Synthesis of porcine brain natriuretic peptide-32 using silver tetrafluoroborate as a new deprotecting reagent of the S-trimethylacetamidomethyl group

Silver tetrafluoroborate (AgBF4) in trifluoroacetic acid (TFA) has been found to cleave the S-trimethylacetamidomethyl (Tacm) group or the S-acetamidomethyl (Acm) group without affecting other functional groups in the peptide chain. Newly isolated porcine brain natriuretic peptide-32 (pBNP-32) was synthesized using AgBF4 and Cys(Tacm) derivatives. The synthetic pBNP-32 had the highest chick rectum relaxant activity among the ANP-BNP families.     

Solution-phase synthesis of porcine brain natriuretic peptide (pBNP) using S-trimethylacetamidomethylcysteine

The hexadodecapeptide corresponding to the entire amino acid sequence of porcine brain natriuretic peptide (pBNP) was synthesized by assembling four segments in solution, followed by HF deprotection and subsequent oxidation to establish an intramolecular disulfide bridge. The synthesis using the newly developed S-trimethylacetamidomethylcysteine [Cys(Tacm)] derivative gave a better yield than that using the S-2,4,6-trimethylbenzylcysteine [Cys(Tmb)] derivative. The chick rectum relaxant activity of the synthetic pBNP was 2.9 times more potent than that of alpha-rat atrial natriuretic peptide (alpha-rANP).     

The N-hydroxymethyl group for stereoselective conjugate addition: application to the synthesis of (-)-statine

[reaction: see text] Efficient synthesis of enantiomerically pure (-)-statine was achieved with the stereoselective intramolecular conjugate addition of the hydroxyl group tethered to the amino group of a configurationally stable N-Boc-L-leucinal derivative.     

Green synthesis of silver nanoparticles using green alga (Chlorella vulgaris) and its application for synthesis of quinolines derivatives

Nanoparticles have been used century ago but have regained their importance in recent years being simple, ecofriendly, pollutant free, nontoxic, low-cost approach, and due good atom economy. In this report, we have demonstrated the synthesis of silver nanoparticles using green algae (Chlorella vulgaris) which in turn was used for synthesis of biologically important quinolines. Algal extract was prepared and treated with silver nitrate solution for the synthesis of silver nanoparticles. Synthesized nanoparticles were characterized with the help of analytical tools like UV, FTIR, X-ray, and SEM and used as a catalyst for the synthesis of quinolines.     

Stereoselective synthesis of pyridinones: application to the synthesis of (-)-barrenazines

[reaction: see text] The stereoselective synthesis of pyridinones was accomplished by the nucleophilic addition of Grignard reagents to a chiral pyridinium salt derived from 4-methoxypyridine. This methodology was applied to an expedient synthesis of (-)-barrenazine A and B. After N-functionalization and 1,4-reduction of the pyridinone system, the corresponding alpha-amino piperidinones readily undergo dimerization to give the hexahydrodipyridinopyrazine skeleton of the barrenazine alkaloids.     

Solid-phase peptide synthesis in water. Part 3: A water-soluble N-protecting group, 2-[phenyl(methyl)sulfonio]ethoxycarbonyl tetrafluoroborate, and its application to solid phase peptide synthesis in water

Chemical synthesis of peptides has been performed in various organic solvents, but the safe disposal of organic solvents is now an important environmental issue. Our aim is to be able to perform solid-phase peptide synthesis in water. For this, we have designed a new water-soluble N-protecting group, 2-[phenyl(methyl)sulfonio]ethoxycarbonyl (Pms), and have studied its introduction onto amino acids. Pms-amino acids were prepared by treating 2-(phenylthio)ethoxycarbonyl amino acids with methyl iodide in the presence of silver tetrafluoroborate. Because sulfur-containing amino acids, such as Met and Cys, were modified by the reaction, we designed a new reagent, 2-[phenyl(methyl)sulfonio]ethyl-4-nitrophenyl carbonate, to introduce the Pms group on amino acids. This reagent is a stable crystalline material and its introduction onto amino acids (including sulfur-containing amino acids) was successful. The solid-phase synthesis of Leu- and Met-enkephalin amides using Pms-protected amino acids was successfully achieved in water.     

The application of 2-(4-chlorophenyl)-sulfonylethoxycarbonyl (CPSEC) group in the synthesis of a DNA segment using the phosphotriester approach

The new base labile CPSEC group has been successfully employed for the protection of the 5′-hydroxyl function to synthesize a “universal Stop codon” DNA sequence: ^5′d(TCAATCAATCA)^3′.     

Synthesis of novel linear exo-bidentate bispyridine ligands and their complexes with silver(i) tetrafluoroborate

Novel exo-bidentate ligands containing two -pyridyl fragments and their complexes with silver(i) tetrafluoroborate were synthesized.     

Studies on the synthesis of (-)-spinosyn a: application of the steric directing group strategy to transannular Diels-Alder reactions

A highly diastereoselective and enantioselective synthesis of the decahydro-as-indacene nucleus 12 of (-)-spinosyn A (1) is reported. By implementing the steric directing group strategy, tricyclic lactone 37 was produced from a remarkably diastereoselective transannular Diels-Alder reaction of lactone 9. The tricyclic core of the natural product was then obtained by using an Ireland-Claisen ring contraction of 37. Reversal of the order of these two steps resulted in an almost complete loss of diastereoselectivity.     

