Selective Inhibition of Histone Deacetylase 10: Hydrogen Bonding to the Gatekeeper Residue is Implicated.

The discovery of isozyme-selective histone deacetylase (HDAC) inhibitors is critical for understanding the biological functions of individual HDACs and for validating HDACs as drug targets. The isozyme HDAC10 contributes to chemotherapy resistance and has recently been described to be a polyamine deacetylase, but no studies toward selective HDAC10 inhibitors have been published. Using two complementary assays, we found Tubastatin A, an HDAC6 inhibitor, to potently bind HDAC10. We synthesized Tubastatin A derivatives and found that a basic amine in the cap group was required for strong HDAC10 binding. HDAC10 inhibitors mimicked knockdown by causing dose-dependent accumulation of acidic vesicles in a neuroblastoma cell line. Furthermore, docking into human HDAC10 homology models indicated that a hydrogen bond between a cap group nitrogen and the gatekeeper residue Glu272 was responsible for potent HDAC10 binding. Taken together, our data provide an optimal platform for the development of HDAC10-selective inhibitors, as exemplified with the Tubastatin A scaffold.

Complementary Quantitative Structure⁻Activity Relationship Models for the Antitrypanosomal Activity of Sesquiterpene Lactones.

Three complementary quantitative structure⁻activity relationship (QSAR) methodologies, namely, regression modeling based on (i) "classical" molecular descriptors, (ii) 3D pharmacophore features, and (iii) 2D molecular holograms (HQSAR) were employed on the antitrypanosomal activity of sesquiterpene lactones (STLs) toward Trypanosoma brucei rhodesiense (Tbr), the causative agent of the East African form of human African trypanosomiasis. In this study, an extension of a previous QSAR study on 69 STLs, models for a much larger and more diverse set of such natural products, now comprising 130 STLs of various structural subclasses, were established. The extended data set comprises a variety of STLs isolated and tested for antitrypanosomal activity within our group and is furthermore enhanced by 12 compounds obtained from literature, which have been tested in the same laboratory under identical conditions. Detailed QSAR analyses yielded models with comparable and good internal and external predictive ability. For a set of compounds as chemically diverse as the one under study, the models exhibited good coefficients of determination (R²) ranging from 0.71 to 0.85, as well as internal (leave-one-out Q2 values ranging from 0.62 to 0.72) and external validation coefficients (P² values ranging from 0.54 to 0.73). The contributions of the various tested descriptors to the generated models are in good agreement with the results of previous QSAR studies and corroborate the fact that the antitrypanosomal activity of STLs is very much dependent on the presence and relative position of reactive enone groups within the molecular structure but is influenced by their hydrophilic/hydrophobic properties and molecular shape.

Flavonoids and Methoxy-galloylquinic Acid Derivatives from the Leaf Extract of Copaifera langsdorffii Desf.

Despite reports on the pharmacological potential of Copaifera langsdorffii Desf. (Leguminosae-Caesalpinioideae) leaf extract, little is known about its chemical composition. In this work, a phytochemical study from the C. langsdorffii ethanol/H2O 7:3 (v/v) extract was undertaken. Separation was performed by high-speed counter-current (HSCCC) and Sephadex LH-20 column chromatographies, followed by preparative HPLC. The EtOAc- and H2O-soluble fractions of the extract furnished the flavonoids quercitrin (1) and afzelin (2) and 3-O-(3-O-methyl-galloyl)quinic acid (3), respectively. The H2O-soluble fraction furnished 3,4-di-O-(3-O-methyl-galloyl)quinic acid (4), 3,5-di-O-(galloyl)-4-O-(3-O-methyl-galloyl)quinic acid (5), and 3,5-di-O-(3-O-methyl-galloyl)-4-O-(galloyl)quinic acid (6). Their chemical structures were elucidated by NMR means.