Photooxidation of acyclovir in aqueous solution

Photodegradation of an aqueous solution of acyclovir in phosphate buffer (pH 7) under aerobic conditions was studied with light of wavelength > 270 nm. Three major products were isolated and identified on the basis of IR, NMR and mass spectral studies. The products are: (2-hydroxyethoxy)methyl spiroiminodihydantoin (2), (2-hydroxyethoxy)methyl(amino)-2-imino-1,2-dihydroimidazole-5-one (3), and 2,2-diamino-4-[(2-hydroxyethoxy)methyl]amino)-5-[2H]-oxazolone (4). Furthermore the effects of D2O as reaction medium, addition of sodium azide and absence of oxygen on the photodegradation of acyclovir were examined, the observations indicating the involvement of singlet oxygen. The formation of the products is explained by the photooxidation of acyclovir.