  Peptide-like molecule, which has a close connection with the origin of life,
has been detected in universe. Mapping observations of HCONH$_2$ and
CH$_3$CONH$_2$, two simplest peptide-like molecules, are performed towards
Sagittarius B2 (Sgr B2) complex with the IRAM 30m telescope. Seven transitions
of HCONH$_2$ and five transitions of CH$_3$CONH$_2$ are used in analysis. The
spatial distribution of excitation temperature and column density of HCONH$_2$
in the molecular envelope of Sgr B2 are obtained by the rotation diagrams.
Assuming the same excitation temperature as HCONH$_2$, the column densities of
CH$_3$CONH$_2$ are also calculated. The results show that excitation
temperature ranges from 6 K to 46 K in the molecular envelope of Sgr B2. The
abundance ratio between HCONH$_2$ and CH$_3$CONH$_2$ are calculated to explore
the relationship among them, as well as HNCO mentioned in our pervious
research. The abundance ratio of CH$_3$CONH$_2$/HCONH$_2$ varies from 10% to
20%, while that of HCONH$_2$/HNCO ranges from 1.5% to 10%. CH$_3$CONH$_2$ is
enhanced with respect to HCONH$_2$ in the northwest region of Sgr B2. One
transition of H$^{13}$CONH$_2$ is detected toward 12 positions of Sgr B2, from
which a $^{12}$C/$^{13}$C ratio of 28.7 is obtained. A time-dependent chemical
model with a short duration of X-ray burst is used to explain the observed
abundances of HCONH$_2$ and CH$_3$CONH$_2$, with the best fitting result at
T$\rm_{dust}$ = 53-56 K. More chemical reactions are required to be included
into the model since the modeled abundance is lower than the observed one at
the observed T$\rm_{dust}$.
