Development and Optimization of 11C-Labeled Radiotracers: A Review of the Modern Quality Control Design Process.

Introduction - Several 11C-tracers have demonstrated high potential in early diagnostic PET imaging applications of neurodegenerative diseases including Alzheimer's and Parkinson's disease. These radiotracers often track critical biomarkers in disease pathogenesis such as tau fibrils ([11C]PBB3) or ß-amyloid plaques ([11C]PiB) associated with such diseases. Purpose - The short review aims to serve as a guideline in the future development of radiotracers for students, postdocs and/or new radiochemists who will be synthesizing clinical grade or novel research 11C-tracers, including knowledge of regulatory requirements. We aim to bridge the gap between novel and established 11C-tracer quality control (QC) processes through exploring the design process and regulatory requirements for 11C-pharmaceuticals. Methods - A literature survey was undertaken to identify articles with a detailed description of the QC methodology and characterization for each of the sections of the review. Overview - First a general summary of 11C-tracer production was presented; this was used to establish possible places for contamination or assurances for a sterile final product. The key mandated QC analyses for clinical use were then discussed. Further, we assessed the QC methods used for established 11C-tracers and then reviewed the routine QC tests for preclinical translational and validation studies. Therefore, both mandated QC methods for clinical and preclinical animal studies were reviewed. Last, some examples of optimization and automation were reviewed, and implications of the QC practices associated with such procedures were considered. Conclusion - All of the common QC parameters associated with 11C-tracers under clinical and preclinical settings (along with a few exceptions) were discussed in detail. While it is important to establish standard, peer-reviewed QC testing protocols for a novel 11C-tracer entering the clinical umbrella, equal importance is needed on preclinical applications to address credibility and repeatability for the study.

Positron Emission Tomography-Computed Tomography Imaging of Selective Lobar Delivery of Stem Cells in Ex Vivo Lung Model of Mechanical Ventilation.

Introduction: The delivery of cell therapies may be an important frontier to treat different respiratory diseases in the near future. However, the cell size, delivery conditions, cell viability, and effect in the pulmonary function are critical factors. We performed a proof-of-concept experiment using ex vivo lungs and novel subglottic airway device that allows for selective lobar isolation and administration of drugs and biologics in liquid solution deep into the lung tissues, while simultaneously ventilating the rest of the lung lobes. Methods: We used radiolabeled cells and positron emission tomography-computed tomography (PET-CT) imaging to demonstrate the feasibility of high-yield cell delivery to a specifically targeted lobe. This study proposes an alternative delivery method of live cells labeled with radioactive isotope into the lung parenchyma and tracks the cell delivery using PET-CT imaging. The technique combines selective lobar isolation and lobar infusion to carry large particles distal to the trachea, subtending bronchial segments and reaching alveoli in targeted regions. Results: The solution with cells and carrier achieved a complete and homogeneous lobar distribution. An increase in tissue density was shown on the computed tomography (CT) scan, and the PET-CT imaging demonstrated retention of the activity at central, peripheral lung parenchyma, and pleural surface. The increase in CT density and metabolic activity of the isotope was restricted to the desired lobe only without leak to other lobes. Conclusion: The selective lobe delivery is targeted and imaging-guided by bronchoscopy and CT to a specific diseased lobe during mechanical ventilation. The feasibility of high-yield cell delivery demonstrated in this study will lead to the development of potential novel therapies that contribute to lung health.

PET imaging of kappa opioid receptors and receptor expression quantified in neuron-derived extracellular vesicles in socially housed female and male cynomolgus macaques.

Recent positron emission tomography (PET) studies of kappa opioid receptors (KOR) in humans reported significant relationships between KOR availability and social status, as well as cocaine choice. In monkey models, social status influences physiology, receptor pharmacology and behavior; these variables have been associated vulnerability to cocaine abuse. The present study utilized PET imaging to examine KOR availability in socially housed, cocaine-naïve female and male monkeys, and peripheral measures of KORs with neuron-derived extracellular vesicles (NDE). KOR availability was assessed in dominant and subordinate female and male cynomolgus macaques (N = 4/rank/sex), using PET imaging with the KOR selective agonist [11C]EKAP. In addition, NDE from the plasma of socially housed monkeys (N = 13/sex; N = 6-7/rank) were isolated by immunocapture method and analyzed for OPRK1 protein expression by ELISA. We found significant interactions between sex and social rank in KOR availability across 12 of 15 brain regions. This was driven by female data, in which KOR availability was significantly higher in subordinate monkeys compared with dominant monkeys; the opposite relationship was observed among males, but not statistically significant. No sex or rank differences were observed for NDE OPRK1 concentrations. In summary, the relationship between brain KOR availability and social rank was different in female and male monkeys. This was particularly true in female monkeys. We hypothesize that lower [11C]EKAP binding potentials were due to higher concentrations of circulating dynorphin, which is consistent with greater vulnerability in dominant compared with subordinate females. These findings suggest that the KOR is an important target for understanding the neurobiology associated with vulnerability to abused drugs and sex differences, and detectable in peripheral circulation.

