Strychnos 1990 - 2004 - Crops for the Future

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Author Title Year Source title Reference Knight, S. D., L. E. Overman and G. Pairaudeau Synthesis applications of cationic aza-cope rearrangements .28. Asymmetric total 1995 Journal of the American Chemical Society 117(21): 5776-5788 Abstract The first asymmetric total syntheses of (-)-strychnine, ent-strychnine, and the Wieland-Gumlich aldehyde are described with full experimental details. The total synthesis of (-)-strychnine was realized in 24 steps and 3% overall yield from (1R,4S)-(+)-4-hydroxy-2-cyclopentenyl acetate (28). This synthesis fully controls the six stereogenic centers and forms the C(20) double bond of (-)- strychnine with high diastereoselection (>20:1). In the first stage of the synthesis, the (R)- cyclopentenylstannane 8 is prepared in nine steps and 30% overall yield (40% with one recycle of 38) as summarized in Scheme 4. Palladium-catalyzed carbonylative coupling of 8 with the 2- iodoaniline derivative 7 provides enone 6, which is converted to the 2-azabicyclo[3.2.1]octane 5 in seven additional steps. This latter sequence proceeds in 36% overall yield (Scheme 6). The central step of the total synthesis is aza-Cope-Mannich rearrangement of 5 which proceeds in 98% yield to form the pentacyclic intermediate 4 (Scheme 7). In five additional steps 4 is converted to the Wieland-Gumlich aldehyde 2, which is the ultimate precursor of (-)strychnine. A slight modification of this synthesis strategy allowed ent-strychnine to be prepared and provided the first samples of this unnatural enantiomer for pharmacological studies (Scheme 8). The efficiency and conciseness of this synthesis provide an important benchmark of the power of the aza-Cope rearrangement-Mannich reaction to solve formidable problems in alkaloid construction. Author Title Year Source title Reference Abstract Kuehne, M. E., C. S. Brook, D. A. Frasier and F. Xu Syntheses of strychnos-type and aspidospermatan-type alkaloids .7. Total synthese 1995 Journal of Organic Chemistry 60(6): 1864-1867 -
Author Title Year Source title Reference Kuehne, M. E., T. S. Wang and D. Seraphin The total synthesis of (+/-)-mossambine 1995 Synlett (5): 557-558 Abstract A radical cyclization providing the pentacyclic strychnos skeleton which can be further elaborated to f o r m t h e a l k a l o i d m o s s a m b i n e i s d e s c r i b e d . Author Title Year Source title Reference Martin, G. E., R. C. Crouch and C. W. Andrews N-15 chemical shifts and long-range h-1-n-15 coupling pathways of selected Stryc 1995 Journal of Heterocyclic Chemistry 32(6): 1759-1766 Abstract The Strychnos alkaloids have been the focal point of considerable synthetic and spectroscopic effort. We now report the N-15 chemical shifts and long-range H-1-N-15 coupling pathways of strychnine, brucine, and holstiine at natural abundance. Long-range coupling pathways were established using a gradient-enhanced HMQC sequence optimized for the observation of H-1-N-15 long-range couplings. Author Title Year Source title Reference Micouin L; Diez A; Castells J; Lopez D; Rubiralta M; Quirion JC; Husson HP Synthetic applications of 2-(1,3-dithian-2-yl)indoles .5. Asymmetric-synthesis of 1995 Tetrahedron Letters 36(10): 1693-1696 Abstract Chiral tetracyclic dasycarpidone-type compounds (alpha R, IS, 5R)-4 and (alpha R, IR, 5S)-16 have been synthesized from 2-(1,3-dithian-2-yl)indole 6 and (alpha R)-N-(beta-hydroxy-alphaphenylethyl)-Delta(3)-piperidein-2-one 8 in three steps, following the methodology that we d e s c r i b e d r e c e n t l y .
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