合成路线1

The ring opening of (-)-2-azabicyclo [2,2,1]hept-5-en-3-one (I) with methanolic HCl gives the methyl ester (II), which is N-protected with Boc2O and TEA, yielding the carbamate (III). The cyclization of (III) with 2-ethyl-1-nitrobutane (IV) by means of phenyl isocyanate and TEA affords the bicyclic compound (V) along with other isomers that are separated by column chromatography. Compound (V) is hydrogenated with H2 over PtO2 in methanol to provide amine (VI), which is acylated with Ac2O, giving the acetamide (VII). N-Boc deprotection of (VII) by means of HCl in ethyl ether yields the amine (VIII), which is condensed with protected isothiourea (IX) by means of HgCl2 to afford the guanidine derivative (X). The hydrolysis of (X) with NaOH provides the carboxylic acid (XI), which is finally deprotected with trifluoroacetic acid to yield the target cyclopentanecarboxylic acid derivative.