New synthetic protocol for the preparation of nucleoside 5'-(N-aryl)phosphoramidate monoesters 4 was developed. It consisted of a condensation of the corresponding nucleoside 5'-H-phosphonates with aromatic- or heteroaromatic amines promoted by diphenyl phosphorochloridate, followed by oxidation of the produced H-phosphonamidates with iodine/water. 5'-(N-Aryl)phosphoramidate monoesters derived from 3'-azido-3'-deoxythymidine (AZT) or 2',3'-dideoxyuridine (ddU) nucleosides and various aromatic and heteroaromatic amines were evaluated as potential anti-HIV drugs. It was found that these compounds act most likely as pronucleotides and that some of them have therapeutic indices superior to those of the reference AZT.

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Nucleotides, their analogues, and other phosphate esters and phosphoramidates often contain the triethylammonium cation as a counterion. We found that this may be lost during chromatographic purification or concentration of solutions, yielding products in acidic forms or containing sub-stoichiometric amounts of the counterion. This in turn may be detrimental, e.g., due to possible decomposition of a compound or inaccurate sample preparation. Correlations between the structure of studied compounds and their susceptibility for cation loss were analyzed. Modifications in preparative techniques were developed to obtain the studied compounds with stoichiometric anion to cation ratios.ᅟGraphical AbstractTriethylammonium salts of phosphate esters and phosphoramidates may lose the cationic component during chromatography or evaporation of solventElectronic supplementary materialThe online version of this article (doi:10.1007/s00216-014-8397-0) contains supplementary material, which is available to authorized users.

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