  We present VLT/X-shooter spectra of 13 galaxies in the redshift range 1< z <
6, which are strongly lensed by massive galaxy clusters. Spectroscopic
redshifts are measured for nine galaxies, while three sources have redshifts
determined from continuum breaks in their spectra. The stellar masses of the
galaxies span four orders of magnitude between 10^7 and 10^11 M_sun and have
luminosities at 1500 A rest-frame between 0.004 and 9 L^* after correcting for
the magnification. This allows us to probe a variety of galaxy types from
young, low-mass starburst galaxies to massive evolved galaxies. The lensed
galaxies with stellar masses less than 10^10 M_sun have a large scatter
compared to the fundamental relation between stellar mass, star formation rates
and oxygen abundances. We provide a modified fit to the fundamental relation
for low-mass, low-metallicity galaxies with a weaker dependence of the
metallicity on either the star formation rate or stellar mass compared to
low-redshift, high-mass and high-metallicity SDSS galaxies.
