AdvisorAndrade, Rodrigo B.
Committee memberAndrade, Rodrigo B.
Davis, Franklin A.
Sieburth, Scott McNeill
Cannon, Kevin C.
Aspidosperma Alkaloids and Bis-aspidosperma Alkaloids
Strychnos Alkaloids and Bis-strychnos Alkaloids
Total Synthesis of Natural Products
Permanent link to this recordhttp://hdl.handle.net/20.500.12613/4093
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AbstractAll Strychnos and Aspidosperma alkaloids possess a core pyrrolo[2,3-d]carbazole ABCE tetracycle. In order to develop an efficient and divergent methodology for the synthesis of Strychnos alkaloids, a streamlined synthetic sequence to the ABCE tetracycle has been developed. It features a Mitsunobu activation of an N-hydroxyethyl gramine intermediate and subsequent intramolecular aza-Baylis-Hillman reaction. This method was first applied in the total synthesis of (±)-alstolucine B. Additional key steps in the synthesis included (1) chemoselective intermolecular and intramolecular Michael additions and (2) a Swern indoline oxidation. The second application of this method was in the first total synthesis of (-)-melotenine A, a novel rearranged Aspidosperma alkaloid with potent biological activity. Additional key steps in the synthesis included (1) a Piers annulation of a vinyl iodide and a methyl ketone to prepare the D ring and (2) a site-selective intermolecular vinylogous aldol reaction
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Concise Syntheses of bis‐Strychnos Alkaloids (−)‐Sungucine, (−)‐Isosungucine, and (−)‐Strychnogucine B from (−)‐StrychnineZhao, Senzhi; Chen, Heng; Sirasani, Gopal; Dobereiner, Graham; Andrade, Rodrigo B.; Teijaro, Christiana; Vaddypally, Shivaiah; Zdilla, Michael; 0000-0001-5375-0241; 0000-0001-6203-9689; 0000-0003-0212-2557; 0000-0001-6885-2021 (2016-06-15)The first chemical syntheses of complex, bis‐Strychnos alkaloids (−)‐sungucine (1), (−)‐isosungucine (2), and (−)‐strychnogucine B (3) from (−)‐strychnine (4) is reported. Key steps included (1) the Polonovski–Potier activation of strychnine N‐oxide; (2) a biomimetic Mannich coupling to forge the signature C23−C5′ bond that joins two monoterpene indole monomers; and (3) a sequential HBr/NaBH3CN‐mediated reduction to fashion the ethylidene moieties in 1–3. DFT calculations were employed to rationalize the regiochemical course of reactions involving strychnine congeners.
Synthesis of Bis-Strychnos Alkaloids (–)-Sungucine, (–)-Isosungucine, and (–)-Strychnogucine B from (–)-StrychnineZhao, Senzhi; Teijaro, Christiana; Chen, Heng; Sirasani, Gopal; Vaddypally, Shivaiah; O'Sullivan, Owen; Zdilla, Michael; Dobereiner, Graham; Andrade, Rodrigo B.; 0000-0001-5375-0241; 0000-0001-6203-9689; 0000-0003-0212-2557; 0000-0001-6885-2021 (2019-03)It was developed a concise synthetic route resulting in the first syntheses of bis-Strychnos alkaloids (-)-sungucine, (-)-isosungucine, and (-)-strychnogucine B from commercially available (-)-strychnine. Employing a highly convergent synthetic strategy, it was demonstrated that both Strychnos monomers could be efficiently prepared from commercially available (-)-strychnine. The venerable Mannich reaction was enlisted to join the two Strychnos monomers in a biomimetic fashion. Subsequent epimerization and olefin isomerization yielded (-)-strychnogucine B. Functional group manipulation transformed (-)-strychnogucine B into (-)-sungucine and (-)-isosungucine. Computational chemistry was employed to rationalize the regiochemical course of key steps en route to the bis-Strychnos targets.
TOTAL SYNTHESIS OF STRYCHNOS AND ASPIDOSPERMATAN ALKALOIDSAndrade, Rodrigo B.; Sieburth, Scott McNeill; Wengryniuk, Sarah E.; Cannon, Kevin C. (Temple University. Libraries, 2017)The Strychnos class of indole alkaloids contain a pyrrolo[2,3-d]carbazole ABCE tetracyclic framework. The second-generation ABCE tetracycle approach was employed in the total synthesis of (±)-20-epi-lochneridine and progress toward total synthesis of (±)-alstolucine B. The second-generation approach featured Mitsunobu activation of the hydroxyethyl group in a gramine intermediate followed by intramolecular aza-Baylis-Hillman reaction. The substrate for hydroboration was redesigned to (±)-18-desmethyl akuammicine (1,1-disubstituted double bond), since the hydroboration of trisubstituted alkenes afforded tertiary alcohol via Markovnikov addition. The key steps were n-Bu3SnH mediated cyclization reaction to accomplish D-ring, tert-butyl hypochlorite indoline oxidation, and anti-Markovnikov hydroboration to introduce a primary alcohol. The total syntheses of Strychnos-Strychnos type bis-indole alkaloids (−)-leucoridine A and C were accomplished from the biomimetic dimerization of (−)-dihydrovalparicine. En route to (−)-dihydrovialparicine, known alkaloids (+)-geissoschizoline and (−)-dehydrogeissoschizoline were also prepared from commercially available N-tosyl indole 3-carboxaldehyde. Key steps consisted of an in situ dimerization of (−)-dihydrovalparicine from (−)-1, 2-dehydrogeissoschizoline with trifluoroacetic acid in the presence of 4 Å molecular sieves. Acid mediated ring-opening of the indolenine in (−)-leucoridine A to afford (−)-leucoridine C. DFT calculations were employed to elucidate the mechanism of dimerization, which suggested that a stepwise aza-Michael/spirocyclization sequence was preferred over the alternate hetero Diels-Alder cycloaddition reaction. A novel domino Michael/Mannich [4+2] annulation method was applied for concise total synthesis of Aspidospermatan alkaloids (+)-20-epi-condyfoline and progress toward the total synthesis of (+)-condyfoline. The additional key steps consisted of a LiHMDS mediated cyclization to form D-ring, dimethyl(methylthio)sulfonium tetrafluoroborate (DMTSF) mediated spirocyclization to form pentacyclic thioether and indoline oxidation with MnO2.