Four novel series of cinnamyl-containing histone deacetylase (HDAC) inhibitors 1-4 are described, containing hydroxamate (1 and 3) or 2-aminoanilide (2 and 4) derivatives. When screened against classI (maize HD1-B and human HDAC1) and classII (maize HD1-A and human HDAC4) HDACs, most hydroxamates and 2-aminoanilides displayed potent and selective inhibition toward classI enzymes. Immunoblotting analyses performed in U937 leukemia cells generally revealed high acetyl-H3 and low acetyl-α-tubulin levels. Exceptions are compounds 3f-i, 3m-o, and 4k, which showed higher tubulin acetylation than SAHA. In U937 cells, cell-cycle blockade in either the G2/M or G1/S phase was observed with 1-4. Five hydroxamates (compounds 1h-l) effected a two- to greater than threefold greater percent apoptosis than SAHA, and in the CD11c cytodifferentiation test some 2-aminoanilides belonging to both series 2 and 4 were more active than MS-275. The highest-scoring derivatives in terms of apoptosis (1k, 1l) or cytodifferentiation (2c, 4n) also showed antiproliferative activity in U937 cells, thus representing valuable tools for study in other cancer contexts. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.