| 摘要 |
A process for the preparation of an aqueous solution of the calcium salt of (6S)-N(5)-methyl-5,6,7,8-tetrahydrofolic acid, whereby (6S)-5,6,7,8-tetrahydrofolic acid having a content of the corresponding (6R)-diastereoisomer in the range from 4% by weight to 8% by weight is methylated in water comprises: treating the methylated reaction mixture with calcium chloride; crystallizing the calcium salt of (6RS)-N(5)-methyl-5,6,7,8-tetrahydrofolic acid from the resulting aqueous solution; and obtaining an aqueous solution of the calcium salt of (6S)-N(5)-methyl-5,6,7,8-tetrahydrofolic acid.
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