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Abstract

Reaction of stereoisomeric 8-bromo-9-(2,3-O-isopropylidene-2,3,4-trihydroxybutyl)adenines (8) with concentrated aqueous ammonia, sodium hydride, potassium tert-butoxide, or 1,8-diazabicyclo[5,4,0]undec-7-ene afforded 4e-O,8-anhydro-9-(2,3-O-isopropylidene-2,3,4-trihydroxybutyl)adenines 9 (derivatives of 1,3-oxazepino[2,3-e]adenine). The CD spectra of optically active stereoisomers of 9 have been studied and it was found that for threo isomers 9a and 9b their character corresponds to 5'-O,8-cycloadenosine. The compounds 9 were also prepared by oxidative cyclization of 9-(2,3-O-isopropylidene-2,3,4-trihydroxybutyl)adenines (7) with lead(IV) acetate in benzene. Reaction of 9-(4-hydroxybutyl)adenine (14) with lead(IV) acetate smoothly afforded the seven-membered ring derivative, 4'-O,8-anhydro-9-(4-hydroxybutyl)adenine (15); no anhydro products with five-, six-, and eight-membered ring were found. 2',3'-O-Isopropylideneinosine (16) reacted with lead(IV) acetate to give 5'-O,8-cyclo-2',3'-O-isopropylideneinosine (17) whereas 9-(4-hydroxybutyl)hypoxanthine (18) afforded no cyclic products.

Keywords: Nucleosides; Acyclic analogs; Purine derivatives.