Separation of the Diastereomers (6R)‐ and (6S)‐5,6,7,8‐Tetrahydro‐L‐biopterin
The mixture of the diastereomers of the tetraacetylderivative IV of (6RS)‐5,6,7,8‐tetrahydro‐L‐biopterin could be separated by fractional crystallisation in methanol into the diastereomers IV A and IV B. Hydrolysis with hydrochloric acid gives the pure, diastereomeric, (6R)‐ and (6S)‐5,6,7,8‐tetrahydro‐L‐biopterins.