catalyzes the formation of l-cysteine from O-acetyl serine and hydrogen sulfide. Here we report nanomolar thiazolidineinhibitors of Mycobacterium tuberculosis CysK1 developed by rational inhibitordesign. The thiazolidine compounds were discovered using the crystal structure of a CysK1–peptide inhibitor complex as template. Pharmacophore modeling and subsequent in vitro screening resulted in an initial