RESIDUE 28Y 18 CONECT C4 3 C5 N3 N9 CONECT C5 3 C4 C6 N7 CONECT C6 3 C5 N1 O6 CONECT C8 3 N7 N9 H1 CONECT N1 3 C6 C2 H2 CONECT N2 2 CAB C2 CONECT N3 3 C4 CAD C2 CONECT O6 1 C6 CONECT N7 3 C5 C8 H3 CONECT N9 2 C4 C8 CONECT CAD 3 N3 CAB H5 CONECT CAB 3 N2 CAD H6 CONECT C2 3 N1 N2 N3 CONECT H1 1 C8 CONECT H2 1 N1 CONECT H3 1 N7 CONECT H5 1 CAD CONECT H6 1 CAB END HET 28Y 18 HETSYN 28Y N2,3-ethenoguanine HETNAM 28Y 3H-imidazo[2,1-b]purin-4(5H)-one FORMUL 28Y C7 H5 N5 O1