Query: McGuigan Gemcitabine phosphoramidate

title: Aryl phosphoramidate derivatives of d4T have improved anti HIV efficacy in tissue culture and may act by the generation of a novel intracellular metabolite.
abstract: New phosphate derivatives of the anti HIV nucleoside analogue d4T were prepared as potential membrane soluble prodrugs of the bioactive free nucleotide. The enhanced antiviral potency and/or reduced cytotoxicity of the derivatives leads to an increase in selectivity relative to the parent nucleoside analogue. Moreover, the derivatives appear to bypass the dependence of the nucleoside on thymidine kinase mediated activation, retaining full activity in thymidine kinase deficient cells. This strongly suggests the successful intracellular delivery of free nucleotides by the masked phosphate triester prodrugs. This is further confirmed by studies using radiolabeled compound which clearly demonstrate the generation of d4T mono di and triphosphates from the prodrug, even in thymidine kinase deficient cells. Moreover, we herein report the generation of a new metabolite, a partially hydrolyzed phosphate diester, alaninyl d4T monophosphate. We suggest that at least part of the antiviral action of the prodrugs derives from the intracellular generation of such novel diesters which may add considerable weight to the suggested further preclinical development of the phosphate prodrugs.

title: Phosphoramidate derivatives of d4T as inhibitors of HIV: the effect of amino acid variation.
abstract: Phosphoramidate derivatives of the nucleoside analogue, 2',3' dideoxy 2',3' didehydro thymidine (d4T) have been prepared as potential membrane soluble pro drugs of the big active free phosphate forms. In particular phenyl phosphates, linked via nitrogen to methyl esterified amino acids, were studied. All compounds were fully characterised by a range of methods (high field multinuclear NMR, mass spectrometry and high performance liquid chromatography (HPLC) and were subjected to in vitro evaluation of their anti HIV efficacy. The nature of the amino acid appeared to be extremely important for the eventual antiviral action. Of the amino acids studied, L alanine was the most efficacious, whilst L proline and glycine were particularly poor. However, an unnatural amino acid moiety, dimethylglycine, could substitute for alanine with little or no loss of activity.

title: Stereoselective and Concentration Dependent Polarized Epithelial Permeability of a Series of Phosphoramidate Triester Prodrugs of d4T: An in Vitro Study in Caco 2 and Madin Darby Canine Kidney Cell Monolayers
abstract: Nucleoside analogs are successful, widely used antiviral and anticancer therapeutics. Nucleotide prodrugs (i.e. pronucleotide) have increasingly been used to improve in vivo efficacy of nucleoside analogs. In this study, we evaluated the permeability of a series of phosphoramidate triester prodrugs of the anti HIV drug 2',3' didehydro 2',3' dideoxythymidine across monolayers of Caco 2, Madin Darby canine kidney (MDCKII) epithelial cell line, and its recombinant clone containing the human MDR1/P gp gene (MDR1 MDCKII) Transport was studied in the apical to basolateral (A B) and the basolateral to apical directions (B A) The impact upon transport of differences in stereochemistry at the chiral phosphate center was evaluated. In the Caco 2 and MDCK models the A B permeability was lower than expected based on the lipophilicity of the compounds, suggesting the involvement of a polarized efflux system and/or metabolic degradation in limiting the absorption of these ester based prodrugs. Average permeability values through cell monolayers obtained in the A B direction were lower than in the B A direction. The inclusion of the P glycoprotein (P gp) inhibitor verapamil in the transport medium markedly increased the permeability in the A B direction, whereas decreasing it in the opposite direction, suggesting an efflux mechanism mainly mediated by P gp. Stereoselective permeability was significant for the most lipophilic compounds, where the diastereoisomer possessing the slower eluting time on a reverse phase high performance liquid chromatography column was transported through Caco 2 and MDCK monolayers at higher rate.

title: Synthesis, Anti Human Immunodeficiency Virus Activity and Esterase Lability of Some Novel Carboxylic Ester Modified Phosphoramidate Derivatives of Stavudine (d4T)
abstract: We report the design, synthesis and antiviral evaluation of a series of lipophilic, masked phosphoramidate derivatives of the anti human immunodeficiency virus (HIV) nucleoside analogue d4T, designed to act as membrane soluble prodrug forms for the free nucleotide. In particular, we report a series of 12 novel compounds with systematic variation in the structure of the carboxylate ester function. In order to rationalize the changes in antiviral action with variation of this moiety we applied our recently developed 31P NMR based assay for carboxyesterase lability to this series. However, no clear positive correlation emerged, indicating that, at least within this series, factors other than simple esterase lability may be the major determinants of antiviral potency.

