  Deuterium fractionation is considered as an important process to infer the
chemical ages of prestellar cores in filaments. We present here the first
magneto-hydrodynamical simulations including a chemical network to study
deuterium fractionation in magnetized and turbulent filaments and their
substructures. The filaments typically show widespread deuterium fractionation
with average values $\gtrsim0.01$. For individual cores of similar age, we
observe the deuteration fraction to increase with time, but also to be
independent of their average properties such as density, virial or
mass-to-magnetic flux ratio. We further find a correlation of the deuteration
fraction with core mass, average H$_2$ density and virial parameter only at
late evolutionary stages of the filament and attribute this to the lifetime of
the individual cores. Specifically, chemically old cores reveal higher
deuteration fractions. Within the radial profiles of selected cores, we notice
differences in the structure of the deuteration fraction or surface density,
which we can attribute to their different turbulent properties. High
deuteration fractions of the order $0.01-0.1$ may be reached within
approximately $200$~kyrs, corresponding to two free-fall times, as defined for
cylindrical systems, of the filaments
