Amino acid derivatives (I) are new. Amino acid derivatives of formula H 2NCH(R 1)CH 2SSCH 2CH(R 2)C(O)NHCH(R 3)C(O)OR 4 (I) and their mineral or organic acid addition salts are new. R 1 = 1-6C optionally unsaturated hydrocarbyl (optionally substituted by OR, SR, S(O)R, phenyl or benzyl), phenyl or benzyl (both optionally substituted by OR, SR or S(O)R or 1-5 halo, preferably F) or T； R = H, 1-4C hydrocarbyl, phenyl or benzyl； T = methylene substituted by aromatic or saturated 5-6 membered heterocycle containing heteroatoms such as N or S, preferably as N-oxide or S-oxide； R 2 = phenyl or benzyl (both optionally substituted by OR, SR, S(O)R, amino (optionally mono- or disubsituted by 1-6C aliphatic group), 5-6 membered aromatic ring or 1-5 halogen (preferably F)), 5-6 membered heteroaromatic ring contaning one O, S or N or T； R 3 = H, OH, OR, 1-6C saturated alkyl (optionally substituted by OR or SR), phenyl or benzyl (both optionally substituted by 1-5 halogen (particularly F), OR or SR)； and OR 4 = hydrophilic ester where the hydrophilicity of the ester provides an octanol-water division coefficient (log K ow) 1.7 to (I). ACTIVITY : Antidepressant； Antiinflammatory； Analgesic. MECHANISM OF ACTION : Neprilysine inhibitor； N-Amino peptidase inhibitor.
