กิตติศักดิ์ ธรรมาภิชัย. Synthetic study of indolizidine alkaloids with structural diversity: Indolizidine 167B, Indolizidine 209D, Tabertingine, Tashiromine and Spiroindolizidine-oxindole. Master's Degree(Chemistry). มหาวิทยาลัยศิลปากร. สำนักหอสมุดกลาง. : Silpakorn University, 2020.
Synthetic study of indolizidine alkaloids with structural diversity: Indolizidine 167B, Indolizidine 209D, Tabertingine, Tashiromine and Spiroindolizidine-oxindole
Abstract:
Indolizidine alkaloids are an important class of secondary metabolites with a variety of reported biological activities and structural diversity. For examples indolizidine 167B and indolizidine 209D have been reported to be non-competitive blockers for muscle type and ganglionic nicotinic receptors. Herein we present a synthetic approach toward 5-aryl and 5-alkylindolizidine frameworks using kinetic resolution of racemic secondary alcohol with a chiral succinimide derivative. The racemic secondary alcohols were obtained from reaction of allylmagnesium bromide and anisaldehyde or heptanal. S-dibenzylaminosuccinimide another starting material was synthesized from L-asparagine. S-dibenzylaminosuccinimide reacted with racemic secondary alcohols using Mitsunobu conditions to give the N-alkylsuccinimide and recovered unreacted alcohol. The N-alkylated product was obtained in highly diastereoselective fashion and this compound and the recovered unreacted secondary alcohol were found to be optically active. This result showed that kinetic resolution of the racemic secondary alcohol occurred during the Mitsunobu reaction. However, the desired product was obtained in low yield. Tabertinggine, another indolizidine alkaloids which have a various biological activities was also study. Tabertinggine isolated from Tabernaemontana Apocyanaceae which are found in America, Africa and Asia. Herein we reported the synthetic of Tabertinggine and Tabertinggine anolog which have a aryl-analog instead of indole ring that provided a less compicated in synthetic route to study a reaction that could be provided for Tabertinggine synthesis. We used N-acyliminium ion cyclization as a key step to construct the tricyclic indolizidine core and tetracyclic indolizidine core for Tabertinggine analog and Tabertinggine respectively. N-dibenzylamino group in indolizidine core was removed using Cope elimination to provide a cyclic enamide that was removed a conjugate double bond by using Cordes reduction method. Alkylation with alkynyl halide provided ene-yne product as a key intermediate. An ene-yne metathesis was used as a key reaction to construct a bridged aza-bicyclo[3.2.1]octene which was an important part of Tabertinggine. Finally, desulfurnation followed by oxidative cleavage provided Tabertinggine. This study has resulted in a synthesis of 5-arylindolizidine, 8-hydroxymethylindolizidine, benzoindolizidine, indoloindolizidine and spiroindolizidine-oxindole systems. In the synthetic study of Tabertinggine, an in situ benzoindolizidine ene-yne intermediate underwent unexpected cyclization to give the 2-azabicyclo[3.2.1]nonane found in Tabertingine.