Processes for preparing ›L!- or ›D!-homoalanin-4-yl-(methyl)phosphinic acid and salts thereof by racemate resolution

A process for preparing ›L!-homoalanin-4-yl(methyl)-phosphinic acid (L-acid), (L-la)) or salts thereof or ›D!-homoalatin-4-yl(methyl)-phosphinic acid (D-acid, (D-la)) or salts thereof ##STR2## from ›DL!-homoalanin-4-yl(methyl)-phosphinic acid (DL-acid, DL-la)) or salts thereof by racemate solution, which comprises

• a) reacting DL acid or salt thereof with a chiral base, selected from the group consisting of alkaloid bases;
• b) allowing the salt of the L acid or D acid and of the chiral base to crystallize out of a solution of the resulting mixture of the disastereomeric salts of D acid, L acid and the chiral base in an aqueous or aqueous-organic solvent in which the salt of the D acid or of the L acid has a higher solubility than the salt of the L acid or D acid, respectively (racemate resolution) and
• c) in the case where the free L acid or D acid is prepared, neutralizing the resulting salt with an acid, or in the case where a salt other than that obtained according to b) is prepared, carrying out a metathesis.