This chapter deals with three biologically active natural products, triclisine, rufescine, and imerubrine. The B3PW91/6-311+G(d,p) level of DFT is used to obtain the optimized structures of molecules under study. We carried out vibrational analyses of triclisine and rufescine at their optimized structures and provided detailed assignments of the prominent vibrational modes. The computed infrared frequencies are found to be in good agreement with the experimentally determined FT-IR spectra of both molecules. Similarly, their properties are also studied with the help of HOMO, LUMO, MESP surfaces, and several electronic as well as thermodynamic parameters. The vibrational spectrum of imerubrine is analyzed and the normal modes are accurately assigned based on the potential energy distribution. The nuclear magnetic resonance shifts of imerubrine are also obtained, analyzed, and compared with the corresponding experimental values. The chemical reactivity of imerubrine is also explained using HOMO, LUMO, and MESP surfaces as well as a number of reactivity descriptors.