A mixed-α,β miniprotein stereochemically reprogrammed to high-binding affinity for acetylcholine

The protein-structure space is limited to L configuration in the asymmetric alpha-amino acid structures; the function space, on other hand, seems limitless because of the chemical diversity in the amino acid side chain structures. The chemical diversity in side chain structure may be multiplied beneficially with the stereochemical diversity in main chain structure; thus, de novo protein design may be explored for customizing molecular structures stereochemically and molecular functions chemically. Illustrating de novo design in the structure space of L and D alphabet, canonical all-beta folds of poly-L structure were reprogrammed as bracelet, boat, and canoe-shaped molecules-the "boat" as a receptor-like pocket and the "canoe" as a metal-ion receptor-simply by mutating specific L-amino acid residues to the corresponding D stereochemical structure. Demonstrating customization of molecular shape stereochemically and function chemically, a 15-residue mixed-alpha, beta miniprotein of canonical poly-L structure is now reprogrammed stereochemically as a cup-shaped receptor for acetylcholine via cation-pi interaction with a triad of aromatic side chains placed in mimicry of the acetylcholine-receptor sites both natural and artificial. Evidence from CD, fluorescence, NMR, DSC, ITC, MD, and molecular-docking studies is presented to show that a rationally designed 15-residue mixed-L, D peptide is a cooperatively ordered molecular fold in the stereochemically specified molecular morphology, submicromolar in affinity of acetylcholine and thus an acetylcholine receptor exceptionally small and simple. .

Synthesis of novel neutrophil-specific imaging agents for Positron Emission Tomography (PET) imaging

A neutrophil-specific peptide, cinnamoyl-F(D)LF(D)LFK (cFLFLFK), was conjugated consecutively with a polyethylene glycol moiety (3.4K) and 2,2',2'',2'''-(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)tetraacetic acid (DOTA) to form cFLFLFK-PEG-DOTA. After (64)Cu labeling, Positron Emission Tomography (PET) imaging was successfully able to detect mouse lung inflammation.

Synthesis of Novel N-Rich Polycyclic Skeletons Based on Azoles and Pyridines

An efficient method for the synthesis of new polycyclic skeletons: triaza-benzofluorenes and triaza-pentalenonaphthalene from bicyclic privileged structures imidazopyridine and imidazothiazole, respectively, has been described using the Pictet-Spengler cyclization.

A double catgrip mixed l and d mini protein only 20 residues long

Stereochemistry limits but also defines proteins, as conformational constructs stereospecific for poly-L structure. Employed as a variable in sequence, stereochemistry could make proteins customizable in the letters of L and D amino acid alphabet. In proof of concept, we previously demonstrated stereochemical reengineering of canonical beta-hairpins as bracelet and boat shaped molecules. Illustrating the prospect for functional design, a 20-residue four-stranded mini-beta protein is now customized stereochemically as a canoe shaped molecule. A conformational construct of four side by side hydrogen-bonded strands in alternately (l)beta, (d)beta conformation, joined via Type-II/II' beta-turns, is planned to be preponderantly apolar in beta-sheet favoring residues, interspersing two ion pairs, and suitably L and D in sequence. Synthesis followed by MD, NMR, CD, and MALDI-MS studies established the molecule as a canoe shaped fold in water, demonstrable in affinity of alkali and alkaline-earth metal ions as expected given its catgrip like elements. Another success in accomplishing a synthetic miniprotein complex in stereochemistry and stereospecific in conformation, exceptionally small yet functional in metal ion affinity, affirms the value in combined L and D alphabet in programming molecular shapes and functions stereochemically.

A novel dodecapeptide from a combinatorial synthetic library exhibits potent antifungal activity and synergy with standard antimycotic agents

There has been a marked expansion in the discovery of new antifungal peptides. This paper describes a novel dodecapeptide, H-Arg-Trp-Trp-Arg-D-Trp-D-Phe-Ile-D-Phe-His-Trp-Arg-Trp-NH(2), derived from a previously described nonapeptide and synthesized by the combinatorial approach. Further, interaction of this peptide with antifungals such as amphotericin B, flucytosine and fluconazole was studied by checkerboard analysis and time-kill assay to obtain the dynamic picture with respect to time. The best synergistic activity was observed with a combination of peptide and fluconazole, followed by peptide and flucytosine.

alpha-Amino acid derivatives as proton pump inhibitors and potent anti-ulcer agents

In a program to identify new anti-ulcer compounds, a series of N-acyl derivatives of alpha-amino acids were screened for their in vitro H(+)/K(+) ATPase inhibitory activity, and in vivo efficacy in Pylorus ligation model. 3D-QSAR studies were carried out and a representative compound 13 was studied for the nature of its proton pump inhibition.

