Crystal structure of 1,2,5-trimethyl-1,2,3,4-tetrahydropyrido[ 4,3-b]carbazole (guatambuine), C18H20N2, from Aspidosperma subincanum Mart.

Abstract

Source of materialThe title compound, guatambuine, a pyrido [4,3-b]carbazole alkaloid, was isolated from the chloroform fraction of the ethanol extract from the stem of Aspidosperma subincanum, a tree of the Apocynaceae family. The crystals of the guatambuine were obtained by recrystallization from MeOH at room temperature. Experimental detailsH atoms attached to C atoms were located on stereochemical grounds and refined with fixed bond lengths and angles, each riding on a carrier atom, with an isotropic displacement parameter amounting to 1.5 (for methyl) or 1.2 (for the other H atoms) times the value of the equivalent isotropic displacement parameter of the atoms to which they are bonded. The H atom attached to the N atom was refined freely. DiscussionThe title compound, 1,2,5-trimethyl-1,2,3,4-tetrahydropyrido [4,3-b]carbazole, belongs to the class of indole alkaloids, a large group of biologically active compounds of naturally occurrence. The indole alkaloids have numerous biological activities such as antitumor, anti-microbial, anti-hypertensive and stimulant for the central nervous system [1]. The occurrence of the indole alkaloids is described at the Apocynaceae, Rubiaceae, and Loganiaceae families [2]. Among the Apocynaceae, the genus Aspidosperma is especially rich in indole alkaloids [3]. Aspidosperma subincanum is a Brazilian medicinal plant used in the treatment of general debility, digestive tract disorders, dysentery and against fever [4]. Previous separate investigations of this plant revealed the presence of more than 15 indole alkaloids [5]. In our search for structurally unique and biologically interesting compounds from Brazilian medicinal plants we are working with the stem and stem bark of A. subincanum. From the ethanolic extract of stem of A. subincanum we isolated guatambuine or N-methyltetrahydroolivacine, which has received considerable interest as result of this anti-tumor activity [6]. Guatambuine was isolated previously from others Aspidosperma species [7].

Aspidosperma species: A review of their chemistry and biological activities

“…In guatambuine (31) and N-methyltetrahydroellipticine (26) the atoms of three rings (A, B and C) are nearly coplanar and the heterocyclic ring D is in a half-chair conformation. The C19 and C14 atoms of the heterocyclic ring D are located in the same plane as the rings A, Β and C, while atoms C3 and N4 are located above and below, respectively (Simone et al, 2006). The chemical shifts of similar carbons of both compounds are similar.…”

“…In 2009, Santos and coworkers isolated oleic acid and guatambuine (u-alkaloid C, N-methyltetrahydroolivacine, 31) from the stem bark of A. subincanum (Santos et al, 2009, Ribeiro et al, 2015. Guatambuine (31) showed antitumour activity (Simone et al, 2006). Subincanadine E (pericine, 38) was first isolated from the Picralima nitida cell suspension culture line in 1982 by Arens and co-workers.…”