C2-Modified Sparteine Derivatives Are a New Class of Potentially Long-Acting Sodium Channel Blockers.

The lupin alkaloid sparteine is a well-known chiral diamine with a range of applications in asymmetric synthesis, as well as a blocker of voltage-gated sodium channels (VGSCs). However, there is only scarce information on the VGSC-blocking activity of sparteine derivatives where the structure of the parent alkaloid is retained. Building on the recent renewed availability of sparteine and derivatives we report herein how modification of sparteine at position 2 produces irreversible blockers of VGSCs. These compounds could be clinically envisaged as long-lasting local anesthetics.

Revisiting the sparteine surrogate: development of a resolution route to the (-)-sparteine surrogate.

The improved performance of the sparteine surrogate compared to sparteine in a range of applications has highlighted the need to develop an approach to the (-)-sparteine surrogate, previously inaccessible in gram-quantities. A multi-gram scale, chromatography-free synthesis of the racemic sparteine surrogate and its resolution via diastereomeric salt formation with (-)-O,O'-di-p-toluoyl-l-tartaric acid is reported. Resolution on a 10.0 mmol scale gave the diastereomeric salts in 33% yield from which (-)-sparteine surrogate of 93 : 7 er was generated. This work solves a key limitation: either enantiomer of the sparteine surrogate can now be readily accessed.

Organocatalytic asymmetric Mannich cyclization of hydroxylactams with acetals: total syntheses of (-)-epilupinine, (-)-tashiromine, and (-)-trachelanthamidine.

An asymmetric, organocatalytic, one-pot Mannich cyclization between a hydroxylactam and acetal is described to provide fused, bicyclic alkaloids bearing a bridgehead N atom. Both aliphatic and aromatic substrates were used in this transformation to furnish chiral pyrrolizidinone, indolizidinone, and quinolizidinone derivatives in up to 89% yield and 97% ee. The total syntheses of (-)-epilupinine, (-)-tashiromine, and (-)-trachelanthamidine also achieved to demonstrate the generality of the process.

An efficient asymmetric synthesis of (-)-lupinine.

The asymmetric synthesis of (-)-lupinine was achieved in 8 steps, 15% overall yield and >99 : 1 dr from commercially available starting materials. The strategy used for the construction of the quinolizidine scaffold involved reaction of an enantiopure tertiary dibenzylamine via two sequential ring-closures which both occurred with concomitant N-debenzylation.

Synthesis and comparison of antiplasmodial activity of (+), (-) and racemic 7-chloro-4-(N-lupinyl)aminoquinoline.

Recently the N-(-)-lupinyl-derivative of 7-chloro-4-aminoquinoline ((-)-AM-1; 7-chloro-4-{N-[(1S,9aR)(octahydro-2H-quinolizin-1-yl)methyl]amino}quinoline) showed potent in vitro and in vivo activity against both Chloroquine susceptible and resistant strains of Plasmodium falciparum. However, (-)-AM-1 is synthesized starting from (-)-lupinine, an expensive alkaloid isolated from Lupinus luteus whose worldwide production is not sufficient, at present, for large market purposes. To overcome this issue, the corresponding racemic compound, derived from synthetic (±)-lupinine was considered a cheaper alternative for the development of a novel antimalarial agent. Therefore, the racemic and the 7-chloro-4-(N-(+)-lupinyl)aminoquinoline ((±)-AM-1; (+)-AM-1) were synthesized and their in vitro antimalarial activity and cytotoxicity compared with those of (-)-AM-1. The (+)-lupinine required for the synthesis of (+)-AM-1 was obtained through a not previously described lipase catalyzed kinetic resolution of (±)-lupinine. In terms of antimalarial activity, (±)-AM1 and (+)-AM1 demonstrated very good activity in vitro against both CQ-R and CQ-S strains of P. falciparum (range IC(50) 16-35 nM), and low toxicity against human normal cell lines (therapeutic index >1000), comparable with that of (-)-AM1. These results confirm that the racemate (±)-AM1 could be considered as a potential antimalarial agent, ensuring a decrease of costs of synthesis compared to (-)-AM1.

[Isomeric derivatives of lupinine and epilupinine--organophosphorus inhibitors of cholinesterases].

The isomeric-structure analysis data of anticholinesterase action of organophosphorous inhibitors with similar structure help in the search of specific effectors and detection of differences in reactivity of various animals' enzymes. This study compared the data of efficacy in respect of 4 mammal and 5 arthropoda cholinesterase preparations for 26 quinolizidine inhibitors, which molecules contain both the isomeric unbranched and branched alkoxyl radicals in the phosphoryl group, and the epimeric lupinine and epilupinine derivatives in the leaving group. The changes in the alkoxyl radical structure of inhibitor molecules act on their efficacy only with respect to the mammal enzymes ("group" inhibitor specificity). The differences between lupinine and epilupinine derivatives were revealed. Highly specific inhibitors of different enzymes were detected among the tested compounds.

