No abstract

A 2,2-dimethylbutynoic acid with a pyridone terminus (1) acts as its self-complement in molecular recognition to form an intermolecularly hydrogen-bonded dimer with hydrogen bonding between the amide and carboxylic acid group. The dimer is found in crystals of 1 by X-ray diffraction, in chloroform solution by 1H-NMR experiments and vapor pressure osmometry, and in the gas phase by FAB-MS.

The reaction of carboxylic acids with carbodiimides is reviewed, and an "introverted" carboxylic acid is proposed as a means of trapping reactive intermediates along the reaction pathway. The introverted acid is a cavitand with the carboxylic function directed toward the floor of the cavity. Its reaction with diisopropyl carboodiimide gives a covalent adduct that is either the elusive O-acylisourea or the commonly encountered N-acylurea.

Histone deacetylase (HDAC) inhibitors have garnered significant attention as cancer drugs. These therapeutic agents have recently been clinically validated with the market approval of vorinostat (SAHA, Zolinza) for treatment of cutaneous T-cell lymphoma. Like vorinostat, most of the small-molecule HDAC inhibitors in clinical development are hydroxamic acids, whose inhibitory activity stems from their ability to coordinate the catalytic Zn2+ in the active site of HDACs. We sought to identify novel, nonhydroxamate-based HDAC inhibitors with potentially distinct pharmaceutical properties via an ultra-high throughput small molecule biochemical screen against the HDAC activity in a HeLa cell nuclear extract. An alpha-mercaptoketone series was identified and chemically optimized. The lead compound, KD5170, exhibits HDAC inhibitory activity with an IC50 of 0.045 micromol/L in the screening biochemical assay and an EC50 of 0.025 micromol/L in HeLa cell-based assays that monitor histone H3 acetylation. KD5170 also exhibits broad spectrum classes I and II HDAC inhibition in assays using purified recombinant human isoforms. KD5170 shows significant antiproliferative activity against a variety of human tumor cell lines, including the NCI-60 panel. Significant tumor growth inhibition was observed after p.o. dosing in human HCT-116 (colorectal cancer), NCI-H460 (non-small cell lung carcinoma), and PC-3 (prostate cancer) s.c. xenografts in nude mice. In addition, a significant increase in antitumor activity and time to end-point occurred when KD5170 was combined with docetaxel in xenografts of the PC-3 prostate cancer cell line. The biological and pharmaceutical profile of KD5170 supports its continued preclinical and clinical development as a broad spectrum anticancer agent.