Synthesis and structure determination of a nucleoside-derived new heterocyclic system: 8H, 10H, 15b(S)-2,3,6,7-tetrahydro-1,5,3- dioxazepino[3,2-c]indolo[3,2-g]pteridine-7-one

Condensation of 5-aminocytidine with N-methylisatin yielded a new heterocyclic system, 8H,10H,15b(S)-2,3,6,7-tetrahydro-1,5,3-dioxazepino[3,2- c]indolo[3,2-g]pteridine-7-one. The assignment of S configuration at position 15b, which is generated as a result of the nucleophilic attack of the 5'- hydroxy of the ribosyl moiety at the position 6 of the cytosine base, is discussed.