Syntheses of Enantiomeric N-(3-Hydroxy-2-phosphonomethoxypropyl) Derivatives of Purine and Pyrimidine Bases

Abstract

Methods of preparation of N-(3-hydroxy-2-phosphonomethoxypropyl) (HPMP) derivatives of (2S)- and (2R)-configuration (compounds I and XXVII, respectively) are described. The general method starts from the corresponding N-(2,3-dihydroxypropyl) derivatives which were converted either into the (R)-enantiomers XIII by reaction of the base with (R)-glycidol butyrate (XII) in the presence of cesium carbonate and subsequent methanolysis, or into the (S)-enantiomers XI by alkylation of the base with (R)-2,2-dimethyl-4-tosyloxymethyl-1,3-dioxolane (V) in the presence of the same reagent. The amino groups on the heterocyclic base in compounds XI and XIII were benzoylated by silylation followed by reaction with benzoyl chloride and the obtained N-benzoates XV and XVII on reaction with trityl chloride afforded the corresponding 3'-O-trityl derivatives XVI and XVIII. These compounds were condensed with bis(2-propyl) p-sulfonyloxymethylphosphonate (XXIII) in dimethylformamide in the presence of sodium hydride to give the fully protected diesters XXIV and XXVIII. These compounds could be selectively acid-hydrolyzed to remove the trityl group only under formation of compounds XXXV, or methanolyzed and then acid-hydrolyzed to remove the trityl and N-benzoyl groups and lead to compounds XXVI and XXX, or treated with bromotrimethylsilane to remove the trityl and 2-propyl group to give phosphonates of the type XXXI. All the three types of compounds were then converted into free phosphonates of the (S)-series (I) and the (R)-series (XXVII). Derivatives of cytosine (Ia, XXVIIa), adenine (Ib, XXVIIb), 2,6-diaminopurine (Ic, XXVIIc) and guanine (Id, XXVIId) were prepared. Condensation of the partially blocked adenine deriavtive XXXV with the tosyl derivative XXIII and subsequent deprotection afforded 9-(S)-(2,3-diphosphonomethoxy propyl)adenine (XLIII). Reaction of the same compound XXXV or its (R)-enantiomer XXXVIII with diethyl phosphonate , followed by deblocking, afforded 3'-O-phosphoryl derivatives (S)-HPMPA (XXXVII) and (R)-HPMPA (XL).