D-Eritadenine (Ia) and L-eritadenine (IIa) were prepared from 5-(adenin-9-yl)-5-deoxyaldofuranoses or enantiomeric 2,3-disubstituted erythronolactones (VIIIb, c, XIV). Oxidation of methyl 2,3-O-isopropylidene-D-ribofuranoside (IX) with periodate in the presence of ruthenium, followed by acid hydrolysis and reduction with sodium borohydride, afforded L-ribonolactone (XI). Its 2,3-O-isopropylidene derivative was subjected to alkaline hydrolysis, followed by oxidation with periodate, reduction with sodium borohydride and reaction with cyclohexanone to give 2,3-O-cyclohexylidene-L-erythronolactone (XIV). Condensation of [U-14C]-adenine with VIIIb, followed by acid hydrolysis, afforded [U-14C-adenine]-D-eritadenine. The threo-eritadenines III and IV were prepared by oxidation of 1-(adenin-9-yl)-1-deoxy-2,3-O-isopropylidenethreitols XVI and XVII with sodium periodate in the presence of ruthenium, followed by acid hydrolysis. Reaction of 9-(2,2-diethoxyethyl)adenine (XIX) with malonic acid gave 4-(adenin-9-yl)-3-butenoic acid (XXI); its methyl ester XXII, prepared by treatment with methanol, was isomerized with triethylamine to give methyl 4-(adenin-9-yl)-2-butenoate (XXIII). Hydroxylation of XXIII with osmium tetroxide afforded the racemic mixture of D- and L-threo-eritadenine (III+ IV). Eritadenines Ia and IIa were active against vaccinia, measles and vesicular stomatitis virus. Eritadenine Ia was also effective against reo- and parainfluenza virus. In general, the antiviral activity of the eritadenines decreased in the order D-erythro (Ia) > L-erythro (IIa) > D- and L-threo (III, IV).