NMR structural analysis of braznitidumine: a new indole alkaloid with 1,2,9-triazabicyclo[7.2.1] system, isolated from Aspidosperma nitidum (Apocynaceae)

摘要

The phytochemical study of the stem bark of Aspidosperma nitidum led to the isolation of a new type of indole alkaloid with a 1,2,9-triazabicyclo[7.2.1] system, which has been called braznitidumine 1. The characterization of its chemical structure was carried out by IR, UV, ESIMS, and 1H, 13C, and 15N NMR by using 1D and 2D (1H 1H COSY, 1H 1H NOESY, 1H 13C HSQC and 1H 13C HMBC) experiments. 1H 1H NOESY results showed that 1 presents a folded conformation with the approximation of the indole and the imidazolidine di-hydropyran groups. This configuration was investigated by theoretical calculations involving geometry optimization (DFT/BLYP/6-31G*) for the conformational analysis of this alkaloid. It confirmed the distance between the two groups in agreement with the NOESY experimental data.