Pseudodistomin B: Revised structure and first total synthesis

Alkaloids from Marine Ascidians

“…Pseudodistomins A ( 253 ) and B ( 254 ), from Pseudodistoma kanoko , represent the first piperidine alkaloids obtained from marine sources [ 164 ]. The structure of the side chains of 253 and 254 has been revised after the first disclosure of the molecules [ 165 , 166 ], while the stereostructure of the piperidine nucleus has been established by synthesis of their tetrahydroacetyl derivatives [ 167 , 168 ]. Other members of the group have been successively isolated, from other Pseudodistoma species, including pseudodistomin C ( 255 ), with the absolute configuration at C-4 and C-5 opposite to those found in 253 and 254 [ 169 ], and pseudodistomins D–F ( 256–258 ) ( Figure 27 ) [ 170 ].…”

Marine natural products

“…Dysidea h e r b u c e ~, ~~~ Asc14)-3p,7a-diols from Pellinu semit u b u l o ~u , ~~~ D-ring unsaturated sterols from Topsentiu uurun-tiu~u,~O@ and 3/3-methoxysterols from Jereicopsis gruphidio-phor~,~Ol do not require detailed treatment since all were identified by using standard methods. The structures of sokotrasterol sulfate (416) and the C,, sterol (417), which were isolated from sponges of the family Halichondriidae, were determined by X-ray analysis.3o2 Two 3-oxo-4-methylene sterols, theonellasterone (41 8) and conicasterone (419), and the Diels-Alder-type dimer bistheonellasterone (420) were isolated from Theonellu swinhoei from Okinawa.,03 Two polyhydroxylated sterols, (421) and (422), were found in a Black Sea specimen of D y s i d e u f r ~g i l i s . ~~~ Contignasterol (423) is a highly oxygenated steroid with the unnatural 14p configuration from the Papua New Guinea sponge Petrosiu c o n t i g n ~t u .…”

(−)-Pseudodistomin E: First Asymmetric Synthesis and Absolute Configuration Assignment

“…Unsurprisingly, there has been interest in the development of syntheses of members of this family of alkaloids in both racemic and enantiopure form, with routes to pseudodistomins A, 5 B, [5][6][7][8][9] C, [10][11][12] D, 13,14 and F 7 having been reported to date. These endeavors have enabled not only the structures of the alkaloids to be confirmed (in fact, the structures of pseudodistomins A and B originally proposed by Kobayashi et al 15 were revealed to be erroneous and were thus revised), 6,16,17 but also their absolute configurations. It is uniquely pseudodistomin E that remains to acquiesce to laboratory synthesis, and hence receive confirmation of its assigned structure and absolute configuration.…”

“…The pseudodistomin alkaloid family comprises six members (Figure ), isolated from the Okinawan tunicate Pseudodistoma kanoko by Kobayashi et al in 1987 (pseudodistomins A and B) and 1995 (pseudodistomin C), and from the ascidian Pseudodistoma megalarva by Freyer et al in 1997 (pseudodistomins D, E, and F). , Unsurprisingly, there has been interest in the development of syntheses of members of this family of alkaloids in both racemic and enantiopure form, with routes to pseudodistomins A, B, − C, − D, , and F having been reported to date. These endeavors have enabled not only the structures of the alkaloids to be confirmed (in fact, the structures of pseudodistomins A and B originally proposed by Kobayashi et al were revealed to be erroneous and were thus revised), ,, but also their absolute configurations. It is uniquely pseudodistomin E that remains to acquiesce to laboratory synthesis, and hence receive confirmation of its assigned structure and absolute configuration.…”