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Two new bisindole alkaloids, leucophyllinines A (1) and B (2) consisting of eburnane and quebrachamine-type skeletons were isolated from the bark of Leuconotis eugeniifolia, and their structures were elucidated on the basis of spectroscopic data. Leucophyllinines A and B showed antiplasmodial activities against Plasmodium falciparum 3D7.

An enantiospecific total synthesis of indole alkaloids eburnamonine, aspidospermidine and quebrachamine is described from lactic acid. Synthesis of all three alkaloids is accomplished from a single chiral building block. Johnson–Claisen rearrangement of a chiral allyl alcohol is the main feature for the installation of the required quaternary centre.

This first part of a planned review on developments in the field of total and formal total synthesis of the post-secodine indole alkaloids concentrates on primary alkaloid types. It reviews the synthesis of secodine, aspidospermane, pseudoaspidospermane and ibogane alkaloids; andranginine is also included. It covers the literature from 1992-1993 up to approximately May 2004. A review with 179 references.

The title compound quebrachamine (Ia) and kopsiyunnanine D (Ib) are synthesized from the same precursor.

The oxidation of (-)-tabersonine (1) with dimethyldioxirane (DMD) in neutral and acidic medium gave 16-hydroxytabersonine-N-oxide (3) and the didehydrovincamine isomers 4 and 5, respectively. (+)-14,15-Didehydro-quebrachamine (7) furnished the hydroxyindolenine 9, and the pentacyclic derivative 11. (+)-Quebrachamine (8) and DMD in neutral medium gave (7S,20S)-(+)-rhazidigenine (12) which was converted to (2R,7S,20S)-(+)-rhazidine (13b) with hydrochloric acid.

The development and utility of cyclopropanes is an ever-growing field within organic chemistry. In particular, donor-acceptor cyclopropanes have been used in a vast array of methods to access a variety of different hetero and carbocyclic molecular scaffolds. Recently, we have developed a Zn(NTf2)2 catalyzed tandem reaction consisting of a nucleophilic ringopening of 1,1-cyclopropanediesters by 2-alkynyl indoles followed by a Conia-ene ring closure, resulting in the efficient one-step synthesis of tetrahydrocarbazoles. These adducts may be further elaborated to carbazoles. The scope and limitations of this method were determined along with a mechanistic study into the function of the zinc catalyst. In an expansion of our work with 1,1-cyclopropanediesters, we have explored the reactivity and utilization of hemimalonate cyclopropanes. To this end, we have developed two unique methods exploring the self-activating nature of these cyclopropanes under catalyst free conditions. Cyclopropane hemimalonates, when treated with sodium azide, undergo a tandem ring-opening decarboxylation to produce γ-azidobutyric acids in good yields. These adducts were hydrogenated to form γ-aminobutyric acid (GABA) methyl esters. Additionally, cyclopropane hemimalonates have led to the facile synthesis of γ-substituted butanolides. Under microwave irradiation, cyclopropane hemimalonates undergo rapid conversion to butanolides in the presence of inorganic salts with an unprecedented retention of stereochemistry. This unique process, in conjunction with a newly developed crossmetathesis method, has been applied to the total synthesis of the naturally occurring, (R)- dodecan-4-olide. Finally, recent efforts to develop a unified approach to piperidine-containing indole natural products have shown great promise. A preliminary investigation into the prospect of a common synthetic intermediate for the synthesis of a variety of indole alkaloids has led to a synthesis of substituted piperidinones and the corresponding piperidines. These common natural product cores are accessed via a reductive amination/lactamization sequence of dimethyl 3-ethyl-3-formylpimelate. The synthetic utility of this initial study has been displayed in the formal synthesis of (+/-)-quebrachamine.

The Rh2(OAc)4-catalyzed reaction of diazoacetate 5 provides ready access to the pivotal cyclic acetal 13 that undergoes Pictet-Spengler-type condensation with tryptamine to directly afford an epimeric mixture of the tetracyclic lactam 17a,b. Lithium aluminum hydride reduction of 17a,b provides the known tetracyclic amino alcohol 18a,b which, overall, constitutes a formal synthesis of (±)-quebrachamine.

