The synthesis of folic acid, multiply labelled with stable isotopes, for bio-availability studies in human nutrition

Two different methods for the synthesis of folic acid, which are suitable for the incorporation of compounds multiply labelled with stable isotopes, are described. The first method is based on the use of a novel reductive amination to link 2-acetylamino-4-hydroxy-6-formylpteridine with p-aminobenzoyl-L-glutamic acid. The second method is based on the penultimate formation of an amide bond between N-2-acetyl-N-10-trifluoroacetylpteroic acid and dimethyl L-glutamate. Both methods have been used to transform [13C6]aniline into folic acid, labelled with [13C6] in the p-aminobenzoate moiety, and [3,3,4,4-2H4]-L-glutamic acid into folic acid, labelled with [2H4] in the glutamate moiety. Doubly labelled [13C6, 2H4]-p-aminobenzoyl-L-glutamate has also been prepared by the former method.