Chiral auxiliary methodology and chiral assays have been developed to establish the enantiomeric purities of erythrulose and 1,3-dihydroxypentan-2-one generated using wild-type (WT) Escherichia coli transketolase (TK). L-Erythrulose was formed in 95% ee and (3S)-1,3-dihydroxypentan-2-one in 58% ee. Since the latter compound was formed in moderate ee, TK libraries were screened to identify higher performing mutants. A colorimetric screen and chiral assay were successfully applied to a 96-well format, and new active TK mutants were identified, which gave 1,3-dihydroxypentan-2-one in high stereoselectivities. Remarkably, active-site single-point mutants were identified that were able to both enhance and reverse the stereoselectivity of TK.