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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/NaBH3 CN-mediated reduction to fashion the ethylidene moieties in 1-3. DFT calculations were employed to rationalize the regiochemical course of reactions involving strychnine congeners., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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. [ABSTRACT FROM AUTHOR]

Eine kurze asymmetrische Synthese von (−) ‐ Melotenin A wurde in 14 Stufen mit 1 % Gesamtausbeute ausgehend von kommerziell erhältlichem N ‐ Tosylindol ‐ 3 ‐ carboxaldehyd abgeschlossen. Schlüsselschritte waren eine Piers ‐ Anellierung, eine intermolekulare vinyloge Aldolreaktion und eine neuartige Eintopfsequenz zur Bildung des ABCE ‐ Tetracyclus. Boc=tert ‐ Butoxycarbonyl, Ts=4 ‐ Toluolsulfonyl. [ABSTRACT FROM AUTHOR]

We have developed a sequential one-pot Mitsunobu/intramolecular aza-Baylis–Hillman reaction to construct the ABCE tetracyclic core of the Strychnos alkaloids and applied this method to the total synthesis of (−)-melotenine A ( 1 ), a novel rearranged Aspidosperma alkaloid with potent cytotoxic 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 to functionalize the E ring. [ABSTRACT FROM AUTHOR]

An abstract of the article "Biomimetic Total Syntheses of (-)-Leucoridines A and C Through the Dimerization of (-)-Dihydrovalparicine" by Praveen Kokkonda and colleagues is presented.

A diagram concerning alkaloid melotenine A synthesis is presented.