title: Phosphoramidate derivatives of d4T with improved anti HIV efficacy retain full activity in thymidine kinase deficient cells
abstract: New phosphate derivatives of the anti HIV nucleoside analogue d4T were prepared as potential membrane soluble pro drugs of the bio active free nucleotide. Some of the derivatives appear to have enhanced antiviral efficacy relative to the parent nucleoside analogue. Moreover, the derivatives appear to by pass the dependence of the nucleoside on thymidine kinase mediated activation, retaining full activity in thymidine kinase deficient cells. The new analogues show particular promise for further pre clinical development.

title: Synthesis and anti HIV activity of some haloalkyl phosphoramidate derivatives of 3' azido 3' deoxythymidine (AZT) potent activity of the trichloroethyl methoxyalaninyl compound.
abstract: Phosphate triester derivatives of AZT have been prepared as membrane soluble pro drugs of the bio active nucleotides, and have been evaluated against HIV 1 in vitro. In particular, the phosphorus centre carries a trichloro or trifluoroethyl group and a carboxyl protected, amino linked amino acid. The compounds are prepared using phosphorochloridate chemistry, and are characterized by a range of techniques. They display potent anti HIV activity and low host toxicity, but surprisingly this activity does not increase on the introduction of the haloalkyl moiety. The trichloroethyl methoxyalaninyl compound is exceptional: here the activity is enhanced 50 fold by the introduction of the trichloroethyl group.

title: Synthesis and Evaluation of Some Novel Phosphoramidate Derivatives of 3' Azido 3' Deoxythymidine (AZT) as Anti HIV Compounds
abstract: A series of monophosphate triester derivatives of 3' azido 3' deoxythymidine (AZT) designed as membrane soluble pro drugs of the nucleotide (AZTMP) have been tested for activity against the human immunodeficiency virus (HIV 1) It has been found that when carboxyl protected, amino linked amino acids, and alkyl chains, are asymmetrically substituted on the 5' phosphate a significant antiviral effect is observed. Moreover, the activity of the compounds is profoundly dependent on the structure of the phosphate moiety, and in particular on the nature of the amino acid.

title: Synthesis and Anti HIV Activity of some Novel Chain Extended Phosphoramidate Derivatives of d4T (Stavudine) Esterase Hydrolysis as a Rapid Predictive Test for Antiviral Potency
abstract: Novel chain extended nucleoside phosphoramidates of the anti human immunodeficiency virus (HIV) drug d4T (stavudine) have been prepared as possible membrane permeable prodrugs of the bio active free 5' monophosphates. Phosphorochloridate chemistry gave the target compounds in moderate to high yields, and all materials were fully characterized by spectroscopic and analytical methods. The compounds are related to the previously reported phenyl methoxyalaninyl derivative of d4T, which was shown to be a potent and selective inhibitor of HIV. In this study theamino acid nitrogen and ester moieties were separated by methylene spacers of between two and six carbon atoms. In vitro evaluation of these compounds indicated an almost complete lack of anti HIV activity, the compounds being several orders of magnitude less potent than the corresponding a amino acid derivatives. The reasons for the virtual lack of anti HIV activity appear to involve poor enzyme mediated hydrolysis.

title: Novel Nucleoside Phosphoramidates as Inhibitors of HIV: Studies on the Stereochemical Requirements of the Phosphoramidate Amino Acid
abstract: Novel phosphoramidate derivatives of the anti HIV nucleoside analogue d4T were designed to act as labile membrane soluble prodrugs of the bio active free nucleotide d4TMP. We herein reveal the very marked dependence of the antiviral activity of these phosphoramidates upon the stereochemistry of the amino acid attached to the phosphate centre; with a strong preference for the L stereochemistry. These phosphate triesters were shown to liberate amino acid derivatives of the nucleotide intracellularly. These novel analogues, typified by alaninyl d4T monophosphate, may act as intracellular sources of the free nucleotides. The alaninyl d4T adducts themselves exert an antiviral effect when administered extracellularly, but again with clear distinctions between the L and D series. This evidence indicates that extracellularly administered blocked triesters derived from L amino acids can generate d4TMP intracellularly, by a new pathway which is highly dependent on the amino acid stereochemistry.

title: Phosphoramidate derivatives of 2',3' didehydro 2',3' dideoxyadenosine [d4A] have markedly improved anti HIV potency and selectivity
abstract: New 5' phosphate derivatives of the nucleoside analogue d4A were prepared as potential membrane soluble prodrugs of the free nucleotide. The anti viral potency and selectivity of the derivatiyes is markedly increased by comparison to the parent nucleoside analogue. The new analogues show particular promise for further pre clinical development.