合成路线1

Ring opening of cis-2-azabicyclo[2.2.1]hept-5-en-3-one (I) with HCl in refluxing methanol gives cis-4-amino-2-cyclopentene-1-carboxylic acid (II), which is esterified with HCl/methanol, yielding the methyl ester (III). The protection of (III) with tert-butoxycarbonyl anhydride and triethylamine in dichloromethane affords carbamate (IV), which is cyclized with 2-ethyl-1-nitrobutane (V) by means of phenyl isocyanate in refluxing benzene to give the cyclopenta-oxazoline (VI). Ring opening of (VI) by hydrogenation with H2 over PtO2 in HCl/methanol yields amine (VII), which is acylated with acetic anhydride and triethylamine in dichloromethane to afford acetamide (VIII). The deprotection of (VIII) with HCl in ethyl ether gives the cyclopentylamine (IX), which is condensed with N,N'-bis(tert-butoxycarbonyl)-O-methylisourea (X) by means of HgCl2 in DMF to yield the protected guanidino compound (XI). Deprotection of the guanidino group of (XI) with trifluoroacetic acid in dichloromethane affords the methyl ester (XII), which is finally hydrolyzed with NaOH in THF/methanol.