Pterin chemistry. 45. A new and clear synthesis of isomer-free pteroyl-gamma-L-glutamyl-L-glutamic acid

A new and unequivocal synthesis of pteroyl-λ-L-glutamyl-L-glutamic acid free of isomers is described. A melt of N(2′)-acetyl-6-formylpterine and trimethyl-N-(p-amino-benzoyl)-λ-L-glutamyl-L-glutamate was quantitatively converted to 6-azomethin-pterine-trimethylester XI. NaBH₄-reduction followed by basic hydrolysis of acetyl and methyl ester groups gives pure pteroyl-λ-glutamyl-glutamic acid in good yield.