The ß-Secretase 1 Enzyme as a Novel Therapeutic Target for Prostate Cancer.

Recent studies have demonstrated the association of APP and Aß with cancer, suggesting that BACE1 may play an important role in carcinogenesis. In the present study, we assessed BACE1's usefulness as a therapeutic target in prostate cancer (PCa). BACE1 expression was observed in human PCa tissue samples, patient-derived xenografts (PDX), human PCa xenograft tissue in nude mice, and transgenic adenocarcinoma of the mouse prostate (TRAMP) tissues by immunohistochemistry (IHC) analysis. Additionally, the downstream product of BACE1 activity, i.e., Aß1-42 expression, was also observed in these PCa tissues by IHC as well as by PET imaging in TRAMP mice. Furthermore, BACE1 gene expression and activity was confirmed in several established PCa cell lines (LNCaP, C4-2B-enzalutamide sensitive [S], C4-2B-enzalutamide resistant [R], 22Rv1-S, 22Rv1-R, PC3, DU145, and TRAMP-C1) by real-time PCR and fluorometric assay, respectively. Treatment with a pharmacological inhibitor of BACE1 (MK-8931) strongly reduced the proliferation of PCa cells in in vitro and in vivo models, analyzed by multiple assays (MTT, clonogenic, and trypan blue exclusion assays and IHC). Cell cycle analyses revealed an increase in the sub-G1 population and a significant modulation in other cell cycle stages (G1/S/G2/M) following MK-8931 treatment. Most importantly, in vivo administration of MK-8931 intraperitoneal (30 mg/kg) strongly inhibited TRAMP-C1 allograft growth in immunocompetent C57BL/6 mice (approximately 81% decrease, p = 0.019). Furthermore, analysis of tumor tissue using the prostate cancer-specific pathway array revealed the alteration of several genes involved in PCa growth and progression including Forkhead O1 (FOXO1). All together, these findings suggest BACE1 as a novel therapeutic target in advanced PCa.

Early Alzheimer's disease-like reductions in gray matter and cognitive function with aging in nonhuman primates.

Introduction: Age-related neuropathology associated with sporadic Alzheimer's disease (AD) often develops well before the onset of symptoms. Given AD's long preclinical period, translational models are needed to identify early signatures of pathological decline. Methods: Using structural magnetic resonance imaging and cognitive assessments, we examined the relationships among age, cognitive performance, and neuroanatomy in 48 vervet monkeys (Chlorocebus aethiops sabaeus) ranging from young adults to very old. Results: We found negative associations of age with cortical gray matter volume (P = .003) and the temporal-parietal cortical thickness meta-region of interest (P = .001). Additionally, cortical gray matter volumes predicted working memory at approximately 1-year follow-up (correct trials at the 20s delay [P = .008]; correct responses after longer delays [P = .004]). Discussion: Cortical gray matter diminishes with age in vervets in regions relevant to AD, which may increase risk of cognitive impairment. This study lays the groundwork for future investigations to test therapeutics to delay or slow pathological decline.

PET Imaging of [11C]MPC-6827, a Microtubule-Based Radiotracer in Non-Human Primate Brains.

