Condensation of L-tyrosine methyl ester (I) with 2-benzoylcyclohexanone (II) in the presence of Pd/C in boiling anisole produced the vinylogous amide intermediate (III) which, in the reaction conditions, experienced a dehydrogenation to furnish benzophenone (IV). Then, coupling of (IV) with 2-(5-methyl-2-phenyloxazol-4-yl)ethanol (V) under Mitsunobu conditions afforded ether (VI). Finally, the ester function of (VI) was hydrolyzed with LiOH to give the title acid.

The 2-aminobenzophenone derivative (III) was prepared by condensation of L-tyrosine methyl ester (I) with 2-benzoylcyclohexanone (II) in refluxing anisole, with concomitant dehydrogenation in the presence of Pd/C. Subsequent Mitsunobu coupling of (III) with 2-(N-Boc-N-methylamino)ethanol (V), prepared from aminoalcohol (IV) and Boc2O, afforded the Boc-protected aminoethyl ether (VI). After removal of the Boc group of (VI) by treatment with trifluoroacetic acid, condensation of the resulting secondary amine (VII) with 2-fluoropyridine (VIII) yielded the 2-aminopyridine derivative (IX). Finally, the methyl ester group of (IX) was hydrolyzed to the title carboxylic acid using LiOH.

Condensation of L-tyrosine methyl ester (I) with 2-benzoylcyclohexanone (II) in the presence of Pd/C in boiling anisole produced the vinylogous amide intermediate (III) which, in the reaction conditions, experienced a dehydrogenation to furnish benzophenone (IV). Then, coupling of (IV) with 2-(5-methyl-2-phenyloxazol-4-yl)ethanol (V) under Mitsunobu conditions afforded ether (VI). Finally, the ester function of (VI) was hydrolyzed with LiOH to give the title acid.

The 2-aminobenzophenone derivative (III) was prepared by condensation of L-tyrosine methyl ester (I) with 2-benzoylcyclohexanone (II) in refluxing anisole, with concomitant dehydrogenation in the presence of Pd/C. Subsequent Mitsunobu coupling of (III) with 2-(N-Boc-N-methylamino)ethanol (V), prepared from aminoalcohol (IV) and Boc2O, afforded the Boc-protected aminoethyl ether (VI). After removal of the Boc group of (VI) by treatment with trifluoroacetic acid, condensation of the resulting secondary amine (VII) with 2-fluoropyridine (VIII) yielded the 2-aminopyridine derivative (IX). Finally, the methyl ester group of (IX) was hydrolyzed to the title carboxylic acid using LiOH.

Condensation of L-tyrosine methyl ester (I) with 2-benzoylcylohexanone (II) and subsequent dehydrogenation in refluxing anisole in the presence of Pd/C affords the benzophenone derivative (III), which is converted into carboxylic acid (V) by Mitsunobu reaction with heterocyclic alcohol (IV) by means of PPh3 and DEAD in THF followed by saponification of the resulting methyl ester with LiOH in THF/MeOH (1). Coupling of (V) with valinol (VI) by means of HOBt/Et3N and EDC稨Cl in CH2Cl2 furnishes amide (VII), which is oxidized by means of 4-methylmorpholine (NMM) and TPAP in CH2Cl2 to furnish aldehyde (VIII). Finally, the desired oxazole is obtained by intramolecular cyclization of (VIII) by means of iodine, PPh3 and Et3N in CH2Cl2.

Condensation of L-tyrosine methyl ester (I) with 2-benzoylcylohexanone (II) and subsequent dehydrogenation in refluxing anisole in the presence of Pd/C affords the benzophenone derivative (III), which is converted into carboxylic acid (V) by Mitsunobu reaction with heterocyclic alcohol (IV) by means of PPh3 and DEAD in THF followed by saponification of the resulting methyl ester with LiOH in THF/MeOH (1). Coupling of (V) with acetic acid hydrazide (VI) by means of HOBt/Et3N and EDC.HCl in CH2Cl2 furnishes the diacyl hydrazide (VII), which is finally converted into the desired thiadiazole derivative by treatment with Lawesson抯 Reagent in refluxing toluene.