Synthesis of Selenoxo Peptides and Oligoselenoxo Peptides Employing LiAlHSeH

Structure-Based Bioisosterism Design, Synthesis, Biological Evaluation and In Silico Studies of Benzamide Analogs as Potential Anthelmintics

A recent screen of 67,012 compounds identified a new family of compounds with excellent nematicidal activity: the ortho-substituted benzamide families Wact-11 and Wact-12. These compounds are active against Caenorhabditis elegans and parasitic nematodes by selectively inhibiting nematode complex II, and they display low toxicity in mammalian cells and vertebrate organisms. Although a big number of benzamides were tested against C. elegans in high-throughput screens, bioisosteres of the amide moiety were not represented in the chemical space examined. We thus identified an opportunity for the design, synthesis and evaluation of novel compounds, using bioisosteric replacements of the amide group present in benzamides. The compound Wact-11 was used as the reference scaffold to prepare a set of bioisosteres to be evaluated against C. elegans. Eight types of amide replacement were selected, including ester, thioamide, selenoamide, sulfonamide, alkyl thio- and oxo-amides, urea and triazole. The results allowed us to perform a structure-activity relationship, highlighting the relevance of the amide group for nematicide activity. Experimental evidence was complemented with in silico structural studies over a C. elegans complex II model as a molecular target of benzamides. Importantly, compound Wact-11 was active against the flatworm Echinococcus granulosus, suggesting a previously unreported pan-anthelmintic potential for benzamides.

Synthesis of an amino phosphinodiselenoic acid ester and β-amino diselenides employing P2Se5

Protic solvents furnished amino phosphinodiselenoic acid esters, whereas β-amino diselenides were obtained exclusively when reactions performed in polar aprotic solvents.

General, Mild, and Metal-Free Synthesis of Phenyl Selenoesters from Anhydrides and Their Use in Peptide Synthesis

A mild, practical, and simple procedure for phenyl selenoesters synthesis from several anhydrides and diphenyl diselenide was developed. This transition-metal-free method provides a straightforward entry to storable Fmoc-amino acid selenoesters which are effective chemoselective acylating reagents. An application to oligopeptide synthesis was illustrated.

Semi-synthesis of thioamide containing proteins

Our laboratory has shown that the thioamide, a single atom O-to-S substitution, can be a versatile fluorescence quenching probe that is minimally-perturbing when placed at many locations in a protein sequence. In order to make these and other thioamide experiments applicable to full-sized proteins, we have developed methods for incorporating thioamides by generating thiopeptide fragments through solid phase synthesis and ligating them to protein fragments expressed in E. coli. To install donor fluorophores, we have adapted unnatural amino acid mutagenesis methods, including the generation of new tRNA synthetases for the incorporation of small, intrinsically fluorescent amino acids. We have used a combination of these two methods, as well as chemoenzymatic protein modification, to efficiently install sidechain and backbone modifications to generate proteins labeled with fluorophore/thioamide pairs.

A facile one pot route for the synthesis of imide tethered peptidomimetics

A simple and efficient method for the synthesis of N,N’-orthogonally protected imide tethered peptidomimetics is presented. The imide peptidomimetics were synthesized by coupling the in situ generated selenocarboxylate of N^α-protected amino acids with N^α-protected amino acid azides in good yields.

R, Krishnamurthy M, Sureshbabu VV. Thionation of di and tripeptides employing thiourea as a sulphur transfer reagent

Thiopeptides have been prepared by thionation employing DMF/PCl₅ and thiourea as a sulphur transfer reagent. The protocol was also successfully used for the thionation of two peptide bonds, amino acid derived arylamides.

Synthesis of α-amino acidato derivatives of niobium and tantalum pentahalides and their conversion into iminium salts

Dinuclear complexes of formula Nb2Cl9[O2CCH(R)NR'R″2-κO,κO] (R = CH2CHMe2, R' = R″ = H, 1a; R = CH2Ph, R' = R″ = H, 1b; R = CH2CH2SCH3, R' = R″ = H, 1c; R = R' = H, R″ = Me, 1d; R = CH2Ph, R' = R″ = Me, 1e; Nb2Cl9[O2C⌈CH(CH2)3NH⌉], 1f) were prepared by allowing NbCl5 to react in dichloromethane with the appropriate α-amino acid in 1:2 amino acid/Nb molar ratio. The 1:1 reactions between MX5 (M = Nb, Ta; X = Cl, Br) and a series of α-amino acids resulted in the formation of the iminium salts [(R)CH═NR'R″2][MX6] (R = CH2Ph, R' = R″ = Me: M = Nb, X = Cl, 2a; M = Nb, X = Br, 2b; M = Ta, X = Cl, 2c; M = Ta, X = Br, 2d; R = CH2Ph, R' = R″ = H, M = Nb: X = Cl, 3a; X = Br, 3b; R = CH2CHMe2, R' = R″ = H, M = Nb, X = Cl, 4; R = R' = H, R″ = Me, M = Nb, X = Cl, 5). The formate/amino acidate derivative NbCl3(O2CH)[O2CCH(CH2Ph)NMe2], 6, was isolated and identified as coproduct of the 1:1 reaction between NbCl5 and N,N-dimethyl-l-phenylalanine, leading to 2a. All of the compounds were characterized by analytical and spectroscopic methods and by X-ray diffractometry in the cases of 2a, 2b, and 2d. Moreover, density functional theory studies were carried out to shed light on mechanistic and structural aspects.

Synthesis of chiral Nβ-protected amino diselenides from the corresponding amino alkyl iodides using NaBH2Se3 as a selenating reagent and their conversion to seleninic acids

Synthesis of N^β-protected amino diselenides and l-selenocystine methyl esters from amino alkyl iodides using NaBH₂Se₃ as an efficient selenating reagent is described. Further the synthesis of N^β-protected amino seleninic acids using 35% aqueous H₂O₂ has been demonstrated.

Synthesis of selenazoles by in situ cycloisomerization of propargyl selenoamides using oxygen-selenium exchange reaction

Herein, we describe an approach toward selenazole preparation based on the cycloisomerization of propargyl selenoamides. The selenoamides were synthesized in situ using the Ishihara reagent with spontaneous cyclization to form the 2,5-disubstituted selenazoles. Heterocylcles 9a-j were prepared using readily available starting materials, and yields ranged from moderate to good (20-80%). Methylselenazole 9a could be transformed into a bromomethyl derivative 13 using NBS. The intermediate 13 would provide a more versatile building block for further derivatizations, e.g., the cyanide 14.

Two-dimensional x-ray correlation spectroscopy of remote core states

Nonlinear all-X-ray signals that involve large core-atom separation compared to the X-ray wavelengths may not be described by the dipole approximation since they contain additional phase factors. Expressions for the rotationally averaged 2D X-ray photon echo signals from randomly oriented systems that take this position-dependent phase into account for arbitrary ratio between the core separation and the resonant wavelength are presented. Application is made to the Se K-edge of a selenium dipeptide system.