4-(Diethylamino)benzaldehyde (DEAB)has been extensively reported as a pan-inhibitor of ALDH isoforms,and here, we report on the synthesis, ALDH isoform selectivity, andcellular potencies in prostate cancer cells of 40 DEAB analogues;three analogues (14, 15, and 16) showed potent inhibitory activity against ALDH1A3, and two analogues(18 and 19) showed potent inhibitory activityagainst ALDH3A1. The gene discussed is LDHA; the disease is prostate cancer.