Discovery of HC-7366: An Orally Bioavailable and Efficacious GCN2 Kinase Activator.

A series of activators of GCN2 (general control nonderepressible 2) kinase have been developed, leading to HC-7366, which has entered the clinic as an antitumor therapy. Optimization resulted in improved permeability compared to that of the original indazole hinge binding scaffold, while maintaining potency at GCN2 and selectivity over PERK (protein kinase RNA-like endoplasmic reticulum kinase). The improved ADME properties of this series led to robust in vivo compound exposure in both rats and mice, allowing HC-7366 to be dosed in xenograft models, demonstrating that activation of the GCN2 pathway by this compound leads to tumor growth inhibition.

New synthesis of (±)-cis-trikentrin A via tandem indole aryne cycloaddition/Negishi reaction. Applications to library development.

We describe herein an efficient new route to the trikentrins and their related structures using a tandem 6,7-indolyne cycloaddition/Negishi cross-coupling reaction starting from a 4,6,7-tribromoindole (obtained in good yield via the Bartoli indole synthesis). The key step of this second generation route to the trikentrins is based on our observation that the 7-bromo substituent appears to undergo selective metal-halogen exchange and elimination to give the 6,7-indolyne, which is trapped in the presence of excess cyclopentadiene. Subsequent Negishi cross-coupling at the 4-bromoindole position with Et(2)Zn gave directly the same intermediate obtained from our previous work. Application of this chemistry to the construction of trikentrin-related libraries using this general cycloaddition/cross-coupling tactic will also be described.

Regioselective Diels-Alder cycloadditions and other reactions of 4,5-, 5,6-, and 6,7-indole arynes.

The regioselectivity of Diels-Alder cycloadditions of indole arynes (indolynes) at all three benzenoid positions was examined. Cycloadditions with the 4,5-and 5,6-indolynes, derived via metal-halogen exchange from the corresponding o-dibromo indoles, showed essentially no selectivity with 2-t-butylfuran. In contrast, the 6,7-indolyne displayed virtually complete preference for the more sterically congested cycloadduct. This same cycloadduct undergoes a facile acid-catalyzed rearrangement to afford the annulated enone, or alternatively, undergoes hydrolysis and oxidation in the presence of air to give the indolobenzoquinone. The 5,6-difluoroindoles show anomolous behavior and give either 5-fluoro-6,7-indolynes with n-BuLi in ether, or 5,6-indolynes with n-BuLi in toluene. We have also demonstrated that benzenoid indolynes can be easily and conveniently generated by the fluoride-induced decomposition of o-trimethylsilyl triflates.

Indole-derived arynes and their Diels-Alder reactivity with furans.

Arynes derived from any position of the ubiquitous indole nucleus are unknown. We have now provided the first evidence for the formation and trapping of the 4,5-, 5,6-, and 6,7-indolynes. A series of o-dihalo indoles (Cl, Br, F) were synthesized and reacted under metal-halogen exchange conditions to give Diels-Alder cycloadducts in high yield with furan. The use of an excess of tert-butyllithium resulted in the rearrangement of the initially formed cycloadduct; however, employing only a slight excess of n-butyllithium cleanly gave cycloadducts with furan.

Experimental and theoretical investigations into the unusual regioselectivity of 4,5-, 5,6-, and 6,7-indole aryne cycloadditions.

The 6,7-indolyne shows remarkable regioselectivity in its cycloaddition with 2-substituted furans. Electron-donating groups give predominantly the more sterically crowded product, while electron-withdrawing groups display the opposite regioselectivity. By contrast, 4,5- and 5,6-indolynes show no regioselectivity. Optimized electronic structure calculations using the M06-2X density functional and 6-311+G(2df,p) basis set revealed that the 6,7-indolynes are highly polar structures and that their cycloadditions have substantial electrophilic substitution character that leads to the observed preference for contrasteric products.

Concise total synthesis of (+/-)-cis-trikentrin A and (+/-)-herbindole A via intermolecular indole aryne cycloaddition.

An efficient nine-step total synthesis of the annulated indole natural products (+/-)-cis-trikentrin A and (+/-)-herbindole A was accomplished via an intermolecular Diels-Alder cycloaddition using our recently developed indole aryne (indolyne) methodology as the key step. This strategy provides rapid access into the trikentrins and the related herbindoles and represents the first application of this methodology to natural products total synthesis. The required 6,7-indolyne precursor was readily constructed by means of the Bartoli indole synthesis with substituted nitrobenzenes and vinyl magnesium bromide.

Novel synthetic inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase activity that inhibit tumor cell proliferation and are structurally unrelated to existing statins.

Pilot-scale libraries of eight-membered medium ring lactams (MRLs) and related tricyclic compounds (either seven-membered lactams, thiolactams or amines) were screened for their ability to inhibit the catalytic activity of human recombinant 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase in vitro. A dozen of the synthetic compounds mimic the inhibition of purified HMG-CoA reductase activity caused by pravastatin, fluvastatin and sodium salts of lovastatin, mevastatin and simvastatin in this cell-free assay, suggesting direct interaction with the rate-limiting enzyme of cholesterol biosynthesis. Moreover, several MRLs inhibit the metabolic activity of L1210 tumor cells in vitro to a greater degree than fluvastatin, lovastatin, mevastatin and simvastatin, whereas pravastatin is inactive. Although the correlation between the concentration-dependent inhibitions of HMG-CoA reductase activity over 10 min in the cell-free assay and L1210 tumor cell proliferation over 4 days in culture is unclear, some bioactive MRLs elicit interesting combinations of statin-like (IC50: 7.4-8.0 microM) and anti-tumor (IC50: 1.4-2.3 microM) activities. The HMG-CoA reductase-inhibiting activities of pravastatin and an MRL persist in the presence of increasing concentrations of NADPH. But increasing concentrations of HMG-CoA block the HMG-CoA reductase-inhibiting activity of pravastatin without altering that of an MRL, suggesting that MRLs and existing statins may have different mechanisms of enzyme interaction and inhibition. When tested together, suboptimal concentrations of synthetic MRLs and existing statins have additive inhibitory effects on HMG-CoA reductase activity. Preliminary molecular docking studies with MRL-based inhibitors indicate that these ligands fit sterically well into the HMG-CoA reductase statin-binding receptor model and, in contrast to mevastatin, may occupy a narrow channel housing the pyridinium moiety on NADP+.