US Patent 7193082 (6S)-5,6,7,8-tetrahydrofolic acid production process

New process for the production of (6S)-5,6,7,8-tetrahydrofolic acid or derivatives thereof starting from the corresponding (6S, 6R) racemic mixture. The procedure comprises in the steps of adding an organic acid to a non-alkaline suspension of (6S,6R)-5,6,7,8-tetraydrofolic acid, up to a pH value in the range of 1 to 3; heating the suspension from 30° to 80° C.; cooling the suspension from 20° to 60° C., with selective crystallization of the (6S)-isomer. The procedure gives the (6S)-isomer in high yields and with a high degree of stereoselectivity. It follows that the synthetic access to a large number of pharmacologically active stereoisomers of folic acid is simpler and more-effective.