  The formation of molecules in the interstellar medium (ISM) remains a complex
and unresolved question in astrochemistry. A group of molecules of particular
interest involves the linkage between a -carboxyl and -amine group, similar to
that of a peptide bond. The detection of molecules containing these
peptide-like bonds in the ISM can help elucidate possible formation mechanisms,
as well as indicate the level of molecular complexity available within certain
regions of the ISM. Two of the simplest molecules containing a peptide-like
bond, formamide (NH2CHO) and acetamide (CH3CONH2), have previously been
detected toward the star forming region Sagittarius B2 (Sgr B2). Recently, the
interstellar detection of propionamide (C2H5CONH2) was reported toward Sgr
B2(N) with ALMA observations at millimeter wavelengths. Yet, this detection has
been questioned by others from the same set of ALMA observations as no
statistically significant line emission was identified from any uncontaminated
transitions. Using the PRrbiotic Interstellar MOlecule Survey (PRIMOS)
observations, we report an additional search for C2H5CONH2 at centimeter
wavelengths conducted with the Green Bank Telescope. No spectral signatures of
C2H5CONH2 were detected. An upper limit for C2H5CONH2 at centimeter wavelengths
was determined to be less than 1.8e14 cm-2 and an upper limit to the
C2H5CONH2/CH3CONH2 ratio is found to be less than 2.34. This work again
questions the initial detection of C2H5CONH2 and indicates that more complex
peptide-like structures may have difficulty forming in the ISM or are below the
detection limits of current astronomical facilities. Additional structurally
related species are provided to aid in future laboratory and astronomical
searches.
