Direct access to site-specifically phosphorylated-lysine peptides from a solid-support.

Phosphorylation is a key process for changing the activity and function of proteins. The impact of phospho-serine (pSer), -threonine (pThr) and -tyrosine (pTyr) is certainly understood for some proteins. Recently, peptides and proteins containing N-phosphorylated amino acids such as phosphoarginine (pArg), phosphohistidine (pHis) and phospholysine (pLys) have gained interest because of their different chemical properties and stability profiles. Due to its high intrinsic lability, pLys is the least studied within this latter group. In order to gain insight into the biological role of pLys, chemical and analytical tools, which are compatible with the labile P(=O)-N bond, are highly sought-after. We recently reported an in-solution synthetic approach to incorporate pLys residues in a site-specific manner into peptides by taking advantage of the chemoselectivity of the Staudinger-phosphite reaction. While the in-solution approach allows us to circumvent the critical TFA cleavage, it still requires several transformations and purification steps to finally deliver pLys peptides. Here we report the synthesis of site-specific pLys peptides directly from a solid support by using a base labile resin. This straightforward and highly efficient approach facilitates the synthesis of various site-specific pLys-containing peptides and lays the groundwork for future studies about this elusive protein modification.

Synthesis of binaphthyl based phosphine and phosphite ligands.

The development of large scale synthesis of enantiopure and thermally stable (R)- and (S)-BINOL molecules constitutes a key milestone in the field of asymmetric catalysis. Particularly, a great variety of chiral binaphthyl-based phosphorus compounds, herein represented by phosphite and phosphine classes, have earned considerable relevance due to their versatility as ligands in enantioselective metal-catalysed reactions, allowing the preparation of optically active products with the desired enantiopurity. This review highlights the most relevant concepts and accounts regarding general synthetic procedures for binaphthyl-based mono- and bidentate phosphites and phosphines. Furthermore, the search for environmentally benign chemical catalytic processes compelled us to also give special attention to the functionalisation of binaphthyl-based phosphorus ligands for use in alternative reaction media. When available, a critical selection of their applications in catalysis is briefly assessed.

Nucleoside phosphitylation using ionic liquid stabilised phosphorodiamidites and mechanochemistry.

A range of nucleoside phosphoramidites incorporating small amino substituents have been readily synthesised using ionic liquid stabilised phosphorodiamidites coupled with mechanochemistry.

A new promising application for highly cytotoxic metal compounds: η6-areneruthenium(II) phosphite complexes for the treatment of alveolar echinococcosis.

Two series of η(6)-areneruthenium(II) phosphite complexes were prepared, characterized, and evaluated in vitro for their toxic potential against Echinococcus multilocularis metacestodes. Neutral complexes of general formula [(η(6)-p-cymene)RuCl(2){P(OR)(3)}] (R = Et, (i)Pr, Ph) with two easily exchangable chloride ligands showed only minor toxicity, whereas the substitution of these moieties against a ß-diketonate (2,2,6,6-tetramethylheptanedionate) ligand led to hydrolytically stable complex salts of type [(η(6)-p-cymene)Ru(ß-diketonate){P(OR)(3)}][BF(4)] (R = Et, (i)Pr, Ph) with comparable in vitro toxicity (50% PGI release at c = 1.4 - 4.7 µM) to the reference drug nitazoxanide (50% PGI release at c = 1.2 µM). In addition, the latter complexes were highly toxic against rat hepatoma cells (IC(50) = 0.40-2.0 µM) and less toxic against human foreskin fibroblasts (IC(50) = 1.1-2.9 µM) and Vero cells (IC(50) = 1.2-8.9 µM). The measured cytotoxicities against mammalian cells are, to the best of our knowledge, among the highest ever observed for ruthenium-based complexes. In conclusion, complex salts of type [(η(6)-p-cymene)Ru(ß-diketonate){P(OR)(3)}][BF(4)] might be interesting candidates for further development toward anthelmintic drugs and/or highly cytotoxic metal compounds.

