The outer parts of the Milky Way disk are believed to be one of the main are nas where the
accretion of external material in the form of dwarf galaxies and subsequent formation of streams is
taking place. The Monoceros stream and the Canis Major and Argo over-densities are notorious
examples. Understanding whether what we detect is the signature of accretion or, more conservatively,
simply the intrinsic nature of the disk, represents one of the major goals of modern Galactic
astronomy. We try to shed more light on the properties of the outer disk by exploring the properties
of distant anti-center old open clusters. We want to verify whether distant clusters follow
the chemical and dynamical behavior of the solar vicinity disk, or whether their properties can be
better explained in terms of an extra-galactic population. VLT high resolution spectra have been
acquired for five distant open clusters: Ruprecht 4, Ruprecht 7, Berkeley 25, Berkeley 73 and Berkeley
75. We derive accurate radial velocities to distinguish field interlopers and cluster members.
For the latter we perform a detailed abundance analysis and derive the iron abundance [Fe/H] and
the abundance ratios of several ålements. Our analysis confirms previous indications that the
radial abundance gradient in the outer Galactic disk does not follow the expectations extrapolated
from the solar vicinity, but exhibits a shallower slope. By combining the metallicity of the five
program clusters with eight more clusters for which high resolution spectroscopy is available, we
find that the mean metallicity in the outer disk between 12 and 21 kpc from the Galactic center is
[Fe/H] ≈ -0.35, with only marginal indications for a radial variation. In addition, all the program
clusters exhibit solar scaled or slightly enhanced ålements, similar to open clusters in the solar
vicinity and thin disk stars. We investigate whether this outer disk cluster sample might belong to
an extra-galactic population, like the Monoceros ring. However, close scrutiny of their properties -
location, kinematics and chemistry - does not convincingly favor this hypothe sis. On the contrary,
they appear more likely genuine Galactic disk clusters. We finally stress the importance to obtain
proper motion measurements for these clusters to constrain their orbits.