Prianosins C and

Zyzzya genus [58]. The structure of prianosin A (= discorhabdin A) (52), including its absolute configuration, was unequivocally defined by X-ray analysis [54], while those of discorhabdins B (54) and D (57) were based on spectral data. The previous structures proposed for prianosins C and D [55] were revised to 2-hydroxydiscorhabdin D (56) and discorhabdin D (57), respectively [59]. A plausible biosynthetic pathway for these compounds suggests the involvement of a-amino acids tyrosine (C-l-N-9) and tryptophan (C-10-C-21) [55]. 

Kobayashi, J., Cheng, J.-F., Yamamura, S., and Ishibashi, M. (1991e) Revised structures of prianosins C and D, antineoplastic alkaloids from the Okinawan marine sponge Prianos mdanos. Tetrahedron Lett., 32, 1227-1228. 

The structure elucidation of prianosin C (488) and prianosin D (484) were first carried out with their acetate forms because of their high polarity and instability in solution. Their structures were determined as C (491) and D (492), and the corresponding acetate derivatives as C (489) and D (490) using spectroscopic techniques, including H- C COSY, DEPT, HOHAHA, and HMBC. 

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... 

Knolker et al. have developed a one-pot diastereoselective spiroannela-tion by electrophilic substitution of an aromatic system with an iron-complexed cation, which led to the construction of the A, B, C, and D rings of the prianosins and discorhabdins. This novel diastereoselective spiroannulation involved the reaction between the tricarbonyliron-complexed cation 520, which was prepared in six steps (2/9), and an arylam-ine, the 6-aminoindoline (521), to construct A, B, C, and D rings (512) (Scheme 61) (220). The stereochemistry of the product was determined by X-ray crystallographic analysis the stereodirecting effect of Fe(CO)3 was indicated to be anti to the aryl ring (2/9). 

Cheng J, Ohizumi Y, Walchli MR, Nakamura H, Hirata Y, Sasaki T, Kobayashi J (1988) Prianosins B, C, and D, novel sulfur-containing alkaloids with potent antineoplastic activity from the Okinawan marine sponge Prianos melanos. J Org Chem 53 4621 624... 

Cheng, )., Ohizumi, Y, Walchli, M.R., Nakamura, H., Hirata, Y, Sasaki, T., and Kobayashi, J. (1988b) Prianosins B, C, and D, novel sulfurantineoplastic activity from sponge Prianos melanos. J. Org. Chem., 53, 4621-4624. 

Prianosins B (487), C (488), and D (484) were found to be cytotoxic against murine lymphomas L1210 and L5178Y cells and human epidermoid carcinoma (KB) cells in vitro, with IC50 values of 2.0,1.8, and >5.0 fig/ml... 

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. 

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... 

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