Macroline, akuammiline, sarpagine, and ajmaline alkaloids from Alstonia macrophylla

Concise Total Synthesis of (−)‐Affinisine Oxindole, (+)‐Isoalstonisine, (+)‐Alstofoline, (−)‐Macrogentine, (+)‐Na‐Demethylalstonisine, (−)‐Alstonoxine A, and (+)‐Alstonisine

“…[16] Unfortunately there was a typographical error on page 3052 of the Tetrahedron Letters, 2015, 56, 3052 [17] which mislabelled the configuration at C-7 as R ; however, the synthesis of the correct stereochemistry 7 S and the properties of synthetic (˗)-affinisine oxindole ( 26 ) are in good agreement with the structure reported by Kam et al . [18] The first enantiospecific total synthesis of (˗)-affinisine oxindole ( 26 ), was carried out in 2015 (see Scheme 2 and later section), [17] which confirmed the absolute configuration at C(7) and C(16) proposed by Kam et al . [18] Later the absolute configuration of compounds 14 , 19 , 20 , and 23 were further confirmed by X-ray crystallographic analysis (Figure 2).…”

“…[18] The first enantiospecific total synthesis of (˗)-affinisine oxindole ( 26 ), was carried out in 2015 (see Scheme 2 and later section), [17] which confirmed the absolute configuration at C(7) and C(16) proposed by Kam et al . [18] Later the absolute configuration of compounds 14 , 19 , 20 , and 23 were further confirmed by X-ray crystallographic analysis (Figure 2). [14a] This stereospecific approach provided entry into either the spirocyclic oxindole of the chitosenine-series 6 [C-7( R )] or the opposite configuration at C(7) in the alstonisine-series 1–4 (Figure 1).…”

“…NOE studies of the synthetic material confirmed the configuration of the spirocyclic center, the configuration at C(16), and the geometry of the C(19),C(20)-double bond to be the same as those reported by Kam et al . [16],[18] …”

“…[16,24,36] The correct C-7 designation of configuration, which is 7 R for macrogentine ( 57 ) and 7 S for alstonoxine A ( 56 ), was recently published in a report in 2014. [18] The natural oxindole (−)-macrogentine ( 57 ) was the second sarpagine/ macroline oxindole isolated, after isoalstonisine ( 35 ), to possess the 7 R configuration at the spirocenter.…”

Indole alkaloids from the Marquesan plant Rauvolfia nukuhivensis and their effects on ion channels

“…From a structural point of view, most of these bioactive alkaloids are found under an additional cyclized form that occurs between an oxygen placed at C-17 and the C-21 carbon (Bi et al, 1994;Liao et al, 2006;Lim et al, 2014;Tran and Kwon, 2005;Wilk et al, 2009). The postulated non cyclized product called macroline that should be at the origin of all macroline derivatives has never been found in nature but two close analogues of this putative precursor have been reported (Gao et al, 2011(Gao et al, , 2012.…”