L-Threonine → N-(4-Hydroxyphenyl)glycine

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We have found that addition of D-glutamic acid (D-GLU), D-asparagine (D-ASN), D-aspartic acid (D-ASP), or D-cysteine (D-CYS), or D-glutamine (D-GLN) in small amounts to a supersaturated solution of threonine in water brings about a preferred crystallization of the threonine in its L-form. Similarly, inclusion of the L-forms of the above additives leads to preferred crystallization of D-threonine. Further, we have found that from a supersaturated aqueous solution of D,L-asparagine, on addition of D-aspartic acid, D-glutamic acid of D-glutamine, there results a preferred crystallization of L-asparagine monohydrate; inclusion of the L-additives leads to preferred crystallization of D-asparagine monohydrate. Further, we have found that addition of L-tyrosine (TYR), L-tyrosine-p-toluene sulfonate (TpTS), L-dopa, L-dopa-p-toluene sulfonate (DpTS), L-α-methyl dopa, L-α-methyl dopa-p-toluene sulfonate (MDpTS), L-phenylalanine (PHE), L-phenylalanine-p-toluene sulfonate (PpTS), L-phenyl glycine (PG), L-phenyl glycine p-toluene sulfonate (PGpTS), L-p-methoxy phenyl glycine (pMPG) or L-p-methoxy phenyl glycine p-toluene sulfonate (pMPGpTS) to a supersaturated solution of pHPGpTS in an 0.5N aqueous solution of p-toluene sulfonic acid causes preferred precipitation of the D-form of pHPGpTS. On acidification the corresponding enantiomer of p-hydroxyphenylglycine can be obtained. Inclusion of the D-additives causes preferred precipitation of the L-form of pHPGpTS.

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