Total syntheses of (-) epilupinine and (-)-tashiromine using imino-aldol reactions.

Short routes to enantiomerically pure indolizidine and quinolizidine alkaloids have been developed using imino-aldol reactions of enolates derived from phenyl 5-chlorovalerate. High levels of syn selectivity (dr ∼13-16:1) were obtained using lithium enolates of phenyl esters in combination with tert-butylsulfinyl imines. The imino-aldol adducts were deprotected and cyclized to afford (-)-epilupinine ((-)-2) and (-)-tashiromine ((-)-1) in two further steps.

Total synthesis of (+)-epilupinine via an intramolecular nitrile oxide-alkene cycloaddition.

Total synthesis of (+)-epilupinine was accomplished in nine steps and in 48% overall yield, in which INOC was used as the key step for the construction of the quinolizidine skeleton. We found that it was an extremely difficult task to prepare the key intermediates (R)-N-(3-nitropropyl)-2-vinylpiperidine or (R)-(2-vinylpiperid-1-yl)propanal by routine methods. Thus, by using Fukuyama's oxime synthesis, a general method was developed for highly efficient conversion of 3-(N,N-dialkylamino)propanols into 3-(N,N-dialkylamino)propanal oximes without using the corresponding aldehydes.

Short access to (+)-lupinine and (+)-epiquinamide via double hydroformylation.

Short and efficient access to (+)-lupinine and (+)-epiquinamide by means of an unprecedented double hydroformylation of a bis-homoallylic azide followed by a tandem catalytic hydrogenation/reductive bis-amination is reported.

Epiquinamide: a poison that wasn't from a frog that was.

In 2003, we reported the isolation, structure elucidation, and pharmacology of epiquinamide (1), a novel alkaloid isolated from an Ecuadoran poison frog, Epipedobates tricolor. Since then, several groups, including ours, have undertaken synthetic efforts to produce this compound, which appeared initially to be a novel, beta2-selective nicotinic acetylcholine receptor agonist. Based on prior chiral GC analysis of synthetic and natural samples, the absolute structure of this alkaloid was established as (1S,9aS)-1-acetamidoquinolizidine. We have synthesized the (1R*,9aS*)-isomer (epi-epiquinamide) using an iminium ion nitroaldol reaction as the key step. We have also synthesized ent-1 semisynthetically from (-)-lupinine. Synthetic epiquinamide is inactive at nicotinic receptors, in accord with recently published reports. We have determined that the activity initially reported is due to cross-contamination from co-occurring epibatidine in the isolated material.

Total synthesis of (+/-)-alpha-isosparteine, (+/-)-beta-isosparteine, and (+/-)-sparteine from a common tetraoxobispidine intermediate.

The three title alkaloids were separately prepared in stereocontrolled fashion from a common tetraoxobispidine precursor, 3,7-diallyl-2,4,6,8-tetraoxo-3,7-diazabicyclo[3.3.1]nonane (16). Bisimide 16 was generated from malonate via acid promoted cyclization of the Knoevenagel condensation adduct 1,1,3,3-propanetetracarboxamide. (+/-)-alpha-Isosparteine (dl-2) was elaborated from 16 in 28% overall yield by a two-directional synthetic sequence composed of four reactions: double addition of allylmagnesium bromide, ring-closing olefin metathesis (RCM), hydrogenation, and borane mediated reduction. (+/-)-beta-Isosparteine (dl-3) was targeted along similar lines by a strategic reversal in allylation and reduction operations on the core synthon. Thus, 16 was advanced to dl-3 in five steps and 12% overall yield by a reaction sequence commencing with sodium borohydride mediated reduction and followed by double Sakurai-type allylation of the resulting bishemiaminal. The synthesis of dl-3 was concluded by RCM and then global reduction (H2, Pd/C; LiAlH4). The final target, (+/-)-sparteine (dl-1), was secured in six steps and 11% overall yield from 16 by monoreduction and Sakurai allylation, followed by allyl Grignard addition and then RCM and global reduction as before. Reasons for the inherent C2-type regioselectivity of net double nucleophilic additions to tetraoxobispidines are discussed and enantioselective oxazaborolidine mediated reduction of the N,N'-dibenzyl congener of 16 is reported.

A direct stereoselective approach to trans-2,3-disubstituted piperidines: application in the synthesis of 2-Epi-CP-99,994 and (+)-epilupinine.

A simple synthesis of enantiomerically pure piperidine esters is described, offering a straightforward access to the trans-2,3-disubstituted piperidine skeleton which is present in a broad range of biologically active compounds.

