Pteroyl-{dblunder}g-glutamyl glutamic acid: a study of a possible synthesis from folic acid

A method for the synthesis of pteroyl- y-glutamyl glutamic acid (and other polyglutamates of folic acid) has been studied using folic acid as the starting material. Dimethyl folate and diethyl folate were prepared and hydrolyzed under basic conditions in dimethyl form-andde and dimethyl sulfoxide respectively. Two compounds identified as monoothyl folates were separated from hydrolysis products by paper and column chromatography. Identification of the compounds as ^ - or ^-ethyl esters could not be established. Difficulty in preparing diethyl folate in half-gram quantities prompted the investigation of dimethyl folate. Only one compound identified as monomethyl folate could be separated by paper or column chromatography. This compound was coupled with diethyl glutamate through a peptide bond by the mixed—anhydride method using isobutyl chloroiormate. ihe esterified product was hydrolyzed in .IN sodium hydroxide to the j.ree acid, fhe product, of doubtful purity, has the same Rf value by paper chromatography as that observed by other sources. The product will sustain the growth of Lactobacillus casex, although whether this is due to pteroyl- ! -glutamyl glutamic acid or folic aci d has not been determined. Tetrazolium bioautography on a paper chromatogram, which has not been successful, would establish or discount the presence of pteroyl-2f-glutarnyl glutamic acid in the product.