Reductive condensation of 2-thienylmethylamine (I) with 2-thiophenecarboxaldehyde (II) in the presence of NaBH(OAc)3 provided bis(2-thienylmethyl)amine (III), which was coupled with N-Boc-2-aminohexanoic acid (IV) by means of EDC and HOBt, yielding amide (V). Acid deprotection of the Boc group of (V) then gave amine (VI).

Treatment of 3,4-(methylenedioxy)cinnamic (VII) with SOCl2 and then with EtOH provided ethyl ester (VIII). Subsequent conjugate addition of the chiral amine (IX) to ester (VIII) in the presence of BuLi gave amino ester (X). Cleavage of benzyl and alpha-methylbenzyl protecting groups of (X) was then achieved by catalytic hydrogenolysis over Pd/C. The resulting primary amine (XI) was acylated with 4-nitrophenyl chloroformate (XII) to produce carbamate (XIII), which was condensed with amine (VI) to generate urea (XIV). Finally, basic hydrolysis of the ethyl ester of (XIV) furnished the title carboxylic acid.

Amine (I) was treated with phosgene to produce isocyanate (II), which was coupled with ethyl 3-amino-3-(3,4-methylenedioxyphenyl)propionate (III), yielding urea (IV). Basic hydrolysis of the ethyl ester of (IV) then gave the title carboxylic acid.