Unambiguously confirming natural products with high C/H ratio or proton-deficient and multi heteroatoms is challenging. A time-saving module-assembly calculation method named ‘Dooerafa’ including of constructing the meta-structures by a grafting method based on the crucial and the limited two dimensional nuclear magnetic resonance (2D NMR) correlations, ‘ring-contraction strategy’ based on mechanic force field and quantum chemical theory, and self-assemble calculations in Python programing for shaping up the structural candidates along with DFT-GIAO calculation was studied. And this method, verified by a known alkaloid spiroreticulatine with structure determined by X-ray diffraction, was performed for the structural elucidation of aaptourinamine which was isolated from marine sponge Aaptos suberitoides, showing us a brand new scaffold of imidazo[4,5,1-ij]pyrrolo[3,2-f]quinolin-7(8H)-one which has a biosynthetically relationship with the bioactive and structurally unique aaptamine alkaloid.