N-Boc-L-Tyrosine methyl ester (I) was alkylated with either 3-(dimethylamino)-1-propanol (II) under Mitsunobu conditions or with N,N-dimethyl-3-chloropropylamine (III) in the presence of K2CO3 to afford N-Boc-L-4-(3-dimethylaminopropoxy)phenylalanine methyl ester (IV). Subsequent acidic cleavage of the N-Boc protecting group of (IV) gave amino ester (V). N-Tosyl-L-5,5-dimethylthiaproline (VII) was obtained by treatment of L-5,5-dimethylthiaproline (VI) with p-toluenesulfonyl chloride in the presence of NaOH. Acid (VII) was then coupled to amino ester (V) using EDC and HOBt to furnish amide (VIII). Finally, basic hydrolysis of the methyl ester group of (VIII) yielded the title compound.

N-Boc-L-Tyrosine methyl ester (I) was alkylated with either 3-(dimethylamino)-1-propanol (II) under Mitsunobu conditions or with N,N-dimethyl-3-chloropropylamine (III) in the presence of K2CO3 to afford N-Boc-L-4-(3-dimethylaminopropoxy)phenylalanine methyl ester (IV). Subsequent acidic cleavage of the N-Boc protecting group of (IV) gave amino ester (V). N-Tosyl-L-5,5-dimethylthiaproline (VII) was obtained by treatment of L-5,5-dimethylthiaproline (VI) with p-toluenesulfonyl chloride in the presence of NaOH. Acid (VII) was then coupled to amino ester (V) using EDC and HOBt to furnish amide (VIII). Finally, basic hydrolysis of the methyl ester group of (VIII) yielded the title compound.