B inhibition as anticancer leads. Copyright (C) 2010 European Peptide Society and John Wiley & Sons, Ltd.

Rational conversion of noncontinuous active regions of proteins into a small orally bioavailable molecule is crucial for the discovery of new drugs based on inhibition of protein-protein interactions. We developed a method that utilizes backbone cyclization as an intermediate step for conversion of the CD4 noncontinuous active region into small macrocyclic molecules. We demonstrate that this method is feasible by preparing small inhibitor for human immunodeficiency virus infection. The lead compound, CG-1, proved orally available in the rat model. (C) 2010 Elsevier Ltd. All rights reserved.

Hydrazine derivatives are of considerable scientific and industrial value. Substituted hydrazines are precursors for many compounds of great interest and importance, among them aza-peptides. (Aza-peptides are peptide analogues in which one or more of the of alpha-carbons, bearing the side chain residues, has been replaced by a nitrogen atom.) Aza-amino acid residues conserve the pharmacophores necessary for biological activity while inducing conformational changes and increased resistance to proteolytic degradation. These properties make aza-peptides attractive tools for structure-activity relationship studies and drug design. We describe the synthesis of N'-substituted 2-(3,5-dimethoxyphenyl)propan-2-yloxycarbonyl (Ddz) protected hydrazines. A general approach for solid phase synthesis of aza-peptides has been developed based oil the in-situ activation of the N-Ddz,N'-substituted hydrazines with phosgene, followed by introduction to the N-terminus of a resin-bound peptide. The Ddz-aza-amino building units include aliphatic, aromatic and functionalized side chains, protected for synthesis by the Fmoc strategy. Solid phase aza-peptide synthesis is demonstrated including selective mild deprotection of Ddz with Mg(ClO4)(2) and coupling of the next amino acid with triphosgene. Ddz deprotection is orthogonal with the Fmoc and Boc protecting groups, making the solid phase Ddz-aza-peptide synthesis compatible with both the Fmoc and the Boc strategies. The Ddz-protected hydrazines have wide applications in the synthesis of substituted hydrazines and in the synthesis of aza containing peptidomimetics. (c) 2008 Elsevier Ltd. All rights reserved.

Cyclic ureas have interesting pharmacological properties that have led to their use as analogs of bioactive compounds. Several synthetic routes for urea formation by cyclization of diamines are known, based on the nucleophilic reaction of the amines with phosgene or phosgene derivatives. We have developed a procedure for a triphosgene mediated, on-resin urea cyclization. Four novel urea macrocyclic molecules were synthesized in order to demonstrate the feasibility of this method.