Inhibition of multi-drug resistant HIV-1 reverse transcriptase by nucleoside ß-triphosphates.

Despite the success of potent reverse transcriptase (RT) inhibitors against human immunodeficiency virus type 1 (HIV-1) in combination regimens, the development of drug resistant RTs constitutes a major hurdle for the long-term efficacy of current antiretroviral therapy. Nucleoside ß-triphosphate analogs of adenosine and nucleoside reverse transcriptase inhibitors (NRTIs) (3'-azido-2',3'-dideoxythymidine (AZT), 3'-fluoro-2',3'-dideoxythymidine (FLT), and 2',3'-didehydro-2',3'-dideoxythymidine (d4T)) were synthesized and their inhibitory activities were evaluated against wild-type and multidrug resistant HIV-1 RTs. Adenosine ß-triphosphate (1) and AZT ß-triphosphate (2) completely inhibited the DNA polymerase activity of wild type, the NRTI multi resistant, and nonnucleoside RT inhibitors (NNRTI) resistant HIV-1 RT at 10nM, 10 and 100 µM, respectively.

Hydrophobicity drives the cellular uptake of short cationic peptide ligands.

Short cationic linear peptide analogs (LPAs, prepared as Arg-C( n )-Arg-C( n )-Lys, where C( n ) represents an alkyl linkage with n = 4, 7 or 11) were synthesized and tested in human breast carcinoma BT-20 and CCRF-CEM leukemia cells for their application as targeting ligands. With constant LPA charge (+4), increasing the alkyl linkage increases the hydrophobic/hydrophilic balance and provides a systematic means of examining combined electrostatic and hydrophobic peptide-membrane interactions. Fluorescently conjugated LPA-C(11) (F-LPA-C(11)) demonstrated significant uptake, whereas there was negligible uptake of the shorter LPAs. By varying temperature (4°C and 37°C) and cell type, the results suggest that LPA-C(11) internalization is nonendocytic and nonspecific. The effect of LPA binding on the phase behavior, structure, and permeability of model membranes composed of dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylserine (DPPC/DPPS, 85/15) was studied using differential scanning calorimetry (DSC), cryogenic transmission electron microscopy (cryo-TEM), and fluorescence leakage studies to gain insight into the LPA uptake mechanism. While all LPAs led to phase separation, LPA-C(11), possessing the longest alkyl linkage, was able to penetrate into the bilayer and caused holes to form, which led to membrane disintegration. This was confirmed by rapid and complete dye release by LPA-C(11). We propose that LPA-C(11) achieves uptake by anchoring to the membrane via hydrophobicity and forming transient membrane voids. LPAs may be advantageous as drug transporter ligands because they are small, water soluble, and easy to prepare.

Synthesis and anti-HIV activities of bis-(cycloSaligenyl) pronucleotides derivatives of 3'-fluoro-3'-deoxythymidine and 3'-azido-3'-deoxythymidine.

Anti-HIV nucleoside monophosphates have limited cellular uptake due to the presence of negatively-charged phosphate group. Bis-(cycloSaligenyl) derivatives containing two anti-HIV nucleosides, 3'-fluoro-3'-deoxythymidine (FLT) and 3'-azido-3'-deoxythymidine (AZT) were synthesized to increase intracellular delivery of nucleoside monophosphates. 2,5-Bis(hydroxymethylene)benzene-1,4-diol was selected as a monocyclic bidentate scaffold and synthesized by three different methods from bis(hydroxymethylene)cyclohexan-1,4-diene-1,4-diol, or diethyl 2,5-dihydroxyterephthalate. The reaction of the tetraol with diisopropylphosphoramidous dichloride in the presence of 2,6-lutidine, followed by conjugation reactions with nucleosides (i.e., FLT and AZT) and oxidation afforded symmetrical and unsymmetrical bis-(cycloSaligenyl) diphosphate triester products, AZT-AZT, FLT-FLT, and FLT-AZT conjugates, in 63-74% overall yields and modest anti-HIV activities (IC50 = 2.8-69.6 µM).

Solid-Phase Synthesis of 5'-O-ß,γ-Methylenetriphosphate Derivatives of Nucleosides and Evaluation of Their Inhibitory Activity Against HIV-1 Reverse Transcriptase.

Bis(dichlorophosphino)methane was converted to a ß,γ-methylenetriphosphitylating reagent. The reagent was immobilized on aminomethyl polystyrene resin-bound linker of 4-acetoxy-3-phenylbenzyl alcohol to afford a polymer-bound ß,γ-methylenetriphosphitylating reagent, which was reacted with unprotected nucleosides followed by oxidation with tert-butyl hydroperoxide, deprotection of cyanoethoxy groups with DBU, and acidic cleavage, to produce 5'-O-ß,γ-methylene triphosphate nucleosides in 53-82% overall yields. Among all the compounds, cytidine 5'-O-ß,γ-methylenetriphosphate inhibited completely RNase H activity of HIV-1 reverse transcriptase at 700 µM.

