| abstract |
Novel O-alkyl tyrosine derivatives of low toxicity have the effect of enhancing absorption of pharmaceutically active substances such as peptides, administered by mouth or as a suppository: compounds of the invention are those of formula (I) below, esters and salts thereof wherein R¹ is a lower alkyl group optionally substituted with an alkyloxy group; X is CO or SO₂; -Y- is either a direct bond, lower alkylene group, substituted or unsubstituted vinylene group, or a group expressed as -CHR³-O- or -O-CHR³-; R² is a substituted or unsubstituted phenyl group, naphthyl group or 2-benzo-furanyl group; R³ is either hydrogen or lower alkly group; or in the formula (I). R₂-Y-X denotes N-benzyloxycarbonyl phenylalanyl, N-benzyloxycarbonyl-4-halogenophenylalanyl, or N-(m-methoxycinnamoyl) phenylalanyl group. |