MDL-100907 can be obtained by several different ways: 1) The condensation of piperidine-4-carboxamide (I) with 2-(4-fluorophenyl)ethyl bromide (II) by means of K2CO3 in hot DMF gives 1-[2-(4-fluorophenyl)ethyl]piperidine-4-carboxamide (III), which by reaction with refluxing POCl3 is converted into the nitrile (IV). The reduction of (IV) with diisobutyl aluminum hydride (DIBAL) in THF affords the aldehyde (V), which by condensation with 1,2-dimethoxybenzene (veratrole) (VI) by means of BuLi in THF affords racemic MDL-100907 (VII). The esterification of (VII) with (S)-2-methoxy-2-phenylacetic acid (VIII) by means of dicyclohexylcarbodiimide (DCC) and dimethyl-aminopyridine (DMAP) in refluxing CHCl3 affords a mixture of diastereomers that is submitted to column chromatography over silica gel to afford the pure diastereomer (IX). Finally, (IX) is saponified with K2CO3 in methanol/ water
2) Racemic MDL-100907 (VII) can also be obtained by reaction of piperidine-4-carboxylic acid (X) with di-tert-butyl dicarbonate (XI) by means of NaOH in tert-butanol/ water, giving piperidine-1,4-dicarboxylic acid 1-mono-tert-butyl ester (XII), which is treated with N,O-dimethylhydroxylamine (XIII) and carbonyldiimidazole (CDI) in dichloromethane to afford the methoxy(methyl)amide (XIV). The condensation of (XIV) with veratrole (VI) by means of BuLi in THF gives 4-(2,3-dimethoxybenzoyl)-piperidine-1-carboxylic acid tert-butyl ester (XV), which is decarboxylated by means of trifluoroacetic acid, yielding ketone (XVI). The condensation of (XVI) with 2-(4-fluorophenyl)ethyl bromide (II) by means of K2CO3 in DMF affords 1-(2,3-dimethoxyphenyl)-1-[1-[2-(4-fluorophenyl)-ethyl]piperidin-4-yl]methanone (XVII). Finally, this compound is reduced with NaBH4 in methanol
3) Racemic MDL-100907 (VII) can also be obtained as follows: The reaction of piperidine-4-carboxylic acid ethyl ester (XVIII) with the previously mentioned bromide (II) by means of K2CO3 as before gives 1-[2-(4-fluorophenyl)ethyl]piperidine-4-carboxylic acid ethyl ester (XIX), which is treated with N,O-dimethylhydroxylamine (XIII) to afford carboxamide (XX). The condensation of (XX) with veratrole (VI) by means of BuLi as before yields the ketonic precursor (XVII), which is finally reduced as before. 4) [11C]-Radiolabeled MDL-100907 can be obtained as follows: Racemic MDL-100907 (VII) is treated with L-Selectride in THF, yielding racemic 1-[1-[2-(4-fluorophenyl)ethyl]piperidin-4-yl]-1-(3-hydroxy-2-methoxy-phenyl)methanol (rac-XXI), which is submitted to semi-preparative HPLC separation over Chiracel OD, affording pure (R-XXI). Finally, this compound is methylated with [11C]-methyl iodide and KOH in HMPA. If this methylation is performed with nonlabeled methyl iodide, MDL-100907 is obtained. 5) The radiolabeling of phenol (R-XXI) can also be performed with better yields using [11C]-methyl trifluoromethanesulfonate (XXII) as methylating agent. Triflate (XXII) is obtained by reaction of silver triflate with [11C]-methyl iodide.
The synthesis of MDL-100907 [11C]-labeled at the 2'-methoxy group has been reported: Condensation of 2-(4-fluorophenyl)ethyl bromide (I) with piperidine-4-carboxylic acid ethyl ester (II) by means of K2CO3 in DMF gives 1-[2-(4-fluorophenyl)ethyl]piperidine-4-carboxylic acid ethyl ester (III), which is treated with N,O-dimethylhydroxylamine and ethylmagnesium bromide in THF to yield compound (IV). Condensation of (IV) with veratrole (V) by means of BuLi in THF affords the 4-benzoylpiperidine derivative (VI), which is reduced with NaBH4 in methanol to give the racemic carbinol (VII). Optical resolution of (VII) by esterification with (S)-2-methoxy-2-phenylacetic acid (VIII) by means of DCC and DMAP in chloroform followed by column chromatography yields the diastereomer (IX), which is hydrolyzed with K2CO3 in methanol to afford MDL-100907 (X). Selective demethylation of (X) with L-selectride in THF gives the 2'-hydroxy derivative (XI), which is finally remethylated with [11C]-methyl iodide and K2CO3 in methanol.
The synthesis of MDL-100907 [11C]-labeled at the 3'-methoxy group has been described: Condensation of 2-(4-fluorophenyl)ethyl bromide (I) with piperidine-4-carboxylic acid ethyl ester (II) by means of K2CO3 in DMF gives 1-[2-(4-fluorophenyl)ethyl]piperidine-4-carboxylic acid ethyl ester (III), which is treated with N,O-dimethylhydroxylamine and ethylmagnesium bromide in THF yielding the carbohydroxamic ester (IV). The condensation of (IV) with the silylated guaiacole (V) by means of n-BuLi in THF affords the 4-benzoylpiperidine (VI), which is reduced with NaBH4 in methanol giving the racemic carbinol (VII). Optical resolution of (VII) by esterification with (S)-2-methoxy-2-phenylacetic acid (VIII) by means of DCC and DMAP in chloroform followed by column chromatography yields the diastereomer (IX), which is simultaneously hydrolyzed and desilylated with K2CO3 in methanol affording the chiral carbinol (X). Finally, (X) is methylated with [11C]-methyl iodide and K2CO3 in methanol.
The condensation of 1,2-dimethoxybenzene (I) with 1-(tert-butoxcarbonyl)-N-methoxy-N-methylpiperidine-4-carboxamide (II) by means of BuLi in THF gives the protected benzoylpiperidine (III), which is deprotected by means of TFA to yield the deprotected piperidine (IV). The reduction of the carbonyl group of (IV) by means of NaBH4 in methanol affords the racemic carbinol (V), which is submitted to optical resolution with (+)-di-O,O'-p-toluyltartaric acid, providing the (+)-(R)-carbinol (VI). Finally, this compound is condensed with 2-(4-fluorophenyl)ethyl bromide (VIII) by means of NaHCO3 in hot DMF.