Corynantheine-type indole alkaloid

Hirsutine (85) is a corynantheine-type indole alkaloid with a C/D cis ring juncture (pseudo stereochemistry). This compound has recently been found to exhibit highly potent inhibition of the replication of the strains of influenza A (subtype H3N2) [63]. The EC50 of hirsutine was 11- to 20-fold more potent than that of the clinically used ribavirin. Exploration of the important structural features of this molecule revealed that the stereochemistry at C-3 (.R) and C-20 (R) as well as the presence of the Nb lone pair were essential for the anti-influenza A activity. Thus, the C-3 epimer, dihydrocorynantheine (86) (normal stereochemistry), was much less active than hirsutine (85). 

Two important books on the biogenesis of indole alkaloids have been published (5, 6), therefore we do not intend to cover the literature of the biogenesis of corynantheine- and yohimbine-type alkaloids. Our chapter begins with the structure elucidation of the alkaloids isolated during the past two decades and proceeds with the synthesis, transformation, as well as spectroscopy of the alkaloids in question. 

In the first slide I summarized what I am going to talk today, the list of target indole alkaloids. My talk consists of two parts, the first part is on the synthesis of yohimbine and its group and the second part on the synthesis of corynantheine and heteroyohimbine types of alkaloids. 

Until recently only monomeric indole and oxindole alkaloids had been isolated from the bark and leaves of Uncaria gambir Roxb. (Rubiaceae). Amongst these were alkaloids of the corynantheine and yohimbine types."" However, from a different batch of plant material five new isomeric alkaloids, the roxburghines A—E, C31H32O2N4, have been isolated in 0.0005—0.005 % yield. ... 

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