We describe the synthesis through visible-light photocatalysis of novel functionalized tetracyclic scaffolds that incorporate a fused azabicyclo[3.2.0]heptan-2-one motif, which are structurally interesting cores with potential in natural product synthesis and drug discovery. The synthetic approach involves an intramolecular [2 + 2] cycloaddition with concomitant dearomatization of the heterocycle via an energy transfer process promoted by an iridium-based photosensitizer, to build a complex molecular architecture with at least three stereogenic centers from relatively simple, achiral precursors. These fused azabicyclo[3.2.0]heptan-2-one-based tetracycles were obtained in high yield (generally >99%) and with excellent diastereoselectivity (>99:1). The late-stage derivatization of a bromine-substituted, tetracyclic indoline derivative with alkyl groups, employing a mild Negishi C−C bond forming protocol as a means of increasing structural diversity, provides additional modularity that will enable the delivery of valuable building blocks for medicinal chemistry. Density functional theory calculations were used to compute the T 1 −S 0 free energy gap of the olefin-tethered precursors and also to predict their reactivities based on triplet state energy transfer and transition state energy feasibility.

Recent mouse knockout studies identified adapter protein-2 associated kinase 1 (AAK1) as a viable target for treating neuropathic pain. Potent small-molecule inhibitors of AAK1 have been identified and show efficacy in various rodent pain models. (S)-1-((2′,6-Bis­(difluoromethyl)-[2,4′-bipyridin]-5-yl)­oxy)-2,4-dimethylpentan-2-amine (BMS-986176/LX-9211) (34) was identified as a highly selective, CNS penetrant, potent AAK1 inhibitor from a novel class of bi­(hetero)­aryl ethers. BMS-986176/LX9211 (34) showed excellent efficacy in two rodent neuropathic pain models and excellent central nervous system (CNS) penetration and target engagement at the spinal cord with an average brain to plasma ratio of 20 in rat. The compound exhibited favorable physicochemical and pharmacokinetic properties, had an acceptable preclinical toxicity profile, and was chosen for clinical trials. BMS-986176/LX9211 (34) completed phase I trials with good human pharmacokinetics and minimum adverse events and is currently in phase II clinical trials for diabetic peripheral neuropathic pain (ClinicalTrials.gov identifier: NCT04455633) and postherpetic neuralgia (ClinicalTrials.gov identifier: NCT04662281).

Indole and indoline rings are important pharmacophoric scaffolds found in marketed drugs, agrochemicals, and biologically active molecules. The [2 + 2] cycloaddition reaction is a versatile strategy for constructing architecturally interesting, sp 3 -rich cyclobutane-fused scaffolds with potential applications in drug discovery programs. A general platform for visible-light mediated intermolecular [2 + 2] cycloaddition of indoles with alkenes has been realized. A substrate-based screening approach led to the discovery of tertbutyloxycarbonyl (Boc)-protected indole-2-carboxyesters as suitable motifs for the intermolecular [2 + 2] cycloaddition reaction. Significantly, the reaction proceeds in good yield with a wide variety of both activated and unactivated alkenes, including those containing free amines and alcohols, and the transformation exhibits excellent regio-and diastereoselectivity. Moreover, the scope of the indole substrate is very broad, extending to previously unexplored azaindole heterocycles that collectively afford fused cyclobutane containing scaffolds that offer unique properties with functional handles and vectors suitable for further derivatization. DFT computational studies provide insights into the mechanism of this [2 + 2] cycloaddition, which is initiated by a triplet−triplet energy transfer process. The photocatalytic reaction was successfully performed on a 100 g scale to provide the dihydroindole analog.

Chemotherapy of prostate cancer with antimitotic agents such as vinblastine and doxorubicin is only marginally effective, due to dose-limiting systemic toxicity. Herein we report the development of peptidyl conjugate 5 of the cytotoxic agent vinblastine (1), along with the results of its in vitro and in vivo evaluation as a pro-drug targeted at prostate cancer cells. Prostate-derived tumors are known to produce significant amounts of prostate specific antigen (PSA), a serine protease with chymotrypsin-like properties. Earlier work in these laboratories established that an appropriately engineered peptidyl pro-drug will release active cytotoxic agent strictly within the microenvironment of the tumor tissue (Garsky, V. M., et al. J. Med.Chem. 2001, 44, 4216-4224). Conjugate 5, which features an octapeptide segment attached by an ester linkage at the 4-position of vinblastine (1), undergoes rapid cleavage by PSA (T(1/2) = 12 min) between the Gln and Ser residues. In nude mouse xenograft studies, 5 reduced circulating PSA levels by 99% and tumor weight by 85% at a dose just below its MTD. By contrast, the putative end-point metabolite, the cytotoxic agent des-acetyl vinblastine (1b), was ineffective in reducing PSA levels and tumor burden at its maximum tolerated doses. Additional data from metabolism studies on 5 support the supervention of a novel in vivo processing mechanism, the spontaneous release of 1b from a dipeptidyl intermediate driven by favorable diketopiperazine formation.

The visible light-promoted intramolecular [2+2] cycloaddition of N-allylcinnamamines and N-allylcinnamamides in the presence of catalytic amounts of [Ir{dF(CF 3 )ppy} 2 (dtbpy)]-PF 6 is reported. Low energy visible light and a high triplet energy iridium-photosensitizer were efficient at promoting the cycloaddition reaction of N-allylcinnamamides and N-allylcinnamamines to the corresponding aryl-3-azabicyclo[3.2.0]heptanones and aryl-3-azabicyclo[3.2.0]heptanes, respectively, [a]