1 Departamento de Química Orgánica E Inorgánica, Facultad de Ciencias, and Instituto Universitario de Investigación del Agua, Cambio Climático Y Sostenibilidad, (IACYS), Universidad de Extremadura, Avenida de Elvas s/n, 06006, Badajoz, Spain. rmarvaz@unex.es.
2 Department of Chemistry and Biochemistry, Quebec Centre for Advanced Materials (QCAM/CQMF), FRQNT, Concordia University, 7141 Sherbrooke St. West, Montreal, QC, H4B 1R6, Canada.
3 Department of Crystallography and Mineralogy, University Complutense, 28040, Madrid, Spain.
4 Departamento de Química Orgánica E Inorgánica, Facultad de Ciencias, and Instituto Universitario de Investigación del Agua, Cambio Climático Y Sostenibilidad, (IACYS), Universidad de Extremadura, Avenida de Elvas s/n, 06006, Badajoz, Spain. pecintas@unex.es.

By paraphrasing one of Kipling's most amazing short stories (How the Leopard Got His Spots), this article could be entitled "How Sugars Became Homochiral". Obviously, we have no answer to this still unsolved mystery, and this perspective simply brings recent models, experiments and hypotheses into the homochiral homogeneity of sugars on earth. We shall revisit the past and current understanding of sugar chirality in the context of prebiotic chemistry, with attention to recent developments and insights. Different scenarios and pathways will be discussed, from the widely known formose-type processes to less familiar ones, often viewed as unorthodox chemical routes. In particular, problems associated with the spontaneous generation of enantiomeric imbalances and the transfer of chirality will be tackled. As carbohydrates are essential components of all cellular systems, astrochemical and terrestrial observations suggest that saccharides originated from environmentally available feedstocks. Such substances would have been capable of sustaining autotrophic and heterotrophic mechanisms integrating nutrients, metabolism and the genome after compartmentalization. Recent findings likewise indicate that sugars' enantiomeric bias may have emerged by a transfer of chirality mechanisms, rather than by deracemization of sugar backbones, yet providing an evolutionary advantage that fueled the cellular machinery.