Indolalkaloide aus den Blättern von Pleiocarpa pycnantha (K. SCHUM.) Stape, var. tubicina (Stapf) Pichon 7. Mitteilung über Pleiocarpa‐Alkaloide [1]

Abstract

Es wird über die Isolierung und Identifizierung der 6 Indolalkaloide Kopsinin (I), 19,20‐Dihydroakuammicin (II), Tubifolin (III), Tubifolidin (IV), Tubotaiwin (V) und Tuboxenin (VII) aus den Blättern von Pleiocarpa pycnantha (K. SCHUM.) STAPF, var. tubicina ( STAPF) PICHON berichtet.

Total synthesis of (−)-kopsinine and ent-(+)-kopsinine

“…17 Although employed in our original synthesis with an analogous substrate bearing a N-benzyl group, 12 the alternative conversion of 12 to the corresponding methyl dithiocarbonate and subsequent SmI 2 -promoted ring closure for formation of the bicyclo[2.2.2]octane 13 proved less productive (45%), albeit without optimization. Reductive removal of the lactam carbonyl of (−)- 13 upon treatment with BH 3 ·THF (THF, 0 °C, 1 h) provided (−)- 14 and subsequent cleavage of the Cbz group (H 2 , 10% Pd/C, EtOAc/MeOH, 25 °C, 30 min, 82% over two steps) afforded natural (−)-kopsinine ( 5 , [α] D −56 ( c 0.15, CHCl 3 ) vs [α] D −76.9 ( c 2.09, CHCl 3 ) 15a and [α] D −69 ( c 0.856, CHCl 3 ) 15c ), which otherwise proved identical in all respects with reported properties of the natural product. We are unclear about the origin of the discrepancy in our optical rotation for (−)-kopsinine relative to that recorded for the natural product 15 as well as those reported for additional synthetic samples ([α] D −43.1 ( c 1.8, CHCl 3 ) 14d and [α] D −65.8 ( c 1.13, CHCl 3 ) 14e ) although we can conclusively say that it is not derived for either the enantiopurity (>99%, Fig.…”

“…The residue was purified by column chromatography (basic alumina, gradient elution, 100% CH 2 Cl 2 to 10% MeOH–CH 2 Cl 2 ) to provide (−)-kopsinine ( 5 , 2.6 mg, 82% over two steps) as a white solid identical in all respects with authentic material: For natural (−)-kopsinine 5 : [α] D 23 −56 ( c 0.15, CHCl 3 ); for ent -(+)-kopsinine 5 : [α] D 23 +57 ( c 0.84, CHCl 3 ) vs lit. [α] D 23 −76.9 ( c 2.09, CHCl 3 ) 15a and [α] D 23 −69±3 ( c 0.856, CHCl 3 ) 15c for natural (−)- 5 ; 1 H NMR (600 MHz, CDCl 3 (passed through a basic alumina)) δ 7.16 (d, J = 7.3 Hz, 1H), 6.98 (t, J = 7.6 Hz, 1H), 6.75 (t, J = 7.4 Hz, 1H), 6.66 (d, J = 7.7 Hz, 1H), 3.76 (s, 3H), 3.34 (q, J = 8.3 Hz, 1H), 3.12 (d, J = 13.5 Hz, 1H), 2.92–3.01 (m, 3H), 2.89 (t, J = 9.6 Hz, 1H), 2.79 (t, J = 11.7 Hz, 1H), 2.64 (t, J = 11.2 Hz, 1H), 1.87–1.96 (m, 2H), 1.52–1.62 (m, 2H), 1.35–1.45 (m, 2H), 1.19–1.34 (m, 4H); 13 C NMR (150 MHz, CDCl 3 ) δ 174.8, 149.1, 140.7, 126.6, 121.6, 119.7, 110.8, 68.4, 66.7, 57.9, 52.0, 50.7, 47.6, 43.8, 36.5, 34.8, 33.92, 33.88, 32.1, 31.8, 17.1; IR (film) υmax 2922, 1726, 1458, 1203, 741, 670 cm −1 ; HRMS (ESI) m/z 339.2067 [(M+H) + , C 21 H 26 N 2 O 2 requires 339.2067].…”

“…However, our original approach suffered from a low conversion in the transformation of 1 to the key conjugate addition substrate and, unlike the efforts leading to 2–4 , was conducted with racemic material. Herein, we report the extension of these studies to the total synthesis of (−)-kopsinine ( 5 ), a Kopsia alkaloid first isolated from Kopsia Longiflora Merr., 15 as well as its unnatural enantiomer ent -(+)-kopsinine that addresses these limitations of our initially reported approach.…”

Synthesis of 3,3′-Disubstituted Indolenines Utilizing the Lewis Acid Catalyzed Alkylation of 2,3-Disubstituted Indoles with Trichloroacetimidates

“…1 Similar indolenine substructures are present in many complex molecules, like strictamine, 2 koumine 3 and tubifoline 4 (Figure 1). In addition, many indoline containing structures (like aspidophylline A 5 and communesin B 6 ) appear readily accessible from similar indolenine substructures.…”

Henrycinols A and B, Two Novel Indole Alkaloids Isolated from Melodinus henryiCraib

“…The dried root powder (1.0 kg) was extracted with 95% EtOH under reflux. The EtOH extracts were concentrated, and the residue was treated with 5% AcOH, followed by neutralization with NH 4 OH to result in pH 9. The aq.…”