合成路线1

The precursor amino acid derivatives were obtained as follows: The condensation of N-Boc-O-benzyltyrosine (I) with tert-butylamine using O-benzotriazol-1-yl-N,N,N',N'-tetramethyluronium hexafluorophosphate (HBTU) gave amide (II). Subsequent deprotection of the Boc group of (II) by means of trifluoroacetic acid provided O-benzyltyrosine tert-butyl amide (III). N-Methyl leucine benzyl ester (IV) was alkylated with 3-bromocyclohexene (V), yielding the cyclohexenyl amine (VI). Hydrogenation of the olefinic double bond of (VI) with concomitant benzyl ester hydrogenolysis in the presence of Pd/C furnished N-cyclohexyl-N-methylleucine (VII). The title dipeptide was finally obtained by HBTU-promoted coupling of amino acids (III) and (VII).