Synthesis and evaluation of phosphopeptides containing iminodiacetate groups as binding ligands of the Src SH2 domain.

Phosphopeptide pTyr-Glu-Glu-Ile (pYEEI) has been introduced as an optimal Src SH2 domain ligand. Peptides, Ac-K(IDA)pYEEIEK(IDA) (1), Ac-KpYEEIEK (2), Ac-K(IDA)pYEEIEK (3), and Ac-KpYEEIEK(IDA) (4), containing 0-2 iminodiacetate (IDA) groups at the N- and C-terminal lysine residues were synthesized and evaluated as the Src SH2 domain binding ligands. Fluorescence polarization assays showed that peptide 1 had a higher binding affinity (K(d) = 0.6 microM) to the Src SH2 domain when compared with Ac-pYEEI (K(d) = 1.7 microM), an optimal Src SH2 domain ligand, and peptides 2-4 (K(d) = 2.9-52.7 microM). The binding affinity of peptide 1 to the SH2 domain was reduced by more than 2-fold (K(d) = 1.6 microM) upon addition of Ni(2+) (300 microM), possibly due to modest structural effect of Ni(2+) on the protein as shown by circular dichroism experimental results. The binding affinity of 1 was restored in the presence of EDTA (300 microM) (K(d) = 0.79 microM). These studies suggest that peptides containing IDA groups may be used for designing novel SH2 domain binding ligands.

Synthesis of nucleoside mono-, di-, and triphosphoramidates from solid-phase cyclosaligenyl phosphitylating reagents.

Chloromethyl polystyrene resin was reacted with 5-hydroxysalicylaldehyde in the presence of potassium carbonate to afford polymer-bound 2-hydroxybenzaldehyde. Subsequent reduction with borane solution produced polymer-bound 2-hydroxybenzyl alcohol. The reaction of immobilized 2-hydroxybenzyl alcohol with appropriate phosphitylating reagents yielded solid-phase cycloSaligenyl mono-, di-, and triphosphitylating reagents, which were reacted with unprotected nucleosides, followed by iodine oxidation, deprotection of cyanoethoxy groups, and the basic cleavage, respectively, to afford 5'-O-nucleoside mono-, di-, and triphosphoramidates in 52-73% overall yield.

Solid-supported reagents for synthesis of nucleoside monothiophosphates, dithiodiphosphates, and trithiotriphosphates.

This unit describes procedures for the selective synthesis of nucleoside monothiophosphates, dithiodiphosphates, and trithiotriphosphates from solid-supported phosphitylating reagents. Rigid and sterically hindered polymer-bound 1,3,2-oxathiaphospholane is reacted selectively with the 5'-hydroxyl group of nucleosides in the presence of 1H-tetrazole. Sulfurization in the presence of Beaucage's reagent (3H-1,2-benzodithiole-3-one 1,1-dioxide) followed by ring-opening with 3-hydroxypropionitrile and basic cleavage in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) through the elimination of polymer-bound ethylene episulfide afford nucleoside monothiophosphates. Furthermore, reaction of polymer-bound diphosphitylating and triphosphitylating reagents, prepared from polymer-bound benzyl alcohol, with unprotected nucleosides, sulfurization with Beaucage's reagent, and acidic cleavage using trifluoroacetic acid cocktail produce nucleoside dithiodiphosphates and trithiotriphosphates in moderate yields.

Solid-supported diphosphitylating and triphosphitylating reagents for nucleoside modification.

This unit describes procedures for synthesis of diphosphitylating and triphosphitylating reagents. The synthesized reagents are first immobilized on appropriate polymer-bound linkers. Rigid and sterically hindered polymer-bound diphosphitylating and triphosphitylating reagents are then reacted selectively with the 5'-hydroxyl group of nucleosides in the presence of excess nucleosides. Typical oxidation with tert-butyl hydroperoxide, deprotection, and final cleavage of the products from the resins using a trifluoroacetic acid cocktail afford various nucleoside 5'-O-diphosphate and nucleoside 5'-O-triphosphate analogs. The use of the diphosphitylating and polymer-bound diphosphitylating reagents in preparation of oligodeoxynucleotides containing diphosphodiester internucleotide bridges is also described. This solid-phase strategy allows for the synthesis of the phosphorylated compounds without the need for nucleoside phosphate precursors, protected nucleosides, or purification of intermediates.