Dysregulation of microtubules is commonly associated with several psychiatric and neurological disorders, including addiction and Alzheimer's disease. Imaging of microtubules in vivo using positron emission tomography (PET) could provide valuable information on their role in the development of disease pathogenesis and aid in improving therapeutic regimens. We developed [11C]MPC-6827, the first brain-penetrating PET radiotracer to image microtubules in vivo in the mouse brain. The aim of the present study was to assess the reproducibility of [11C]MPC-6827 PET imaging in non-human primate brains. Two dynamic 0-120 min PET/CT imaging scans were performed in each of four healthy male cynomolgus monkeys approximately one week apart. Time activity curves (TACs) and standard uptake values (SUVs) were determined for whole brains and specific regions of the brains and compared between the "test" and "retest" data. [11C]MPC-6827 showed excellent brain uptake with good pharmacokinetics in non-human primate brains, with significant correlation between the test and retest scan data (r = 0.77, p = 0.023). These initial evaluations demonstrate the high translational potential of [11C]MPC-6827 to image microtubules in the brain in vivo in monkey models of neurological and psychiatric diseases.

In vivo comparison of N-11CH3 vs O-11CH3 radiolabeled microtubule targeted PET ligands.

Altered dynamics of microtubules (MT) are implicated in the pathophysiology of a number of brain diseases. Therefore, radiolabeled MT targeted ligands that can penetrate the blood brain barrier (BBB) may offer a direct and sensitive approach for diagnosis, and assessing the clinical potential of MT targeted therapeutics using PET imaging. We recently reported two BBB penetrating radioligands, [11C]MPC-6827 and [11C]HD-800 as specific PET ligands for imaging MTs in brain. The major metabolic pathway of the above molecules is anticipated to be via the initial labeling site, O-methyl, compared to the N-methyl group. Herein, we report the radiosynthesis of N-11CH3-MPC-6827 and N-11CH3-HD-800 and a comparison of their in vivo binding with the corresponding O-11CH3 analogues using microPET imaging and biodistribution methods. Both O-11CH3 and N-11CH3 labeled MT tracers exhibit high specific binding and brain. The N-11CH3 labeled PET ligands demonstrated similar in vivo binding characteristics compared with the corresponding O-11CH3 labeled tracers, [11C]MPC-6827 and [11C]HD-800 respectively.

Radiosynthesis and evaluation of [11C]CMP, a high affinity GSK3 ligand.

Dysfunction of GSK3 is implicated in the etiology of many brain, inflammatory, cardiac diseases, and cancer. PET imaging would enable in vivo detection and quantification of GSK3 and can impact the choice of therapy, allow non-invasive monitoring of disease progression and treatment effects. In this report, the synthesis and evaluation of a high affinity GSK3 ligand, [11C]2-(cyclopropanecarboxamido)-N-(4-methoxypyridin-3-yl)isonicotinamide, ([11C]CMP, (3), (IC50 = 3.4 nM, LogP = 1.1) is described. [11C]CMP was synthesized in 25 ±â€¯5% yield by radiomethylating the corresponding phenolate using [11C]CH3I. The radioligand exhibited modest uptake in U251 human glioblastoma cell lines with ∼50% specific binding. MicroPET studies in rats indicated negligible blood-brain barrier (BBB) penetration of [11C]CMP, despite its high affinity and suitable logP value for BBB penetration. However, administration of cyclosporine prior to [11C]CMP injection showed significant improvement in brain radioactivity uptake and the tracer binding. This finding indicates that [11C]CMP might be a P-gp efflux substrate and therefore has some limitations for routine in vivo PET evaluations in brain.

Amino Acid Uptake Measured by [18F]AFETP Increases in Response to Arginine Starvation in ASS1-Deficient Sarcomas.

Rational: In a subset of cancers, arginine auxotrophy occurs due to the loss of expression of argininosuccinate synthetase 1 (ASS1). This loss of ASS1 expression makes cancers sensitive to arginine starvation that is induced by PEGylated arginine deiminase (ADI-PEG20). Although ADI-PEG20 treatment is effective, it does have important limitations. Arginine starvation is only beneficial in patients with cancers that are ASS1-deficient. Also, these tumors may metabolically reprogram to express ASS1, transforming them from an auxotrophic phenotype to a prototrophic phenotype and thus rendering ADI-PEG20 ineffective. Due to these limitations of ADI-PEG20 treatment and the potential for developing resistance, non-invasive tools to monitor sensitivity to arginine starvation are needed. Methods: Within this study, we assess the utility of a novel positron emission tomography (PET) tracer to determine sarcomas reliant on extracellular arginine for survival by measuring changes in amino acid transport in arginine auxotrophic sarcoma cells treated with ADI-PEG20. The uptake of the 18F-labeled histidine analogue, (S)-2-amino-3-[1-(2-[18F]fluoroethyl)-1H-[1,2,3]triazol-4-yl]propanoic acid (AFETP), was assessed in vitro and in vivo using human-derived sarcoma cell lines. In addition, we examined the expression and localization of cationic amino acid transporters in response to arginine starvation with ADI-PEG20. Results: In vitro studies revealed that in response to ADI-PEG20 treatment, arginine auxotrophs increase the uptake of L-[3H]arginine and [18F]AFETP due to an increase in the expression and localization to the plasma membrane of the cationic amino acid transporter CAT-1. Furthermore, in vivo PET imaging studies in mice with arginine-dependent osteosarcoma xenografts showed increased [18F]AFETP uptake in tumors 4 days after ADI-PEG20 treatment compared to baseline. Conclusion: CAT-1 transporters localizes to the plasma membrane as a result of arginine starvation with ADI-PEG20 in ASS1-deficient tumor cells and provides a mechanism for using cationic amino acid transport substrates such as [18F]AFETP for identifying tumors susceptible to ADI-PEG20 treatment though non-invasive PET imaging techniques. These findings indicate that [18F]AFETP-PET may be suitable for the early detection of tumor response to arginine depletion due to ADI-PEG20 treatment.