Basic instinct: design, synthesis and evaluation of (+)-sparteine surrogates for asymmetric synthesis.

(-)-Sparteine, a naturally occurring lupin alkaloid, is widely used as a chiral ligand for asymmetric synthesis. To address the limitation that sparteine is only available as its (-)-antipode, our group introduced a family of (+)-sparteine surrogates that are structurally similar to (+)-sparteine but lack the D-ring. After briefly summarising the design aspect, this feature article provides an overview of synthetic routes to the sparteine surrogates and a detailed comparison with (-)-sparteine in a range of asymmetric reactions. The main conclusions are: (i) the (+)-sparteine surrogates are most easily prepared starting from (-)-cytisine extracted from Laburnum anagyroides seeds; (ii) in nearly all examples, use of the (+)-sparteine surrogates produced essentially equal but opposite enantioselectivity compared to (-)-sparteine and (iii) the N-Me-substituted (+)-sparteine surrogate is the most useful and versatile of those investigated.

Stereocontrolled synthesis and alkylation of cyclic beta-amino esters: asymmetric synthesis of a (-)-sparteine surrogate.

A convenient method for the stereoselective synthesis of cyclic beta-amino esters from an iodo alphabeta-unsaturated ester and alpha-methylbenzylamine is described. Subsequent enolate generation and alkylation proceeds with complete stereocontrol, with the two stereogenic centres working together. In this way, a functionalised piperidine suitable for alkaloid natural product synthesis was prepared. The usefulness of the methodology is exemplified with the concise synthesis of a (-)-sparteine surrogate.

A practical synthesis of (+/-)-alpha-isosparteine from a tetraoxobispidine core.

[reaction: see text] The title alkaloid was synthesized in racemic form from 3,7-diallyl-2,4,6,8-tetraoxo-3,7-diazabicyclo[3.3.1]nonane (7) by a regioselective diallylation reaction followed by double ring-closing olefin metathesis and exhaustive reduction. Tetraoxobispidine 7 was itself prepared in three simple operations from dimethyl malonate. The entire sequence to alpha-isosparteine was conducted on a multigram scale and proceeded without recourse to chromatography.

Cascade iminium ion reactions for the facile synthesis of quinolizidines. Concise syntheses of (+/-)-epilupinine and (-)-epimyrtine.

Several novel cascade processes have been designed and developed that involve sequential reactions of imines and iminium ions to form substituted quinolizidine ring systems in a single step from simple and readily available starting materials. The utility and promise of these cascade reactions is evident from their application to extraordinarily concise syntheses of the representative quinolizidine alkaloids (+/-)-epilupinine and (-)-epimyrtine.

A synthesis of (+/-)-sparteine.

In a synthesis of racemic sparteine, Diels-Alder reaction between dimethyl bromomesaconate 14 and dicyclopentenyl 4, followed by cyclopropane formation, set up the stereochemistry at C-1 and C-5 as S and R, respectively, in a meso intermediate 8. The stereochemistry at C-2 and C-4 was then secured by a moderately diastereoselective protonation of the bis-enolate 17 derived from the diester 8 by reductive cleavage with lithium in liquid ammonia. The C=C in the racemic diester 19 was ozonolysed and the diketone converted by Beckmann rearrangement into the bis-lactam . Reduction of the bis-lactam with lithium aluminium hydride and intramolecular nucleophilic displacement gave racemic sparteine 1. Some ideas for making this synthesis amenable to a synthesis of enantiomerically enriched sparteine are presented.

A synthesis of (+/-)-sparteine.

(+/-)-Sparteine has been synthesised with stereochemistry controlled in such a way as to make the route amenable to an efficient synthesis of either enantiomer.

Concise asymmetric synthesis of (-)-sparteine.

A six-step asymmetric synthesis of natural (-)-sparteine from ethyl 7-iodohept-2-enoate is reported, involving a connective Michael addition of an amino ester-derived enolate to an alpha,beta-unsaturated amino ester.

Evaluation of (+)-sparteine-like diamines for asymmetric synthesis.

Three new (+)-sparteine-like diamines were prepared from (-)-cytisine and evaluated as sparteine surrogates in the alpha-lithiation rearrangement of cyclooctene oxide and the palladium(II)/diamine catalyzed oxidative kinetic resolution of 1-indanol. The new diamines exhibited opposite enantioselectivity to that observed with (-)-sparteine but increasing the steric hindrance of the N-alkyl group beyond N-Et had a detrimental effect on enantioselectivity. The optimal N-Me diamine was evaluated with much success in five other (-)-sparteine-mediated processes involving different metals (lithium, magnesium, and copper) and different types of reaction mechanisms.