Synthesis of N-Fmoc amino acids carrying the four DNA nucleobases in the side chain

Four new N-Fmoc α-amino acids carrying a nucleobase in the side chain were prepared starting from L-glutamic acid. N-Boc-glutamic acid α benzyl ester underwent a radical decarboxylation in the presence of CBrCl3 to give the corresponding 2-amino-4-bromobutanoic acid derivative. The four nucleobases (adenine, cytosine, thymine and guanine) were introduced 'via' nucleophilic substitution of the bromide using a different synthetic protocol for each base. The Boc protection was changed to Fmoc and the benzyl ester deprotected to give the four amino acids in good yields and in a suitable form for solid phase peptide synthesis. The preparation of the insecticidal dipeptide NK 374200 is also described.