PURPOSE: To provide a novel thiol carboxylic acid derivative useful as an inhibitor of neutral metal-protease enzymes belonging to collagenases, and thus effective for the treatment of arthritis.

CONSTITUTION: A compound of formula I [R1 is OH, alkoxy, aryloxy, NR6R7 (R6 and R7 each represents H, alkyl, or a 6-7-membered ring together with N) etc.; R2 is H, alkanoyl or aroyl; R3 is 3-6C alkyl; R4 is (CH2)m (m is 4-12)], e.g. 3-acetylmercapto-6-methyl-4-[(2-oxoazacyclotridec-3-yl)aminocarbonyl]heptoic acid methyl ester. Such a compound can be obtained by first reacting a compound of formula II with a thiol expressed as L-SH (L is sulfur-protecting group) to yield a compound of formula III, then breaking off the radical L if needed, and performing the mutual transformation of R1.