Lundurine alkaloids

The major alkaloids of K. tenuis are lundurines A-C (220-222), which contain a novel ring system incorporating a cyclopropyl unit. These alkaloids are obviously closely related biogenetically to the lapidilectines and may well be derived from an intermediate such as lO-methoxy-3-oxolapidilectine B 181). 

The main tetracyclic core of these alkaloids has been synthesized via %-endo-dig cyclization of alkynyl indole catalyzed by AuCls, which affords exclusively the desired azocine[5,4—hjindole derivative (Scheme 1.41) [239]. Thus, based on previously reported results, our objective was to develop an efficient approach toward the total synthesis of lundurines. 

Lundurines A-D [17, 18] are a new type of indole alkaloids characterized by the presence of a cyclopropyl moiety embedded within a hexacyclic ring system that includes a l//-azocine[5,4-h]indole ring unit (Fig. 4.4). 

Lundurines are a new type of indole alkaloids, which are characterized by an unusual carbon skeleton (Fig. 4.7) [17, 18]. In addition, lundurines B and D have displayed in vitro cytotoxicity towards B16 melanoma cells (lundurine B IC50 2.8 pl/mL), and lundurine B is also proved effective in circumventing multidrug resistance in vincristine-resistant KB cells. 

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