This compound has been obtained by two similar ways: 1) The reaction of 6-chloropurine-2-amine (I) with 6,6-dimethyl-5,7-dioxaspiro[2.5]octane-4,8-dione (II) by means of K2CO3 in DMF gives the expected condensation product (III), which is methanolized with HCl/methanol yielding 2-[2-(2-amino-6-methoxypurin-9-yl)ethyl]malonic acid dimethyl ester (IV). The reduction of (IV) with NaBH4 in tert-butanol/methanol affords the corresponding diol (V), which is finally converted into pecnciclovir by hydrolysis with 2N NaOH. 2) The reaction of purine (I) with 3-bromopropane-1,1,1-tricarboxylic acid triethyl ester (VI) by means ofK2CO3 in DMF gives the expected condensation product (VII), which is partially decarboxylated with sodium methoxide in methanol yielding 2-[2-(2-amino-6-chloropurin-9-yl)ethyl]malonic acid diethyl ester (VIII). The reduction of (VIII) with NaBH4 in tert-butanol/methanol followed by acetylation with acetic anhydride affords the corresponding diol diacetate (IX), which is finally converted into penciclovir by hydrlysis with 2N HCl.
The synthesis of penciclovir by two related ways has been reported: 1) The reaction of 2-(hydroxymethyl)butane-1,4-diol (I) with formaldehyde (or an aldehyde such as trimethylacetaldehyde) (II) by means of H2SO4 (or p-toluenesulfonic acid, TsOH) gives the dioxane (III), which by reaction first with methanesulfonyl chloride and triethylamine and then with NaI in acetone affords the corresponding 5-(2-iodoethyl)-1,3-dioxane (IV). The reaction of (IV) with 2-amino-6-chloropurine (V) by means of K2CO3 in DMF gives the corresponding condensation product (VI), which is finally hydrolyzed and deprotected with refluxing 2M aqueous HCl. 2) The reaction of triol (I) with 2,2-dimethoxypropane (VII) by means of TsOH gives the corresponding 1,3-dioxane (VIII), which by reaction with triphenylphosphine and CBr4 is converted to the 5-(2-bromoethyl) derivative (IX). The reaction of (IX) with the purine (V) by means of K2CO3 as before affords the corresponding condensation product (X), which is hydrolyzed and deprotected with 2M HCl as before.
A synthesis of famciclovir that corresponds to that previously published and studies on its oral bioavailability in rats and mice, identifying famciclovir as the preferred prodrug of BRL-39123 (penciclovir), have been published.
The reaction of purine (I) with 3-bromopropane-1,1,1-tricarboxylic acid triethyl ester (II) by means ofK2CO3 in DMF gives the expected condensation product (III), which is partially decarboxylated with sodium methoxide in methanol yielding 2-[2-(2-amino-6-chloropurin-9-yl)ethyl]malonic acid diethyl ester (IV). The reduction of (IV) with NaBH4 in tert-butanol/methanol followed by acetylation with acetic anhydride affords the corresponding diol diacetate (V), which is finally converted into famciclovir by reductive dechlorination with H2 over Pd/C in ethyl acetate/triethylamine.