Synthesis of heterocyclic triads by Pd-catalyzed cross-couplings and evaluation of their cell-specific toxicity profile

Rongalite in PEG-400 as a general and reusable system for the synthesis of 2,5-disubstituted chalcogenophenes

Herein we report the use of rongalite in PEG-400 as a general, efficient, and environmentally benign reductive system for the synthesis of a wide range of 2,5-disubstituted chalcogenophenes from elemental sulfur, selenium and tellurium.

Specific RITA Modification Produces Hyperselective Cytotoxicity While Maintaining In Vivo Antitumor Efficacy

The preclinical antitumor agent RITA (2,5-bis[5-hydroxymethyl-2-thienyl] furan, NSC 652287), an analog of the natural product α-terthiophene, failed during the development phase due to acute pulmonary toxicity in animal models. A series of synthetic modifications to RITA's heterocyclic scaffold resulted in activity ranging from broadly cytotoxic to highly selective. In the NCI 60-cell line screen, these "hyperselective" agents (e.g., imatinib) are rare. A selectivity index (SI) was developed to quantify this desirable feature, which is 20 for imatinib, whereas RITA's SI is only 0.10. One of the described hyperselective RITA analogs (SI = 7.9) completely lost activity in the presence of a known SULT1A1 inhibitor. These results, coupled with previous evidence that RITA is a SULT1A1 substrate, suggest that carbinol modification by a sulfate leaving group and subsequent formation of a reactive carbocation may explain RITA's broad cytotoxicity. Although SULT1A1 expression is required for susceptibility, hyperselective analogs exhibited reduced association of activity with SULT1A1 mRNA expression compared with RITA, apparently requiring some additional target(s). In support of this hypothesis, there is a strong correlation (P < 0.01, r = 0.95) between quantum mechanically calculated energy barriers for carbocation formation from sulfonated analogs and SI, indicating that hyperselective RITA analogs generate reactive carbocations less readily after sulfate activation. Importantly, narrowing the cytotoxicity profile of RITA did not eliminate its analogs' in vivo antitumor activity, as several new hyperselective agents, NSC 773097 (1), 773392 (2), and 782846 (6), displayed impressive activity against A498 xenografts in mice.

Reactivity of bromoselenophenes in palladium-catalyzed direct arylations

The reactivity of 2-bromo- and 2,5-dibromoselenophenes in Pd-catalyzed direct heteroarylation was investigated. From 2-bromoselenophene, only the most reactive heteroarenes could be employed to prepare 2-heteroarylated selenophenes; whereas, 2,5-dibromoselenophene generally gave 2,5-di(heteroarylated) selenophenes in high yields using both thiazole and thiophene derivatives. Moreover, sequential catalytic C2 heteroarylation, bromination, catalytic C5 arylation reactions allowed the synthesis of unsymmetrical 2,5-di(hetero)arylated selenophene derivatives in three steps from selenophene.

RITA Mimics: Synthesis and Mechanistic Evaluation of Asymmetric Linked Trithiazoles

The established cytotoxic agent RITA contains a thiophene-furan-thiophene backbone and two terminal alcohol groups. Herein we investigate the effect of using thiazoles as the backbone in RITA-like molecules and modifying the terminal groups of these trithiazoles, thereby generating 41 unique structures. Incorporating side chains with varied steric bulk allowed us to investigate how size and a stereocenter impacted biological activity. Subjecting compounds to growth inhibition assays on HCT-116 cells showed that the most potent compounds 7d, 7e, and 7h had GI₅₀ values of 4.4, 4.4, and 3.4 μM, respectively, versus RITA (GI₅₀ of 800 nM). Analysis of these compounds in apoptosis assays proved that 7d, 7e, and 7h were as effective as RITA at inducing apoptosis. Evaluating the impact of 7h on proteins targeted by RITA (p53, c-Myc, and Mcl-1) indicated that it acts via a different mechanism of action to that of RITA. RITA suppressed Mcl-1 protein via p53, whereas compound 7h suppressed Mcl-1 expression via an alternative mechanism independent of p53.

Design, synthesis and anticancer mechanistic studies of linked azoles

Herein we report the synthesis and biological activity evaluation of 2,4 linked azole-containing molecules.

Palladium-catalyzed 2,5-diheteroarylation of 2,5-dibromothiophene derivatives

Conditions allowing the one pot 2,5-diheteroarylation of 2,5-dibromothiophene derivatives in the presence of palladium catalysts are reported. Using KOAc as the base, DMA as the solvent and only 0.5–2 mol % palladium catalysts, the target 2,5-diheteroarylated thiophenes were obtained in moderate to good yields and with a wide variety of heteroarenes such as thiazoles, thiophenes, furans, pyrroles, pyrazoles or isoxazoles. Moreover, sequential heteroarylation reactions allow the access to 2,5-diheteroarylated thiophenes bearing two different heteroaryl units.