Glioblastoma Stem Cells and Their Microenvironment.

Glioblastoma (GBM) is the most common primary malignant astrocytoma associated with a poor patient survival. Apart from arising de novo, GBMs also occur due to progression of slower growing grade III astrocytomas. GBM is characterized by extensive hypoxia, angiogenesis, proliferation and invasion. Standard treatment options such as surgical resection, radiation therapy and chemotherapy have increased median patient survival to 14.6 months in adults but recurrent disease arising from treatment resistant cancer cells often results in patient mortality. These treatment resistant cancer cells have been found to exhibit stem cell like properties. Strategies to identify or target these Glioblastoma Stem Cells (GSC) have proven to be unsuccessful so far. Studies on cancer stem cells (CSC) within GBM and other cancers have highlighted the importance of paracrine signaling networks within their microenvironment on the growth and maintenance of CSCs. The study of GSCs and their communication with various cell populations within their microenvironment is therefore not only important to understand the biology of GBMs but also to predict response to therapies and to identify novel targets which could stymy support to treatment resistant cancer cells and prevent disease recurrence. The purpose of this chapter is to introduce the concept of GSCs and to detail the latest findings indicating the role of various cellular subtypes within their microenvironment on their survival, proliferation and differentiation.

Peptide-based PET imaging of the tumor restricted IL13RA2 biomarker.

Peptides that target cancer cell surface receptors are promising platforms to deliver diagnostic and therapeutic payloads specifically to cancer but not normal tissue. IL13RA2 is a tumor-restricted receptor found to be present in several aggressive malignancies, including in the vast majority of high-grade gliomas and malignant melanoma. This receptor has been successfully targeted for diagnostic and therapeutic purposes using modified IL-13 ligand and more recently using a specific peptide, Pep-1L. In the current work, we establish the in vitro and in vivo tumor binding properties of radiolabeled Pep-1L, designed for tumor imaging. We radiolabeled Pep-1L with Copper-64 and demonstrated specific cell uptake in the IL13RA2-over expressing G48 glioblastoma cell line having abundant IL13RA2 expression. [64Cu]Pep-1L binding was blocked by unlabeled ligand, demonstrating specificity. To demonstrate in vivo tumor uptake, we intravenously injected into tumor-bearing mice and demonstrated that [64Cu]Pep-1L specifically bound tumors at 24 hours, which was significantly blocked (3-fold) by pre-injecting unlabeled peptide. To further demonstrate specificity of Pep-1L towards IL13RA2 in vivo, we exploited an IL13RA2-inducible melanoma tumor model that does not express receptor at baseline but expresses abundant receptor after treatment with doxycycline. We injected [64Cu]Pep-1L into mice bearing IL13RA2-inducible melanoma tumors and performed in vivo PET/CT and post-necropsy biodistribution studies and found that tumors that were induced to express IL13RA2 receptor by doxycycline pretreatment bound radiolabeled Pep-1L 3-4 fold greater than uninduced tumors, demonstrating receptor specificity. This work demonstrates that [64Cu]Pep-1L selectively binds hIL13RA2-expressing tumors and validates Pep-1L as an effective platform to deliver diagnostics and therapeutics to IL13RA2-expressing cancers.

