Dominique Cahard

Aryloxy Phosphoramidate Triesters as Pro-Tides

We herein describe the development of aryloxy phosphoramidate triesters as an effective pro-tide motif for the intracellular delivery of charged bio-active antiviral nucleoside monophosphates. The review covers the discovery of such aryl phosphoramidates, their mechanism of action and structure-activity relationships. The application of this strategy to a range of antiviral nucleosides is highlighted.

Phosphoramidate derivatives of d4T as inhibitors of HIV: The effect of amino acid variation

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.

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.

Synthesis, Anti-Human Immunodeficiency Virus Activity and Esterase Lability of Some Novel Carboxylic Ester-Modified Phosphoramidate Derivatives of Stavudine (d4T)

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.

Activities of masked 2',3'-dideoxynucleoside monophosphate derivatives against human immunodeficiency virus in resting macrophages.

ABSTRACT The anti-human immunodeficiency virus (HIV) activity of aryloxyphosphoramidate protides of a number of anti-HIV nucleoside analogues was assessed in resting primary monocyte-macrophages (M/M). While 2′,3′-dideoxythymidine (d4T), 2′,3′-dideoxyadenosine (ddA), and 2′,3′-dideoxy-2′,3′-didehydroadenosine (d4A) protides showed an anti-HIV activity that was 25- to 625-fold greater than the parent nucleotides d4T, ddA, and d4A, respectively, other aryloxyphosphoramidate protides showed similar or even lower anti-HIV activities than their parent compounds. This variable anti-HIV effect is most likely related to the different dynamics of intracellular nucleoside monophosphate release from the protides. Our results indicate the potential advantage of therapeutic use of this approach for some nucleotide analogues to affect HIV replication in M/M, one of the major reservoirs of HIV in vivo.

A QSAR study investigating the effect of L-alanine ester variation on the anti-HIV activity of some phosphoramidate derivatives of d4T.

A QSAR study, involving the use of calculated physical properties (TSAR), and the use of a neural network approach (TSAR), has been performed concerning the anti-HIV activity and cytotoxic effects of a series of d4T phosphoramidate derivatives with varying L-alanine esters. Models were obtained which allow reliable predictions for the anti-HIV activity, and cytotoxicity, of these derivatives.

Phosphoramidates as potent prodrugs of anti-HIV nucleotides: studies in the amino region

Novel phosphoramidate derivatives of the anti-HIV nucleoside analogues AZT and d4T have been prepared by phosphorochloridate chemistry. These materials are designed to act as labile membrane-soluble prodrugs of the bio-active free nucleotides. All compounds were fully characterised by a range of methods and were subjected to evaluation in vitro of their anti-HIV efficacy. A notable feature of the current study was that any attempt to replace the amino acid moiety of the phosphoramidate with a simple amine lead to a marked, virtually total loss of activity. Such simple phenyl alkylamino phosphate derivatives of either d4T or AZT inhibit HIV replication at cytotoxic concentrations and have no detectable antiviral selectivity. This clearly highlights the vital role played by the amino acid in the antiviral efficacy of the blocked phosphoramidates.

Marked inhibitory activity of masked aryloxy aminoacyl phosphoramidate derivatives of dideoxynucleoside analogues against visna virus infection

Lipophilic masked aryloxyaminoacylphosphoramidate derivatives of 2,3-dideoxynucleoside (ddN) analogues with potent anti-HIV activity (i.e., stavudine [d4T], azidothymidine [AZT], dideoxycytidine [ddC], 3thio-2,3-dideoxy cytidine [3TC], dideoxyadenosine [ddA], and 2,3-didehydro-2,3-dideoxyadenosine [d4A]) activity were evaluated for their activity against visna virus (VV) in sheep choroid plexus (SCP) cells. The activity of several prodrug derivatives against VV proved markedly superior to that of the corresponding free ddN analogues. In particular, the d4A and ddA prodrug derivatives were exquisitely inhibitory in this model system (50% effective concentration [EC50], < or = 0.003 microM), and their anti-VV potency exceeded by at least 200-fold the antiviral potency of the corresponding free nucleosides. Marked differences were noted in the anti-VV potencies of several of the test compounds depending on the nature of the amino acid linked to the 5-phosphate moiety, the nature of the nucleoside, or both. In view of the stability of the prodrugs in lamb serum, the VV infection model in lambs may be considered highly useful for investigating the in vivo antiretroviral efficacy of these type of drugs, particularly the d4T, ddA, and d4A prodrug derivatives.

Lactate cannot substitute for alanine in D4T-based anti-HIV nucleotide prodrugs - despite efficient esterase-mediated hydrolysis

As part of our on-going effort to deliver masked phosphates of antiviral nucleosides inside living cells we have previously discovered that amino acid-derived phosphoramidates are particularly effective. Here we report that lactate analogues, with a simple change of bridging nitrogen for oxygen, are virtually inactive as antiviral agents and apparently do not achieve intracellular nucleoside phosphate delivery.

Metabolism and anti-HIV activity of phosphoramidate derivatives of D4T-MP with variations in the amino acid moiety

The metabolism of different phosphoramidate prodrugs of d4T-MP, in which the phosphate group is linked to a phenyl group and the alkyl ester of an amino acid was studied in crude CEM cell extracts. Significant (80-100%) conversion to the amino acyl d4T-MP metabolite was obtained with derivatives containing L-alanine or methyl-L-aspartic acid. A lower degree of conversion was seen with derivatives containing L-phenylalanine, L-methionine, methyl-L-glutamic acid or L-leucine. Derivatives containing D-alanine, beta-alanine, glycine, L-valine or L-lactate showed no conversion to the amino acyl d4T-MP metabolite. Overall, there was a close correlation between the anti-HIV activity of these prodrugs and their conversion rate to the amino acyl d4T-MP metabolite. Our data suggest that the enzymes involved in the formation of the amino acyl d4T-MP metabolite have a rather stringent specificity for L-alanine as the amino acid moiety. In addition, these enzymes were found to be markedly species-dependent, their activities being highest in mouse serum, followed by guinea pig serum, but only minimal in human serum. Mouse serum therefore appears to be the medium of choice to isolate and identify the enzymes that are involved in the metabolism of these phosphoramidate prodrugs.