acetone or acetonitrile at ice bath temperature the 1 alkyloxycarbonyl derivatives 7 12 in tables 3 5 were synthesized from the reaction of the potassium salt of 5 fu with the corresponding alkyl chloroformates in acetone at room temperature for one hour the 3 alkylcarbonyl derivatives 13 16 in tables 6 8 were synthesized from the reaction of the corresponding 1 3 bisalkylcarbonyl derivatives with one equivalent of t butylamine in ether at room temperature until the reaction was complete by tlc the 1 3 bisalkylcarbonyl derivatives 17 20 in tables 9 and 10 were synthesized from the reaction of 5 fu with three equivalents of the corresponding acyl chlorides in the presence of three equivalents of triethylamine at room temperature for three hours the diffusion cell experiments were conducted as described by sloan et al in j invest dermatol vol 87 page 244 1986 and sherertz et al in j invest dermatol vol 89 page 147 1987 the results from these experiments are recorded in the tables as j i flux of 5 fu through the skin indicating the relative extent of transdermal delivery c s a measure of the amount of 5 fu in the skin after the applied formulation of prodrug was removed indicating the relative extent of dermal delivery and j j flux.