Synthesis and structure-activity relationship analysis of bicyclophosphorothionate blockers with selectivity for housefly gamma-aminobutyric acid receptor channels.

BACKGROUND: Bicyclophosphorothionates (2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane-1-sulfides) are blockers (or non-competitive antagonists) of gamma-aminobutyric acid (GABA) receptor channels. Twenty-two bicyclophosphorothionates with different 3- and 4-substituents were synthesised, and [(3)H]4'-ethynyl-4-n-propylbicycloorthobenzoate (EBOB) binding assays were performed to evaluate their affinities for housefly and rat GABA receptors. RESULTS: Introduction of an isopropyl group at the 3-position enhanced the affinity of bicyclophosphorothionates for housefly GABA receptors and reduced the affinity towards rat GABA receptors. The 4-isopentyl-3-isopropylbicyclophosphorothionate showed the highest affinity for housefly GABA receptors (IC(50) = 103 nM) among the analogues tested, while the 4-cyclohexylbicyclophosphorothionate showed the highest affinity for rat GABA receptors (IC(50) = 125 nM). Among the bicyclophosphorothionates synthesised to date, the former analogue exhibited the highest selectivity for housefly GABA receptors, with an IC(50)(rat)/IC(50)(fly) ratio of approximately 97. Three-dimensional GABA receptor models successfully explained the structure-activity relationships of the bicyclophosphorothionates. CONCLUSION: The results indicate that minor structural modifications of blockers can change their selectivity for insect versus mammalian GABA receptors. The substituent at the 3-position of the bicyclophosphorothionates dictates selectivity for housefly versus rat GABA receptors. This information should prove useful for the design of safer insecticides and parasiticides.

Diastereoselective hydrophosphonylation of imines using (R,R)-TADDOL phosphite. Asymmetric synthesis of alpha-aminophosphonic acid derivatives.

Efficient synthesis of alpha-aminophosphonic acid derivatives is achieved, the key step being a diastereoselective hydrophosphonylation of N-diphenylphosphinyl imines using a readily available chiral cyclic (R,R)-TADDOL-phosphite derived from inexpensive natural tartaric acid.

Generation of chiral phosphonium dialkyl phosphite as a highly reactive P-nucleophile: application to asymmetric hydrophosphonylation of aldehydes.

The generation of chiral tetraaminophosphonium dialkyl phosphite has been detected by low-temperature NMR analysis, and its synthetic potential as a remarkably reactive P-nucleophile has been successfully demonstrated by its application to the establishment of highly efficient and enantioselective hydrophosphonylation of various aldehydes. A systematic evaluation of the organic-base-dependent generation of the requisite ion pair and its reactivity and selectivity as a P-nucleophile reveals that the structure of the cationic conjugate acid of the base is a key element both for substantial generation of phosphite anions with prominent nucleophilicity and for rigorous stereocontrol. This study provides not only experimental demonstration of the importance of the phosphite tautomer in the P-C bond formation process but also a general yet valuable framework for the molecular design of even superior chiral organic base catalysts.

Stereoselective synthesis of alpha-glycosyl phosphites and phosphoramidites via O-selective glycosylation of H-phosphonate derivatives.

A highly stereo- and chemoselective glycosylation of H-phosphonate derivatives with glycosyl iodides was discovered as a reverse reaction of the formation of a glycosyl iodide from a glycosyl phosphite and I- under mild acidic conditions. Further study on the unique reaction showed that the reaction provided various alpha-glycosyl phosphites and phosphoramidites in a highly stereoselective manner with complete O-selectivity.

Design and synthesis of peptide-oligonucleotide conjugates as potential artificial ribonucleases.

A series of peptide-oligonucleotide conjugates was synthesized. The peptide fragment was attached to the middle part of DNA sequence. For this purpose the new amidophosphite dC with linker at C5-position was synthesized.

