Optical resolution of n-acetyl-indoline-2-carboxylic acid with phenylglycinol

Processes for: a) separating the enantiomers of indoline-2-carboxylic acid of formula 1 comprising of (i) combining the (R, S)-indoline-2-carboxylic acid with (1S)- or (1R)-10-camphorsulfonic acid as the resolving agent in a resolution solvent and crystallizing from the said mixture the diastereomeric salt of (S)- or (R)-indoline-2-carboxylic acid with optically pure (1S)- or (1R)-10-camphorsulfonic acid; (ii) regenerating the (S)- or (R)-indoline-2-carboxylic acid from the crystallized diastereomeric salt by using a suitable base or basic ion-exchange resin; and b) for the optical resolution of N-acetyl-indoline-2-carboxylic acid of formula 2 comprising of: (i) combining the (R, S)-N-acetyl-indoline-2-carboxylic acid with (S)- or (R)-phenylglycinol as the resolving agent in a resolution solvent and crystallizing from the said mixture the diastereomeric salt of (S)- or (R)-N-acetyl-indoline-2-carboxylic acid with optically pure phenylglycinol; (ii) regenerating the (S)- or (R)-N-acetyl-indoline-2-carboxylic acid from the crystallized salt by using a suitable acid or acidic ion-exchange resin. The non-selected enantiomer may then be racemized and the process (a) or (b) repeated thus to obtain substantial conversion of the material to one enantiomer.