The salification of racemic narwedine (I) with di-p-toluoyl-D-tartaric acid (II) produces high yields of the 1:1 (III) or the 2:1 (IV) salts with a high enantiomeric enhancement (97% and 98% e.e., respectively), a dinamic optical enrichement being produced. In a second step, salts (III) and (IV) are reduced to (-)-galanthamine with L-Selectride, which is finally purified up to >99% e.e. by crystallization of its hydrobromide.
The bromination of 3,4-dimethoxybenzaldehyde (I) with Br2 in methanol gives the 6-bromo-3,4-dimethoxybenzaldehyde (II), which is regioselectively demethylated with conc. H2SO4 yielding 6-bromo-3-hydroxy-4-methoxybenzaldehyde (III). The reductocondensation of (III) with 2-(4-hydroxyphenyl)ethylamine (IV) by means of NaBH4 in ethanol affords the secondary amine (V), which is formylated with ethyl formate and formic acid in dioxane furnishing the formamide (VI). The oxidative cyclization of (VI) by means of potassium ferricyanide and K2CO3 in toluene/water gives the (+/-)-bromoformylnarwedine (VII), which is protected with propyleneglycol (VIII) and TsOH in hot toluene yielding the ketal (IX). The reduction of the formyl group of (IX) with LiAlH4 in THF affords racemic narwedine (X), which is submitted to a crystallization-induced chiral transformation using a catalytic amount of seed crystals of (-)-narwedine in refluxing ethanol containing TEA, an 80% of (-)-narwedine (XI) is obtained. Finally, this compound is stereoselectively reduced to the target compound by means of L-selectride in THF.
The bromination of 3,4-dimethoxybenzaldehyde (I) with Br2 in acetic acid gives 2-bromo-4,5-dimethoxybenzaldehyde (II), which is selectively demethylated with H2SO4 yielding 2-bromo-5-hydroxy-4-methoxybenzaldehyde (III). The reductocondensation of (III) with 2-(4-hydroxyphenyl)ethylamine (IV) by means of NaBH4 affords the secondary amine (V), which is formylated with ethyl formate in dioxane/DMF giving the formamide (VI). The cyclization of (VI) by means of potassium hexacyanoferrate (III) and K2CO3 in hot toluene yields racemic N-formylbromonarwedine (+/-)(VII), which is reduced with lithium tri-tert-butoxyaluminum hydride furnishing a mixture of N-demethylbromogalanhamine (+/-)(VIII) and N-demethylepibromogalanthamine (+/-)(IX). After chromatographic separation of the two racemic epimers, resolution of racemic (+/-)(VIII) is carried out employing di-p-toluoyl tartaric acid to afford the required levo isomer. Alkylation of (-)(VIII) with 1-(3-chloropropyl)piperidine (X) gives (XI), which is finally converted to the title compound by reductive debromination in the presence of Zn and CaCl2.
The enantioselective condensation of 2-bromovanillin (I) with cyclohexenecarboxylate (II) by means of the chiral phosphine ligand (III) gives the chiral aryl ether (IV), which is reduced with DIBAL to yield the diol (V). The protection of (V) with Tbdms-OTf affords the bis silyl ether (VI), which is cyclized by means of Pd(OAc)2 to furnish the tetrahydrodibenzofuran (VII). The deprotection of (VII) with TBAF gives the diol (VIII), which is chemoselectively oxidized with MnO2 to yield the hydroxyaldehyde (IX). The reductocondensation of (IX) with methylamine and NaBH3CN affords the secondary amine (X), which is protected with Boc2O, providing the carbamate (XI). The oxidation of (XI) with DMP gives the aldehyde (XII), which is condensed with the phosphonium bromide (XIII) and NaHMDS, yielding the vinyl ether (XIV). The deprotection and cyclization of (XIV) by means of TFA affords the seven-member ring hemiaminal (XV), which is reduced with NaBH3CN to provide deoxygalanthamine (XVI). The epoxidation of (XVI) with dimethyldioxirane (DMDO) and TsOH furnishes the epoxide (XVII), which is regioselectively opened with diphenyl diselenide and NaBH4 to give the alpha-hydroxy selenide (XVIII). Elimination of the selenide group of (XVIII) by oxidation with NaIO4 at 80 C yielded isogalanthamine (XIX), which is finally isomerized to the target compound by treatment with Osborn's rhenium catalyst (Ph3SiO-ReO3).