Solid-phase synthesis of symmetrical 5',5'-dinucleoside mono-, di-, tri-, and tetraphosphodiesters.

Four classes of phosphitylating reagents were subjected to reactions with aminomethyl polystyrene resin-bound p-acetoxybenzyl alcohol to yield the corresponding polymer-bound mono-, di-, tri-, and tetraphosphitylating reagents. The solid-phase reagents were reacted with unprotected nucleosides (e.g., thymidine, adenosine, 3'-azido-3'-deoxythymidine, cytidine, or inosine) in the presence of 5-(ethylthio)-1H-tetrazole. Polymer-bound nucleosides underwent oxidation with tert-butyl hydroperoxide, deprotection of cyanoethoxy groups with DBU, and the acidic cleavage, respectively, to afford 5',5'-dinucleoside mono-, di-, tri-, and tetraphosphodiesters in 59-78% yield.

Protein pyrophosphorylation by inositol pyrophosphates is a posttranslational event.

In a previous study, we showed that the inositol pyrophosphate diphosphoinositol pentakisphosphate (IP(7)) physiologically phosphorylates mammalian and yeast proteins. We now report that this phosphate transfer reflects pyrophosphorylation. Thus, proteins must be prephosphorylated by ATP to prime them for IP(7) phosphorylation. IP(7) phosphorylates synthetic phosphopeptides but not if their phosphates have been masked by methylation or pyrophosphorylation. Moreover, IP(7) phosphorylated peptides are more acid-labile and more resistant to phosphatases than ATP phosphorylated peptides, indicating a different type of phosphate bond. Pyrophosphorylation may represent a novel mode of signaling to proteins.

Metal-binding properties of a dicysteine-containing motif in protein tyrosine kinases.

Studying the structural consequences of the direct binding of arsenite, cadmium, cobalt, nickel, and lead to a number of protein tyrosine kinases led to the discovery of the metal-binding properties of a dicysteine-containing motif in the C-terminal (CT) lobe of the kinases. Of all the synthesized peptides derived from different domains of c-Src and Csk, only peptides based on a dicysteine-containing motif located in the CT lobe of the kinase domain-CPESLHDLMCQC and CPESLHDLMC in c-Src, and CPPAVYDVMKNC in Csk-exhibited significant conformational changes in the presence of all metals, as shown by circular dichroism (CD) analyses. Furthermore, CD analysis of natural enzymes c-Src, Csk, Fyn, c-Abl, Lck, EGFR, and c-Src domains containing the CT lobe in the presence of metals showed a significant concentration-dependent conformational change. ICP-MS, (113)Cd NMR, (33)S NMR, and/or molecular modeling studies of CPESLHDLMC and CPPAVYDVMKNC confirmed the binding between the free sulfhydryl groups of the cysteine residues and Cd(II) or As(III). UV-titration studies suggested a high-affinity interaction between Cd(II) and As(III) and the peptides (K(d) values in the range of 0.6-18.3 nM).

Synthesis of polymer-bound 4-acetoxy-3-phenylbenzaldehyde derivatives: applications in solid-phase organic synthesis.

Aminomethyl polystyrene resin was reacted with 4-(5'-formyl-2'-hydroxyphenyl)benzoic acid and 4-(5'-formyl-2'-hydroxyphenyl)phenyl propionic acid, respectively, in the presence of 1-hydroxybenzotriazole and 1,3-diisopropylcarbodiimide to yield polymer-bound benzaldehydes. The phenolic group in resins was acetylated with acetic anhydride to afford two polymer-bound 4-acetoxybenzaldehydes. The reductive amination of polymer-bound linkers by amines and sodium triacetoxyborohydride, followed by sulfonylation with arylsulfonyl chloride derivatives in the presence of pyridine and the cleavage with TFA/DCM/H2O, produced pure sulfonamides.

Solid-phase synthesis of dinucleoside and nucleoside-carbohydrate phosphodiesters and thiophosphodiesters.

Unprotected nucleosides (ROH) were reacted with two polymers bound to N,N-diisopropylamino-1,3,2-oxathiaphospholane in the presence of 1H-terazole. Oxidation with tert-butyl hydroperoxide or sulfurization with Beaucage's reagent, followed by the 1,3,2-oxathiaphospholane ring opening with unprotected nucleosides or carbohydrates (R'OH) in the presence of DBU, afforded nucleoside-(5'-5')-nucleoside or nucleoside-carbohydrate phosphodiester and thiophosphodiester derivatives through the elimination of polymer-bound ethylene episulfide. This strategy offers the advantages of facile isolation of final products and monosubstitution of unprotected nucleosides and carbohydrates.

Application of a solid-phase beta-triphosphitylating reagent in the synthesis of nucleoside beta-triphosphates.