There are two major impediments to scaling up alkene metathesis: reducing the amount of the expensive Ru catalyst required, and minimizing residual Ru in the product. Robert H. Grubbs of Caltech developed (Organic Lett. 2009, 11, 1261) a family of silica-supported Ru complexes, exemplified by 1. At 0.75 mol % of 1, the rate of cyclization of 2 to 3 was maintained over eight cycles. The solution of product 3 showed < 5 ppb Ru. Hassan S. Bazzi and David E. Bergbreiter of the Texas A&M campuses in Qatar and College Station also reported (Organic Lett. 2009, 11, 665) a durable polymer-bound Ru metathesis catalyst that maintained its activity over many cycles. Most metathesis catalysts are strongly E selective. Amir H. Hoveyda of Boston College designed (J. Am. Chem. Soc. 2009, 131, 3844) a chiral Mo catalyst that was both highly enantioselective and strongly Z selective, converting the prochiral 4 into the alkene 6. Professor Hoveyda also took advantage (J. Am. Chem. Soc. 2009, 131, 8378) of the known propensity of Ru metathesis catalysts for H bonding, showing that metathesis of the prochiral cyclopropene 7 proceeded with remarkable diastereocontrol. This appears to be a generally useful protocol for assembling enantiomerically pure alkylated quaternary stereogenic centers. It is also possible to encapsulate the Ru catalyst. Ned B. Bowden of the University of Iowa pioneered the use of PDMS thimbles for this purpose. He has now shown (Organic Lett. 2009, 11, 33) that by subsequently adding AD-mix, cross-metathesis can be followed directly by enantioselective dihydroxylation. Ring-opening cross-metathesis of an unsymmetrical alkene such as 13 could give two different products. Alberto Avenoza and Jesús H. Busto of the Universidad de La Rioja established (J. Org. Chem. 2009, 74, 1736) that by tuning the electronic nature of the participating alkene, either product can be obtained with high selectivity. Metathesis can be used to close larger rings. Conformational effects are important. Motoo Tori of Tokushima Bunri University observed (Tetrahedron Lett. 2009, 50, 2225) that although 18 cyclized efficiently, the other three precursors that were diastereomeric on the cyclopentane ring did not undergo ring-closing metathesis.

A variety of methodologies developed in our research group have inspired the three separate projects reported. First, the total synthesis of (±)-quebrachamine was performed in 13 steps and 17.8% overall yield. Highlights of the synthesis include an efficient preparation of a functionalized indole core via a [3+2] annulation cycloaddition reaction between a functionalized nitrile and donor-acceptor cyclopropane and a photo induced 9-membered ring closure. Secondly, we have reported the most efficent and highest yielding route to several tetrahydroisoquinocarbazoles, where the core was prepared in six steps from tryptophol in 51% overall yield. This work highlights for the first time the synthetic utility of the dipolar C-2 alkylation of 3-substituted indoles with 2-alkoxycyclopropanoate esters. The synthesis also features a selective SmBr2-HMPA promoted ring closure of an aldehyde onto a sterically congested trisubstituted alkene. Lastly, we have developed efficient syntheses towards several fragments of biselide A, which could be used to explore both ring closing metathesis and relay ring closing metathesis to construct the 14-membered macrolactone. The trans-THF ring was furnished by using our second generation Co(nmp)2 catalyst in a Mukaiyama oxidative cyclization, while the chloroalkene moiety was introduced with a chloropalladation reaction. Key steps in the synthesis of the southern fragment included a Sharpless asymmetric kinetic resolution, or a diastereoselective aldol reaction. Significant synthetic efforts toward biselide E have also been reported. We have designed an efficient method to access the western fragment, which also employed our second generation Co(nmp)2 catalyst in a Mukaiyama oxidative cyclization to furnish the trans-THF ring. A proficient method towards the eastern fragment was also designed, using a Suzuki coupling reaction as the key step.

