Prianosin, synthesis

Nucleophilic attack of the electron-rich aromatic ring 124 to the cationic complex 123, and intramolecular amination afforded the intermediate 125 for the synthesis of discorhabdin and prianosin alkaloids [29]. 

Yamamura et al. developed an efficient route to the synthesis of the A, B, C, D, and E rings of the prianosins and discorhabdins, which led them successfully to synthesize discorhabdin C (Scheme 59) (210-212). Because their route involves the synthesis of the pyrroloquinoline skeleton of the pyrroloquinoline type alkaloids (213-217), they have also achieved the synthesis of batzelline C and isobatzelline C (213,214). Their synthesis involved first the construction of the C, D, and E rings as in 505, starting from 502, which was synthesized in three steps (212). Reaction of 502 with... 

A synthetic methodology has been under investigation for the synthesis of discorhabdins and prianosins by Confalone et al. using intramolecular... 

Our group accomplished the total syntheses of discorhabdin C in 1992 [38], makaluvamine F in 1999 [39, 40], and discorhabdin A in 2002 [41, 42]. We also accomplished the first total synthesis of prianosin B in 2009 [43]. We now report the progress towards the synthesis of pyrroloiminoquinone alkaloids, mainly since 2000 including our studies, in this chapter. 

Discorhabdin alkaloids have the richest structure-diversity among the marine pyrroloiminoquinone alkaloids, and new discorhabdins are still being discovered. Although many synthetic studies have been carried out, only a few total syntheses of the natural discorhabdins have been reported. The total synthesis of discorhabdin C was accomplished by our group and Yamamura s group at almost the same time, and later by the Heathcock group. Heathcock et al. also synthesized discorhabdin E at the same time. Those discorhabdins are rather simple. The more complex discorhabdins, discorhabdin A and prianosin B, were synthesized only by us. 

Prianosin B is the oxidized discorhabdin A, whose C16-17 bond is double bond. We found that the detosylation and dehydrogenation reaction of the pyrroloiminoqumone unit proceeded using a catalytic amount of NaN3 in good yield. We then applied the reactions to the total synthesis of prianosin B (Scheme 33). Thus, the treatment of 98... 

Wada Y, Otani K, Endo N, Harayama Y, Kamimura D, Yoshida M, Fujioka H, Kita Y (2009) The first total synthesis of prianosin B. Tetrahedron 65 1059-1062... 

Nishiyama S, Cheng JF, Tao XL, Yamamura S (1991) Synthetic studies on novel sulfur-containing alkaloids, prianosins and discorhahdins total synthesis of discorhabdin C. Tetrahedron Lett 32 4151-4154... 

Sequences for the synthesis of the more complex discorhabdins, discorhabdin A and prianosin B, have been developed only in our laboratoiy. Discorhabdin A, which has a unique sulfur-containing fused ring structure, incorporating azacarbocyclic spirocyclohexanone and pyrroloiminoquinone systems, displays the most powerful cytotoxic activity among isolated members of the discorhabdin family. 

Knolker, H.J. and Hartmann, K. (1991) Transition metal-diene complexes in organic synthesis part 8. Iron-mediated approach to the discorhabdin and prianosin alkaloids. Synlett, 428-430. 

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