Synthesis of new beta-amidodehydroaminobutyric acid derivatives and of new tyrosine derivatives using copper catalyzed C-N and C-O coupling reactions

Abstract

Several beta-amidodehydroaminobutyric acid derivatives were prepared from N,C-diprotected beta-bromodehydroaminobutyric acids and amides by a copper catalyzed C-N coupling reaction. The best reaction conditions include the use of a catalytic amount of CuI, N,N’-dimethylethylenediamine as ligand and K2CO3 as base in toluene at 110 ºC. The stereochemistry of the products was determined using NOE difference experiments and the results obtained are in agreement with an E-stereochemistry. Thus, the stereochemistry is maintained in the case of the E-isomers of beta-bromodehydroaminobutyric acid dervatives, but when the Z-isomers were used as substrates the reaction proceeds with inversion of configuration. The use of beta-bromodehydrodipeptides as substrates was also tested. It was found that the reaction outcome depend on the stereochemistry of the beta-bromodehydrodipeptide and on the nature of the first amino acid residue. The products isolated were the beta-amidodehydrodipeptide derivatives and/or the corresponding dihydropyrazines. The same catalytic system (CuI/N,N’-dimethylethylene diamine) was used in the C-O coupling reactions between a tyrosine derivative and aryl bromides. The new O-aryltyrosine derivatives were isolated in moderate to good yields. The photophysical properties of two of these compounds were studied in four solvents of different polarity. The results show that these compounds after deprotection can used as fluorescence markers.