Alpha Particle Enhanced Blood Brain/Tumor Barrier Permeabilization in Glioblastomas Using Integrin Alpha-v Beta-3-Targeted Liposomes.

Glioblastoma (GBM) is the most common primary malignant astrocytoma characterized by extensive invasion, angiogenesis, hypoxia, and micrometastasis. Despite the relatively leaky nature of GBM blood vessels, effective delivery of antitumor therapeutics has been a major challenge due to the complications caused by the blood-brain barrier (BBB) and the highly torturous nature of newly formed tumor vasculature (blood tumor barrier-BTB). External beam radiotherapy was previously shown to be an effective means of permeabilizing central nervous system (CNS) barriers. By using targeted short-ranged radionuclides, we show for the first time that our targeted actinium-225-labeled αvß3-specific liposomes (225Ac-IA-TLs) caused catastrophic double stranded DNA breaks and significantly enhanced the permeability of BBB and BTB in mice bearing orthotopic GBMs. Histologic studies revealed characteristic α-particle induced double strand breaks within tumors but was not significantly present in normal brain regions away from the tumor where BBB permeability was observed. These findings indicate that the enhanced vascular permeability in these distal regions did not result from direct α-particle-induced DNA damage. On the basis of these results, in addition to their direct antitumor effects, 225Ac-IA-TLs can potentially be used to enhance the permeability of BBB and BTB for effective delivery of systemically administered antitumor therapeutics. Mol Cancer Ther; 16(10); 2191-200. ©2017 AACR.

Metabolic PET Imaging in Oncology.

OBJECTIVE: In this article, we provide a general overview of how cancer cells subvert critical metabolic pathways to support their growth and unchecked division. Furthermore, we outline how molecular imaging can diagnostically exploit the resulting differences between cancer and normal cells. CONCLUSION: Molecular PET can provide valuable information about the metabolic dysregulation in cancer.

Radiosynthesis and in Vivo Evaluation of [11C]A1070722, a High Affinity GSK-3 PET Tracer in Primate Brain.

Dysfunction of glycogen synthase kinase 3 (GSK-3) is implicated in the etiology of Alzheimer's disease, Parkinson's disease, diabetes, pain, and cancer. A radiotracer for functional positron emission tomography (PET) imaging could be used to study the kinase in brain disorders and to facilitate the development of small molecule inhibitors of GSK-3 for treatment. At present, there is no target-specific or validated PET tracer available for the in vivo monitoring of GSK-3. We radiolabeled the small molecule inhibitor [11C]1-(7-methoxy- quinolin-4-yl)-3-(6-(trifluoromethyl)pyridin-2-yl)urea ([11C]A1070722) with high affinity to GSK-3 (Ki = 0.6 nM) in excellent radiochemical yield. PET imaging experiments in anesthetized vervet/African green monkey exhibited that [11C]A1070722 penetrated the blood-brain barrier (BBB) and accumulated in brain regions, with highest radioactivity binding in frontal cortex followed by parietal cortex and anterior cingulate, and with the lowest bindings found in caudate, putamen, and thalamus, similarly to the known distribution of GSK-3 in human brain. Our studies suggest that [11C]A1070722 can be a potential PET radiotracer for the in vivo quantification of GSK-3 in brain.

Automated radiochemical synthesis and biodistribution of [¹¹C]l-α-acetylmethadol ([¹¹C]LAAM).

Long-acting opioid agonists methadone and l-α-acetylmethadol (LAAM) prevent withdrawal in opioid-dependent persons. Attempts to synthesize [(11)C]-methadone for PET evaluation of brain disposition were unsuccessful. Owing, however, to structural and pharmacologic similarities, we aimed to develop [(11)C]LAAM as a PET ligand to probe the brain exposure of long-lasting opioids in humans. This manuscript describes [(11)C]LAAM synthesis and its biodistribution in mice. The radiochemical synthetic strategy afforded high radiochemical yield, purity and specific activity, thereby making the synthesis adaptable to automated modules.

18F-AFETP, 18F-FET, and 18F-FDG imaging of mouse DBT gliomas.