The oxidative cyclization of the formamide derivative (I) with iodosobenzene bis(trifluoroacetate) (PIFA) gives the tricyclic semiquinone (II), which is debenzylated by means of TFA and Me2S and cyclized with Ms-OH to yield the tetracyclic ketone (III). Elimination of the extra OH group of (III) by means of Tf2O, Pd(OAc)2 and TEA affords the intermediate (IV), which is reduced by means of L-Selectride and LiAlH4 to provide racemic galanthamine (V). Finally, this compound is submitted to optical resolution to furnish the target (-)-galanthamine. Alternatively, the protection of the ketonic group of (IV) with ethyleneglycol and PPTS gives the spiroketal (VI), which is selectively reduced with LiAlH4 and hydrolyzed with HCl to yield racemic narwedine (VII). Finally, the reduction of (VII) with L-Selectride affords the already described racemic galanthamine.
The reaction of (-)-galanthamine hydrobromide (I) with H2O2 in formic acid at 100 C gives 8-bromo-(-)galanthamine (II), which is then treated with LiAlD4 and D2O to yield the target deuterated compound.
The reduction of (-)-narwedine (I) with BuLi, D2, tris(sec-butyl)borane and N,N,N',N'-tetramethylethylenediamine in hexane gives the target deuterated compound.
The reduction of (-)-narwedine (I) with BuLi, 3H2, tris(sec-butyl)borane and N,N,N',N'-tetramethylethylenediamine in hexane gives the target tritiated compound.
The esterification of the carboxylic acid (II) with 2-iodo-6-methoxyphenol (I) by means of EDC and DMAP in dichloromethane gives the corresponding ester (III), which is cyclized by means of a Pd catalyst and TlOAc in refluxing acetonitrile to yield the spiranic 1-benzopyranone (IV). The cleavage of the ethylene ketal group of (IV) with Ph3C-BF4 in dichloromethane affords the spiranic diketone (V), which is dehydrogenated with (Ph-SeO)2O in refluxing dichloromethane to provide the spiranic cyclohexadienone (VI). The reaction of dienone (VI) with methylamine resulted in a spontaneous Michael addition to give the N-methylamide (VII), which is cyclized with paraformaldehyde and TFA yielding the tetracyclic compound (VIII). The enantioselective reduction of the ketonic group of (VIII) with L-Selectride in THF affords the alcohol (IX), which is finally reduced with LiAlH4 providing the target galanthamine.
The condensation of 2-bromo-3-hydroxy-4-methoxybenzaldehyde (I) with the cyclohexenecarboxylate (II) by means of a Pd catalyst and a chiral auxiliary gives the chiral aryl ether (III), which is treated with methyl orthoformate and Ts-OH in methanol to yield the dimethylacetal (IV). The reduction of the ester group of (IV) by means of DIBAL affords the methanol derivative (V), which is treated with acetone cyanohydrin, PPh3 and Ts-OH to provide the acetonitrile derivative (VI). The cyclization of (VI) by means of Pd(OAc)2 and Ag2CO3 in refluxing toluene leads to the tetrahydro dibenzofuran derivative (VII), which is diastereoselectively oxidized by means of SeO2 in hot dioxane to give the chiral secondary alcohol (VIII). The reaction of (VIII) with methylamine in methanol yields the methylimine (IX), which is submitted to reductocyclization by means of DIBAL to afford the tetracyclic intermediate (X). This compound, without isolation, is reduced with NaBH3CN to provide the target galanthamine.
The N-demethylation of galantamine (I) by means of MCPBA and FeSO4 in dichloromethane gives the N-demethylated compound (II), which is then remethylated with 14C-methyl iodide and diisopropylamine (DIA) in methanol to obtain the target labeled compound.
The O-demethylation of galantamine (I) by means of BuLi and butanethiol in HMPT gives the O-demethylated compound (II), which is then remethylated with 14C-methyl iodide, KOH and 1,3-dimethylimidazolidin-2-one (DMIO) to obtain the target labeled compound.
The O-demethylation of galantamine (I) by means of BuLi and butanethiol in HMPT gives the O-demethylated compound (II), which is then remethylated with fully deuterated 13C-methanol, DIAD and PPh3 in THF to obtain the target labeled compound.