PURPOSE: To provide optically pure compounds useful as intermediates for producing peptides having a renin-prohibiting activity.

CONSTITUTION: The compound of formula I [wherein (n) is 1 or 2; R1 represents H, a 1-8C alkyl, benzyl, -COR4 (wherein R4 represents an alkyl or aryl), an amino-protecting group; R2 represents H, a 1-8C alkyl, benzyl;, or R1 and R2 are joining to form morphorine ring of phthalimide together with; R3 represents hydroxyl, a 1-10C alkoxy, benzyloxy, -NR5R6 (R5 and R6 are each H, 1-6C alkyl or phenyl); x represents S- or R-type C], for example ethyl N-tert- butoxycarbonyl-2-R-S-amino-2-[2-(1,3-dithiolano)] acetate, is obtained by reacting racemic compound of formula II (wherein R1' and R3' are the same as R1 and R3, but R1' is not H and R3' is not hydroxyl) with a protein hydrolase (e.g. esterase) in a two-layers medium comprising water and water insoluble solvent at a temperature of 20 to 40°C and pH or 6 to 8.