Derived optically active acid d-2- (6-methoxy-2-naphthyl) -propionic acid and pharmaceutical compositions containing it.

ACID S- [D-2- (6-metoxy-2-naphthyl) propionyl] D-2MERCAPTOPROPIONAMIDOACETICO has the following formula: HAS IMPROVED THE THERAPEUTIC PROPERTIES, not only in comparison with the active principle of principle, namely, naproxen , BUT ALSO WITH RESPECT TO THE DERIVATIVE racemic CORRESPONDING TO KNOW THE COMPOUND (D, 1).