<p>Umbilical cord blood (UCB) is a clinically validated and readily available source for hematopoietic stem cell transplantation (HSCT). However, its widespread application in adults is constrained by the limited hematopoietic stem cell (HSC) dose per unit, necessitating effective strategies for ex vivo HSC expansion while preserving stemness. We conducted a phenotypic screen using a miniaturized scaffold library to identify novel small molecules capable of expanding human UCB-HSCs. This effort identified 8-methyl-4-((4-isopropylphenyl)amino)-[1,2,4]triazolo[4,3-a]quinoxaline (designated 8-Me-PIQ) as a potent activator of HSC expansion. In serum-free cultures, 8-Me-PIQ significantly increased the frequency and absolute number of phenotypic HSCs (CD34⁺CD38⁻CD45RA⁻CD90⁺CD49f⁺). Critically, primary and secondary transplantation in immunodeficient mice demonstrated that 8-Me-PIQ-expanded CD34⁺ HSC and progenitor cells (HSPCs) retained robust long-term multilineage reconstitution and self-renewal capacity, confirming functional stem cell maintenance. Mechanistically, transcriptomic analysis of 8-Me-PIQ-treated HSPCs revealed significant downregulation of gene signatures associated with oxidative phosphorylation and ribosome biogenesis. Functional assays confirmed a quiescent-like metabolic state, demonstrating reduced mitochondrial mass, decreased mitochondrial reactive oxygen species, and a lower oxygen consumption rate (OCR). We further show that 8-Me-PIQ attenuates ribosome biogenesis through the inhibition of RNA polymerase I transcriptional activity, establishing a direct link between the compound, translational control, and the maintenance of protein homeostasis during ex vivo culture. These findings provide a promising small-molecule candidate for improving UCB transplantation outcomes and offer new insights into the metabolic and translational checkpoints governing HSC stemness.&#xa0;</p> Graphical Abstract <p></p>