合成路线1

Reaction of 4,6-dimethylpyridin-2-amine (I) with isoamyl nitrite and HCl gives 2-chloro-4,6-dimethylpyridine (II), which is treated with hydrazine in diethylene glycol at 140 C yielding 2-hydrazino-4,6-dimethylpyridine (III). Cyclization of (III) with cyclohexanone (IV) in refluxing diethylene glycol affords the tetrahydro-alpha-carboline (V), which is dehydrogenated with Pd in refluxing diethylene glycol, giving the alpha-carboline (VI). The alkylation of (VI) with the benzyl bromide (VII) by means of potassium tert-butoxide in DMF yields the adduct (VIII), which is hydrolyzed with concentrated H2SO4 to provide the carboxylic acid (IX). Finally, this acid is condensed with (R)-2-hydroxy-1-phenylethylamine (X) by means of HOBT and EDC in CH2Cl2, giving a diastereomeric mixture of the corresponding amides that is resolved by column chromatography. The benzyl bromide intermediate (VII) has been obtained as follows: Esterification of 2-(4-methylphenyl)acetic acid (XI) with tert-butanol and DCC and DMAP in CH2Cl2 gives the corresponding tert-butyl ester (XII), which is condensed with cyclopentyl bromide (XIII) by means of t-BuOK in DMF to yield racemic 2-cyclopentyl-2-(4-methylphenyl)acetic acid tert-butyl ester (XIV). Finally, this compound is brominated with NBS and AIBN in refluxing CCl4.