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.

Potent and selective Aurora kinase inhibitors were identified from the combinatorial expansion of the 1,4,5,6-tetrahydropyrrolo[3,4-c]pyrazole bi-cycle, a novel and versatile scaffold designed to target the ATP pocket of protein kinases. The most potent compound reported in this study had an IC(50) of 0.027 microM in the enzymatic assay for Aur-A inhibition and IC(50)s between 0.05 microM and 0.5 microM for the inhibition of proliferation of different tumor cell lines.

The crystal structure of dicarbonylpentamethylcyclopentadienylchromium dimer has been determined by a single-crystal three-dimensional X-ray diffraction study. The structure consists of discrete centrosymmetric [(7r-(CH3)sCs)Cr(CO),]2 units, each with a short Cr-Cr bond distance [2.280 (2) A], The Cr-Cr triple bond length in [(7r-(CH3)5C5)Cr(CO)2]2 is greater than the Cr-Cr quadruple bond lengths in Li4[Cr2(CH3)8]-4C4H80 [1.98 A] and Cr2(C3Hs)4 [1.98 A] but less than the Cr-Cr distance in Cr2(02CCH3)4-2H"0 [2.362 A] for which a quadruple bond has also been suggested. Carbonyl groups, two per chromium, are staggered with respect to the Cr-Cr axis and the Cr-C-0 atoms are nearly collinear [angles 170.8 (6), 174.8 (6)°]. Detailed analysis of bond distances and angles suggests that the carbonyl groups are essentially terminal. The (CH3)SC5 rings exhibit nearly perfect Csv symmetry and are trans with respect to the Cr-Cr axis. However, Cr-C(ring) distances are nonequivalent; this is ascribed to steric crowding between the ring and carbonyl groups which forces the latter to lie over the Cr-Cr bond [Cr'-Cr-CQ angles 73.0 (3), 79.1 (3)°]. Short contacts are also observed between the carbonyl groups and the molecule appears to be quite crowded sterically. Crystallographic data are as follows: space group P2, ¡n; unit cell a = 8.717 (6) A, b = 14.716 (4) A, c = 9.867 (5) A, ß = 112.00 (5)°; U = 1173 A3; <2calcd for Z = 2 is 1.408 and dobsu is 1.41 (2) g/cm3. Diffractometer data (1411 independent reflections with F2 > 3 ) were used to refine the structure anisotropically to final values of RF = 0.053 and RwF =

NMR-based binding and functional screening performed with FAXS (fluorine chemical shift anisotropy and exchange for screening) and 3-FABS (three fluorine atoms for biochemical screening) represents a potential alternative approach to high-throughput screening for the identification of novel potential drug candidates. The major limitation of this method in its current status is its intrinsic low sensitivity that limits the number of tested compounds. One approach for overcoming this problem is the use of a cryogenically cooled (19)F probe that reduces the thermal noise in the receiver circuitry. Sensitivity improvement in the two screening techniques achieved with the novel cryogenic (19)F probe technology permits an increased throughput, detection of weaker binders and inhibitors (relevant in a fragment-based lead discovery program), detection of slow binders, and reduction in protein and substrate consumption. These aspects are analyzed with theoretical simulations and experimental quantitative performance evaluation. Application of 3-FABS combined with the cryogenic (19)F probe technology to rapid screening at very low enzyme concentrations and the current detection limits reached with this approach are also presented.