Abnormal proliferation mediated by disruption of the normal cell cycle mechanisms is a hallmark of virtually all cancer cells. Compounds targeting complexes between cyclin-dependent kinases (CDK) and cyclins, such as CDK2/cyclin A and CDK2/cyclin E, and inhibiting their kinase activity are regarded as promising antitumor agents to complement the existing therapies. From a high-throughput screening effort, we identified a new class of CDK2/cyclin A/E inhibitors. The hit-to-lead expansion of this class is described. X-ray crystallographic data of early compounds in this series, as well as in vitro testing funneled for rapidly achieving in vivo efficacy, led to a nanomolar inhibitor of CDK2/cyclin A (N-(5-cyclopropyl-1H-pyrazol-3-yl)-2-(2-naphthyl)acetamide (41), PNU-292137, IC50 = 37 nM) with in vivo antitumor activity (TGI > 50%) in a mouse xenograft model at a dose devoid of toxic effects.

Quantification of BrdU incorporation into DNA is a widely used technique to assess the cell cycle status of cells. DNA denaturation is required for BrdU detection with the drawback that most protein epitopes are destroyed and classical antibody staining techniques for multiplex analysis are not possible. To address this issue we have developed a novel method that overcomes the DNA denaturation step but still allows detection of BrdU. Cells were pulsed for a short time by 5-ethynyl-2'-deoxyuridine, which is incorporated into DNA. The exposed nucleotide alkyne group of DNA was then derivatized in physiologic conditions by the copper (I)-catalyzed azide-alkyne cycloaddition (CuAAC) using BrdU azides. The resulting DNA-bound bromouracil moiety was subsequently detected by commercial anti-BrdU mAb without the need for a denaturation step. Continuous labeling with EdU showed a slightly increased anti-proliferative activity compared to BrdU. However, using a lower concentration of EdU for labeling can compensate for this. Alkynyl tags could be detected quickly by a highly specific reaction using BrdU azides. Fluorescence quenching by the DNA dye PI using both BrdU azides was negligible. Our labeling method is suitable for FCM and HCA and shows a higher signal to noise ratio than other methods. This method also allowed multiplex analysis by simultaneous detection of EdU-BrdU, caspase-3, and phospho-histone 3 mAbs, proving sensitivity and feasibility of this new technique. In addition, it has the potential for use in vivo, as exemplified for bone marrow studies. We have established a new method to determine the position of cells in the cell cycle. This is superior when compared to traditional BrdU detection since it allows multiplex analysis, is more sensitive and shows less quenching with PI. The method provides new opportunities to investigate changes in protein expression at different cell cycle stages using pulse labeling experiments.

Two new caryophyllene sesquiterpenes have been isolated from Pestalotiopsis sp., an endophytic fungus associated with the bark and leaves of Taxus brevifolia. Pestalotiopsin A (1) has a novel oxatricyclic ring system while pestalotiopsin B (3) exists as two slowly equilibrating atropisomers (6:5 ratio of ββ:βα) in chloroform solution at room temperature. Structures of 1 and 3 were determined by spectroscopic analyses and single-crystal X-ray diffraction.

No abstract

A traceless solid-phase synthesis of oxazoles 4 via Robinson-Gabriel reaction of solid-supported alpha-acylamino ketones 2 has been achieved. The reaction requires that the cyclization precursor be linked to a benzhydrylic-type linker (compounds 2) and that trifluoroacetic anhydride be used as the cyclodehydrating agent. The solvent has a dramatic effect on the latter reaction, which goes to completion and follows a cyclative-type mechanism only when an ethereal solvent is used. Different synthetic routes have been investigated toward assembling compounds 2. The most straightforward one, which we have validated more extensively, comprises the reaction of Merrifield alpha-methoxyphenyl (MAMP) resin with an alpha-amino ketone to form compounds 1, which are, in turn, acylated. Other methodologies and strategies allowing for the synthesis of compounds 1 that have been investigated include direct alkylation of Rink amide resin; reductive amination of the latter with alpha-keto aldehydes; reaction of MAMP resin with alpha-amino alcohols, followed by oxidation; and protection of Rink amide resin with either 2,4-dinitrosulfonyl or allyl group, followed by alkylation and removal of protecting group. In addition, we disclose a novel variant of the Ugi four-component reaction that allows for the preparation of compounds 2 in a single synthetic step.