First Interstellar Detection of Methyl Carbamate: A New Observational Anchor for Glycine Chemistry

Abstract

Glycine-the simplest amino acid-has remained undetected in the interstellar medium despite decades of sensitive searches, motivating alternative approaches to constrain its astrochemical origin. A promising strategy is to investigate the broader $\rm C_{2}H_{5}O_{2}N$ isomer family and identify detectable members that can serve as observational anchors for glycine-related chemistry. Herein, we report the first robust interstellar detection of methyl carbamate toward the hot molecular core G358.93-0.03 MM1 using ALMA 1 mm observations. Ten unblended rotational transitions are identified, yielding a column density of (4.21$\pm0.84)\times10^{15} \rm cm^{-2}$ and an excitation temperature of $204\pm10$ K. We also searched for other $\rm C_{2}H_{5}O_{2}N$ isomers with available rotational spectroscopic data, including glycine, but none were detected, allowing us to derive upper limits on their column densities. The resulting abundance pattern deviates significantly from the Minimum Energy Principle predictions, highlighting that the $\rm C_{2}H_{5}O_{2}N$ family is shaped primarily by kinetic chemical process rather than thermodynamic equilibrium. The observed methyl carbamate abundance is consistent with a grain-surface formation scenario involving radical-radical recombination ($\rm CH_{3}$O + $\rm NH_{2}$CO), further supported by its correlated abundances with its proposed precursors, methanol and formamide, across diverse astrophysical environments. This detection establishes methyl carbamate as a new observational anchor for glycine chemistry, providing critical constraints on the formation pathways of amino-acid-related molecules in star-forming regions.