Lipophilic 5'-alkyl phosphate esters of 1-.beta.-D-arabinofuranosylcytosine and its N4-acyl and 2,2'-anhydro-3'-O-acyl derivatives as potential prodrugs

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Abstract
Lipophilic 5''-(alkyl phosphate) esters of 1-.beta.-D-arabinofuranosylcytosine (ara-C) and several N4-acyl and 3''-O-acyl-2,2''-anhydro derivatives of ara-C were synthesized as potential prodrugs of ara-C 5''-monophosphate (ara-CMP). Alkylphosphorylation of ara-C, N4-palmitoyl-ara-C and N4-stearoyl-ara-C was achieved in a single continuous operation by allowing the nucleoside to react with POCl3 in trimethyl or triethyl phosphate and adding the appropriate anhydrous alcohol directly to the intermediate phosphorodichloridate without isolation. Similar reaction of cytidine yielded cytidine 5''-(alkyl phosphate) esters, which on treatment with myristoyl or palmitoyl chloride in the presence of boron trifluoride gave 3''-O-acyl-2,2''-anhydro-ara-C 5''-(alkyl phosphate) esters. Ara-C 5''-(n-butyl phosphate), N4-palmitoyl-ara-C 5''-(n-butyl phosphate) and 2,2''-anhydro-3''-O-palmitoyl-ara-C 5''-(n-butyl phosphate) were tested against L1210/ara-C leukemia in mice in the hope that this kinase-deficient tumor would respond to treatment with these prephosphorylated derivatives, but no activity was observed. Of the simple 5''-(alkyl phosphate) esters tested in culture against L1210 leukemic cells, only ara-C 5''-(glyceryl phosphate) showed toxicity comparable to ara-CMP (ID50 [median inhibitory dose] = 0.35 and 0.65 .mu.M, respectively), suggesting that .beta.-hydroxyalkyl phosphate esters may be worthwhile to examine further as prodrugs of ara-CMP.