合成路线1

The condensation between 3-(bromoacetyl)pyridine (I) and either formamide or formamidine acetate produced the intermediate 4-(3-pyridyl)imidazole (II). Alternatively, intermediate (II) was prepared by palladium-catalyzed coupling between 1-trityl-4-iodoimidazole (III) and diethyl(3-pyridyl)borane (IV), followed by acidic deprotection of the resultant 1-trityl-4-(3-pyridyl)imidazole (V). In a further procedure, iodoimidazole (III) was converted to the corresponding Grignard reagent (VI), which was then coupled with 3-bromopyridine (VII) in the presence of ZnCl2 and palladium catalyst, yielding adduct (V). Subsequent acid-catalyzed deprotection gave intermediate (II). Michael addition of crotonaldehyde (VIII) to imidazole (II) furnished the (pyridylimidazolyl)butyraldehyde (IX). Condensation of aldehyde (IX) with the macrocyclic N-amino carbamate (X) produced the intermediate imine (XI), which was reduced to the corresponding amino derivative using sodium cyanoborohydride. The resultant epimeric mixture was separated by chromatography to provide the title (3R)-diastereoisomer. Alternatively, the reductive alkylation of (X) with aldehyde (IX) was carried out in the presence of sodium triacetoxyborohydride.