Unusual indole alkaloid–pyrrole, –pyrone, and –carbamic acid adducts from Alstonia angustifolia

Two new alkaloids from Asparagus stipularis Forssk. roots

“…The two signals at d C 136.7 (C-8) and 132.7 (C-2), were in agreement with the presence of anindole moiety (Wehrli and Nishida, 1979;Ashour et al, 2007). Furthermore, the signals at d C 109.3-136.7 (seven methines and five quaternary carbons), were in agreement with the presence of indole and pyrrole moieties (Monnerat et al, 2005;Tan et al, 2010). The two signals at d C 50.5 and 25.3 were assigned to the two methylene groups (a-and b-CH 2 , respectively).…”

“…, which were assigned to protons at positions 4, 5, 6 and 7, respectively and in agreement with an ortho-disubstituted benzene ring. Another three correlated aromatic signals with small coupling constants, at d H 6.91 (1H, br.s), 6.27 (1H, dd, J = 4.2, 2.4 Hz) and 7.37 (1H, dd, J = 4.2, 1.8 Hz), were assigned to the protons at positions 2 0 , 3 0 and 4 0 , respectively on the pyrrole moiety (Silverstein et al, 1991;Tan et al, 2010). Further examination of the 1 H NMR spectrum, showed a singlet signal at d H 9.81 (NH) and two correlated signals at d H 4.47 (2H, m) and 3.39 (2H, m), which were assigned to two methylene groups (a-and b-CH 2 , respectively).…”

Living on pyrrolic foundations – Advances in natural and artificial bioactive pyrrole derivatives

“…Considering alkaloids containing a pyrrole ring as a constituent of their structure, alkaloids obtained from marine creatures are of particular interest [4e10]. Research is being also carried out on systems produced by plants [24]. In recent years, lamellarins (Fig.…”

Development of an Alkaloid–Pyrone Annulation: Synthesis of Pleiomaltinine

“…Further rearrangements of the alkaloidal-pyrone structures were observed, including a formal [1,3] shift to access a 1-substituted carbazole. Application of the pyrone annulation to the plant-derived alkaloid pleiocarpamine resulted in the synthesis of the unusual alkaloid-pyrone pleiomaltinine.…”

“…Rearrangements were also attempted with cycloadducts 17 and 19 in an attempt to produce carbazole-hydroxypyrone structures bearing a fully substituted carbon. Unfortunately, the use of thermal and Lewis acid (for example, Zn(OTf) 2 , Yb(OTf) 3 , or Sc(OTf) 3 ) conditions with these substrates has thus far proved unsuccessful. The major reaction pathway observed in these cases was retrocycloaddition to afford the starting indole or b-carboline.…”