合成路线1

Protection of methyl (R)-3-aminobutyrate (VI) with di-tert-butyl dicarbonate provided the Boc derivative (VII), which was alkylated with 3-cyanobenzyl bromide (VIII) in the presence of lithium bis(trimethylsilyl)amide at -78 C to afford adduct (IX). Acid deprotection of the Boc group of (IX) yielded amino ester (X). Alternatively, (X) was obtained by protection of methyl 3-aminobutyrate (VI) with benzyl chloroformate, followed by alkylation with 3-cyanobenzyl bromide to give (XI). The carbobenzoxy group of (XI) was then deprotected by hydrogenation over Pd/C. Coupling of amino ester (X) with acid chloride (V) gave rise to amide (XII). Conversion of (XII) to the required amidine was then achieved by treatment with methanolic HCl, followed by reaction of the resulting imidate with ammonia in boiling MeOH. The title compound was isolated after conversion to the trifluoroacetate salt.