A beta-triphosphitylating reagent was subjected to reaction with aminomethyl polystyrene resin-bound p-acetoxybenzyl alcohol to yield the corresponding polymer-bound beta-triphosphitylating reagent. The solid-phase reagent was reacted with unprotected nucleosides (e.g., 3'-azido-3'-deoxythymidine, cytidine, thymidine, uridine, inosine, or adenosine) in the presence of 1H-tetrazole. Polymer-bound nucleosides underwent oxidation with t-butyl hydroperoxide, deprotection of cyanoethoxy groups with DBU, and the acidic cleavage, respectively, to afford only monosubstituted 5'-O-beta-triphosphorylated nucleosides.

Structural basis for domain-domain communication in a protein tyrosine kinase, the C-terminal Src kinase.

The catalytic activity of protein tyrosine kinases is commonly regulated by domain-domain interactions. The C-terminal Src kinase (Csk) contains a catalytic domain and the regulatory SH3 and SH2 domains. Both the presence of the regulatory domains and binding of specific phosphotyrosine-containing proteins to the SH2 domain activate Csk. The structural basis for both modes of activation is investigated here. First, the SH3-SH2 linker is crucial for Csk activation. Mutagenic and kinetic studies demonstrate that this activation is mediated by a cation-pi interaction between Arg68 and Trp188. Second, Ala scanning and kinetic analyses on residues in the SH2-catalytic domain interface identify three functionally distinct types of residues in mediating the communication between the SH2 and the catalytic domains. Type I residues are important in mediating a ligand-triggered activation of Csk because their mutation severely reduces Csk activation by the SH2 domain ligand. Type II residues are involved in suppressing Csk activity, and their mutation activates Csk, but makes Csk less sensitive to activation by the SH2 ligand. Both type I and type II residues are likely involved in mediating SH2 ligand-triggered activation of Csk. Type III residues are those located in the SH2 domain whose mutation severely decreases Csk catalytic activity without affecting the SH2 ligand-triggered activation. These residues likely mediate SH2 activation of Csk regardless of SH2-ligand interaction. These studies lead us to propose a domain-domain communication model that provides functional insights into the topology of Csk family of protein tyrosine kinases.

Selective diphosphorylation, dithiodiphosphorylation, triphosphorylation, and trithiotriphosphorylation of unprotected carbohydrates and nucleosides.

[chemical reaction: see text]. Aminomethyl polystyrene resin-bound linkers of p-acetoxybenzyl alcohol were subjected to reactions with diphosphitylating and triphosphitylating reagents to yield the corresponding polymer-bound diphosphitylating and triphosphitylating reagents, respectively. A number of unprotected carbohydrates and nucleosides were reacted with the polymer-bound reagents. Oxidation with tert-butyl hydroperoxide or sulfurization with Beaucage's reagent, followed by removal of cyanoethoxy group with DBU and the acidic cleavage, respectively, afforded only one type of monosubstituted nucleoside and carbohydrate diphosphates, dithiodiphosphates, triphosphates, and trithiotriphosphates with high regioselectivity.

Polymer-bound oxathiaphospholane: a solid-phase reagent for regioselective monothiophosphorylation and monophosphorylation of unprotected nucleosides and carbohydrates.

Two polymers bound to N,N-diisopropylamino-1,3,2-oxathiaphospholane were reacted with unprotected carbohydrates and nucleosides in the presence of 1H-tetrazole, followed by oxidation with tert-butyl hydroperoxide or sulfurization with Beaucage's reagent. The 1,3,2-oxathiaphospholane ring-opening with 3-hydroxypropionitrile, followed by treatment with DBU, afforded the corresponding monophosphate and monothiophosphate derivatives, respectively, through the elimination of polymer-bound ethylene episulfide. Reactions using this strategy offer the advantages of high regioselectivity, monosubstitution, and facile isolation and recovery of products.

Solid-phase reagents for selective monophosphorylation of carbohydrates and nucleosides.

Two classes of aminomethyl polystyrene resin-bound linkers of p-acetoxybenzyl alcohol were subjected to reactions with 2-cyanoethyl N,N-diisopropylchlorophosphoramidite to produce the corresponding polymer-bound phosphitylating reagents. These were reacted with a number of unprotected nucleosides and carbohydrates in the presence of 1H-tetrazole. Oxidation with tert-butyl hydroperoxide followed by removal of the cyanoethoxy group with 1,8-diazabicyclo[5.4.0]undec-7-ene afforded the corresponding polymer-bound phosphate diesters. Acidic cleavage of the p-acetoxybenzyl alcohol linker yielded monophosphorylated products with high regioselectivity and trapped linkers on the resins that can be reused.