The beta-amino acid (II) was prepared by Knoevenagel condensation of 4-chlorobenzaldehyde (I) with malonic acid in the presence of ammonium acetate. After protection of the amino group of (II) with Fmoc-Cl, the protected amino acid (III) was attached to the trityl chloride polystyrol resin, yielding the amino acid-bound resin (IV). The Fmoc group of (IV) was then removed using piperidine in DMF to afford (V). N-Fmoc-hydrazine (VI) was carbonylated with phosgene to obtain the oxadiazolone (VII). This was condensed with the amino resin (V) producing adduct (VIII). Deprotection of the Fmoc group of (VIII), followed by coupling with N-Fmoc-3-aminobenzoic acid (IX), furnished (X). After a new deprotection of (X) with piperidine in DMF, the guanidino group was introduced by condensation with N,N'-bis-Boc-1-guanylpyrazole to give (XI). Finally, deprotection and cleavage of the resin adduct (XI) was carried out with trifluoroacetic acid in the presence of triisopropylsilane.

The beta-amino acid (II) was prepared by Knoevenagel condensation of 4-chlorobenzaldehyde (I) with malonic acid in the presence of ammonium acetate. After protection of the amino group of (II) with Fmoc-Cl, the protected amino acid (III) was attached to the trityl chloride polystyrol resin, yielding the amino acid-bound resin (IV). The Fmoc group of (IV) was then removed using piperidine in DMF to afford (V). N-Fmoc-hydrazine (VI) was carbonylated with phosgene to obtain the oxadiazolone (VII). This was condensed with the amino resin (V) producing adduct (VIII). Deprotection of the Fmoc group of (VIII), followed by coupling with N-Fmoc-3-aminobenzoic acid (IX), furnished (X). After a new deprotection of (X) with piperidine in DMF, the guanidino group was introduced by condensation with N,N'-bis-Boc-1-guanylpyrazole to give (XI). Finally, deprotection and cleavage of the resin adduct (XI) was carried out with trifluoroacetic acid in the presence of triisopropylsilane.