Patrick Perlmutter

β-Amino Acids: Versatile Peptidomimetics

The use of peptidomimetics has emerged as a powerful means for overcoming the limitations inherent in the physical characteristics of peptides thus improving their therapeutic potential. A peptidomimetic approach that has emerged in recent years with significant potential, is the use of β-amino acids. β-Amino acids are similar to α-amino acids in that they contain an amino terminus and a carboxyl terminus. However, in β-amino acids two carbon atoms separate these functional termini. β-amino acids, with a specific side chain, can exist as the R or S isomers at either the α (C2) carbon or the β (C3) carbon. This results in a total of 4 possible diastereoisomers for any given side chain. The flexibility to generate a vast range of stereo- and regioisomers, together with the possibility of disubstitution, significantly expands the structural diversity of β-amino acids thereby providing enormous scope for molecular design. The incorporation of β-amino acids has been successful in creating peptidomimetics that not only have potent biological activity, but are also resistant to proteolysis. This article reviews the rapidly expanding applications of β-amino acids in the design of bioactive peptide analogues ranging from receptor agonists and antagonists, MHC-binding peptides, antimicrobial peptides and peptidase inhibitors. Given their structural diversity taken together with the ease of synthesis and incorporation into peptide sequences using standard solid-phase peptide synthesis techniques, β-amino acids have the potential to form a new platform technology for peptidomimetic design and synthesis.

T Cell Determinants Incorporating β-Amino Acid Residues Are Protease Resistant and Remain Immunogenic In Vivo

A major hurdle in designing successful epitope-based vaccines resides in the delivery, stability, and immunogenicity of the peptide immunogen. The short-lived nature of unmodified peptide-based vaccines in vivo limits their therapeutic application in the immunotherapy of cancers and chronic viral infections as well as their use in generating prophylactic immunity. The incorporation of β-amino acids into peptides decreases proteolysis, yet its potential application in the rational design of T cell mimotopes is poorly understood. To address this, we have replaced each residue of the SIINFEKL epitope individually with the corresponding β-amino acid and examined the resultant efficacy of these mimotopes. Some analogs displayed similar MHC binding and superior protease stability compared with the native epitope. Importantly, these analogs were able to generate cross-reactive CTLs in vivo that were capable of lysing tumor cells that expressed the unmodified epitope as a surrogate tumor Ag. Structural analysis of peptides in which anchor residues were substituted with β-amino acids revealed the basis for enhanced MHC binding and retention of immunogenicity observed for these analogs and paves the way for future vaccine design using β-amino acids. We conclude that the rational incorporation of β-amino acids into T cell determinants is a powerful alternative to the traditional homologous substitution of randomly chosen naturally occurring α-amino acids, and these mimotopes may prove particularly useful for inclusion in epitope-based vaccines.

A simple synthesis of 2-methylidene-3-aminopropanoates

Abstract Coupling of ethyl acrylate to N-(para-toluenesulphonyl)imines of aromatic aldehydes is readily achieved using 1,4-diazabicyclo[2.2.2]octane as catalyst.

β-Amino acid-containing hybrid peptides—new opportunities in peptidomimetics

Hybrid peptides consisting of alpha-amino acids with judiciously placed beta-amino acids show great promise as peptidomimetics in an increasing range of therapeutic applications. This reflects a combination of increased stability, high specificity and relative ease of synthesis.

Epitope Discovery and Their Use in Peptide Based Vaccines

With recent advances in the design and delivery of peptide-based therapeutics there has been a growing interest on the use of peptides in vaccine design. Moreover, functional dissection and proteomic analysis of the immunogenic epitopes of proteins from pathogenic micro-organisms, cancers and self-tissues targeted by autoimmune responses, have broadened the range of target epitopes and given clues to enhancing peptide immunogenicity. Consistent with these observations; peptides can be synthesised with defined chemical modifications to mimic natural epitopes and/or deliberately introduce protease resistant peptide bonds to regulate their processing independent of tissue specific proteolysis and to stabilize these compounds in vivo. We discuss the potential of peptide-based vaccines for the treatment of chronic viral diseases and cancer and review recent developments in the field of epitope discovery and peptide-based vaccines.

Diastereoselection in the nucleophilic conjugate addition of amines to 2-hydroxyalkylpropenoates

Abstract Nucleophilic conjugate addition of benzylamine to 2-hydroxyalkylpropenoates 1a-c proceeds in high yield with modest diastereoselection. However, addition of benzylamine to the silyl ether of 1c produces only the anti-isomer 2d in high yield.

The stereochemistry of organometallic compounds: XXXVI. Regio- and stereo-chemical control in the nickel-catalysed hydrocyanation of silylalkynes

Abstract The regioselectivity of hydrocyanation of silylalkynes can be controlled by varying the size of the groups attached to silicon leading, for example, to efficient preparations of E -3-trialkylsilyl-2-alkyl-2-alkenenitriles. High yields of the silylalkene nitriles can be obtained by using either acetone cyanohydrin or hydrogen cyanide as reagents.

A Single β-Amino Acid Substitution to Angiotensin II Confers AT 2 Receptor Selectivity and Vascular Function

Novel AT2R ligands were designed by substituting individual &bgr;-amino acid in the sequence of the native ligand angiotensin II (Ang II). Relative ATR selectivity and functional vascular assays (in vitro AT2R-mediated vasorelaxation and in vivo vasodepressor action) were determined. In competition binding experiments using either AT1R- or AT2R- transfected HEK-293 cells, only &bgr;-Asp1-Ang II and Ang II fully displaced [125I]-Ang II from AT1R. In contrast, &bgr;-substitutions at each position of Ang II exhibited AT2R affinity, with &bgr;-Tyr4-Ang II and &bgr;-Ile5-Ang II exhibiting ≈1000-fold AT2R selectivity. In mouse aortic rings, &bgr;-Tyr4-Ang II and &bgr;-Ile5-Ang II evoked vasorelaxation that was sensitive to blockade by the AT2R antagonist PD123319 and the nitric oxide synthase inhibitor L-NAME. When tested with a low level of AT1R blockade, &bgr;-Ile5-Ang II (15 pmol/kg per minute IV for 4 hours) reduced blood pressure (BP) in conscious spontaneously hypertensive rats (&bgr;-Ile5-Ang II plus candesartan, −24±4 mm Hg) to a greater extent than candesartan alone (−11±3 mm Hg, n=7, P<0.05), an effect that was abolished by concomitant PD123319 infusion. However, in an identical experimental protocol, &bgr;-Tyr4-Ang II had no influence on BP (n=10), and it was less stable than &bgr;-Ile5-Ang II in plasma stability assays. Thus, this study demonstrated that a single &bgr;-amino acid substitution resulted in a compound that demonstrated both in vitro vasorelaxation and in vivo depressor activity via AT2R. This approach to the design and synthesis of novel AT2R-selective peptidomimetics shows great potential to provide insight into AT2R function.

Synthesis of a ring F building block for the ciguatoxins

The preparation of a new ring F building block for the marine polyether toxins, the ciguatoxins, employing ascorbic acid as a chiral pool starting material, is reported.

Synthesis of Stapled β3-Peptides through Ring-Closing Metathesis

The first synthesis of carbon-stapled beta(3)-peptides is reported. The precursor beta(3)-peptides, with O-allyl beta-serines located in an i/i+3 relationship, were prepared on solid phase. We show that efficient ring-closing metathesis (RCM) of these new beta(3)-peptides proceeds smoothly either in solution or on an appropriate solid support. All products were generated with high selectivity for the E-isomer.