Biomimetic synthesis of silver nanoparticles using Syzygium aromaticum (clove) extract: Catalytic and antimicrobial effects

In the current work, we followed a green chemistry route to prepare and characterize the silver nanoparticles (AgNPs) using Syzygium aromaticum (clove) extract at room temperature. Suitably, the clove extract acted as a reducing agent as well as a capping agent, and these reactions occurred rapidly. The formation of the AgNPs was confirmed by the observation of the distinct absorption peak at a wavelength of 418 nm using ultraviolet–visible (UV–Vis) spectroscopy, and a morphological study confirmed the uniform distribution of the optimally spherical nanoparticles. Fourier transform infrared spectroscopy (FTIR) results indicated the methoxy and allyl functional groups of eugenol of the clove extract to be responsible for the bioreduction of silver ions and for the stabilization of the resulting nanoparticles (flavonoids). We also found the AgNPs to be effective catalysts of the degradation of three pollutant organic dyes viz., 4‐nitrophenol, methylene blue and rhodamine B, in the presence of excess NaBH₄. The antibacterial and antifungal activities of the bio‐synthesized AgNPs were also explored. Overall, the results suggested the potential use of clove extract as a resource for the synthesis of AgNPs having a broad range of possible commercial and biomedical applications.     

Wire-coated silver(I) ion-selective electrode based on 2-mercaptobenzothiazole (MBT) ionophore: application to the determination of silver in real samples.

A new wire-coated silver ion-selective electrode with a wider concentration range (10(-7) M - 10(-1) M) was developed using 2-mercaptobenzothiazole (MBT) as a neutral ionophore. An optimum mixture of PVC, ionophore, dioctylphtalate (DOP) as a plasticizer and sodium tetraphenylborate (NaTPB) as an ion-pairing agent was used in preparing the coatings. The effect of various parameters, such as the electrode bed nature, coating composition and solution pH, on the efficiency of the electrode is described. It has been shown that platinum acts as a more suitable bed for electrode preparation, and exhibits a slope of 59.5 +/- 1 mV over the whole range of studied concentrations. The selectivity coefficient of the electrode towards various interfering cations as well as its reproducibility, response time and lifetime of the electrode were estimated. The developed electrode was successfully used for the determination of trace amounts of silver in human hair and photographic waste as real samples and in the potentiometric titration of halides as an indicator electrode.     

A general method for one-step synthesis of monofluoroiodane(III) reagents using silver difluoride

Herein we report a new general method for one-step synthesis of four kinds of fluoroiodane(III) reagents by treating the corresponding aryl iodides with silver difluoride (AgF₂). This is the first method applicable for the synthesis of all four fluoroiodane(III) reagents including p-iodotoluene difluoride (1), fluoro-benziodoxole (2), fluoro-benziodoxolone (3), and fluoro-N-acetylbenziodazole (4). AgF₂ was firstly employed in the direct oxidative fluorination of iodobenzene and thus has shown its outstanding oxidation and fluorine-transfer ability. The use of AgF₂ has improved the synthesis of fluoroiodane(III) reagents by shortening the reaction steps, avoiding the use of hazardous reagents, and simplifying the experimental operations. It was worth noting that we have developed the first one-step direct synthetic method for 3, while 3 can only be synthesized through Cl→F ligand exchange reaction previously.     

Solution-phase synthesis of alpha-rat atrial natriuretic peptide (alpha-rANP)

alpha-Rat atrial natriuretic peptide (alpha-rANP) was synthesized by assembling five peptide fragments in solution, followed by HF-dimethylselenide-m-cresol deprotection and subsequent air-oxidation. Synthetic alpha-rANP exhibited more potent diuretic and natriuretic activity in rats than synthetic alpha-hANP.     

A novel synthesis of substituted quinolines using ring-closing metathesis (RCM): its application to the synthesis of key intermediates for anti-malarial agents

A method for synthesizing substituted quinolines using ruthenium-catalyzed ring-closing metathesis as a key step has been developed. Substituted 1,2-dihydroquinolines, 4-silyloxy-1,2-dihydroquinoline and 4-methoxy-1,2-dihydroquinoline, were successfully synthesized in excellent yields via ene-ene metathesis and silyl or alkyl enol ether-ene metathesis, respectively. The synthetic intermediates of the antimalarial agents quinine, chloroquine, and PPMP-quinine hybrid were efficiently synthesized by this methodology.     

Solution-phase synthesis of alpha-human atrial natriuretic peptide (alpha-hANP)

Alpha-human atrial natriuretic peptide (alpha-hANP) was synthesized by assembling six peptide fragments in solution followed by deprotection with HF and subsequent air-oxidation. The trimethylbenzyl group was employed as an S-protecting group of cysteine. The HF-dimethylselenide-m-cresol system was employed as a final deprotecting reagent and, at the same time, as a reducing reagent of Met(O). Synthetic alpha-hANP elicited potent diuretic and natriuretic activity in rats.     

Stereoselective synthesis of beta-(chloro)vinylsilanes using a regio- and (E)-stereoselective bis-stannylation of unsymmetrically substituted butadiynes: application to the synthesis of a masked triyne

[reaction: see text] A highly regio- and stereoselective bis-stannylation of unsymmetrically substituted butadiyne 3 provides bis-stannane 4. Selective lithiation of the internal tin residue effects a 1,4-retro-Brook rearrangement to afford vinylsilane 5. This was elaborated into the novel diethynylethene 1, which also functions as a masked triyne.     

Electrochemical synthesis of silver nanoparticles-coated gold nanoporous film electrode and its application to amperometric detection for trace Cr(VI)

A simple and rapid approach for the electrochemical synthesis of Ag nanoparticles-coated gold nanoporous film (AgGNF) on a gold substrate was reported. The solid gold electrode (SGE) was directly anodized under a high potential of 5 V, and then reduced to obtain gold nanoporous film (AuNF) by freshly prepared ascorbic acid. The Ag nanoparticles (AgNPs) were grown on the AuNF electrode by potential-step electrodeposition. The resulting AgGNF composites electrodes were characterized by scanning electron micro...