Chiral pyranoside phosphite-oxazolines: a new class of ligand for asymmetric catalytic hydrogenation of alkenes.

We have described the first successful application of a phosphite-oxazoline ligand library in the asymmetric Ir-catalyzed hydrogenation of several unfunctionalized olefins. The introduction of a bulky biaryl phosphite moiety in the ligand design is highly adventitious in the product outcome. By carefully selecting the ligand components, we obtained high activities (TOFs up to >1500 mol x (mol x h)(-1) at 1 bar of H2) and enantioselectivities (ee values up to >99%) and, at the same time, show a broad scope for different substrate types. So, this is an exceptional ligand class that competes favorably with a few other ligand series that also provide high ee values for tri- and disubstituted substrate types.

Large-bite bis(phosphite) ligand containing mesocyclic thioether moieties: synthesis, reactivity, group 11 (Cu(I), Au(I)) metal complexes and anticancer activity studies on a human cervical cancer (HeLa) cell line.

The large-bite bis(phosphite) ligand [{(-OC(10)H(6)(mu-S)C(10)H(6)O-)P{mu-(-OC(10)H(6)(mu-S)C(10)H(6)O-)}P(-OC(10)H(6)(mu-S)C(10)H(6)O-)}] (Pinsertion markP) () was obtained by the reaction of PCl(3) and thiobis(2,2'-naphthol) (). The stoichiometric reactions of with elemental sulfur and selenium afforded the corresponding chalcogenide derivatives [(E)Pinsertion markP(E)] (, E = S; , E = Se) in good yield. Treatment of two equivalents of [ClAu(SMe(2))] with afforded a dinuclear complex [ClAu(Pinsertion markP)AuCl] (), whereas the 1 : 1 reaction with CuI yielded the [(Pinsertion markP)CuI] () complex. The copper(i) complex on treatment with various pyridyl derivatives, produced mixed-ligand complexes [(Pinsertion markP)CuI(NC(5)H(5))] (), [(Pinsertion markP)Cu(2,2'-bpy)]I (), [(Pinsertion markP)Cu(1,10-phen)]I () and {[(Pinsertion markP)Cu(4,4'-bpy)]I}(infinity) (). The compounds were tested for their cytotoxic activity on the human cervical cancer (HeLa) cell line. Compounds and were found to inhibit proliferation of HeLa cells significantly. These agents also induced apoptotic cell death in cancer cells. Evidence presented in this study indicated that the compounds and activate the tumor suppressor protein p53 in the colon adenocarcinoma (HCT-116) cell line.

Solid-phase parallel synthesis of phosphite ligands.

Various routes for the synthesis of polymer-bound phosphites and phosphoramidites have been investigated. In the presence of a suitable activator the supported phosphoramidites react cleanly with alcohols to give the corresponding monodentate phosphite ligands in solution. We have applied this novel solid-phase route in the parallel synthesis of several monodentate chiral and achiral phosphite ligands.

Modular phosphite-oxazoline/oxazine ligand library for asymmetric pd-catalyzed allylic substitution reactions: scope and limitations-origin of enantioselectivity.

A library of phosphite-oxazoline/oxazine ligands L1-L15 a-h has been synthesized and screened in the Pd-catalyzed allylic substitution reactions of several substrate types. These series of ligands can be prepared efficiently from easily accessible hydroxyl amino acid derivatives. Their modular nature enables the substituents/configurations in the oxazoline/oxazine moiety, alkyl backbone chain and in the biaryl phosphite moiety to be easily and systematically varied. By carefully selecting the ligand components, therefore, high regio- and enantioselectivities (ee values up to 99 %) and good activities have been achieved in a broad range of mono- and disubstituted linear hindered and unhindered liner and cyclic substrates. The NMR studies on the Pd-pi-allyl intermediates provide a deeper understanding about the effect of the ligand parameters on the origin of enantioselectivity. It also indicates that the nucleophilic attack takes place predominantly at the allylic terminal carbon atom located trans to the phosphite moiety.