A diastereoselective route to an enantiopure 4,4-disubstituted cyclohex-2-en-1-ol has been developed using the synthetic equivalent of chiral 4-hydroxycyclohex-2-en-1-one. Its stereochemistry has been determined by its transformation into the Aspidosperma indole alkaloid (+)-quebrachamine.

This review is focused on recent synthetic achievements and ongoing work in our laboratory using phenylglycinol-derived oxazolopiperidone lactams as starting materials for the enantioselective synthesis of piperidine-containing alkaloids: madangamines, 2,5-disubstituted decahydroquinoline and 1-substituted tetrahydroisoquinoline alkaloids, the indole alkaloids 20S- and 20R-dihydrocleavamine and quebrachamine, and indole alkaloids of the uleine and silicine groups.

This review is focused on recent synthetic achievements and ongoing work in our laboratory using phenylglycinol-derived oxazolopiperidone lactams as starting materials for the enantioselective synthesis of piperidine-containing alkaloids: madangamines, 2,5-disubstituted decahydroquinoline and 1-substituted tetrahydroisoquinoline alkaloids, the indole alkaloids 20 S- and 20 R-dihydrocleavamine and quebrachamine, and indole alkaloids of the uleine and silicine groups.

A diastereoselective route to an enantiopure 4,4-disubstituted cyclohex-2-en-1-ol has been developed using the synthetic equivalent of chiral 4-hydroxycyclohex-2-en-1-one. Its stereochemistry has been determined by its transformation into the Aspidosperma indole alkaloid (+)-quebrachamine.

Ten alkaloids, 15α-hydroxy-14,15-dihydrovindolinine, 15α-hydroxy-14,15-dihydro-16-epi-vindolinine, vindolinine, epivindolinine, vindolinine N (b)-oxide, epivindolinine N (b)-oxide, kopsinine, 15-hydroxykopsinine, vincadifformine and quebrachamine were isolated from Melodinus morsei . The first two are new compounds, with their structures elucidated by spectroscopic methods.

The indolealkaloids aspidospermine and quebrachamine have been isolated in crystalline form by a relatively rapid fractionation from the extract of a powdered material designated “Quebracho” derived from an Aspidosperma tree species. We present a novel isocratic LC method that provides baseline resolution of these two compounds and of the structurally related yohimbine in less than 15 min. Gas chromatography—mass spectrometry was employed to identify these compounds as well as several minor derivatives of aspidospermine during and after the purification process. Aspidospermine and quebrachamine like yohimbine have been found to possess adrenergic blocking activities for a variety of urogenital tissues.

The 13C shifts of 16α- and 16β-substituted derivatives of quebrachamine, 14,15-dehydroquebrachamine, cleavamine, 15,20α-dihydrocleavamine and 15,20β-dihydrocleavamine are determined and correlated with possible conformations of these tetracycles. The method of analysis of the C(16) configuration of these compounds, which emanated from this study, is used for the determination of the configuration of the site of coupling of vindoline and cleavamine β-chloroindolenine.

Squelettes des produits etudies: hexahydro benzo [a] quinolizine, octahydro indolo [2,3-a] quinolizine, spiro [indoline-3:1'-indolizidine], hexahydro indolizino [8,7-b] indole, berbine, indolizino [8,1-cd] carbazole; synthese egalement de quebrachamine

An enantioselective route to both the (+)- and (–)-enantiomers of the Aspidosperma-type indole alkalloid, quebrachamine, has been established using a single chiral lactone obtained from L-glutamic acid or D-mannitol.

Par recristallisation de la quebrachamine on obtient la rhazidine et par reaction photochimique on obtient le decahydro ethyl-2 methano-2,5 indolo [3,2-d] benzazepine-1ol-12b

An enantioselective route to both the (+)- and (–)-enantiomers of the Aspidosperma-type indole alkalloid, quebrachamine, has been established using a single chiral lactone obtained from L-glutamic acid or D-mannitol.

Die Titelverbindungen (VIa) bzw. (VIb) werden wie im Schema angegeben, ausgehend von den entsprechenden Thiolactamen (I) mit den Olefinen (II), synthetisiert.

(+)-Quebrachamine (1) has been synthesised enantioselectively using L-glutamic acid as a chiral template.