Unprecedented SnCl2-Mediated Cyclization of Nitro Arenes via N−N Bond Formation†

[reaction: see text] A mild, efficient, one-pot protocol for the cyclization of nitro-aryl substrates using SnCl(2) has been described. The mechanistic course of the reaction suggests the involvement of a hydroxylamine intermediate leading to an intramolecular cyclization via N-N bond formation. The versatility of the methodology has been demonstrated by using two nitro-aryl substrates derived from dihydroisoquinolines and dihydro-beta-carbolines. The intramolecular cyclization led to the formation of indazoles in high yields and purities.

A modified strategy for Pictet-Spengler reaction leading to the synthesis of imidazoquinoxalines on solid phase

An alternative strategy for Pictet-Spengler reaction involving an N-1 linked aromatic amine of imidazole and aldehydes is described. This is in contrast to a typical Pictet-Spengler reaction, which involves an aliphatic amine attached to the carbon of an activated aromatic nucleus and an aldehyde. Our strategy commences with the nucleophilic replacement of fluorine in resin-bound o-fluoro-nitrobenzoic acid with mono- or disubstituted imidazole, followed by reduction of the nitro group to give an N1 linked aromatic amine of the resin-bound imidazole. This was subsequently treated with an aldehyde in toluene at 80 degrees C and then oxidized in the presence of DDQ to give resin-bound imidazoquinoxalines. Finally, acidolytic cleavage furnished the desired compounds in high yields and purities.

Solid-Phase Synthesis of 2-Aminoquinazolinone Derivatives with Two- and Three-Point Diversity

A versatile solid-phase method for the synthesis of various substituted 2-amino-4(3H)-quinazolinones with two- and three-point diversity is described. The synthesis commenced with the generation of polymer-bound S-methylisothiourea followed by N-acylation with different substituted o-nitrobenzoic acid. Finally, reduction of the nitro group triggered intramolecular cyclization via formation of guanidine to afford 2-amino-4(3H)-quinazolinone and its derivatives in high yields and purities.

Identification of a novel antifungal nonapeptide generated by combinatorial approach

It is becoming clear that antimicrobial peptides are important components of the innate defences of all species of life. They kill very rapidly, do not easily select resistant mutants and are synergistic with potentially toxic conventional therapeutic agents against microbes. This paper describes an attempt to expand a lead hexapeptide motif synthesized through combinatorial approach. A cationic peptide H-Arg-Trp-Trp-Arg-D-Trp-D-Phe-Ile-D-Phe-His-NH2 was found to be active with a therapeutic index of >17. I was proposed that the combination of peptide with known antifungal agents may identify synergistic combinations that would ideally reduce the dosage of conventional antifungals as well as their associated toxicity. Nine different pathogenic strains and species of Candida and two of Cryptococcus neoformans were employed in chequerboard method and in time kill assays to evaluate the synergistic effect of the lead peptide in combination with amphotericin B, 5-flucytosine, ketoconazole and fluconazole. We found synergistic interaction between the peptide and all four drugs against Cryptococcus isolates whilst both synergistic and additive combinations occurred when Candida isolates were used.

New Application of Pictet−Spengler Reaction Leading to the Synthesis of an Unusual Seven-Membered Heterocyclic Ring System

A novel strategy for the Pictet-Spengler reaction is reported. Our strategy involves reaction of arylamines, linked to the N-1 of disubstituted imidazoles, with aldehydes in the presence of p-TsOH. The iminium ion generated in situ undergoes C-C bond formation with the C-5 of the imidazoles to furnish triazabenzoazulenes as a novel heterosystem. Our strategy differs from conventional Pictet-Spengler reaction since the latter utilizes only aliphatic amines in which the amine functionality is linked to a C instead of N of the activated aromatic moiety.