Mild and convenient N-formylation protocol in water-containing solvents

We have realized that N-formylations of free amines of some drug leads can improve PK/PD property of parent molecules without decreasing their biological activities. In order to selectively formylate primary amines of polyfunctional molecules, we have sought a mild and convenient formylation reaction. In our screening of N-formylation of an α-amino acid, L-phenylalanine, none of formylation conditions reported to date yielded the desired HCO-L-Phe-OH with satisfactory yield. N-Formylations of amino acids with HCO₂H require the reactions in a water-containing media and suppress polymerization reactions due to the competitive reactions among carboxylic acids. We found that N-formylations of α-amino acids could be achieved with a water-soluble peptide coupling additive, an oxyma derivative, (2,2-dimethyl-1,3-dioxolan-4-yl)methyl-2-cyano-2-(hydroxyimino)acetate (2), EDCI, and NaHCO₃ in water or a mixture of water and DMF system, yielding N-formylated α-amino acids with excellent yields. Moreover, these conditions could selectively formylate primary amines over secondary amines at a controlled temperature. A usefulness of these conditions was demonstrated by selective formylation of daptomycin antibiotic which contains three different amino groups.