Concise total synthesis of (+/-)-aspidospermidine and computational study: FT-IR, NMR, NBO, NLO, FMO, MEP diagrams

Abstract

Aspidospermidine is a member of the compound class known as aspidospermaten-type alkaloids. Aspidospermidine is among the most highly sought aspidosperma alkaloid targets because it comprises the basic skeletal features of this family of natural products, particularly the complex and characteristic pentacyclic ABCDE framework. In this study, we used a new strategy developed to synthesize (+/-)aspidospermidine. The key steps involve a novel cyclization in a single step through an indoline substructure, leading to a versatile pentacyclic intermediate. The power of this concept has been demonstrated through the expedient, total syntheses of well-known alkaloid natural products including limaspermidine, vincadifformine, minovincine and cylindrocarine. Additionally, the PES scan has been performed to determine the stable conformers of the aspidospermidine compound at B3LYP/6-31G(d,p) level of theory in the gas phase and the stable conformers have been used to further analyses. The H-1 and C-1 NMR chemical shifts of the aspidospermidine compound have been observed by NMR spectroscopy and compared with the simulated by the GIAO (Gauge-Independent Atomic Orbital) approach. The vibrational modes determined by the FT-IR spectroscopy has been compared to the simulated vibrational modes of the aspidospermidine. The NBO analysis has been employed to elucidate the important intramolecular interactions causing the molecular stability and the optical properties of the aspidospermidine have been investigated by NLO analysis. The FMO analysis and MEP diagrams have been used to predict the physicochemical and quantum chemical properties being important to explore the chemical reactivity behavior of the aspidospermidine. (C) 2018 Elsevier B.V. All rights reserved.