Abstract
The first total synthesis of the pyrrolo[2,3-c]quinoline alkaloid trigonoine B (1) was accomplished via a six-step sequence involving the construction of an N-substituted 4-aminopyrrolo[2,3-c]quinoline framework via electrocyclization of 2-(pyrrol-3-yl)benzene containing a carbodiimide moiety as a 2-azahexatriene system. The employed six-step sequence afforded trigonoine B (1) in 9.2% overall yield. The described route could be employed for the preparation of various N-substituted 4-aminopyrroloquinolines with various biological activities.
Highlights
In 2011, two novel alkaloids, namely trigonoine A and B, were isolated from the leaves of Trigonostemon lii by Hao and co-workers [1]
We report the first total synthesis of trigonoine B (1) involving the construction of a pyrrolo[2,3-c]quinoline framework by electrocyclization of 2-(pyrrol-3-yl)benzene containing a carbodiimide moiety as a 2-azahexatriene system
The synthesis of the precursor pyrroloquinoline 9 possessing a substituted amino group at the 4-position could be achieved by the electrocyclization of pyrrol-3-ylbenzene 10 containing a carbodiimide moiety as a 2-azahexatriene system
Summary
In 2011, two novel alkaloids, namely trigonoine A and B, were isolated from the leaves of Trigonostemon lii by Hao and co-workers [1]. In addition to trigonoine B, aplidiopsamine A (2) [2] and marinoquinolines 3 [3] are natural products that possess the pyrrolo[2,3-c]quinoline skeleton (Figure 1). We recently reported the total syntheses of marinoquinolines A (3a), B (3b), and E (3e) comprising the pyrrolo[2,3-c]quinoline skeleton [25].
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