Stereochemical features making deoxycholic acid derived tropos biphenylphosphites efficient chiral ligands for rhodium: the asymmetric hydrogenation of dimethylitaconate as a case study.

Different deoxycholic acid derived biphenylphosphites, whose tropos nature was ascertained by NMR and CD measurements, were used in the rhodium-catalyzed asymmetric hydrogenation of dimethylitaconate achieving enantiomeric excesses up to 91%. The comparison of these results to those obtained using the corresponding atropoisomeric binaphthyl analogues, together with NMR and CD measurements on the rhodium complexes of some phosphites, allowed us to shed light on the nature of the active catalytic species and on the asymmetric induction process and hence to recognize the most appropriate stereochemical features to reach good levels of enantioselectivity.

Synthesis of solution-phase phosphoramidite and phosphite ligand libraries and their in situ screening in the rhodium-catalyzed asymmetric addition of arylboronic acids.

Herein, we report the automated parallel synthesis of solution-phase libraries of phosphoramidite ligands for the development of enantioselective catalysts. The ligand libraries are screened in situ in the asymmetric rhodium-catalyzed addition of arylboronic acids to aldehydes and imines. It is shown that the described methodology results in the straightforward discovery of leads for highly efficient enantioselective catalysts.

(3,4)-connected zincophosphites as structural analogues of zinc hydrogen phosphate.

The synthesis and crystal structures of three new open-framework zincophosphites with helical channels are reported here in the context of the synthetic design of an open architecture from three- and four-connected polyhedral centers. These zincophosphites were prepared under hydrothermal conditions from HF-containing media in mixed water-ethylene glycol solvents. Their three-dimensional frameworks consist of alternating ZnO4(6-) tetrahedra and HPO3(2-) trigonal pyramids with an overall framework composition of [Zn3(HPO3)4]2-. The topology was analyzed by converting these zincophosphites from their (3,4)-connected network into a four-connected framework. The symmetry and charge density of three different structure-directing agents dictate the symmetry and framework density of resulting inorganic frameworks. These zincophosphites are structural analogues of a known hydrogen phosphate, suggesting that the bonding difference between -P-H and -P-OH plays an insignificant role in the formation of phosphite and hydrogen phosphate open frameworks.

Mechanism and applications of phosphite dehydrogenase.

Phosphite dehydrogenase catalyzes the NAD+-dependent oxidation of hydrogen phosphonate (common name phosphite) to phosphate in what amounts to a formal phosphoryl transfer reaction from hydride to hydroxide. This review places the enzyme in the context of phosphorus redox metabolism in nature and discusses the results of mechanistic investigations into its reaction mechanism. The potential of the enzyme as a NAD(P)H cofactor regeneration system is discussed as well as efforts to engineer the cofactor specificity of the protein.

Environmentally benign beta-stereoselective glycosidations of glycosyl phosphites using a reusable heterogeneous solid acid, montmorillonite K-10.

Environmentally benign and stereoselective beta-glycosidations of glycopyranosyl phosphites and alcohols using a reusable heterogeneous solid acid, montmorillonite K-10, as an activator have been developed. By these glycosidations, beta-gluco-, 2-deoxy-beta-gluco-, and beta-mannopyranosides were selectively produced in good to high yields.

C2-symmetric diphosphinite ligands derived from carbohydrates. The strong influence of remote stereocenters on asymmetric rhodium-catalyzed hydrogenation.

Modular ligands of C(2) symmetry (13a-e, 14a,b,d, and ent-9), systematically modified at positions 2 and 5, were easily prepared from d-glucosamine, D-glucitol, and tartaric acid, respectively. The application of these ligands in the rhodium-catalyzed hydrogenation of methyl acetamidoacrylate, methyl acetamidocinnamate, and dimethyl itaconate shows that both the configuration and the substituents at positions 2 and 5 of the tetrahydrofuran backbone have a strong influence on the enantioselectivty of the processes.