| Summary: | We present the observational results of a precursor of glycine, methylamine (CH _3 NH _2 ), together with methanol (CH _3 OH) and methanimine (CH _2 NH) for the high-mass star-forming regions NGC 6334I, G10.47+0.03, G31.41+0.3, and W51 e1/e2 using the Atacama Large Millimeter/submillimeter Array. The molecular abundances of these sources were derived using the CASSIS spectrum analyzer and compared with our state-of-the-art three-phase chemical model NAUTILUS . We found that the observed abundance ratio of CH _3 NH _2 /CH _3 OH is between 0.008 and 1.0 for all sources, except for NGC 6334I MM3, where a ratio less than 0.002 is found. This may be due to its later evolutionary stage relative to the other cores. We also found that the observed CH _3 NH _2 /CH _3 OH ratio agrees well with the three-phase chemical model NAUTILUS , which includes the formation of CH _3 NH _2 on the grain surface via a series of hydrogenation processes of HCN. This result clearly shows the importance of hydrogenation processes to form CH _3 NH _2 .
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