forming regions” (CHESS).]{} [We report the first detection of interstellar and . Both species are observed in absorption against the continuum of the protostar. From the analysis of their hyperfine structure, accurate excitation temperature and column density values have been determined. The latter were combined with the column density of the parent species to derive the deuterium fractionation in amidogen. Our findings point out a high deuteration level of amidogen radical in IRAS 16293-2422, with a deuterium enhancement about one order of magnitude higher than that predicted by earlier astrochemical models. Such a high enhancement can only be reproduced by a gas-grain chemical model if the pre-stellar phase preceding the formation of the protostellar system lasts long, of the order of one million years. ]{} [The amidogen D/H ratio measured in the low-mass protostar IRAS 16293-2422 is comparable to the one derived for the related species imidogen and much higher than that observed for ammonia. Additional observations of these species will give more insights into the mechanism of ammonia formation and deuteration in the ISM. We finally indicate the current possibilities to further explore these species at submillimeter wavelengths.]{}

Introduction
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Despite the low cosmic abundance of deuterium (D/H = 