Published 2021 April 30 • © 2021. The American Astronomical Society. All rights reserved.Rodríguez Almeida, L. F.Jiménez Serra, I.Rivilla, V. M.Martín Pintado, J.Zeng, S.Tercero, B.De Vicente, P.Colzi, L.Rico Villas, F.Martín, S.Requena Torres, M. A.Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-07372022-02-152022-02-152021-04-30The Astrophysical Journal Letters 912(1): L11(2021)2041-8205https://iopscience.iop.org/article/10.3847/2041-8213/abf7cbhttp://hdl.handle.net/20.500.12666/557The chemical compounds carrying the thiol group (-SH) have been considered essential in recent prebiotic studies regarding the polymerization of amino acids. We have searched for this kind of compound toward the Galactic Center quiescent cloud G+0.693–0.027. We report the first detection in the interstellar space of the trans-isomer of monothioformic acid (t-HC(O)SH) with an abundance of ~1 × 10−10. Additionally, we provide a solid confirmation of the gauche isomer of ethyl mercaptan (g-C2H5SH) with an abundance of ~3 × 10−10, and we also detect methyl mercaptan (CH3SH) with an abundance of ~5 × 10−9. Abundance ratios were calculated for the three SH-bearing species and their OH analogs, revealing similar trends between alcohols and thiols with increasing complexity. Possible chemical routes for the interstellar synthesis of t-HC(O)SH, CH3SH, and C2H5SH are discussed, as well as the relevance of these compounds in the synthesis of prebiotic proteins in the primitive Earth.engAstrochemistryChemical AbundancesInterstellar moleculesGalactic centerinfo:eu-repo/semantics/article10.3847/2041-8213/abf7cb2041-8213http://dx.doi.org/10.13039/100012818http://dx.doi.org/10.13039/501100011033http://dx.doi.org/10.13039/501100000781http://dx.doi.org/10.13039/501100000780info:eu-repo/semantics/restrictedAccess