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

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 5′-O-β,γ-methylenetriphosphate derivatives of nucleosides and evaluation of their inhibitory activity against HIV-1 reverse transcriptase

Bis(dichlorophosphino)methane was converted to a β,γ-methylenetriphosphitylating reagent. The reagent was immobilized on aminomethyl polystyrene resin-bound linker of 4-acetoxy-3-phenylbenzyl alcohol to afford a polymer-bound β,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-β,γ-methylene triphosphate nucleosides in 53–82% overall yields. Among all the compounds, cytidine 5′-O-β,γ-methylenetriphosphate inhibited completely RNase H activity of HIV-1 reverse transcriptase at 700 μM. [Refer to PDF for graphical abstract

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). [Refer to PDF for graphical abstract

Synthesis of nucleoside 5′-\u3cem\u3eO\u3c/em\u3e-α,β-methylene-β-triphosphates and evaluation of their potency towards inhibition of HIV-1 reverse transcriptase

A polymer-bound α,β-methylene-β-triphosphitylating reagent was synthesized and subjected to reactions with unprotected nucleosides, followed by oxidation, deprotection of cyanoethoxy groups, and acidic cleavage to afford nucleoside 5′-O-α,β-methylene-β-triphosphates. Among all the compounds, cytidine 5′-O-α,β-methylene-β-triphosphate inhibited RNase H activity of HIV-1 reverse transcriptase with a Ki value of 225 μM

Synthesis of Nucleoside 5′-O-α,β-methylene-β-triphosphates and Evaluation of Their Potency Towards Inhibition of HIV-1 Reverse Transcriptase

A polymer-bound α,β-methylene-β-triphosphitylating reagent was synthesized and subjected to reactions with unprotected nucleosides, followed by oxidation, deprotection of cyanoethoxy groups, and acidic cleavage to afford nucleoside 5′-O-α,β-methylene-β-triphosphates. Among all the compounds, cytidine 5′-O-α,β-methylene-β-triphosphate inhibited RNase H activity of HIV-1 reverse transcriptase with a Ki value of 225 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 (Kd = 0.6 μM) to the Src SH2 domain when compared with Ac-pYEEI (Kd = 1.7 μM), an optimal Src SH2 domain ligand, and peptides 2–4 (Kd = 2.9–52.7 μM). The binding affinity of peptide 1 to the SH2 domain was reduced by more than 2-fold (Kd = 1.6 μM) upon addition of Ni2+ (300 μM), possibly due to modest structural effect of Ni2+ on the protein as shown by circular dichroism experimental results. The binding affinity of 1 was restored in the presence of EDTA (300 μM) (Kd = 0.79 μM). These studies suggest that peptides containing IDA groups may be used for designing novel SH2 domain binding ligands. [Refer to PDF for graphical abstract

Symmetrical Dinucleosides

The authors have reported the utility of 1 for the preparation of sulfonamides (J. Org. Chem. 2006, 71, 7915). To the best of the authors’ knowledge, this is the first report of the synthesis of 5¢,5¢-dinucleoside 5¢,5¢-phosphodiesters by using polymer-bound phosphitylating reagents

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-π 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. © 2006 Elsevier Ltd. All rights reserved