  Formamide (NH$_2$CHO) has previously been detected in several star-forming
regions and is thought to be a precursor for different prebiotic molecules. Its
formation mechanism is still debated, however. Observations of formamide,
related species and their isopotologues may provide useful clues to the
chemical pathways leading to their formation. The Protostellar Interferometric
Line Survey (PILS) represents an unbiased high angular resolution and
sensitivity spectral survey of the low-mass protostellar binary IRAS 16293-2422
with the Atacama Large Millimeter/submillimeter Array (ALMA). We detect for the
first time the three singly deuterated forms of NH$_2$CHO (NH$_2$CDO, cis- and
trans-NHDCHO) as well as DNCO towards the component B of this binary source.
The images reveal that the different isotopologues are all present in the same
region. Based on observations of the $^{13}$C isotopologues of formamide and a
standard $^{12}$C/$^{13}$C ratio, the deuterium fractionation is found to be
similar for the three different forms with a value of about 2%. The DNCO/HNCO
ratio is also comparable to the D/H ratio of formamide ($\sim$1%). These
results are in agreement with the hypothesis that NH$_2$CHO and HNCO are
chemically related through grain surface formation.