UNLABELLED: The goal of this study was to evaluate the (18)F-labeled nonnatural amino acid (S)-2-amino-3-[1-(2-(18)F-fluoroethyl)-1H-[1,2,3]triazol-4-yl]propanoic acid ((18)F-AFETP) as a PET imaging agent for brain tumors and to compare its effectiveness with the more-established tracers O-(2-(18)F-fluoroethyl)-l-tyrosine ((18)F-FET) and (18)F-FDG in a murine model of glioblastoma. The tracer (18)F-AFETP is a structural analog of histidine and is a lead compound for imaging cationic amino acid transport, a relatively unexplored target for oncologic imaging. METHODS: (18)F-AFETP was prepared using the click reaction. BALB/c mice with intracranially implanted delayed brain tumor (DBT) gliomas (n = 4) underwent biodistribution and dynamic small-animal PET imaging for 60 min after intravenous injection of (18)F-AFETP. Tumor and brain uptake of (18)F-AFETP were compared with those of (18)F-FDG and (18)F-FET through small-animal PET analyses. RESULTS: (18)F-AFETP demonstrated focally increased uptake in tumors with good visualization. Peak tumor uptake occurred within 10 min of injection, with stable or gradual decrease over time. All 3 tracers demonstrated relatively high uptake in the DBTs throughout the study. At late time points (47.5-57.5 min after injection), the average standardized uptake value with (18)F-FDG (1.9 ± 0.1) was significantly greater than with (18)F-FET (1.1 ± 0.1) and (18)F-AFETP (0.7 ± 0.2). The uptake also differed substantially in normal brain, with significant differences in the standardized uptake values at late times among (18)F-FDG (1.5 ± 0.2), (18)F-FET (0.5 ± 0.05), and (18)F-AFETP (0.1 ± 0.04). The resulting average tumor-to-brain ratio at the late time points was significantly higher for (18)F-AFETP (7.5 ± 0.1) than for (18)F-FDG (1.3 ± 0.1) and (18)F-FET (2.0 ± 0.3). CONCLUSION: (18)F-AFETP is a promising brain tumor imaging agent, providing rapid and persistent tumor visualization, with good tumor-to-normal-brain ratios in the DBT glioma model. High tumor-to-brain, tumor-to-muscle, and tumor-to-blood ratios were observed at 30 and 60 min after injection, with higher tumor-to-brain ratios than obtained with (18)F-FET or (18)F-FDG. These results support further development and evaluation of (18)F-AFETP and its derivatives for tumor imaging.

Development of (18)F-labeled PET probes for imaging cell proliferation.

In recent years, two different methods have been developed to image cell proliferation with the functional imaging technique, Positron emission Tomography (PET), proliferation rate and proliferative status. Proliferation rate is a measure of the tumor doubling time and uses radiolabeled analogs of the DNA precursor thymidine. This approach measures the activity of the enzyme thymidine kinase 1 (TK1) and provides a pulse label of the S phase fraction of a tumor. Proliferative status provides a measure of the ratio of proliferating (P) and quiescent (Q) cells in a tumor. This imaging approach for measuring proliferative status involves measuring the sigma-2 (σ(2)) receptor status of a tumor, the only protein which has been validated for making this measurement in vivo with PET. This article provides an overview of the biological information obtained from these different imaging strategies, and the development of radiotracers for imaging proliferation rate and proliferative status.

Aza-Nazarov cyclization cascades.

Benzamides with tethered acetal groups undergo reactions in CF(3)SO(3)H to give ring-fused isoindolinones by a cyclization cascade. The reaction initially forms an N-acyliminium ion which then gives the isoindolinone by the aza-Nazarov reaction. An unusual variant also cyclizes at the allylic position.

N-heterocyclic superelectrophiles and evidence for single electron transfer chemistry.

In reactions with benzene and related substrates, an oxazole-based superelectrophile is found to be significantly more reactive than a related monocationic species. Theoretical calculations estimate that the lowest unoccupied molecular orbital (LUMO) for the superelectrophile is about 4 eV lower in energy than the LUMOs of comparable monocations. When the oxazole-based superelectrophile is reacted with ferrocene, a dimeric product is formed in high yield. The dimerization occurs by a single electron transfer reaction between the dicationic superelectrophile and ferrocene, followed by coupling of the radical cations.

Superacid-promoted reactions of alpha-ketoamides and related systems.

The superacid-promoted reactions of alpha-hydroxy and alpha-ketoamides have been studied. Ionization of these compounds leads to varied aryl-substituted oxyindole products. In some cases, electrocyclization can lead to substituted fluorene products. Dicationic, superelectrophilic intermediates are proposed as intermediates leading to the products from alpha-hydroxy and alpha-ketoamides.