Peptides containing 4-amino-1,2-dithiolane-4-carboxylic acid (Adt): conformation of Boc-Adt-Adt-NHMe and NH...S interactions

Asparagusic Acid - A Unique Approach toward Effective Cellular Uptake of Therapeutics: Application, Biological Targets, and Chemical Properties

The synthetic approaches towards unique asparagusic acid and its analogues as well as its chemical use, the breadth of its biological properties and their relevant applications have been explored. The significance of the 1,2-dithiolane ring tension in dithiol-mediated uptake and its use for the intracellular transport of molecular cargoes is discussed alongside some of the challenges that arise from the fast thiolate-disulfide interchange. The short overview with the indication of the available literature on natural 1,2-dithiolanes synthesis and biological activities is also included. The general review structure is based on the time-line perspective of the application of asparagusic acid moiety as well as its primitive derivatives (4-amino-1,2-dithiolane-4-carboxylic acid and 4-methyl-1,2-dithiolane-4-carboxilic acid) used in clinics/cosmetics, focusing on the recent research in this area and including international patents applications.

Peptide flatlandia: a new-concept peptide for positioning of electroactive probes in proximity to a metal surface

A helical hexapeptide was designed to link in a rigid parallel orientation to a gold surface. The peptide sequence of the newly synthesized compound is characterized by the presence of two 4-amino-1,2-dithiolane-4-carboxylic acid (Adt) residues (positions 1 and 4) to promote a bidentate interaction with the gold surface, two L-Ala residues (positions 2 and 5) and two-aminoisobutyric acid (Aib) residues (positions 3 and 6) to favor a high population of the 310-helix conformation. Furthermore, a ferrocenoyl (Fc) probe was inserted at the N-terminus to investigate the electronic conduction properties of the peptide. X-Ray photoelectron spectroscopy and scanning tunneling microscopy techniques were used to characterize the binding of the peptide to the gold surface and the morphology of the peptide layer, respectively. Several electrochemical (cyclic voltammetry, chronoamperometry, square wave voltammetry) techniques were applied to analyze the electrochemical activity of the Fc probe, along with the influence of the peptide 3D-structure and the peptide layer morphology on electron transfer processes.

Synthesis and bioactivity of secondary metabolites from marine sponges containing dibrominated indolic systems

Marine sponges. (e.g., Hyrtios sp., Dragmacidin sp., Aglophenia pleuma, Aplidium cyaneum, Aplidium meridianum.) produce bioactive secondary metabolites involved in their defence mechanisms. Recently it was demonstrated that several of those compounds show a large variety of biological activities against different human diseases with possible applications in medicinal chemistry and in pharmaceutical fields, especially related to the new drug development process. Researchers have focused their attention principally on secondary metabolites with anti-cancer and cytotoxic activities. A common target for these molecules is the cytoskeleton, which has a central role in cellular proliferation, motility, and profusion involved in the metastatic process associate with tumors. In particular, many substances containing brominated indolic rings such as 5,6-dibromotryptamine, 5,6-dibromo-N-methyltryptamine, 5,6-dibromo-N-methyltryptophan (dibromoabrine), 5,6-dibromo-N,N-dimethyltryptamine and 5,6-dibromo-L-hypaphorine isolated from different marine sources, have shown anti-cancer activity, as well as antibiotic and anti-inflammatory properties. Considering the structural correlation between endogenous monoamine serotonin with marine indolic alkaloids 5,6-dibromoabrine and 5,6-dibromotryptamine, a potential use of some dibrominated indolic metabolites in the treatment of depression-related pathologies has also been hypothesized. Due to the potential applications in the treatment of various diseases and the increasing demand of these compounds for biological assays and the difficult of their isolation from marine sources, we report in this review a series of recent syntheses of marine dibrominated indole-containing products.

The cis-4-amino-L-proline residue as a scaffold for the synthesis of cyclic and linear endomorphin-2 analogues

Endomorphin-2 (EM-2: Tyr-Pro-Phe-Phe-NH(2)) is an endogenous tetrapeptide that combines potency and efficacy with high affinity and selectivity toward the μ opioid receptor, the most responsible for analgesic effects in the central nervous system. The presence of the Pro(2) represents a crucial factor for the ligand structural and conformational properties. Proline is in fact an efficient stereochemical spacer, capable of inducing favorable spatial orientation of aromatic rings, a key factor for ligand recognition and interaction with receptors. Here the Pro(2) has been replaced by 4(S)-NH(2)-2(S)-proline (cAmp), a proline/GABA cis-chimera residue. This bivalent amino acid maintains the capacity to influenc the tetrapeptide conformation and offers the opportunity to generate new linear models and unusually constrained cyclic analogues characterized by an N-terminal Tyr bearing a free α-amino group. The results indicate that the new analogues do not show affinity for both δ and κ opioid receptors and bind only poorly to the μ receptors (for cyclopeptide 9: K(i)(μ) = 660 nM; GPI (IC(50)) = 1.4% at 1 μM; for linear tetrapeptide acid 13: K(i)(μ) = 2000 nM; GPI (IC(50)) = 0% at 1 μM; for linear tetrapeptide amide 15: K(i)(μ) = 310 nM; GPI (IC(50)) = 894 nM).

Conformationally constrained histidines in the design of peptidomimetics: strategies for the χ-space control

A successful design of peptidomimetics must come to terms with χ-space control. The incorporation of χ-space constrained amino acids into bioactive peptides renders the χ¹ and χ² torsional angles of pharmacophore amino acids critical for activity and selectivity as with other relevant structural features of the template. This review describes histidine analogues characterized by replacement of native α and/or β-hydrogen atoms with alkyl substituents as well as analogues with α, β-didehydro unsaturation or C^α-C^β cyclopropane insertion (ACC derivatives). Attention is also dedicated to the relevant field of β-aminoacid chemistry by describing the synthesis of β²- and β³-models (β-hHis). Structural modifications leading to cyclic imino derivatives such as spinacine, aza-histidine and analogues with shortening or elongation of the native side chain (nor-histidine and homo-histidine, respectively) are also described. Examples of the use of the described analogues to replace native histidine in bioactive peptides are also given.