Phenylalanine enamide derivatives of formula (1) are described: wherein R1 is a group Ar1L2Ar2Alk—in which: Ar1 is an optionally substituted aromatic or heteroaromatic group; L2 is a covalent bond or a linker atom or group; Ar2 is an optionally substituted arylene or heteroarylene group; and Alk is a chain in which R is a carboxylic acid (—CO2H) or a derivative or biostere thereof; X is an —O— or —S— atom or —N(R2)— group in which: Rx, Ry and Rz which may be the same or different is each a hydrogen atom or an optional substituent; or Rz is an atom or group as previously defined and Rx and Ry are joined together to form an optionally substituted spiro linked cycloaliphatic or heterocycloaliphatic group; and the salts, solvates, hydrates and N-oxides thereof. The compounds are able to inhibit the binding of integrins to their ligands and are of use in the prophylaxis and treatment of immuno or inflammatory disorders or disorders involving the inappropriate growth or migration of cells.